Newer cancer therapiesNewer cancer therapies

AngiotherapyAngiotherapyuse of agents that inhibit angiogenesisuse of agents that inhibit angiogenesis

Angiogenic therapyAngiogenic therapyRationale1) tumour growth is angiogenesis-dependent2) targets the genetically-stable microvascular endothelial cell3) anti-angiogenic compounds are cytostatic

(a)Nascent vessels consist of a tube of ECs, which mature into specialized capillaries, arteries and veins.

(b) Capillaries consist of ECs surrounded by basement membrane and a sparse layer of pericytes embedded within the EC basement membrane. Capillary endothelial layer can be continuous (muscle), fenestrated (kidney/ endocrine glands) or discontinuous (liver sinusoids). The endothelia of the blood-brain barrier or blood-retina barrier are further specialized to include tight junctions, and are thus impermeable to various molecules.

(c) Arterioles and venules have an increased coverage of mural cells compared with capillaries.

Composition of nascent and mature blood vessel wallsComposition of nascent and mature blood vessel walls

Steps in network formation and maturation during Steps in network formation and maturation during embryonic (physiological) angiogenesisembryonic (physiological) angiogenesis

Key differences in tumour Key differences in tumour vasculaturevasculature

Different flow Different flow characteristics / characteristics / blood volumeblood volume

Microvasculature Microvasculature permeabilitypermeability

Increased Increased fractional fractional volume of volume of extravascular, extravascular, extracellular extracellular spacespace

Steps in network formation and maturation during Steps in network formation and maturation during tumour angiogenesistumour angiogenesis

Cellular mechanisms of tumour angiogenesis Cellular mechanisms of tumour angiogenesis (1) host vascular network expands (1) host vascular network expands

by budding of endothelial by budding of endothelial sprouts or formation of bridges sprouts or formation of bridges (angiogenesis); (angiogenesis);

(2) tumour vessels remodel and (2) tumour vessels remodel and expand by the insertion of expand by the insertion of interstitial tissue columns into interstitial tissue columns into the lumen of pre-existing vessels the lumen of pre-existing vessels (intussusception); and (intussusception); and

(3) endothelial cell precursors (3) endothelial cell precursors (angioblasts) home from the (angioblasts) home from the bone marrow or peripheral bone marrow or peripheral blood into tumours and blood into tumours and contribute to the endothelial contribute to the endothelial lining of tumour vessels lining of tumour vessels (vasculogenesis)(vasculogenesis)

(4) Lymphatic vessels around (4) Lymphatic vessels around tumours drain the interstitial tumours drain the interstitial fluid and provide a gateway for fluid and provide a gateway for metastasizing tumour cells. metastasizing tumour cells.

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Angiogenesis-overviewAngiogenesis-overview

Nature Reviews Drug Discovery 1, 415-426 (2002)

Angiogenesis-overviewAngiogenesis-overview Balance between inhibitory factors (endostatin) and angiogenic factors (VEGF, bFGF) Tumour cells release pro-angiogenic factors which activate receptors (VEGFR) also stimulates secretion and activation of MMPs which degrade the basement membraneThis allows activated endothelial cells to migrate towards tumour, helped by integrinsECs deposit a new basement membrane and secrete growth factors such as platelet-derived growth factor (PDGF), which attract supporting cells to stabilize the new vessel.

VEGF – Vascular Endothelial Growth FactorbFGF - basic Fibroblast Growth FactorMMPs – Matrix MetalloProteinases

‘‘cryptic’ angiogenesis inhibitorscryptic’ angiogenesis inhibitors

AngiostatinAngiostatin 38kDa fragment of 38kDa fragment of

plasminogenplasminogen

EndostatinEndostatin 20kDa fragment of 20kDa fragment of

collagen XVIIIcollagen XVIII Endothelial cell specificEndothelial cell specific Complete regression in Complete regression in

micemice No drug resistanceNo drug resistance

Inactive until they are released from the parent protein by enzymatic cleavage

EndostatinEndostatin Discovered in 1995 by Judah Folkman et alDiscovered in 1995 by Judah Folkman et al Phase I clinical trial in 1999Phase I clinical trial in 1999Dr. James Watson predicted that Dr. Folkman would cure all Dr. James Watson predicted that Dr. Folkman would cure all

cancer within 2 yearscancer within 2 years

Dr. Folkman’s responseDr. Folkman’s response““If you are a mouse and have cancer we can If you are a mouse and have cancer we can take good care of you. I respectfully disagree take good care of you. I respectfully disagree because in our experiments we mostly sacrifice because in our experiments we mostly sacrifice the mice. So, I don't know if that qualifies as the mice. So, I don't know if that qualifies as taking good care”taking good care”

www.pbs.org/wgbh/ nova/cancer/program.html

Integrins – the ‘velcro’ of the cellIntegrins – the ‘velcro’ of the cell The cell moves by "ruffling" it's membrane. This is done by a The cell moves by "ruffling" it's membrane. This is done by a

series of actin fibers, whose function is controlled by the series of actin fibers, whose function is controlled by the integrins. These fibers cause the cell membrane to move in integrins. These fibers cause the cell membrane to move in certain directions, and the integrins attach to the matrix as this certain directions, and the integrins attach to the matrix as this happens, pulling the cell along a micrometer at a time happens, pulling the cell along a micrometer at a time

Representation of the clinical drug Representation of the clinical drug development process development process

suggested differences in end points between studies that are suggested differences in end points between studies that are targeted at cytotoxic agents compared with studies to test targeted at cytotoxic agents compared with studies to test angiogenic modulators angiogenic modulators

DLT, dose-limiting toxicity; DLT, dose-limