Review Article Blood Brain Barrier: A Challenge for ...downloads.hindawi.com/journals/bmri/2015/320941.pdf · mentioned BBB as a controversial problem for brain tumor chemotherapy

Review ArticleBlood Brain Barrier A Challenge for Effectual Therapy ofBrain Tumors

Arijit Bhowmik Rajni Khan and Mrinal Kanti Ghosh

Signal Transduction in Cancer and Stem Cells Laboratory Division of Cancer Biology and Inflammatory DisorderCouncil of Scientific and Industrial Research-Indian Institute of Chemical Biology (CSIR-IICB) 4 Raja SC Mullick RoadJadavpur Kolkata 700 032 India

Correspondence should be addressed to Mrinal Kanti Ghosh mrinalresgmailcom

Received 11 August 2014 Revised 27 October 2014 Accepted 4 November 2014

Academic Editor Yoshinori Marunaka

Copyright copy 2015 Arijit Bhowmik et alThis is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Brain tumors are one of the most formidable diseases of mankind They have only a fair to poor prognosis and high relapserate One of the major causes of extreme difficulty in brain tumor treatment is the presence of blood brain barrier (BBB) BBBcomprises different molecular components and transport systems which in turn create efflux machinery or hindrance for theentry of several drugs in brain Thus along with the conventional techniques successful modification of drug delivery and noveltherapeutic strategies are needed to overcome this obstacle for treatment of brain tumors In this review we have elucidated somecritical insights into the composition and function of BBB and along with it we have discussed the effective methods for delivery ofdrugs to the brain and therapeutic strategies overcoming the barrier

1 Introduction

Brain is the most delicate organ of human body Severaldiseases like encephalitis neurological disorders multiplesclerosis stroke and tumor induce deterioration of brainfunction The development of new therapeutic approachesfor these diseases is a difficult challenge and there is noeffective treatment for almost all the brain diseases In mostof the cases the major cause of the failure in the developmentof drugs to treat brain diseases is the presence of BBBOut of the several brain disorders brain tumors commonlyhave poor prognosis which varies according to the typeand grade of the tumor Due to the presence of BBB drugdelivery to brain tumors has long been a problematic issueSome group of researchers like Vick et al and Donelli et almentioned BBB as a controversial problem for brain tumorchemotherapy [1 2] They indicated that BBB is not the onlyfactor responsible for impeding the success of brain tumorchemotherapy but later studies revealed the involvement ofBBB in drug restriction to different brain neoplasias [3ndash6]

Brain tumors can be classified into two major classesnamely primary brain tumors that start in the brain andsecondary brain tumors that are generated by the cancer

cells that migrated from tumors developed in other partsof the body Primary brain tumors can arise from differenttype of brain cells or even from the membranes aroundthe brain (meninges) nerves or glands The most commontype of primary tumors in the brain is glioma whicharises from the glial tissue of the brain Gliomas compriseseveral types namely astrocytoma oligodendroglioma andependymomas Astrocytomas are further classified as gradeI (pilocytic) grade II (fibrillary) grade III (anaplastic) andgrade IV (glioblastoma multiforme or GBM) BBB is poorlydeveloped in these types of brain tumors causing an increasedvascular permeability [7]

It has been shown earlier that leaky interendothelialtight junction is present in human glioma [8] due to thefact that poorly differentiated neoplastic astrocytes do notrelease factors essential for BBB function [9ndash11] This tightjunction opening causes increased chances of cerebral edemaoccurrence [12] It is also observed that BBB stability inlower grade gliomas is better than that in GBM As thedegree of BBB disruption differs from the malignancy ofthe tumor treatment of low grade brain tumors is still achallenging task because of the presence of almost intactBBB On the contrary recent studies have suggested that

Hindawi Publishing CorporationBioMed Research InternationalVolume 2015 Article ID 320941 20 pageshttpdxdoiorg1011552015320941

2 BioMed Research International

Table 1 Type of common brain cancers and their BBB status

Type of brain tumors Origin Involvement of BBB Status of BBB

Primary

AstrocytomasPilocytic

astrocytoma(grade I)

Usually from astrocytes ofcerebellum Yes Not well formed

Fibrillarymixed oligoastrocytoma(grade II)

From neoplastic astrocytes Yes Mostly intact

Anaplastic astrocytoma (gradeIII)

From brain astrocytes whichinfiltrate through white matter ofcerebral hemisphere dura and

spinal fluid

Yes Altered or disrupted

Glioblastoma multiforme(GBM) (grade IV) From glial cells Yes Altered or disrupted

Oligodendrogliomas From oligodendrocytes and glialprecursor cells Yes Mostly intact

Ependymomas From ependyma Yes Intact

Meningiomas From meninges of brain andcentral nervous system No mdash

Schwannomas From Schwann cells No mdash

Craniopharyngiomas From pituitary gland embryonictissue Yes Intact or disrupted

Germinomas Germ cell tumors from pinealgland No mdash

Medulloblastomas From cerebellum below thetentorium of brain Yes Intact

Pineocytoma From pineal parenchyma No mdashPineoblastoma From pineal parenchyma No mdash

Secondary Different metastatic cancers tobrain

From cancers like breast lungbowel kidney ovary and skin Yes Intact or disrupted

although the BBB may be disrupted at or near the core ofthe high grade brain tumors most certainly it seems to beintact near the growing edge of the tumor where the invasivetumor cells may reside The presence of the intact BBB insuch regions of the tumors can considerably impede drugdelivery to these regions [13ndash15] On the other hand lackof BBB has been observed in other primary brain tumorslike meningiomas schwannomas or pineocytomas [16ndash18]Disrupted BBB also exists in metastatic secondary braintumors but the disruption is negligible in smaller aggregatesof metastatic tumor cells Therefore the drug delivery tothese micrometastatic regions is not optimum consequentlythe tumor keeps growing and ultimately reaches to clinicallysignificant size Thus along with the existing therapeuticmodalities new approaches of therapy are needed to combatagainst the BBB of different brain tumors (see Table 1)

2 BBB

BBB protects neural tissues in the brain and works as adiffusion barrier that impedes the influx of toxins and othercompounds from blood to the brain BBB was discoveredin 1880s It took almost 70 years to successfully provethe existence of BBB by electron microscopic cytochemical

studies [19 20] Later in 1981 Stewart and Wiley explainedthe initial understanding about the uniqueness of BBB tightjunction and its physiology [21]

Molecular character of BBB shows the presence of twotypes of cellular junctions the intercellular adherens junctionand the paracellular tight junction The functional integrityof BBB is maintained by adherens junction that is composedof vascular endothelium (VE) cadherin actinin and catenin[22] But the major functionality of BBB is maintained bytight junctions as they are primarily responsible for perme-ability through BBB [23 24] The BBB in adult is comprisedof a complex cellular network The main components ofthis system are brain endothelial cells highly specializedbasal membrane a plenty of pericytes embedded in the basalmembrane and astrocytic end-feet (see Figure 1)

Brain Endothelial Cells These cells are required for properbarrier formation and interaction with the adjacent cellsThey are also known as brain microvascular endothelialcells (BMECs) The BMECs differ from the endothelialcells present in the other organs in the following ways(i) paracellular movement of molecules is prevented bycontinuous tight junctions present between brain endothelialcells (ii) BMECs have few cytoplasmic vesicles and more

BioMed Research International 3

Dura

ArachnoidCSFSubarachnoid spacePia

Astrocytes

Blood vessel

BloodTight junction

Endothelial cellsPericyte

Basal membrane

Astrocytic end feet

Plasma membrane

JAM

ZO1ZO2

ZO3

Cingulin

ClaudinOccludin

Figure 1 A pictorial representation of the BBB and its tight junction structure The figure shows an irrigated blood vessel in the brain whichforms the BBB The BBB is constituted by endothelial cells with tight junctions surrounded by pericytes and astrocytic end-feet The tightjunction is further established by the interaction of proteins like claudins occludin junction adhesion molecules and cytoplasmic accessoryproteins (ZO1 ZO2 and ZO3) of adjacent endothelial cellsThe details of each component of the BBB are mentioned in the text of this review

mitochondria and (iii) detectable transendothelial path likeintracellular vesicular transport is not present in BMECs [2225] Complex intercellular tight junctions restrict the passivediffusion of molecules into the brain and therefore the bloodvessels showing extremely high transendothelial electricalresistance (TEER) in vivo [26] BMECs are also endowedwiththe ability to shuttle essential nutrients andmetabolites acrossthe BBB which include molecules like efflux transporters(p-glycoprotein) These transporters contribute to the BBBproperties by efflux of small lipophilic molecules that are ableto diffuse into BMECs back to the blood stream

Basal Membrane It consists of type IV collagen fibronectinand laminin that completely covers the capillary endothelialcell layers Pericytes are embedded in this membrane andsurrounded by astrocytic end-feet The potential function ofthis membrane is to restrict the movement of the solutes[27 28]

Pericytes The contractile cells which are wrapped aroundthe endothelial cells are called pericytes These cells play anessential role in the formation of BBB in several ways such

as by regulating the expressions of BBB-specific genes inendothelial cells by inducing polarization of astrocytic end-feet surrounding CNS blood vessels and also they inhibitCNS immune cells from damaging the proper formationof BBB Besides these cells also help in reduction of theexpression of molecules that increase vascular permeability[29]

Astrocytic End-Feet It is assumed earlier that the astrocyticend-feet encircling endothelial cells do not play substantialrole in maintenance of BBB [30] But recent study byNuriya et al 2013 indicated the heterogeneity of diffu-sion patterns around astrocytic end-feet [31] They provedthe existence of some astrocytic end-feet which can formtight networks that are able to block free diffusion ofmolecules across them The types of blood vessels andmorphological differences in the gliovascular interface likethe space between the endothelial cells and astrocytic end-feet determine the heterogeneity of diffusion patterns Thusthese networks cover the blood vessels tightly which sug-gests the potential functional roles of astrocytic end-feet[32]


21 Molecular Composition of BBB The tight junction of BBBmainly consists of three main integral membrane proteinsnamely occludin claudin and junction adhesion moleculesOther than that cytoplasmic accessory proteins like zonulaoccludens (ZO 1 ZO 2 ZO 3 etc) cingulin and others arealso present in BBB (see Figure 1)

Occludin It is the first transmembrane protein of the tightjunction to be discovered Occludin was first identified in1993 by immunogold freeze fracture microscopy in chicken[33] and then in mammals [34] It is formed by four trans-membrane domains a long carboxy-terminal cytoplasmicdomain a short amino-terminal cytoplasmic domain andtwo extracellular loops The ZO proteins are directly associ-ated with cytoplasmic domain of occludin Phosphorylationof specific SerThrTyr residues of occludin regulates itsinteraction with ZO proteins which in turn plays a regulatoryrole in tight junction formation [35]

ClaudinsThese are amultigene family of at least 24membersThey form tight junctions through homophilic ldquoclaudin-claudinrdquo interactions mediated by their extracellular loops[36] Carboxy terminal of claudins binds to the cytoplas-mic proteins including ZO family members [37] Occludinsand claudins can also assemble into heteropolymers toform intramembranous strands It has been proposed thatthese strands contain fluctuating channels which allow theselective diffusion of ions and hydrophilic molecules [38]Claudins-1 -3 -5 and -12 have been shown to participatein the formation of tight junctions between BMECs [9 1039 40] Each claudin regulates the diffusion of a group ofmolecules of specific size

Junction Adhesion Molecules (JAM) These proteins belongto the immunoglobulin superfamily Three JAM-related pro-teins JAM-A JAM-B and JAM-C have been investigated inrodent brain sections In human it is observed that JAM-Aand JAM-Care expressed in the tight junctions of BBBbut notJAM-B [41] JAM-B can be found in seminiferous epithelialcells [42] All JAMproteins comprise a single transmembranedomain the extracellular portion has two immunoglobulinlike loops They regulate the formation of tight junctionsduring the acquisition of cell polarity [43]

Cytoplasmic Accessory Proteins Cytoplasmic proteins likezonula occludens proteins (ZO 1 ZO 2 and ZO 3) cingulin7H6 and several others are also involved in tight junctionformation Zonula occludens are proteins belonging to thefamily of membrane associated guanylate kinase (MAGUK)[44] They provide the cytoskeletal anchorage for the trans-membrane tight junction and control spatial distribution ofclaudins [24] Cingulins are actomyosin-associated proteinswith large globular N-terminal ldquoheadrdquo domain coiled-coilldquorodrdquo domain and small globular C-terminal ldquotailrdquo Cingulinhelps in BBB formation by interacting with ZO proteins andjunction adhesion molecules

22 Transporters of BBB Endogenous compounds and drugsmay cross BBB by different mechanisms such as passive

diffusion carrier-mediated transport (like GLUT1 mediatedtransport) endocytosis and active transport [45ndash52] Par-ticipation of various transport proteins is there in mostof these transport systems These different transport pro-teins of brain mediate the uptake and extrusion of variousmetabolites and compounds The efflux and influx trans-porter systems of BBB comprise transporters like ATP-binding cassette (ABC) transporters and solute carrier (SLC)transporters

221 ABC Transporters ABC (ATP-binding cassette) trans-porters are ATP-driven drug efflux pumps present in theBBB which include P-glycoprotein breast cancer resistanceprotein and members of the multidrug resistance relatedproteins [53] These proteins form a key characteristic of theBBB by localizing at the luminal side of brain capillariesThey collectively impede brain uptake of a large variety oflipophilic molecules xenobiotics potentially toxic metabo-lites and drugs ABC transporters show broad substratespecificity and have been characterized by one or two cyto-plasmically located nucleotide binding domains acting as acatalytic domain for nucleotide hydrolysisThere are 48 genesencodingABC transporter superfamily of proteins which aresubdivided into 7 distinct subfamilies (ABCA toABCG) [54]All ABC transporters have three highly conserved motifsknown as Walker A Walker B motifs and the ABC signatureC motif (ie ALSGGQ) [55] It has been suggested that thisdomain may be involved in substrate recognition and ATPhydrolysis [56]

(1) P-glycoprotein (P-gp) It is a 170-kDa efflux transporterdiscovered in Chinese hamster ovary cells [57] P-gp isencoded by multidrug resistant (MDR) genes [58] TwoMDR isoforms have been identified in human tissues MDR-1 and MDR-2 [59 60] MDR1 encoded P-gp is a majorefflux transporter of BBB the expression of which is likelyevolved to protect the brain from exposure to potentiallyneurotoxic xenobiotics Thus it is considered that P-gphas a key role in the maintenance of accurate homeostaticenvironment required for proper neuronal function [61]TheMDR1 gene product is 1280 amino acids in length and hastwo homologous halves each consists of six transmembranedomains and ATP- binding site On the first extracellularloop two to four glycosylation sites are present [62] In thebrain P-gp is localized to both the luminal and abluminalsides of BBB endothelium [63] and to the apical plasmamembrane of choroid plexus epithelial cells [64] Substratesof P-gp are usually nonpolar weakly amphipathic compoundswhich significantly vary in molecular size The differenttypes of endogenous substrates of P-gp include cytokineslipids steroid hormones and peptides [65] P-gp has a vastendogenous and exogenous substrate profile that rendersdifficulty in drug delivery across the BBB

(2) Breast Cancer Resistance Protein (BCRP) It was firstidentified in the MCF-7AdrVp breast cancer cell line [66]It is also known as a ldquohalf-transporterrdquo Its molecular weightis approximately 72 kDa and it is composed of 655 aminoacids It has six transmembrane domains and both the C- and


Transporters of human BBB

ATP-binding cassette Solute carriertransporters transporters

P-glycoprotein Breast cancer Multidrugresistance protein resistance proteins

(MRP1 MRP4 and MRP5)

Proton coupled Organic anion Nucleosideoligopeptide transporters polypeptide transporterstransporters (OATP1A2 OATP1C1 and

Monocarboxylate

OATP3A1)

Organic ion Equilibrative nucleoside Concentrative nucleosidetransporters transporters transporters transporters

(MCT1 MCT2 (ENT1 ENT2 (CNT2)MCT4 and MCT8) ENT3 and ENT4)

Organic cationPeptide Peptidehistidine Organic aniontransporters transporters transporters transporters

(PEPT1 PEPT2) (PHT1 PHT2) (OCT1 OCT2 (OAT1 OAT2 andOCT3 OCTN1 and OCTN2) OAT3)

Figure 2 Schematic classification of transporters of human BBB Two main classes of drug transporters are ATP-binding cassette (ABC)transporters and solute carrier transporters Each of them is further classified into several other transporters mentioned in the flowchartMore information about each of the transporters is mentioned in the text

N-terminus regions are located on the intracellular side of theplasma membrane [67]

Furthermore the extracellular loops of the protein con-tain two to three sites for N-linked glycosylation Accordingto the earlier reports the functional capabilities of thetransporter and its cellular localization are not dependenton these glycosylation sites [67 68] It is also known thatBCRP forms functional homo- or heterodimers to maintainthe efflux activity [69] BCRP is expressed at the luminal sideof capillary endothelial cells in astrocytes andmicroglia [70ndash72] The substrate specificity of BCRP not only is limitedto the physiological substrates such as glutathione steroidhormones and folic acid [73] but also transports manystructurally diverse therapeutic compounds Significantlythe specificity of BCRP to the substrates overlaps with thesubstrate specificity of P-gp [74] It is also known thathigh expression of these BCRP proteins causes significantresistance to different cancer chemotherapeutic drugs [7576]

(3)Multidrug Resistance Proteins (MRPs) It is well establishedthat MRP family has 9 homologues designated as MRP1ndash9 and these isoforms have overlapping substrate profilesOut of these expression of MRP1ndash6 has been observed inhuman brain [77] whereas multiple MRPs like MRP1 4and 5 have been detected in the human BBB [72 78 79]Existence of other MRPs namely MRP2 3 and 6 and alongwith these MRP1 4 and 5 has also been noticed in other

vertebrates like rat cow pig and fish But presence of themin human BBB is still questionable Structural similaritycan be observed in MRP1 2 3 and 6 as each of thempossesses 3 transmembrane domains (TMD) designated asTMD0 TMD1 and TMD2 respectively TMD1 and TMD2contain 6 alpha helices whereas TMD0 contains only 5 alphahelices [80 81] It is believed that TMDs are assembled inthe plasma membrane pore through which the transport ofsubstrates occurs [80] On the contrary MRP4 and MRP5have structural similarity with P-gp that lack TMD0 [80 82]but in all the MRP homologues the conserved cytoplasmiclinker (L0) portion is essential for transport function MRP14 and 5 are restricted to the luminal membrane of humanbrain capillary endothelial cells [81]The localization ofMRPssuggests that they play a crucial role in drug efflux transportthrough BBB

222 Solute Carrier (SLC) Transporters SLC transportersbelong to SLC superfamily which comprises 43 knownsubfamilies of SLC transporters (SLC1ndashSLC43) At the BBBSLC15A1 SLC16 SLC21 SLC22 SLC28 and SLC29 areexpressed [83] The major SLC transporters include protoncoupled oligopeptide transporters monocarboxylate trans-porters organic anion polypeptide transporters organic ion(anion and cation) transporters and nucleoside transporters(see Figure 2) [84 85] Most of these transporters of BBBregulate the transport of brain tumor drugs by hinderingtheir entry into the tumor regions Generally these SLC


transporters do not require ATP to translocate substratesacross BBB however the electrochemical or concentrationgradients of solute are essentially required for this type oftransportation

(1) Proton Coupled Oligopeptide Transporters (POT) POTbelongs to SLC15A family solute carrier transportersNames of the subfamilies of POT are peptide transporters(PEPT) and peptidehistidine transporter (PHT) Peptidetransporter-1 (PEPT1 SLC15A1) and peptide transporter-2(PEPT2 SLC15A2) are the members of PEPT subfamilywhereas PHT comprises peptidehistidine transporter-1(PHT1 SLC15A4) and peptidehistidine transporter-2(PHT2 SLC15A3) [86 87] These oligopeptide transportersare able to transport small peptides across the BBB by anelectrochemical proton gradient [88] Structural similaritycan be observed in POT family members due to the presenceof 12 120572-helical transmembrane domains with intracellular-ly located C- andN-terminal regions Two to seven glycosyla-tion sites exist in the extracellular loops while intracellularloops have protein kinase A and C phosphorylation sites[86 89] Other than the above-mentioned peptide trans-porters peptide uptake and distribution in brain are alsodetermined by peptide transport system (PTS) expressedendogenously at the BBB endothelium [90] In the BBBseven transport systems have been found for transport ofpeptides which includes PTS1ndashPTS7 PTSs PTS2 PTS4 andPTS6 are bidirectional whereas the rest are unidirectionalThe unidirectional PTSs PTS1 and PTS5 facilitate brain-to-blood peptide transport whereas PTS3 and PTS7 are knownfor reverse process [90]

(2) Monocarboxylate Transporters (MCTs) Generally theMCTs facilitate the rapid transport of monocarboxylatesacross the biological membranes In brain MCTs not onlyassist the transport of the monocarboxylates for uptake intothe neurons but also mediate the transport of some drugsacross the BBB [91] These MCTs are members of solutecarrier family 16 (SLC16) SLC16 has 14 members out ofwhich only six have been functionally characterized andthose MCTs are MCT1ndash4 MCT8 and the T-type amino acidtransporter-1 (TAT-1MCT10) (326 327) MCT1 MCT2 andMCT4 are the most important BBB transporters whereasactive MCT8 expression has also been detected in BBB[92ndash94] The MCT1 protein is present in the membrane ofthe capillary endothelium and astrocytes while MCT2 andMCT4 are found on neurons and astrocytes respectively[95 96]

(3) Organic Anion Transporters Polypeptides (OATPs) Thesemembrane influx transporters are present in BBB to regulatecellular uptake of a number of endogenous compounds andclinically important drugs [97]The human OATP comprises11 members OATP1A2 1B1 1B3 1C1 2A1 2B1 3A1 4A1 4C15A1 and 6A1 [98ndash100] whereOATP1A2 is the first discoveredhuman member of the OATP family [101] The OATP genesare classified within the SLCO (formerly SLC21A) familyMembers of the same OATPs family share sim40 [99]whereas members of individual subfamilies possess sim60

amino acid sequence similarity This group of transportershas broad substrate specificity The OATP dependent trans-port of the substrates does not require ATP as energy sourceyet it is conducted by electrochemical gradients that utilizean inorganic or organic solute as a driving force The OATPsfamily members OATP1A2 1C1 2A1 2B1 3A1 and 4A1 arepresent in human brain [99] OATP1A2 is the only humanOATP isoform whose expression and function are widelyestablished at BBB The localization of OATP1A2 can beobserved at both the luminal and abluminal membranesof human BBB endothelial cells [102] The endogenoussubstrates of OATP1A2 are bilirubin bromosulfophthaleincholate deltorphin-II estradiol-17120573-glucuronide estrone-3-sulfate glycocholate hydroxyurea PGE2 reverse-T3 tau-rocholate taurochenodeoxycholate tauroursodeoxycholateT4 T3 and so forth [103] whereas a broad exogenoustherapeutic substrate specificity can be noticed for this kindof OATPs OATP1C1 and OATP3A1 are known to be presentin both apical and basal sides of the brain endothelial cellsand blood cerebrospinal fluid barrier respectively while theexact role of other OATPs is yet to be determined [104 105]

(4) Organic Ion Transporters These transporters can beclassified into two specific types (i) organic anion trans-porters (OATs) and (ii) organic cation transporters (OCTs)These transporters are the members of SLC transporter 22superfamily (SLC22A) [83 106]

(i) Organic Anion Transporters (OATs) The OAT familycomprises OAT 1ndash6 and the renal specific transporter (RST)[107ndash111] This classification is based on ATP-dependentenergy requirements and involvement of Na+ ion [112]Movement of the organic anions across biological mem-branes is determined by these OATs Various endogenousmolecules like anionic metabolites of neurotransmittershormones prostaglandins and exogenous molecules such asdifferent drugs are known to cross the biological membraneby these OATs [113]The general structure of OATs comprises12 membrane-spanning 120572-helices and several glycosylationand PKC sites which can be found on extracellular loopsconnecting helices 6 and 7 [113] In brain OAT3 is the mosthighly expressed isoform It is reported earlier that OAT3is present in the abluminal (brain side) and brush-bordermembrane (CSF side) of brain capillary endothelial cells andchoroid plexus epithelial cells respectively [114 115] Otherthan this OAT1 OAT2 and OAT4ndash6 are also expressed inbrain [78 105 109 114ndash117] But the proper localization andfunction of these OATs are yet to be known

(ii) Organic Cation Transporters (OCTs) OCTs regulate thetransport mechanisms to facilitate the passage of organiccations through biological membranes [118] According totheir transport capabilities OCTs are categorized into twosubgroups namely oligospecific organic cation transportersand polyspecific organic cation transporters Apart from thisorganic cation transporters can also be classified as chemicalpotential sensitive organic cation transporters (OCTs) andH+ gradient-dependent novel organic transporters (OCTNs)OCTs comprise OCT1ndash3 whereas OCTN transport system


includes OCTN1 and OCTN2 [119] Cellular influx and effluxof various cationic substrates are maintained by OCTs andOCTNs respectively [120 121] All OCT family membersgenerally contain 12 120572-helical transmembrane domains withintracellular N- and C-termini Furthermore large extracel-lular loop between TMD1 and TMD2 and small intercellularloop connecting TMD6 and TMD7 are also present inOCT family members In brain OCT1ndash3 are localized tothe basolateral membrane of BMECs and choroid plexusepithelial cells [122ndash124] and OCTN2 is reported to belocalized to the luminal side of the BBB [125ndash127] whereasOCTN1 is reportedly absent in human CNS tissue [128]Other than the transport of endogenous organic cationsOCT family members may also play crucial role in drugpenetration through BBB [129]

(5) Nucleoside Transporters The nucleosides play a majorrole as second messengers in many signal transductionpathways Thus their regulation of them is crucial forproper neuronal function [130] The recycling pathways fornucleosides transportation into CNS tissue are needed asbrain cannot synthesize nucleosides de novo Depending onthe Na+ dependence nucleoside the membrane transportersare again classified into two subcategories equilibrativenucleoside transporters (ENTs) and concentrative nucleosidetransporters (CNTs) ENTs are the members of the SLC29Atransporter family and are Na+-independent whereas CNTsare the members of the SLC28A transporter family andare Na+-dependent [131 132] In humans four isoforms ofENTs have been discovered which are ENT1ndash4 [133ndash135]All of them possess 11 120572-helical transmembrane domainswith intracellular N-terminus and extracellular C-terminusregions Each and every isoform of ENTs also possesses alarge cytoplasmic loop and an extracellular loop [136 137]ENT1 ENT2 and ENT4 are ubiquitously expressed in braintissue and are localized to cellular membranes [138ndash140]CNTs also have three isoforms CNT1ndash3 They are integralmembrane proteins with 13 transmembrane 120572-helices anda large extracellular C-terminal region present in variousregions of brain [85] and work as antiporters CNT1 andCNT2 transport nucleosides into the cell in exchange forsodium ions while CNT3 transports nucleosides in exchangefor either sodium ions or protons [141] But prominentexpression of CNT2 protein has been observed at the luminalside of the BBB endothelium Other than the endogenousnucleoside transporters CNTs are also responsible for thecellular uptake of a number of nucleoside-derived drugs [85]

23 Aberrant Expression of BBB Components in Brain TumorsBBB components claudins and occludins are either down-regulated or not at all expressed in brain tumors Loss ofclaudin-1 and downregulation of claudin-3 and claudin-5expressions in high grade glioma are reported earlier [9 142]This variation of expression of claudins causes looseningof BBB tight junctions but the involvement of claudins inthe mechanism for the compromised tight junction functionin BBB is not very clear Claudin-1 proteins are known toregulate different signaling pathways which in turn alterthe expression and function of different cell-cell adhesion

molecules [143] It is also reported that claudin-5 regulatesBBB permeability during the metastasis of brain tumors[144] Loss of expression of another transmembrane proteinoccludin inmicrovessels is also observed in astrocytomas andmetastatic adenocarcinomas The probability of their contri-bution to endothelial tight junction opening is also very high[11] High grade astrocytomas secrete vascular endothelialgrowth factor (VEGF) which downregulates the expressionof occludins and increases endothelial cell permeability [145]However besides VEGF cytokines and scatter factor orhepatocyte growth factor are also secreted by astrocytomaand other brain tumors These factors are believed to beinvolved in the downregulation of tight junction moleculesleading to its leakage [146 147]

3 Drug Delivery Approaches andCurrent Advances in Brain Tumor Therapy

Most of the brain tumor drugs are ineffective due to their lim-ited entry throughBBBNowadays scientific communities areinterested in providing solutions to this problem and it is notsurprising that most of the brain tumor patients could benefitfrom the improved drug delivery approaches Few establishedapproaches are intra-arterial drug delivery intrathecal andintraventricular drug administration intratumoral deliveryreceptor-mediated transport disruption of BBB inhibition ofdrug efflux by BBB and the use of intranasal drug deliveryroute

The clinical trials of intra-arterial delivery in brain tumordrugs showminimal improvement in survival of brain tumorpatients [148ndash154] but recently the neurosurgeons of NewYork Presbyterian HospitalWeill Cornell Medical Center forthe first time showed the successful intra-arterial deliveryof monoclonal antibody like bevacizumab to the tumorregion by means of transient blood brain barrier disruption[155] In case of intrathecal drug administration the drugspossess limited ability to enter the extracellular space ofbrain from the CSF [156ndash159] The convection enhanceddiffusion (CED) technique is used in transcranial braindrug delivery approaches to evade the BBB for forcefuldelivery of fluid into the brain and to increase the effectiveinfiltration of drug into tumor region [160] Application ofmicrodialysis in neurooncology is also well established sinceit has been proposed as an efficient method of intratumoraldrug delivery This method employs the passive diffusionof a drug across the BBB [161 162] and distributes drugsaway from the dialysis catheter [163] On the other hand thereceptor-mediated endocytosis and exocytosis facilitate theentry of the therapeutic compounds across the BBB of braintumors Receptor targetedmonoclonal antibody-based drugsare delivered across the BBB by the help of receptor-mediatedtransport systems [164 165] Another traditional approachto solve the problem of drug delivery into the brain isBBB disruption Osmotic disruption technique bradykinin-analogue or alkylglycerol mediated disruption techniqueMRI-guided focused ultrasound BBB disruption techniqueand so forth are used to disrupt the BBB [166ndash169] Thoughbradykinin analogue mediated delivery of drug is abandoned


due to its ineffectiveness when administered in combinationwith carboplatin Recently MRI-guided focused ultrasoundBBB disruption technique is used to disrupt BBB for effectivedrug delivery [170]

P-glycoproteins (P-gp) of the ABC drug efflux trans-porters are present not only in low grade brain tumors butalso in different malignant glioma cells [171] Modulation ofP-gpmay cause effective delivery of drugs to the tumor nicheThe poor in vivo efficacy of the first generation P-gp mod-ulators (verapamil cyclosporine A tamoxifen and severalcalmodulin antagonists) is due to their low binding affini-ties which necessitated the use of high doses resulting inintolerable toxicity [172]The coadministration of the second-generation P-gp modulators (dexverapamil dexniguldipinevalspodar (PSC 833) and biricodar (VX-710)) [173 174] andchemotherapy agents in clinical trials has provided lim-ited success hence third-generation P-gp modulators comein the scenario These modulators include anthranilamidederivative tariquidar (XR9576) cyclopropyldibenzosuberanezosuquidar (LY335979) laniquidar (R101933) and elacridar(GF120918) [175ndash178] Kemper et al showed 5-fold increasein brain uptake of paclitaxel by combinatorial treatmentwith elacridar (GF120918) [178] Other than P-gp inhibitorsMRP inhibitors (like sulfinpyrazone probenecid etc) andBCRP inhibitors (fumitremorginC and its analogues) are alsoreported as transporter inhibitors [172 179] Ongoing clinicaltrials with these new P-gp inhibitors should prove whetherthis approach will result in increased survival of brain tumorpatients

A promising drug delivery technique that can bypassthe BBB is the usage of intranasal drug delivery route Thistechnique eliminates the risk of surgery and the nonspecificspillover effect of drug to normal tissue Intranasal deliveryprovides successful drug targeting mechanism which utilizesthe unique anatomic connections of olfactory and trigeminalnerves of nasal mucosa and the central nervous system [180181] The drugs administered through this path reach thecerebrospinal fluid (CSF) spinal cord and brain parenchymavery rapidly This delivery system has been proven to besuccessful in delivering anticancer agents to the brain likeraltitrexed 5-fluorouracil GRN163 and methotrexate [182ndash185] Further studies about intranasal therapeutic agents areneeded and it could be a major candidate for clinical trials inbrain tumor patients

Current techniques and new approaches in drug deliveryacross the BBB can be classified as follows

31 Modification of Existing Drugs The ability of drug tocross the BBB depends on few factors like molecular size(should be less than 500Da) charge (should have lowhydrogen bonding capabilities) and lipophilicity (shouldhave high lipophilicity) [186]Thus chemical modification ofbrain tumor drugs refers to the process of making an existingdrug smaller in size more perfectly charged and more lipidsoluble [187] (Table 2) Existing brain tumor drugs may alsobe modified to make analogue of the ligand to the particularreceptor present in the BBB or the ligand or a peptide canbe linked to a drug against the cellular receptors of BBB Thedrug melphalan has been modified by using this approach

where melphalan nitrogen mustard (mechlorethamine) waslinked to phenylalanine [188] Another approach of drugmodification is the use of lipid carriers for efficient transportthrough BBB One example of such modification is incorpo-ration of small drugs in fatty acids like N-docosahexaenoicacid (DHA) [189 190] Drugs are also modified in such a waythat they acquire increased capillary permeability but aftercrossing the BBB they undergo an enzymatic reaction andreturn to their active state This approach is also known asprodrug therapy [191 192]

32 Nanosystem Based Delivery Nanosystems are colloidalcarriers that mainly consist of liposomes and polymericnanoparticles while other systems including solid lipidnanoparticles polymeric micelles and dendrimers have alsobeen studied recently Sizes of these nanosystems vary within1ndash1000 nm These kinds of functionalized drug colloidalcarriers can act as a vehicle to deliver antitumor drugs to braintumor tissues These nanosystems generally use passive dif-fusion mechanism as they rely on increased vascular perme-ability of brain tumor location but usage of active chemicallymodified drugs with nanoparticles and receptor-mediatedor adsorptive endocytosis processes of nanoparticle deliveryhave also been reported [219ndash221] Conjugation of ligandstargeting BBB on the surface of the nanosystem increasestheir specificity for brain tumors One of the importantfeatures of these nanosystems is that they can circulate in thebloodstream for a prolonged time period But the interactionof the nanosystemswith the reticuloendothelial system (RES)causes its rapid removal from systemic circulation [222]Therefore to minimize the interactions of nanosystems withtheRES polyethylene glycol (PEG) coating or direct chemicallinking of PEG to the particle surface is a widely acceptedapproach These colloidal nanosystems comprise liposomesand nanoparticles which have shownpotential to target braintumors as drug carriers Furthermore studies are going on forthe development of novel transport-enhancing nanocarriersfor brain tumor treatment

321 Liposomes Liposome is a good carrier system for thedelivery of therapeutic agents for brain tumors They areeasy to prepare biocompatible less toxic and commerciallyavailable Along with PEGylation the liposomes can alsobe modified with monoclonal antibodies against transferrinreceptors (OX-26) glial fibrillary acidic proteins (GFAP)or human insulin receptors [223] Effective delivery ofdrugs like 5-fluorouracil (5-FU) and sodium borocaptate(Na210B12H11SH BSH) to high grade brain tumors has beenachieved by liposome mediated delivery [224 225] Mod-ified liposomes like p-aminophenyl-120572-D-mannopyranoside(MAN) and transferrin conjugated daunorubicin liposomesand trans-activating transcriptional peptide (TATp)modifiedliposomes have also been used in vitro and in vivo fortargeting brain tumors [226 227]

322 Nanoparticles Polymeric nanoparticles (NP) are col-loidal particles which can be found in the form of nanocap-sules or nanospheres The drugs are dissolved entrapped


Table 2 Recent modifications of few important brain tumor drugs

Drug name Mode of action Modification type Examples Usual route ofadministration

Targeted brain tumortype Reference

Temozolomide Alkylating agent Nanoparticle based

Polysorbate-80 coatedPBCA nanoparticles asfeasible carrier for TMZdelivery to the brain

[193]

Transferrin-appendedPEGylated nanoparticlesfor TMZ delivery tobrain

[194]

TMZ solid lipidnanoparticles(TMZ-SLNs)

Oral Glioblastomamultiforme [195]

Polysorbate-80 coatedTMZ loaded PLGAbased supermagneticnanoparticles

[196]

TMZ loaded in PLGAnanoparticle [197]

TMZ loaded in chitosannanoparticle [198]

TMZ loaded in albuminnanoparticle [199]

Carmustine(BCNU)

Alkylating agent

Liposomespolymermicrochips andmicrospheres

Gliadel [200]

Nanoparticles

Chitosansurface-modifiedpoly(lactide-co-glycolide) nanoparticlesloaded with BCNU

WaferimplantIVoral

Glioblastomamultiformemedulloblastoma andlow gradeastrocytoma

[201]

Catanionic solid lipidnanoparticles (CASLNs)carrying BCNU

[202]

BCNU-loadedpoly(lactic acid) (PLA)nanoparticle

[203]

Doxorubicin(DOX)

Anthracyclinesinhibitingnucleic acidsynthesis

LiposomeLong-circulatingPEGylated liposomes tocross blood brain barrier

[204]

Nanoparticle

Cationic solid lipidnanoparticles (CASLNs)loaded with DOX

IV Glioblastomamultiforme [205]

Human serum albuminnanoparticles loadedwith DOX

[206]

Lomustine(CCNU)

Alkylatingnitrosoureacompound

Liposomes ormicrocapsules

Administration ofCCNU-Lips andinclusion complexsolution of CCNU withhydroxypropyl-120573-cyclodextrin(CCNU-Sol)

OralOligodendrogliomas

and mixedoligoastrocytomas

[207]

Vincristine(Oncovin) Vinca alkaloid Liposome

Vincristine sulfateliposome PEGylatedliposome

IV

Anaplasticoligoastrocytoma andoligodendrogliomametastatic secondary

brain tumors

[208 209]


Table 2 Continued



CisplatinPlatinum-containinganticancer drugs

LiposomeTransferrin-modifiedcisplatin liposomeCis-lipo(Tf)

IV

Gliomamedulloblastoma andother types of brain

tumors

[210]

CarboplatinPlatinum-basedantineoplasticagents

Liposomes Liposomal carboplatin IV


tumors

[211]

Methotrexate Antimetaboliteand antifolate Nanoparticle Magnetic nanoparticles Oralinjection

Malignant braintumors brainlymphoma

[212]

Etoposide (ETP) Topoisomeraseinhibitor Nanoparticle

ETP-encapsulatedcationic solid lipidnanoparticles(ETP-CASLNs) graftedwith 5-HT-moduline IVoral Malignant brain

tumors

[213]

Liposomal etoposide [211]

Actinomycin(dactinomycin)

Polypeptideantibiotics Liposome Liposome encapsulated

actinomycin IVSecondary braintumor child brain

tumor[214]

IrinotecanDNAtopoisomerase Iinhibitor

Liposome Nanoliposomalirinotecan IV Glioblastoma

multiforme [215]

Paclitaxel (Taxol) Taxanes

ChemicalTx-6710-O-deacetylpaclitaxel10-monosuccinyl ester

[216]

Liposomes

Polysorbate 80 coatedpoly(120576-caprolactone)-poly(ethylene glycol)-poly(120576-caprolactone) (PCEC)micelles

IV High grade gliomaoligodendroglioma [217]

Paclitaxel plusartemether liposomes [218]

encapsulated adsorbed or chemically linked to the surfaceof the NPs The polymer structure and the drug trap-ping method determine the drug characteristics and itsrelease kinetics from the nanoparticles [228] One exam-ple of nanoparticle drug delivery approach is the usageof nanoparticles coated choline derivative that is reportedto be transported across brain-derived endothelial cellsby the cation transporter system [229] Other remarkablesystems are polysorbate-coated doxorubicin nanoparticlesand doxorubicin-loaded folic acid-decorated nanoparticleswhich cause effective penetration of drugs through BBB[230 231] Brain tumors can also be selectively targeted bybionanocapsules conjugated with anti-human EGFR anti-body that recognizes EGFRvIII known to be overexpressedin high grade brain tumors like glioblastoma multiforme[232] Those bionanocapsules may also contain virus activeproteins vaccines genes or small interference RNA fortargeted therapy of brain tumors Solid lipid nanoparticles(SLNs) which are the dispersions of solid lipid stabilized

with emulsifier or emulsifiercoemulsifier complex in waterare also known for delivering brain tumor drugs like camp-tothecin doxorubicin and paclitaxel to brain effectively[233] Furthermore gold nanoparticles and carbon nanopar-ticles (like carbon nanotubes graphene and carbon dots)are also able to deliver drugs (like doxorubicin) successfully[234ndash237] Thus nanoparticles may be considered as one ofthe most promising tools to deliver therapeutic drugs acrossthe BBB to treat brain tumors [238]

Other nanosystems like polymeric micelles and den-drimers are also effective for targeted delivery of drugs tothe tumors in the brain Formation of polymeric micellesoccurs spontaneously in aqueous solutions of amphiphilicblock copolymers whereas dendrimers are highly branchedpolymer molecules formed by a central core These types ofnanopreparations loaded with anticancer drugs should beconsidered as highly potential antitumor nanomedicines asthey have the ability to cross the BBB by modulating BBBtransporters like P-gp or glucose transporters [239ndash241]


33 Delivery Systems Used in Gene Therapy Effective treat-ment of brain tumor can be obtained from intracerebralimplantation of a therapeutic gene inserted into a viral vectorIt is a specifically targeted therapy where volume of theimplantation is very low (lt1mm3) Thus the expression ofexogenous gene is highly localized But gene reformulationmay cause the generalised expression of exogenous gene inthe total brain tumor niche Few examples of carriers in thistype of therapeutic systems are viral vectors like adenovirusherpes simplex virus (HSV) and nonviral gene delivery sys-tem like cationic liposome-DNA complexes [242ndash244] TheO6-methylguanine-DNAmethyltransferase (MGMT) upreg-ulation inGBMmakes it resistant to Temozolomide (TMZ) awell-known drug for gliomaTherefore upregulation of wild-type (wt) p53 expression is needed which downmodulatesMGMT Since p53 therapy for GBM is not very efficient dueto the presence of the blood brain barrier (BBB) a systemicnanodelivery platform (scL) for tumor-specific targeting(primary and metastatic) has been developed by Kim et al Ithas been observed that the combination of scL-p53 and TMZincreased the antibrain tumor efficacy of TMZ [245] Anotherreport shows the efficacy of CMV-specific T cell therapy asit is reported that the expression of human cytomegalovirus(CMV) antigens in GBM tissues is pretty high Distinct geneexpression correlated with the better clinical response isrecorded for the high grade brain tumor patients who availedthemselves of CMV-specific T cell therapy [246]

34 Effective Delivery ofTherapeutic Peptides Towards fulfill-ing the goal of effective therapy recently selective peptideshave been developed against brain cancer Discovery of novelpeptide as novel specific chemical entity is encouraged bythe identification of several proteinpeptide receptors andtumor-related peptidesproteins those expressed in braincancer cells Small sized less toxic peptides are advantageousover the monoclonal antibodies (mAbs) and large proteinsthat have large size and high toxicity have poor rate of BBBcrossing Other major advantages of peptides are their BBBpenetrating ability in brain tumors ease of synthesis andmodification and good biocompatibility [247] Chlorotoxinis such a peptide which selectively binds to glioma cells[248] Somatostatin analogues which can be defined aspeptide receptor radionuclide therapeutic agents are the onlyapproved cancer therapeutic peptides in themarket [249] andthere are reports of their binding to the cellular receptorsin brain tumors in vivo [250] Another new approach ofbrain tumor therapy is developing vaccines consisting ofpeptides derived from the protein sequence of brain tumor-associated or specific antigens [251] Autologous DC vaccineagainst CD133 (a marker of GBM) survivin peptide vaccinerindopepimut (also known as CDX-110) against EGFRVIIIand so forth are the examples of peptide vaccines for highgrade brain tumors and these are now under clinical trials[252ndash254]

35 Molecular Trojan Horses (MTH) Recently a new tech-nique is used to ferry drug molecules across the BBB whichis called Molecular Trojan Horse (MTH) mediated drug

delivery Delivery of particular substances to the brain afterattaching them to a protein which can cross BBB is the mainfocus of this type of delivery system One of the recent pro-gresses ofMTH is ldquoTrojan horse liposomerdquo (THL) technology[255ndash257]The application of this technology to transvascularnonviral gene therapy of brain represents a potential way outof the transvascular brain gene delivery problem The THLis constructed with PEG-conjugated lipids which encapsulateplasmid DNA encoding proteins or shRNAsiRNA Markeddecrease in expression of EGFR protein in the tumor regionwas noticed after using THL mediated RNAi gene therapyThis resulted in a 90 increase in survival time of brain tumorpatients [258]

36 Drug Delivery Targeting Brain Cancer Stem Cells Cancerstem cells (CSCs) are the tumor initiating cells present in thetumor niche These cells cause drug resistance metastasisand relapse of cancer Most of the current chemotherapeuticmolecules are able to destroy the cancer cells but not theCSCs Thus to kill these CSCs in brain tumors effectivetreatment modalities are needed which should also have theability to cross the BBB for example curcumin encapsulatedin nanoparticles caused a dose-dependent growth inhibitionof brain tumorCSCs andneurospheres [259]Other than thistargeting active genes likeMGMT inbrainCSCs by liposomeswith anti-MGMT siRNA for oral Temozolomide therapy anddestruction of brain CSCs niche by mAb-vectorized SWNT(single-walled carbon nanotubes) for hypothermic treatmentalso resulted in destruction of CSCs [260 261]The efficacy ofthe CSC targeting drugs can be improved by optimisation ofchemo- and nanotherapies novel gene-silencing techniquesand drug efflux inhibition techniques which may increasesurvivability of the brain tumor patients

4 Concluding Remarks

Modern era of brain cancer therapy is characterized by noveltarget specific drugs with efficient delivery strategies How-ever the prognosis and median survival of the brain tumorpatients are not satisfactory till date This is due to molecularheterogeneity of the brain tumors presence of CSCs and lackof effective drug delivery because of the presence of BBBRapid progress is needed in the sector of brain tumor char-acterization and BBB research Till now most effective drugsfor brain tumor therapies are Temozolomide ProcarbazineCarmustine (BCNU) Lomustine (CCNU) and VincristineBetter modification of these drugs or identification of newchemical entities with enhanced efficacy and low side effectis always commendable Alternatively identification of drugswhich canmodulate BBB components or transporter systemscould be an effective future strategy Another potentialfuture approach is combinatorial therapy where throughBBB destructionmodification tumor cellsCSCs could betargeted easily Modern techniques like nanotherapy mayfacilitate this kind of approach Therefore future researchis needed to focus on the development of more specifictargeting strategies to cure brain cancer overcoming theabove-mentioned difficulties arising due to the presence ofthe BBB


Abbreviations

BBB Blood brain barrierGBM Glioblastoma multiformeCSF Cerebrospinal fluidVE Vascular endotheliumBMEC Brain macrovascular endothelial cellsCNS Central nervous systemZO Zonula occludensJAM Junction adhesion moleculesGLUT1 Glucose transporter 1ATP Adenosine triphosphateABC ATP-binding cassetteSLC Solute carrierP-gp P-glycoproteinMDR Multidrug resistantBCRP Breast cancer resistance proteinMRP Multidrug resistance proteinsTMD Transmembrane domainsPOT Proton coupled oligopeptide transportersPEPT Peptide transportersPHT Peptidehistidine transporterPTS Peptide transport systemMCT Monocarboxylate transportersTAT T-type amino acid transporterOATP Organic anion transporters polypeptidesOAT Organic anion transportersOCT Organic cation transportersOCTN Organic cation transporter novelENT Equilibrative nucleoside transportersCNT Concentrative nucleoside transportersVEGF Vascular endothelial growth factorCED Convection enhanced diffusionLDL Low density lipoproteinRMP Receptor-mediated permeabilizerMRI Magnetic resonance imagingRES Reticuloendothelial systemPEG Polyethylene glycolGFAP Glial fibrillary acidic proteinsNP NanoparticleEGFR Epidermal growth factor receptorEGFRvIII Epidermal growth factor receptor variant IIISLN Solid lipid nanoparticleHSV Herpes simplex virusMGMT O6-Methylguanine-DNA methyltransferaseCMV CytomegalovirusmAbs Monoclonal antibodiesDC Dendritic cellMTH Molecular Trojan HorseTHL Trojan horse liposomeshRNA Short hairpin RNAsiRNA Small interfering RNARNAi RNA interferenceCSC Cancer stem cellSWNT Single-walled carbon nanotubes

Conflict of Interests

The authors declare no conflict of interests

Authorsrsquo Contribution

Mrinal Kanti Ghosh Arijit Bhowmik and Rajni Khan wroteand analyzed the paper

Acknowledgment

This work was supported by grants from Council of Scien-tific and Industrial Research (CSIR) (EMPOWER OLP-002MEDCHEM BSC-0108 and miND BSC-0115)

References

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[2] M G Donelli M Zucchetti and M DrsquoIncalci ldquoDo anticanceragents reach the tumor target in the human brainrdquo CancerChemotherapy and Pharmacology vol 30 no 4 pp 251ndash2601992

[3] W M Pardridge ldquoCNS drug design based on principles ofblood-brain barrier transportrdquo Journal of Neurochemistry vol70 no 5 pp 1781ndash1792 1998

[4] S I Rapoport ldquoModulation of blood-brain barrier permeabil-ityrdquo Journal of Drug Targeting vol 3 no 6 pp 417ndash425 1996

[5] A Tsuji and I Tamai ldquoSodium- and chloride-dependenttransport of taurine at the blood-brain barrierrdquo Advances inExperimental Medicine and Biology vol 403 pp 385ndash391 1996

[6] D R Groothuis ldquoThe blood-brain and blood-tumor barriersa review of strategies for increasing drug deliveryrdquo Neuro-Oncology vol 2 no 1 pp 45ndash49 2000

[7] D R Groothuis F J Vriesendorp B Kupfer et al ldquoQuantitativemeasurements of capillary transport in human brain tumors bycomputed tomographyrdquo Annals of Neurology vol 30 no 4 pp581ndash588 1991

[8] D M Long ldquoCapillary ultrastructure and the blood-brain bar-rier in humanmalignant brain tumorsrdquo Journal of Neurosurgeryvol 32 no 2 pp 127ndash144 1970

[9] S Liebner A Fischmann G Rascher et al ldquoClaudin-1 andclaudin-5 expression and tight junctionmorphology are alteredin blood vessels of human glioblastoma multiformerdquo ActaNeuropathologica vol 100 no 3 pp 323ndash331 2000

[10] S Liebner U Kniesel H Kalbacher and H Wolburg ldquoCor-relation of tight junction morphology with the expression oftight junction proteins in blood-brain barrier endothelial cellsrdquoEuropean Journal of Cell Biology vol 79 no 10 pp 707ndash7172000

[11] M C Papadopoulos S Saadoun C J Woodrow et alldquoOccludin expression in microvessels of neoplastic and non-neoplastic human brainrdquo Neuropathology and Applied Neurobi-ology vol 27 no 5 pp 384ndash395 2001

[12] K Lamszus J Laterra M Westphal and E M Rosen ldquoScatterfactorhepatocyte growth factor (SFHGF) content and func-tion in human gliomasrdquo International Journal of DevelopmentalNeuroscience vol 17 no 5-6 pp 517ndash530 1999

[13] M W Pitz A Desai S A Grossman and J O Blakeley ldquoTis-sue concentration of systemically administered antineoplasticagents in human brain tumorsrdquo Journal of Neuro-Oncology vol104 no 3 pp 629ndash638 2011

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[17] S Ammoun and C O Hanemann ldquoEmerging therapeutictargets in schwannomas and other merlin-deficient tumorsrdquoNature Reviews Neurology vol 7 no 7 pp 392ndash399 2011

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[35] R Rao ldquoOccludin phosphorylation in regulation of epithelialtight junctionsrdquo Annals of the New York Academy of Sciencesvol 1165 pp 62ndash68 2009

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[38] K Matter and M S Balda ldquoHoley barrier claudins and theregulation of brain endothelial permeabilityrdquoThe Journal of CellBiology vol 161 no 3 pp 459ndash460 2003

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[40] A Schrade H Sade P-O Couraud I A Romero B BWekslerand J Niewoehner ldquoExpression and localization of claudins-3and -12 in transformed human brain endotheliumrdquo Fluids andBarriers of the CNS vol 9 no 1 article 6 2012

[41] M Aurrand-Lions C Johnson-Leger CWong L Du Pasquierand B A Imhof ldquoHeterogeneity of endothelial junctions isreflected by differential expression and specific subcellularlocalization of the three JAM family membersrdquo Blood vol 98no 13 pp 3699ndash3707 2001

[42] G Gliki K Ebnet M Aurrand-Lions B A Imhof and RH Adams ldquoSpermatid differentiation requires the assemblyof a cell polarity complex downstream of junctional adhesionmolecule-Crdquo Nature vol 431 no 7006 pp 320ndash324 2004

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[44] JHaskins L Gu E SWittchen JHibbard andB R StevensonldquoZO-3 a novel member of the MAGUK protein family foundat the tight junction interacts with ZO-1 and occludinrdquo TheJournal of Cell Biology vol 141 no 1 pp 199ndash208 1998

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[48] M Simionescu A Gafencu and F Antohe ldquoTranscytosis ofplasma macromolecules in endothelial cells a cell biologicalsurveyrdquo Microscopy Research and Technique vol 57 no 5 pp269ndash288 2002

[49] A M Wolka J D Huber and T P Davis ldquoPain and theblood-brain barrier obstacles to drug deliveryrdquoAdvanced DrugDelivery Reviews vol 55 no 8 pp 987ndash1006 2003

[50] L B Thomsen J Lichota T N Eskehave et al ldquoBrain deliverysystems via mechanism independent of receptor-mediatedendocytosis and adsorptive-mediated endocytosisrdquo CurrentPharmaceutical Biotechnology vol 13 no 12 pp 2349ndash23542012

[51] N J Abbott and I A Romero ldquoTransporting therapeuticsacross the blood-brain barrierrdquoMolecular Medicine Today vol2 no 3 pp 106ndash113 1996

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[53] D J Begley ldquoABC transporters and the blood-brain barrierrdquoCurrent Pharmaceutical Design vol 10 no 12 pp 1295ndash13122004

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[60] I B Roninson J E ChinKChoi et al ldquoIsolation of humanmdrDNA sequences amplified inmultidrug-resistant KB carcinomacellsrdquo Proceedings of the National Academy of Sciences of theUnited States of America vol 83 no 12 pp 4538ndash4542 1986

[61] L Sanchez-Covarrubias L M Slosky B J Thompson et al ldquoP-glycoprotein modulates morphine uptake into the CNS a rolefor the non-steroidal anti-inflammatory drug diclofenacrdquo PLoSONE vol 9 no 2 Article ID e88516 2014

[62] T W Loo and D M Clarke ldquoP-glycoprotein Associationsbetween domains and between domains and molecular chaper-onesrdquo Journal of Biological Chemistry vol 270 no 37 pp 21839ndash21844 1995

[63] R Bendayan P T Ronaldson D Gingras and M BendayanldquoIn situ localization of P-glycoprotein (ABCB1) in human andrat brainrdquo Journal of Histochemistry and Cytochemistry vol 54no 10 pp 1159ndash1167 2006

[64] V V Rao J L Dahlheimer M E Bardgett et al ldquoChoroidplexus epithelial expression of MDR1 P glycoprotein and mul-tidrug resistance-associated protein contribute to the blood-

cerebrospinal-fluid drug-permeability barrierrdquo Proceedings ofthe National Academy of Sciences of the United States of Americavol 96 no 7 pp 3900ndash3905 1999

[65] T Litman T Zeuthen T Skovsgaard and W D Stein ldquoCom-petitive non-competitive and cooperative interactions betweensubstrates of P-glycoproteins as measured by ATPase activityrdquoBiochimica et Biophysica Acta Molecular Basis of Disease vol1361 no 2 pp 169ndash176 1997

[66] Y-N Chen L A Mickley A M Schwartz E M ActonJ Hwang and A T Fojo ldquoCharacterization of adriamycin-resistant human breast cancer cells which display overexpres-sion of a novel resistance-related membrane proteinrdquo TheJournal of Biological Chemistry vol 265 no 17 pp 10073ndash100801990

[67] L A Doyle W Yang L V Abruzzo et al ldquoA multidrugresistance transporter from human MCF-7 breast cancer cellsrdquoProceedings of the National Academy of Sciences of the UnitedStates of America vol 95 no 26 pp 15665ndash15670 1998

[68] K Mohrmann M A J van Eijndhoven A H Schinkeland J H M Schellens ldquoAbsence of N-linked glycosylationdoes not affect plasma membrane localization of breast cancerresistance protein (BCRPABCG2)rdquo Cancer Chemotherapy andPharmacology vol 56 no 4 pp 344ndash350 2005

[69] T Nakanishi L A Doyle B Hassel et al ldquoFunctional Charac-terization of Human Breast Cancer Resistance Protein (BCRPABCG2) Expressed in theOocytes ofXenopus laevisrdquoMolecularPharmacology vol 64 no 6 pp 1452ndash1462 2003

[70] G Lee K Babakhanian M Ramaswamy A Prat K Wosikand R Bendayan ldquoExpression of the ATP-binding cassettemembrane transporter ABCG2 in human and rodent brainmicrovessel endothelial and glial cell culture systemsrdquo Pharma-ceutical Research vol 24 no 7 pp 1262ndash1274 2007

[71] T Eisenblatter S Huwel and H-J Galla ldquoCharacterisation ofthe brain multidrug resistance protein (BMDPABCG2BCRP)expressed at the blood-brain barrierrdquo Brain Research vol 971no 2 pp 221ndash231 2003

[72] W Zhang J Mojsilovic-Petrovic M F Andrade H Zhang MBall and D B Stanimirovic ldquoThe expression and functionalcharacterization of ABCG2 in brain endothelial cells andvesselsrdquoThe FASEB Journal vol 17 no 14 pp 2085ndash2087 2003

[73] Q Mao and J D Unadkat ldquoRole of the breast cancer resistanceprotein (ABCG2) in drug transportrdquo The AAPS Journal vol 7no 1 pp E118ndashE133 2005

[74] F Staud and P Pavek ldquoBreast cancer resistance protein(BCRPABCG2)rdquo The International Journal of Biochemistry ampCell Biology vol 37 no 4 pp 720ndash725 2005

[75] D D Ross W Yang L V Abruzzo et al ldquoAtypical multidrugresistance breast cancer resistance protein messenger RNAexpression in mitoxantrone-selected cell linesrdquo Journal of theNational Cancer Institute vol 91 no 5 pp 429ndash433 1999

[76] K Miyake L Mickley T Litman et al ldquoMolecular cloningof cDNAs which are highly overexpressed in mitoxantrone-resistant cells demonstration of homology to ABC transportgenesrdquo Cancer Research vol 59 no 1 pp 8ndash13 1999

[77] A T Nies G Jedlitschky J Konig et al ldquoExpression andimmunolocalization of the multidrug resistance proteinsMRP1-MRP6 (ABCC1-ABCC6) in human brainrdquoNeurosciencevol 129 no 2 pp 349ndash360 2004

[78] H Bronger J Konig K Kopplow et al ldquoABCC drug effluxpumps and organic anion uptake transporters in humangliomas and the blood-tumor barrierrdquo Cancer Research vol 65no 24 pp 11419ndash11428 2005


[79] D S Miller S N Nobmann H Gutmann M Toeroek JDrewe and G Fricker ldquoXenobiotic transport across isolatedbrain microvessels studied by confocal microscopyrdquo MolecularPharmacology vol 58 no 6 pp 1357ndash1367 2000

[80] P Borst R Evers M Kool and J Wijnholds ldquoA family ofdrug transporters the multidrug resistance-associated pro-teinsrdquo Journal of the National Cancer Institute vol 92 no 16pp 1295ndash1302 2000

[81] S Dallas D S Miller and R Bendayan ldquoMultidrug resistance-associated proteins expression and function in the centralnervous systemrdquo Pharmacological Reviews vol 58 no 2 pp140ndash161 2006

[82] Y-J Lee H Kusuhara and Y Sugiyama ldquoDo multidrugresistance-associated protein-1 and -2 play any role in the elim-ination of estradiol-17 120573-glucuronide and 2 4-dinitrophenyl-S-glutathione across the blood-cerebrospinal fluid barrierrdquoJournal of Pharmaceutical Sciences vol 93 no 1 pp 99ndash1072004

[83] H Kusuhara and Y Sugiyama ldquoActive efflux across the blood-brain barrier role of the solute carrier familyrdquo NeuroRx vol 2no 1 pp 73ndash85 2005

[84] M A Hediger M F Romero J-B Peng A Rolfs H Takanagaand E A Bruford ldquoThe ABCs of solute carriers physiologicalpathological and therapeutic implications of humanmembranetransport proteinsrdquo Pflugers Archiv European Journal of Physiol-ogy vol 447 no 5 pp 465ndash468 2004

[85] MMolina-Arcas F J Casado andM Pastor-Anglada ldquoNucleo-side transporter proteinsrdquo Current Vascular Pharmacology vol7 no 4 pp 426ndash434 2009

[86] H Daniel and G Kottra ldquoThe proton oligopeptide cotrans-porter family SLC15 in physiology and pharmacologyrdquo PflugersArchiv vol 447 no 5 pp 610ndash618 2004

[87] D Herrera-Ruiz and G T Knipp ldquoCurrent perspectiveson established and putative mammalian oligopeptide trans-portersrdquo Journal of Pharmaceutical Sciences vol 92 no 4 pp691ndash714 2003

[88] SM Carl D J Lindley D Das et al ldquoABC and SLC transporterexpression and proton oligopeptide transporter (POT) medi-ated permeation across the human bloodndashbrain barrier cell linehCMECD3 [corrected]rdquoMolecular Pharmaceutics vol 7 no 4pp 1057ndash1068 2010

[89] D E Smith C E Johanson andR F Keep ldquoPeptide and peptideanalog transport systems at the blood-CSF barrierrdquo AdvancedDrug Delivery Reviews vol 56 no 12 pp 1765ndash1791 2004

[90] W A Banks and A J Kastin ldquoBrain-to-blood transport ofpeptides and the alcohol withdrawal syndromerdquo Annals of theNew York Academy of Sciences vol 739 pp 108ndash118 1994

[91] A P Halestrap and M C Wilson ldquoThe monocarboxylatetransporter familymdashrole and regulationrdquo IUBMB Life vol 64no 2 pp 109ndash119 2012

[92] B E Enerson and L R Drewes ldquoMolecular features regulationand function of monocarboxylate transporters implications fordrug deliveryrdquo Journal of Pharmaceutical Sciences vol 92 no 8pp 1531ndash1544 2003

[93] K Pierre and L Pellerin ldquoMonocarboxylate transporters in thecentral nervous system distribution regulation and functionrdquoJournal of Neurochemistry vol 94 no 1 pp 1ndash14 2005

[94] A Ceballos M M Belinchon E Sanchez-Mendoza etal ldquoImportance of monocarboxylate transporter 8 for theblood-brain barrier-dependent availability of 3531015840-triiodo-L-thyroninerdquo Endocrinology vol 150 no 5 pp 2491ndash2496 2009

[95] S Broer B Rahman G Pellegri et al ldquoComparison of lactatetransport in astroglial cells and monocarboxylate transporter 1(MCT 1) expressing Xenopus laevis oocytes Expression of twodifferent monocarboxylate transporters in astroglial cells andneuronsrdquo Journal of Biological Chemistry vol 272 no 48 pp30096ndash30102 1997

[96] L Pellerin A P Halestrap and K Pierre ldquoCellular and subcel-lular distribution of monocarboxylate transporters in culturedbrain cells and in the adult brainrdquo Journal of NeuroscienceResearch vol 79 no 1-2 pp 55ndash64 2005

[97] M Niemi ldquoRole of OATP transporters in the disposition ofdrugsrdquo Pharmacogenomics vol 8 no 7 pp 787ndash802 2007

[98] T Mikkaichi T Suzuki M Tanemoto S Ito and T Abe ldquoTheorganic anion transporter (OATP) familyrdquo Drug Metabolismand Pharmacokinetics vol 19 no 3 pp 171ndash179 2004

[99] B Hagenbuch and P J Meier ldquoOrganic anion transport-ing polypeptides of the OATPSLC21 family phylogeneticclassification as OATPSLCO super-family new nomenclatureand molecularfunctional propertiesrdquo Pflugers Archiv EuropeanJournal of Physiology vol 447 no 5 pp 653ndash665 2004

[100] J Konig A Seithel U Gradhand and M F FrommldquoPharmacogenomics of human OATP transportersrdquo Naunyn-Schmiedebergrsquos Archives of Pharmacology vol 372 no 6 pp432ndash443 2006

[101] G A Kullak-Ublick B Hagenbuch B Stieger et al ldquoMolecularand functional characterization of an organic anion transport-ing polypeptide cloned from human liverrdquo Gastroenterologyvol 109 no 4 pp 1274ndash1282 1995

[102] W Lee H Glaeser L H Smith et al ldquoPolymorphismsin human organic anion-transporting polypeptide 1A2(OATP1A2) implications for altered drug disposition andcentral nervous system drug entryrdquo The Journal of BiologicalChemistry vol 280 no 10 pp 9610ndash9617 2005

[103] M Roth A Obaidat and B Hagenbuch ldquoOATPs OATs andOCTs the organic anion and cation transporters of the SLCOand SLC22A gene superfamiliesrdquo British Journal of Pharmacol-ogy vol 165 no 5 pp 1260ndash1287 2012

[104] R D Huber B Gao M-A S Pfandler et al ldquoCharacterizationof two splice variants of human organic anion transportingpolypeptide 3A1 isolated from human brainrdquo American Journalof Physiology Cell Physiology vol 292 no 2 pp C795ndashC8062007

[105] G A BaldeshwilerA Structure Function Study of Organic AnionTransporting Polypeptide 1c1 (Oatp1c1) 2011

[106] J W Jonker and A H Schinkel ldquoPharmacological and physio-logical functions of the polyspecific organic cation transportersoct1 2 and 3 (SLC22A1-3)rdquo Journal of Pharmacology andExperimental Therapeutics vol 308 no 1 pp 2ndash9 2004

[107] H Kusuhara T Sekine N Utsunomiya-Tate et al ldquoMolecularcloning and characterization of a new multispecific organicanion transporter from rat brainrdquo The Journal of BiologicalChemistry vol 274 no 19 pp 13675ndash13680 1999

[108] S H Cha T Sekine H Kusuhara et al ldquoMolecular cloningand characterization of multispecific organic anion transporter4 expressed in the placentardquo Journal of Biological Chemistry vol275 no 6 pp 4507ndash4512 2000

[109] T Sekine N Watanabe M Hosoyamada Y Kanai and HEndou ldquoExpression cloning and characterization of a novelmultispecific organic anion transporterrdquoThe Journal of Biologi-cal Chemistry vol 272 no 30 pp 18526ndash18529 1997


[110] D H Sweet and J B Pritchard ldquoThe molecular biology ofrenal organic anion and organic cation transportersrdquo CellBiochemistry and Biophysics vol 31 no 1 pp 89ndash118 1999

[111] J C Monte M A Nagle S A Eraly and S K Nigam ldquoIden-tification of a novel murine organic anion transporter familymember OAT6 expressed in olfactory mucosardquo Biochemicaland Biophysical Research Communications vol 323 no 2 pp429ndash436 2004

[112] T Sekine S H Cha and H Endou ldquoThe multispecific organicanion transporter (OAT) familyrdquo Pflugers Archiv vol 440 no3 pp 337ndash350 2000

[113] A E Riedmaier A T Nies E Schaeffeler and M SchwabldquoOrganic anion transporters and their implications in pharma-cotherapyrdquo Pharmacological Reviews vol 64 no 3 pp 421ndash4492012

[114] S Mori H Takanaga S Ohtsuki et al ldquoRat organic aniontransporter 3 (rOAT3) is responsible for brain-to-blood effluxof homovanillic acid at the abluminal membrane of braincapillary endothelial cellsrdquo Journal of Cerebral Blood Flow andMetabolism vol 23 no 4 pp 432ndash440 2003

[115] D H Sweet D S Miller J B Pritchard Y Fujiwara D RBeier and S K Nigam ldquoImpaired organic anion transport inkidney and choroid plexus of organic anion transporter 3 (Oat3(Slc22a8)) knockout micerdquoThe Journal of Biological Chemistryvol 277 no 30 pp 26934ndash26943 2002

[116] T Sekine S H Cha M Tsuda et al ldquoIdentification of multi-specific organic anion transporter 2 expressed predominantlyin the liverrdquo FEBS Letters vol 429 no 2 pp 179ndash182 1998

[117] G L Youngblood and D H Sweet ldquoIdentification and func-tional assessment of the novelmurine organic anion transporterOat5 (Slc22a19) expressed in kidneyrdquo The American Journal ofPhysiologymdashRenal Physiology vol 287 no 2 pp F236ndashF2442004

[118] H Koepsell ldquoOrganic cation transporters in intestine kidneyliver and brainrdquo Annual Review of Physiology vol 60 pp 243ndash266 1998

[119] H Koepsell and H Endou ldquoThe SLC22 drug transporterfamilyrdquo Pflugers Archiv vol 447 no 5 pp 666ndash676 2004

[120] D Grundemann J Babin-Ebell F Martel N Ording ASchmidt and E Schomig ldquoPrimary structure and functionalexpression of the apical organic cation transporter from kidneyepithelial LLC-PK1 cellsrdquo Journal of Biological Chemistry vol272 no 16 pp 10408ndash10413 1997

[121] G Ciarimboli and E Schlatter ldquoRegulation of organic cationtransportrdquo Pflugers Archiv vol 449 no 5 pp 423ndash441 2005

[122] C-J Lin Y Tai M-T Huang et al ldquoCellular localization ofthe organic cation transporters OCT1 and OCT2 in brainmicrovessel endothelial cells and its implication for MPTPtransport across the blood-brain barrier and MPTP-induceddopaminergic toxicity in rodentsrdquo Journal of Neurochemistryvol 114 no 3 pp 717ndash727 2010

[123] D Dickens A Owen A Alfirevic et al ldquoLamotrigine is asubstrate for OCT1 in brain endothelial cellsrdquo BiochemicalPharmacology vol 83 no 6 pp 805ndash814 2012

[124] X Wu R Kekuda W Huang et al ldquoIdentity of the organiccation transporter OCT3 as the extraneuronal monoaminetransporter (uptake2) and evidence for the expression of thetransporter in the brainrdquo The Journal of Biological Chemistryvol 273 no 49 pp 32776ndash32786 1998

[125] XWu R L GeorgeW Huang et al ldquoStructural and functionalcharacteristics and tissue distribution pattern of rat OCTN1 an

organic cation transporter cloned from placentardquo Biochimica etBiophysica Acta Biomembranes vol 1466 no 1-2 pp 315ndash3272000

[126] A Inano Y Sai H Nikaido et al ldquoAcetyl-L-carnitine per-meability across the blood-brain barrier and involvement ofcarnitine transporter OCTN2rdquo Biopharmaceutics and DrugDisposition vol 24 no 8 pp 357ndash365 2003

[127] A-M Lamhonwah C A Ackerley A Tilups V D Edwards RJ Wanders and I Tein ldquoOCTN3 is a mammalian peroxisomalmembrane carnitine transporterrdquo Biochemical and BiophysicalResearch Communications vol 338 no 4 pp 1966ndash1972 2005

[128] I Tamai H Yabuuchi J-I Nezu et al ldquoCloning and char-acterization of a novel human pH-dependent organic cationtransporter OCTN1rdquo The FEBS Letters vol 419 no 1 pp 107ndash111 1997

[129] R Ohashi I Tamai H Yabuuchi et al ldquoNa+-dependentcarnitine transport by organic cation transporter (OCTN2)its pharmacological and toxicological relevancerdquo Journal ofPharmacology and ExperimentalTherapeutics vol 291 no 2 pp778ndash784 1999

[130] J M Lauder ldquoNeurotransmitters as growth regulatory signalsrole of receptors and second messengersrdquo Trends in Neuro-sciences vol 16 no 6 pp 233ndash240 1993

[131] J RMackey R SManiM Selner et al ldquoFunctional nucleosidetransporters are required for gemcitabine influx and manifesta-tion of toxicity in cancer cell linesrdquo Cancer Research vol 58 no19 pp 4349ndash4357 1998

[132] J H Gray R P Owen and KM Giacomini ldquoThe concentrativenucleoside transporter family SLC28rdquo Pflugers Archiv vol 447no 5 pp 728ndash734 2004

[133] M A Cabrita S A Baldwin J D Young and C E CassldquoMolecular biology and regulation of nucleoside and nucle-obase transporter proteins in eukaryotes and prokaryotesrdquoBiochemistry and Cell Biology vol 80 no 5 pp 623ndash638 2002

[134] S A Baldwin S Y M Yao R J Hyde et al ldquoFunctionalcharacterization of novel human andmouse equilibrative nucle-oside transporters (hENT3 andmENT3) located in intracellularmembranesrdquo The Journal of Biological Chemistry vol 280 no16 pp 15880ndash15887 2005

[135] C Wang W Lin H Playa S Sun K Cameron and J K Buo-lamwini ldquoDipyridamole analogs as pharmacological inhibitorsof equilibrative nucleoside transporters Identification of novelpotent and selective inhibitors of the adenosine transporterfunction of human equilibrative nucleoside transporter 4(hENT4)rdquo Biochemical Pharmacology vol 86 no 11 pp 1531ndash1540 2013

[136] R J Hyde C E Cass J D Young and S A Baldwin ldquoThe ENTfamily of eukaryote nucleoside and nucleobase transportersrecent advances in the investigation of structurefunction rela-tionships and the identification of novel isoformsrdquo MolecularMembrane Biology vol 18 no 1 pp 53ndash63 2001

[137] M Sundaram S Y M Yao J C Ingram et al ldquoTopologyof a human equilibrative nitrobenzylthioinosine (NBMPR)-sensitive nucleoside transporter (hENT1) implicated in thecellular uptake of adenosine and anti-cancer drugsrdquo Journal ofBiological Chemistry vol 276 no 48 pp 45270ndash45275 2001

[138] R S Mani J R Hammond J M J Marjan et al ldquoDemon-stration of equilibrative nucleoside transporters (hENT1 andhENT2) in nuclear envelopes of cultured human choriocarci-noma (BeWo) cells by functional reconstitution in proteolipo-somesrdquoThe Journal of Biological Chemistry vol 273 no 46 pp30818ndash30825 1998


[139] C R Crawford D H Patel C Naeve and J A Belt ldquoCloning ofthe human equilibrative nitrobenzylmercaptopurine riboside(NBMPR)-insensitive nucleoside transporter ei by functionalexpression in a transport-deficient cell linerdquo The Journal ofBiological Chemistry vol 273 no 9 pp 5288ndash5293 1998

[140] K Engel M Zhou and J Wang ldquoIdentification and characteri-zation of a novel monoamine transporter in the human brainrdquoThe Journal of Biological Chemistry vol 279 no 48 pp 50042ndash50049 2004

[141] K M Smith S K Slugoski A M L Loewen et alldquoThe broadly selective human Na+nucleoside cotransporter(hCNT3) exhibits novel cation-coupled nucleoside transportcharacteristicsrdquoThe Journal of Biological Chemistry vol 280 no27 pp 25436ndash25449 2005

[142] H Wolburg K Wolburg-Buchholz J Kraus et al ldquoLocal-ization of claudin-3 in tight junctions of the blood-brainbarrier is selectively lost during experimental autoimmuneencephalomyelitis and human glioblastoma multiformerdquo ActaNeuropathologica vol 105 no 6 pp 586ndash592 2003

[143] P Dhawan A B Singh N G Deane et al ldquoClaudin-1 regu-lates cellular transformation and metastatic behavior in coloncancerrdquo The Journal of Clinical Investigation vol 115 no 7 pp1765ndash1776 2005

[144] W Jia R Lu T AMartin andW G Jiang ldquoThe role of claudin-5 in blood-brain barrier (BBB) and brain metastases (review)rdquoMolecular Medicine Reports vol 9 no 3 pp 779ndash785 2014

[145] D C Davies ldquoBlood-brain barrier breakdown in septicencephalopathy and brain tumoursrdquo Journal of Anatomy vol200 no 6 pp 639ndash646 2002

[146] H E de Vries M C M Blom-Roosemalen M van Oosten etal ldquoThe influence of cytokines on the integrity of the blood-brain barrier in vitrordquo Journal of Neuroimmunology vol 64 no1 pp 37ndash43 1996

[147] K Lamszus N O Schmidt S Ergun and M Westphal ldquoIsola-tion and culture of human neuromicrovascular endothelial cellsfor the study of angiogenesis in vitrordquo Journal of NeuroscienceResearch vol 55 no 3 pp 370ndash381 1999

[148] A L Cowles and J D Fenstermacher ldquoTheoretical considera-tions in the chemotherapy of brain tumorsrdquo in Antineoplasticand Immunosuppressive Agents Part I A C Sartorelli and D GJohns Eds pp 319ndash329 Springer Berlin Germany 1974

[149] J D Fenstermacher and A L Cowles ldquoTheoretic limitationsof intracarotid infusions in brain tumor chemotherapyrdquo CancerTreatment Reports vol 61 no 4 pp 519ndash526 1977

[150] W W Eckman C S Patlak and J D Fenstermacher ldquoAcritical evaluation of the principles governing the advantagesof intra arterial infusionsrdquo Journal of Pharmacokinetics andBiopharmaceutics vol 2 no 3 pp 257ndash285 1974

[151] J Fenstermacher and J Gazendam ldquoIntra-arterial infusions ofdrugs and hyperosmotic solutions as ways of enhancing CNSchemotherapyrdquo Cancer Treatment Reports vol 65 supplement2 pp 27ndash37 1981

[152] Y Hirano K Mineura K Mizoi and N Tomura ldquoTherapeuticresults of intra-arterial chemotherapy in patients with malig-nant gliomardquo International Journal of Oncology vol 13 no 3pp 537ndash542 1998

[153] E J Dropcho S S Rosenfeld J Vitek B L Guthrie andR B Morawetz ldquoPhase II study of intracarotid or selectiveintracerebral infusion of cisplatin for treatment of recurrentanaplastic gliomasrdquo Journal of Neuro-Oncology vol 36 no 2pp 191ndash198 1998

[154] S Gundersen K Lote and K Watne ldquoA retrospective studyof the value of chemotherapy as adjuvant therapy to surgeryand radiotherapy in grade 3 and 4 gliomasrdquo European Journalof Cancer vol 34 no 10 pp 1565ndash1569 1998

[155] H A Riina J F Fraser S Fralin J Knopman R J Scheff andJ A Boockvar ldquoSuperselective intraarterial cerebral infusionof bevacizumab a revival of interventional neuro-oncology formalignant gliomardquo Journal of Experimental Therapeutics andOncology vol 8 no 2 pp 145ndash150 2009

[156] R G Blasberg C S Patlak and W R Shapiro ldquoDistributionof methotrexate in the cerebrospinal fluid and brain afterintraventricular administrationrdquoCancer Treatment Reports vol61 no 4 pp 633ndash641 1977

[157] R G Blasberg ldquoMethotrexate cytosine arabinoside and BCNUconcentration in brain after ventriculocisternal perfusionrdquoCancer Treatment Reports vol 61 no 4 pp 625ndash631 1977

[158] R G Blasberg ldquoPharmacodynamics and the blood-brain bar-rierrdquo National Cancer Institute monograph vol 46 pp 19ndash271977

[159] D R Groothuis and R M Levy ldquoThe entry of antiviral andantiretroviral drugs into the central nervous systemrdquo Journal ofNeuroVirology vol 3 no 6 pp 387ndash400 1997

[160] D W Laske R J Youle and E H Oldfield ldquoTumor regressionwith regional distribution of the targeted toxin TF- CRM107 inpatients with malignant brain tumorsrdquo Nature Medicine vol 3no 12 pp 1362ndash1368 1997

[161] L H Parsons and J B Justice Jr ldquoQuantitative approaches to invivo brain microdialysisrdquo Critical Reviews in Neurobiology vol8 no 3 pp 189ndash220 1994

[162] E C M De Lange B A G De Boer and D D BreimerldquoMicrodialysis for pharmacokinetic analysis of drug transportto the brainrdquo Advanced Drug Delivery Reviews vol 36 no 2-3pp 211ndash227 1999

[163] K H Dykstra J K Hsiao P F Morrison et al ldquoQuantitativeexamination of tissue concentration profiles associated withmicrodialysisrdquo Journal of Neurochemistry vol 58 no 3 pp 931ndash940 1992

[164] WM Pardridge ldquoBlood-brain barrier drug targeting the futureof brain drug developmentrdquoMolecular Interventions vol 3 no2 pp 90ndash51 2003

[165] V Chandramohan J H Sampson I Pastan and D D BignerldquoToxin-based targeted therapy for malignant brain tumorsrdquoClinical and Developmental Immunology vol 2012 Article ID480429 2012

[166] D Fortin C Gendron M Boudrias and M-P GarantldquoEnhanced chemotherapy delivery by intraarterial infusion andblood-brain barrier disruption in the treatment of cerebralmetastasisrdquo Cancer vol 109 no 4 pp 751ndash760 2007

[167] C V Borlongan and D F Emerich ldquoFacilitation of drug entryinto the CNS via transient permeation of blood brain barrierlaboratory and preliminary clinical evidence from bradykininreceptor agonist Cereportrdquo Brain Research Bulletin vol 60 no3 pp 297ndash306 2003

[168] K Matsukado T Inamura S Nakano M Fukui R T Bartusand K L Black ldquoEnhanced tumor uptake of carboplatin andsurvival in glioma-bearing rats by intracarotid infusion ofbradykinin analog RMP-7rdquoNeurosurgery vol 39 no 1 pp 125ndash134 1996

[169] B Erdlenbruch V Jendrossek H Eibl and M LakomekldquoTransient and controllable opening of the blood-brain barrierto cytostatic and antibiotic agents by alkylglycerols in ratsrdquoExperimental Brain Research vol 135 no 3 pp 417ndash422 2000


[170] M Kinoshita N McDannold F A Jolesz and K HynynenldquoNoninvasive localized delivery of Herceptin to the mousebrain by MRI-guided focused ultrasound-induced blood-brainbarrier disruptionrdquo Proceedings of the National Academy ofSciences of theUnited States of America vol 103 no 31 pp 11719ndash11723 2006

[171] F Leweke M S Damian C Schindler and W SchachenmayrldquoMultidrug resistance in glioblastoma Chemosensitivity testingand immunohistochemical demonstration of P-glycoproteinrdquoPathology Research and Practice vol 194 no 3 pp 149ndash1551998

[172] L A Doyle and D D Ross ldquoMultidrug resistance mediated bythe breast cancer resistance proteinBCRP (ABCG2)rdquoOncogenevol 22 no 47 pp 7340ndash7358 2003

[173] S F Bates C Chen R Robey M Kang W D Figg and TFojo ldquoReversal of multidrug resistance lessons from clinicaloncologyrdquo Novartis Foundation Symposia vol 243 pp 83ndash1852002

[174] HThomas andHM Coley ldquoOvercomingmultidrug resistancein cancer an update on the clinical strategy of inhibiting P-glycoproteinrdquo Cancer Control vol 10 no 2 pp 159ndash165 2003

[175] R Michael A Folkes P Ashworth et al ldquoReversal of P-glycoprotein mediated multidrug resistance by novel anthranil-amide derivativesrdquo Bioorganic amp Medicinal Chemistry Lettersvol 9 no 4 pp 595ndash600 1999

[176] A H Dantzig R L Shepard K L Law et al ldquoSelectivity of themultidrug resistance modulator LY335979 for P- glycoproteinand effect on cytochrome P-450 activitiesrdquo Journal of Pharma-cology and Experimental Therapeutics vol 290 no 2 pp 854ndash862 1999

[177] L Van Zuylen A Sparreboom A Van Der Gaast et al ldquoTheorally administered P-glycoprotein inhibitor R101933 does notalter the plasma pharmacokinetics of docetaxelrdquoClinical CancerResearch vol 6 no 4 pp 1365ndash1371 2000

[178] E M Kemper A E van Zandbergen C Cleypool et alldquoIncreased penetration of paclitaxel into the brain by inhibitionof P-glycoproteinrdquo Clinical Cancer Research vol 9 no 7 pp2849ndash2855 2003

[179] G Fricker and D S Miller ldquoModulation of drug transporters atthe blood-brain barrierrdquo Pharmacology vol 70 no 4 pp 169ndash176 2004

[180] R G Thorne C R Emory T A Ala and W H Frey IIldquoQuantitative analysis of the olfactory pathway for drug deliveryto the brainrdquo Brain Research vol 692 no 1-2 pp 278ndash282 1995

[181] D Dhanda W Frey II D Leopold and U KompellaldquoApproaches for drug deposition in the human olfactory epithe-liumrdquo Drug Development amp Delivery vol 5 pp 64ndash72 2005

[182] D Wang Y Gao and L Yun ldquoStudy on brain targeting ofraltitrexed following intranasal administration in ratsrdquo CancerChemotherapy and Pharmacology vol 57 no 1 pp 97ndash1042006

[183] T Sakane S Yamashita N Yata and H Sezaki ldquoTransnasaldelivery of 5-fluorouracil to the brain in the ratrdquo Journal of DrugTargeting vol 7 no 3 pp 233ndash240 1999

[184] R Hashizume T Ozawa S M Gryaznov et al ldquoNew therapeu-tic approach for brain tumors intranasal delivery of telomeraseinhibitor GRN163rdquo Neuro-Oncology vol 10 no 2 pp 112ndash1202008

[185] F Wang X Jiang andW Lu ldquoProfiles of methotrexate in bloodand CSF following intranasal and intravenous administrationto ratsrdquo International Journal of Pharmaceutics vol 263 no 1-2pp 1ndash7 2003

[186] C A Lipinski F Lombardo B W Dominy and P J FeeneyldquoExperimental and computational approaches to estimate sol-ubility and permeability in drug discovery and developmentsettingsrdquo Advanced Drug Delivery Reviews vol 46 no 1ndash3 pp3ndash26 2001

[187] W M Pardridge ldquoTransport of small molecules through theblood-brain barrier biology andmethodologyrdquoAdvanced DrugDelivery Reviews vol 15 no 1ndash3 pp 5ndash36 1995

[188] D R Groothuis B E Lippitz I Fekete et al ldquoThe effect of anamino acid-lowering diet on the rate of melphalan entry intobrain and xenotransplanted gliomardquo Cancer Research vol 52no 20 pp 5590ndash5596 1992

[189] V E Shashoua and G W Hesse ldquoN-docosahexaenoyl 3hydroxytyramine a dopaminergic compound that penetratesthe blood-brain barrier and suppresses appetiterdquo Life Sciencesvol 58 no 16 pp 1347ndash1357 1996

[190] M O Bradley N L Webb F H Anthony et al ldquoTumortargeting by covalent conjugation of a natural fatty acid topaclitaxelrdquo Clinical Cancer Research vol 7 no 10 pp 3229ndash3238 2001

[191] M E Sherman Y S Erozan R B Mann et al ldquoStereotacticbrain biopsy in the diagnosis of malignant lymphomardquo TheAmerican Journal of Clinical Pathology vol 95 no 6 pp 878ndash883 1991

[192] T Yoshikawa T Sakaeda T Sugawara K Hirano and V JStella ldquoA novel chemical delivery system for brain targetingrdquoAdvanced Drug Delivery Reviews vol 36 no 2-3 pp 255ndash2751999

[193] X-H Tian X-N Lin F Wei et al ldquoEnhanced brain targetingof temozolomide in polysorbate-80 coated polybutylcyanoacry-late nanoparticlesrdquo International Journal of Nanomedicine vol6 pp 445ndash452 2011

[194] A Jain G Chasoo S K Singh A K Saxena and S K JainldquoTransferrin-appended PEGylated nanoparticles for temozolo-mide delivery to brain in vitro characterisationrdquo Journal ofMicroencapsulation vol 28 no 1 pp 21ndash28 2011

[195] G Huang N Zhang X Bi andM Dou ldquoSolid lipid nanoparti-cles of temozolomide potential reduction of cardial andnephrictoxicityrdquo International Journal of Pharmaceutics vol 355 no 1-2 pp 314ndash320 2008

[196] Y Ling K Wei F Zou and S Zhong ldquoTemozolomide loadedPLGA-based superparamagnetic nanoparticles for magneticresonance imaging and treatment of malignant gliomardquo Inter-national Journal of Pharmaceutics vol 430 no 1-2 pp 266ndash2752012

[197] D S Jain R B Athawale A N Bajaj et al ldquoUnravelingthe cytotoxic potential of Temozolomide loaded into PLGAnanoparticlesrdquo DARU Journal of Pharmaceutical Sciences vol22 article 18 2014

[198] C Abrudan I S Florian A Baritchii et al ldquoAssessment oftemozolomide action encapsulated in chitosan and polymernanostructures on glioblastoma cell linesrdquo Romanian Neuro-surgery vol 21 no 1 pp 18ndash29 2014

[199] J Tao P Hua-Nan Y Jin-Na et al ldquoPreparation and braindelivery evaluation of temozolomide-loaded albumin nanopar-ticlesrdquo Chinese Journal of Pharmaceuticals vol 44 no 1 pp 41ndash45 2013

[200] D A Bota A Desjardins J A Quinn M L Affronti andH S Friedman ldquoInterstitial chemotherapy with biodegrad-able BCNU (Gliadel) wafers in the treatment of malignantgliomasrdquoTherapeutics and Clinical Risk Management vol 3 no5 pp 707ndash715 2007


[201] L Qian J Zheng K Wang et al ldquoCationic core-shell nanopar-ticles with carmustine containedwithinO6-benzylguanine shellfor glioma therapyrdquo Biomaterials vol 34 no 35 pp 8968ndash89782013

[202] Y-C Kuo and C-T Liang ldquoInhibition of human brain malig-nant glioblastoma cells using carmustine-loaded catanionicsolid lipid nanoparticles with surface anti-epithelial growthfactor receptorrdquo Biomaterials vol 32 no 12 pp 3340ndash33502011

[203] C Kang X Yuan Y Zhong et al ldquoGrowth inhibition againstintracranial C6 glioma cells by stereotactic delivery of BCNUby controlled release from poly(DL-lactic acid) nanoparticlesrdquoTechnology in Cancer Research and Treatment vol 8 no 1 pp61ndash70 2009

[204] K Fabel J Dietrich P Hau et al ldquoLong-term stabilization inpatients with malignant glioma after treatment with liposomaldoxorubicinrdquo Cancer vol 92 no 7 pp 1936ndash1942 2001

[205] Y-C Kuo and C-T Liang ldquoCatanionic solid lipid nanoparticlescarrying doxorubicin for inhibiting the growth ofU87MGcellsrdquoColloids and Surfaces B Biointerfaces vol 85 no 2 pp 131ndash1372011

[206] S Wohlfart A S Khalansky S Gelperina et al ldquoEfficientchemotherapy of rat glioblastoma using doxorubicin-loadedPLGA nanoparticles with different stabilizersrdquo PLoS ONE vol6 no 5 Article ID e19121 2011

[207] J P Wang X L Zhu Y W Xi D F Wang and G H HuangldquoPreparation of lomustine loaded liposomes and studies of itspharmacokinetics and tissue distribution propertiesrdquo Journalof Chinese Pharmaceutical Sciences vol 19 no 5 pp 353ndash3622010

[208] A Y Bedikian N E Papadopoulos K B Kim et al ldquoA pilotstudy with vincristine sulfate liposome infusion in patients withmetastatic melanomardquo Melanoma Research vol 18 no 6 pp400ndash404 2008

[209] R Saito J R Bringas T R McKnight et al ldquoDistribution ofliposomes into brain and rat brain tumormodels by convection-enhanced delivery monitored with magnetic resonance imag-ingrdquo Cancer Research vol 64 no 7 pp 2572ndash2579 2004

[210] Q Lv L-M Li M Han et al ldquoCharacteristics of sequentialtargeting of brain glioma for transferrin-modified cisplatinliposomerdquo International Journal of Pharmaceutics vol 444 no1-2 pp 1ndash9 2013

[211] A Fiorillo G Maggi N Greco et al ldquoSecond-line chemother-apywith the association of liposomal daunorubicin carboplatinand etoposide in children with recurrent malignant braintumorsrdquo Journal of Neuro-Oncology vol 66 no 1-2 pp 179ndash1852004

[212] M Wankhede A Bouras M Kaluzova and C G Hadji-panayis ldquoMagnetic nanoparticles an emerging technology formalignant brain tumor imaging and therapyrdquo Expert Review ofClinical Pharmacology vol 5 no 2 pp 173ndash186 2012

[213] Y-C Kuo and T-Y Hong ldquoDelivering etoposide to the brainusing catanionic solid lipid nanoparticles with surface 5-HT-modulinerdquo International Journal of Pharmaceutics vol 465 no1-2 pp 132ndash142 2014

[214] R L Juliano and D Stamp ldquoPharmacokinetics of liposome-encapsulated anti-tumor drugs studieswith vinblastine actino-mycin D cytosine arabinoside and daunomycinrdquo BiochemicalPharmacology vol 27 no 1 pp 21ndash27 1978

[215] P-Y Chen T Ozawa D C Drummond et al ldquoComparingroutes of delivery for nanoliposomal irinotecan shows superior

anti-tumor activity of local administration in treating intracra-nial glioblastoma xenograftsrdquoNeuro-Oncology vol 15 no 2 pp189ndash197 2013

[216] B J Turunen H Ge J Oyetunji et al ldquoPaclitaxel succinateanalogs anionic and amide introduction as a strategy to impartblood-brain barrier permeabilityrdquo Bioorganic and MedicinalChemistry Letters vol 18 no 22 pp 5971ndash5974 2008

[217] Y Wang C Wang C Gong G Guo F Luo and Z QianldquoPolysorbate 80 coated poly (120576-caprolactone)-poly (ethyleneglycol)-poly (120576-caprolactone) micelles for paclitaxel deliveryrdquoInternational Journal of Pharmaceutics vol 434 no 1-2 pp 1ndash82012

[218] X-Y Li Y Zhao M-G Sun et al ldquoMultifunctional liposomesloaded with paclitaxel and artemether for treatment of invasivebrain gliomardquo Biomaterials vol 35 no 21 pp 5591ndash5604 2014

[219] J M Provenzale S Mukundan and M Dewhirst ldquoThe role ofblood-brain barrier permeability in brain tumor imaging andtherapeuticsrdquo American Journal of Roentgenology vol 185 no3 pp 763ndash767 2005

[220] J Kreuter ldquoInfluence of the surface properties on nanoparticle-mediated transport of drugs to the brainrdquo Journal ofNanoscience and Nanotechnology vol 4 no 5 pp 484ndash4882004

[221] Y Jallouli A Paillard J Chang E Sevin and D BetbederldquoInfluence of surface charge and inner composition of porousnanoparticles to cross blood-brain barrier in vitrordquo Interna-tional Journal of Pharmaceutics vol 344 no 1-2 pp 103ndash1092007

[222] S M Moghimi A C Hunter and J C Murray ldquoLong-circulating and target-specific nanoparticles theory to prac-ticerdquo Pharmacological Reviews vol 53 no 2 pp 283ndash318 2001

[223] W M Pardridge ldquoVector-mediated drug delivery to the brainrdquoAdvanced Drug Delivery Reviews vol 36 no 2-3 pp 299ndash3211999

[224] V Soni D V Kohli and S K Jain ldquoTransferrin-conjugatedliposomal system for improved delivery of 5-fluorouracil tobrainrdquo Journal of Drug Targeting vol 16 no 1 pp 73ndash78 2008

[225] A Doi S Kawabata K Iida et al ldquoTumor-specific targeting ofsodium borocaptate (BSH) to malignant glioma by transferrin-PEG liposomes a modality for boron neutron capture therapyrdquoJournal of Neuro-oncology vol 87 no 3 pp 287ndash294 2008

[226] X Ying H Wen W-L Lu et al ldquoDual-targeting daunorubicinliposomes improve the therapeutic efficacy of brain glioma inanimalsrdquo Journal of Controlled Release vol 141 no 2 pp 183ndash192 2010

[227] B Gupta T S Levchenko and V P Torchilin ldquoTAT peptide-modified liposomes provide enhanced gene delivery to intracra-nial human brain tumor xenografts in nude micerdquo OncologyResearch vol 16 no 8 pp 351ndash359 2007

[228] L Juillerat-Jeanneret ldquoCritical analysis of cancer therapy usingnanomaterialsrdquo inNanotechnologies for the Life Sciences Wiley-VCH 2007

[229] L Fenart A Casanova B Dehouck et al ldquoEvaluation of effectof charge and lipid coating on ability of 60-nm nanoparticlesto cross an in vitro model of the blood-brain barrierrdquo Journalof Pharmacology and Experimental Therapeutics vol 291 no 3pp 1017ndash1022 1999

[230] D Wu and W M Pardridge ldquoBlood-brain barrier transport ofreduced folic acidrdquo Pharmaceutical Research vol 16 no 3 pp415ndash419 1999


[231] B Petri A Bootz A Khalansky et al ldquoChemotherapy ofbrain tumour using doxorubicin bound to surfactant-coatedpoly (butyl cyanoacrylate) nanoparticles revisiting the role ofsurfactantsrdquo Journal of Controlled Release vol 117 no 1 pp 51ndash58 2007

[232] Y Tsutsui K Tomizawa M Nagita et al ldquoDevelopment ofbionanocapsules targeting brain tumorsrdquo Journal of ControlledRelease vol 122 no 2 pp 159ndash164 2007

[233] H L Wong R Bendayan A M Rauth Y Li and X Y WuldquoChemotherapy with anticancer drugs encapsulated in solidlipid nanoparticlesrdquo Advanced Drug Delivery Reviews vol 59no 6 pp 491ndash504 2007

[234] H Chen X Zhang S Dai et al ldquoMultifunctional gold nanostarconjugates for tumor imaging and combined photothermal andchemo-therapyrdquoTheranostics vol 3 no 9 pp 633ndash649 2013

[235] W-H Chen X-D Xu H-Z Jia et al ldquoTherapeuticnanomedicine based on dual-intelligent functionalizedgold nanoparticles for cancer imaging and therapy in vivordquoBiomaterials vol 34 no 34 pp 8798ndash8807 2013

[236] Z Liu and X-J Liang ldquoNano-carbons as theranosticsrdquo Thera-nostics vol 2 no 3 pp 235ndash237 2012

[237] S-Y Qin J Feng L Rong et al ldquoTheranostic GO-basednanohybrid for tumor induced imaging and potential combi-national tumor therapyrdquo Small vol 10 no 3 pp 599ndash608 2014

[238] K K Jain ldquoUse of nanoparticles for drug delivery in glioblas-toma multiformerdquo Expert Review of Neurotherapeutics vol 7no 4 pp 363ndash372 2007

[239] AVKabanov EV Batrakova andDWMiller ldquoPluronic blockcopolymers as modulators of drug efflux transporter activity inthe blood-brain barrierrdquo Advanced Drug Delivery Reviews vol55 no 1 pp 151ndash164 2003

[240] E V Batrakova and A V Kabanov ldquoPluronic block copolymersevolution of drug delivery concept from inert nanocarriers tobiological response modifiersrdquo Journal of Controlled Releasevol 130 no 2 pp 98ndash106 2008

[241] R S Dhanikula A Argaw J-F Bouchard and P HildgenldquoMethotrexate loaded polyether-copolyester dendrimers forthe treatment of gliomas enhanced efficacy and intratumoraltransport capabilityrdquoMolecular Pharmaceutics vol 5 no 1 pp105ndash116 2008

[242] C M Kramm N G Rainov M Sena-Esteves et al ldquoHerpesvector-mediated delivery of marker genes to disseminatedcentral nervous system tumorsrdquo Human Gene Therapy vol 7no 3 pp 291ndash300 1996

[243] J Chen T Bezdek J Chang et al ldquoA glial-specific repress-ible adenovirus vector for brain tumor gene therapyrdquo CancerResearch vol 58 no 16 pp 3504ndash3507 1998

[244] H E J Hofland D Nagy J-J Liu et al ldquoIn vivo gene transferby intravenous administration of stable cationic lipidDNAcomplexrdquo Pharmaceutical Research vol 14 no 6 pp 742ndash7491997

[245] S-S Kim A Rait E Kim et al ldquoNanoparticle carrying thep53 gene targets tumors including cancer stem cells sensitizesglioblastoma to chemotherapy and improves survivalrdquo ACSNano vol 8 no 6 pp 5494ndash5514 2014

[246] A Schuessler C Smith L Beagley et al ldquoAutologous T-celltherapy for cytomegalovirus as a consolidative treatment forrecurrent glioblastomardquo Cancer Research vol 74 no 13 pp3466ndash3476 2014

[247] A M Thayer ldquoImproving peptidesrdquo Chemical amp EngineeringNews Archive vol 89 no 22 pp 13ndash20 2011

[248] L Soroceanu Y Gillespie M B Khazaeli and H SontheimerldquoUse of chlorotoxin for targeting of primary brain tumorsrdquoCancer Research vol 58 no 21 pp 4871ndash4879 1998

[249] M Z Strowski and A D Blake ldquoFunction and expression ofsomatostatin receptors of the endocrine pancreasrdquo Molecularand Cellular Endocrinology vol 286 no 1-2 pp 169ndash179 2008

[250] K De A Bhowmik A Behera I Banerjee M K Ghosh andM Misra ldquoSynthesis radiolabeling and preclinical evaluationof a new octreotide analog for somatostatin receptor-positivetumor scintigraphyrdquo Journal of Peptide Science vol 18 no 12pp 720ndash730 2012

[251] R A Henderson S Mossman N Nairn and M A CheeverldquoCancer vaccines and immunotherapies emerging perspec-tivesrdquo Vaccine vol 23 no 17-18 pp 2359ndash2362 2005

[252] R A Fenstermaker and M J Ciesielski ldquoChallenges in thedevelopment of a survivin vaccine (SurVaxM) for malignantgliomardquo Expert Review of Vaccines vol 13 no 3 pp 377ndash3852014

[253] J H Sampson G E Archer D A Mitchell et al ldquoAn epidermalgrowth factor receptor variant III-targeted vaccine is safeand immunogenic in patients with glioblastoma multiformerdquoMolecular Cancer Therapeutics vol 8 no 10 pp 2773ndash27792009

[254] L W Xu K K H Chow M Lim and G Li ldquoCurrentvaccine trials in glioblastoma a reviewrdquo Journal of ImmunologyResearch vol 2014 Article ID 796856 10 pages 2014

[255] R J Boado ldquoBlood-brain barrier transport of non-viral geneand RNAi therapeuticsrdquo Pharmaceutical Research vol 24 no9 pp 1772ndash1787 2007

[256] N Shi andW M Pardridge ldquoNoninvasive gene targeting to thebrainrdquo Proceedings of the National Academy of Sciences of theUnited States of America vol 97 no 13 pp 7567ndash7572 2000

[257] W M Pardridge ldquoGene targeting in vivo with pegylatedimmunoliposomesrdquoMethods in Enzymology vol 373 pp 507ndash528 2003

[258] Y Zhang Y-F Zhang J Bryant A Charles R J Boado andW M Pardridge ldquoIntravenous RNA interference gene therapytargeting the human epidermal growth factor receptor prolongssurvival in intracranial brain cancerrdquo Clinical Cancer Researchvol 10 no 11 pp 3667ndash3677 2004

[259] K J Lim S Bisht E E Bar A Maitra and C G EberhartldquoA polymeric nanoparticle formulation of curcumin inhibitsgrowth clonogenicity and stem-like fraction inmalignant braintumorsrdquoCancer Biology andTherapy vol 11 no 5 pp 464ndash4732011

[260] T Kato A Natsume H Toda et al ldquoEfficient delivery ofliposome-mediated MGMT-siRNA reinforces the cytotoxity oftemozolomide in GBM-initiating cellsrdquo Gene Therapy vol 17no 11 pp 1363ndash1371 2010

[261] C-H Wang S-H Chiou C-P Chou Y-C Chen Y-J Huangand C-A Peng ldquoPhotothermolysis of glioblastoma stem-likecells targeted by carbon nanotubes conjugated with CD133monoclonal antibodyrdquo Nanomedicine Nanotechnology Biologyand Medicine vol 7 no 1 pp 69ndash79 2011

Submit your manuscripts athttpwwwhindawicom

PainResearch and TreatmentHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom

Volume 2014

ToxinsJournal of

VaccinesJournal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

AntibioticsInternational Journal of

ToxicologyJournal of


StrokeResearch and TreatmentHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Drug DeliveryJournal of



Advances in Pharmacological Sciences

Tropical MedicineJournal of


Medicinal ChemistryInternational Journal of


AddictionJournal of



BioMed Research International

Emergency Medicine InternationalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014


Autoimmune Diseases


Anesthesiology Research and Practice

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of


Pharmaceutics


MEDIATORSINFLAMMATION

of


Table 1 Type of common brain cancers and their BBB status

Type of brain tumors Origin Involvement of BBB Status of BBB

Primary

AstrocytomasPilocytic

astrocytoma(grade I)

Usually from astrocytes ofcerebellum Yes Not well formed

Fibrillarymixed oligoastrocytoma(grade II)

From neoplastic astrocytes Yes Mostly intact

Anaplastic astrocytoma (gradeIII)

From brain astrocytes whichinfiltrate through white matter ofcerebral hemisphere dura and

spinal fluid

Yes Altered or disrupted

Glioblastoma multiforme(GBM) (grade IV) From glial cells Yes Altered or disrupted

Oligodendrogliomas From oligodendrocytes and glialprecursor cells Yes Mostly intact

Ependymomas From ependyma Yes Intact

Meningiomas From meninges of brain andcentral nervous system No mdash

Schwannomas From Schwann cells No mdash

Craniopharyngiomas From pituitary gland embryonictissue Yes Intact or disrupted

Germinomas Germ cell tumors from pinealgland No mdash

Medulloblastomas From cerebellum below thetentorium of brain Yes Intact

Pineocytoma From pineal parenchyma No mdashPineoblastoma From pineal parenchyma No mdash

Secondary Different metastatic cancers tobrain

From cancers like breast lungbowel kidney ovary and skin Yes Intact or disrupted

although the BBB may be disrupted at or near the core ofthe high grade brain tumors most certainly it seems to beintact near the growing edge of the tumor where the invasivetumor cells may reside The presence of the intact BBB insuch regions of the tumors can considerably impede drugdelivery to these regions [13ndash15] On the other hand lackof BBB has been observed in other primary brain tumorslike meningiomas schwannomas or pineocytomas [16ndash18]Disrupted BBB also exists in metastatic secondary braintumors but the disruption is negligible in smaller aggregatesof metastatic tumor cells Therefore the drug delivery tothese micrometastatic regions is not optimum consequentlythe tumor keeps growing and ultimately reaches to clinicallysignificant size Thus along with the existing therapeuticmodalities new approaches of therapy are needed to combatagainst the BBB of different brain tumors (see Table 1)

2 BBB

BBB protects neural tissues in the brain and works as adiffusion barrier that impedes the influx of toxins and othercompounds from blood to the brain BBB was discoveredin 1880s It took almost 70 years to successfully provethe existence of BBB by electron microscopic cytochemical

studies [19 20] Later in 1981 Stewart and Wiley explainedthe initial understanding about the uniqueness of BBB tightjunction and its physiology [21]

Molecular character of BBB shows the presence of twotypes of cellular junctions the intercellular adherens junctionand the paracellular tight junction The functional integrityof BBB is maintained by adherens junction that is composedof vascular endothelium (VE) cadherin actinin and catenin[22] But the major functionality of BBB is maintained bytight junctions as they are primarily responsible for perme-ability through BBB [23 24] The BBB in adult is comprisedof a complex cellular network The main components ofthis system are brain endothelial cells highly specializedbasal membrane a plenty of pericytes embedded in the basalmembrane and astrocytic end-feet (see Figure 1)

Brain Endothelial Cells These cells are required for properbarrier formation and interaction with the adjacent cellsThey are also known as brain microvascular endothelialcells (BMECs) The BMECs differ from the endothelialcells present in the other organs in the following ways(i) paracellular movement of molecules is prevented bycontinuous tight junctions present between brain endothelialcells (ii) BMECs have few cytoplasmic vesicles and more


Dura


Astrocytes

Blood vessel

BloodTight junction


Basal membrane

Astrocytic end feet

Plasma membrane

JAM

ZO1ZO2

ZO3

Cingulin

ClaudinOccludin
























Monocarboxylate

OATP3A1)












































[193]


[194]




[196]




Carmustine(BCNU)

Alkylating agent


Gliadel [200]

Nanoparticles


WaferimplantIVoral


[201]


[202]


[203]

Doxorubicin(DOX)



[204]

Nanoparticle




[206]

Lomustine(CCNU)






[207]



IV


brain tumors

[208 209]


Table 2 Continued





IV


tumors

[210]




tumors

[211]



[212]



tumors

[213]





tumor[214]



multiforme [215]



[216]

Liposomes
















Abbreviations






Acknowledgment


References






















































































































































































































































































Volume 2014

ToxinsJournal of

VaccinesJournal of















AddictionJournal of






Autoimmune Diseases




Journal of


Pharmaceutics



of


Dura


Astrocytes

Blood vessel

BloodTight junction


Basal membrane

Astrocytic end feet

Plasma membrane

JAM

ZO1ZO2

ZO3

Cingulin

ClaudinOccludin
























Monocarboxylate

OATP3A1)












































[193]


[194]




[196]




Carmustine(BCNU)

Alkylating agent


Gliadel [200]

Nanoparticles


WaferimplantIVoral


[201]


[202]


[203]

Doxorubicin(DOX)



[204]

Nanoparticle




[206]

Lomustine(CCNU)






[207]



IV


brain tumors

[208 209]


Table 2 Continued





IV


tumors

[210]




tumors

[211]



[212]



tumors

[213]





tumor[214]



multiforme [215]



[216]

Liposomes
















Abbreviations






Acknowledgment


References






















































































































































































































































































Volume 2014

ToxinsJournal of

VaccinesJournal of















AddictionJournal of






Autoimmune Diseases




Journal of


Pharmaceutics



of


















Monocarboxylate

OATP3A1)












































[193]


[194]




[196]




Carmustine(BCNU)

Alkylating agent


Gliadel [200]

Nanoparticles


WaferimplantIVoral


[201]


[202]


[203]

Doxorubicin(DOX)



[204]

Nanoparticle




[206]

Lomustine(CCNU)






[207]



IV


brain tumors

[208 209]


Table 2 Continued





IV


tumors

[210]




tumors

[211]



[212]



tumors

[213]





tumor[214]



multiforme [215]



[216]

Liposomes
















Abbreviations






Acknowledgment


References






















































































































































































































































































Volume 2014

ToxinsJournal of

VaccinesJournal of















AddictionJournal of






Autoimmune Diseases




Journal of


Pharmaceutics



of







Monocarboxylate

OATP3A1)












































[193]


[194]




[196]




Carmustine(BCNU)

Alkylating agent


Gliadel [200]

Nanoparticles


WaferimplantIVoral


[201]


[202]


[203]

Doxorubicin(DOX)



[204]

Nanoparticle




[206]

Lomustine(CCNU)






[207]



IV


brain tumors

[208 209]


Table 2 Continued





IV


tumors

[210]




tumors

[211]



[212]



tumors

[213]





tumor[214]



multiforme [215]



[216]

Liposomes
















Abbreviations






Acknowledgment


References






















































































































































































































































































Volume 2014

ToxinsJournal of

VaccinesJournal of















AddictionJournal of






Autoimmune Diseases




Journal of


Pharmaceutics



of


































[193]


[194]




[196]




Carmustine(BCNU)

Alkylating agent


Gliadel [200]

Nanoparticles


WaferimplantIVoral


[201]


[202]


[203]

Doxorubicin(DOX)



[204]

Nanoparticle




[206]

Lomustine(CCNU)






[207]



IV


brain tumors

[208 209]


Table 2 Continued





IV


tumors

[210]




tumors

[211]



[212]



tumors

[213]





tumor[214]



multiforme [215]



[216]

Liposomes
















Abbreviations






Acknowledgment


References






















































































































































































































































































Volume 2014

ToxinsJournal of

VaccinesJournal of















AddictionJournal of






Autoimmune Diseases




Journal of


Pharmaceutics



of

























[193]


[194]




[196]




Carmustine(BCNU)

Alkylating agent


Gliadel [200]

Nanoparticles


WaferimplantIVoral


[201]


[202]


[203]

Doxorubicin(DOX)



[204]

Nanoparticle




[206]

Lomustine(CCNU)






[207]



IV


brain tumors

[208 209]


Table 2 Continued





IV


tumors

[210]




tumors

[211]



[212]



tumors

[213]





tumor[214]



multiforme [215]



[216]

Liposomes
















Abbreviations






Acknowledgment


References






















































































































































































































































































Volume 2014

ToxinsJournal of

VaccinesJournal of















AddictionJournal of






Autoimmune Diseases




Journal of


Pharmaceutics



of

















[193]


[194]




[196]




Carmustine(BCNU)

Alkylating agent


Gliadel [200]

Nanoparticles


WaferimplantIVoral


[201]


[202]


[203]

Doxorubicin(DOX)



[204]

Nanoparticle




[206]

Lomustine(CCNU)






[207]



IV


brain tumors

[208 209]


Table 2 Continued





IV


tumors

[210]




tumors

[211]



[212]



tumors

[213]





tumor[214]



multiforme [215]



[216]

Liposomes
















Abbreviations






Acknowledgment


References






















































































































































































































































































Volume 2014

ToxinsJournal of

VaccinesJournal of















AddictionJournal of






Autoimmune Diseases




Journal of


Pharmaceutics



of







[193]


[194]




[196]




Carmustine(BCNU)

Alkylating agent


Gliadel [200]

Nanoparticles


WaferimplantIVoral


[201]


[202]


[203]

Doxorubicin(DOX)



[204]

Nanoparticle




[206]

Lomustine(CCNU)






[207]



IV


brain tumors

[208 209]


Table 2 Continued





IV


tumors

[210]




tumors

[211]



[212]



tumors

[213]





tumor[214]



multiforme [215]



[216]

Liposomes
















Abbreviations






Acknowledgment


References






















































































































































































































































































Volume 2014

ToxinsJournal of

VaccinesJournal of















AddictionJournal of






Autoimmune Diseases




Journal of


Pharmaceutics



of


Table 2 Continued





IV


tumors

[210]




tumors

[211]



[212]



tumors

[213]





tumor[214]



multiforme [215]



[216]

Liposomes
















Abbreviations






Acknowledgment


References






















































































































































































































































































Volume 2014

ToxinsJournal of

VaccinesJournal of















AddictionJournal of






Autoimmune Diseases




Journal of


Pharmaceutics



of










Abbreviations






Acknowledgment


References






















































































































































































































































































Volume 2014

ToxinsJournal of

VaccinesJournal of















AddictionJournal of






Autoimmune Diseases




Journal of


Pharmaceutics



of


Abbreviations






Acknowledgment


References






















































































































































































































































































Volume 2014

ToxinsJournal of

VaccinesJournal of















AddictionJournal of






Autoimmune Diseases




Journal of


Pharmaceutics



of








































































































































































































































































Volume 2014

ToxinsJournal of

VaccinesJournal of















AddictionJournal of






Autoimmune Diseases




Journal of


Pharmaceutics



of





































































































































































































































Volume 2014

ToxinsJournal of

VaccinesJournal of















AddictionJournal of






Autoimmune Diseases




Journal of


Pharmaceutics



of




































































































































































































Volume 2014

ToxinsJournal of

VaccinesJournal of















AddictionJournal of






Autoimmune Diseases




Journal of


Pharmaceutics



of




































































































































































Volume 2014

ToxinsJournal of

VaccinesJournal of















AddictionJournal of






Autoimmune Diseases




Journal of


Pharmaceutics



of





































































































































Volume 2014

ToxinsJournal of

VaccinesJournal of















AddictionJournal of






Autoimmune Diseases




Journal of


Pharmaceutics



of





































































































Volume 2014

ToxinsJournal of

VaccinesJournal of















AddictionJournal of






Autoimmune Diseases




Journal of


Pharmaceutics



of





































































Volume 2014

ToxinsJournal of

VaccinesJournal of















AddictionJournal of






Autoimmune Diseases




Journal of


Pharmaceutics



of





































Volume 2014

ToxinsJournal of

VaccinesJournal of















AddictionJournal of






Autoimmune Diseases




Journal of


Pharmaceutics



of





Volume 2014

ToxinsJournal of

VaccinesJournal of















AddictionJournal of






Autoimmune Diseases




Journal of


Pharmaceutics



of

Documents

Review Article Blood Brain Barrier: A Challenge for ...downloads.hindawi.com/journals/bmri/2015/320941.pdf · mentioned BBB as a controversial problem for brain tumor chemotherapy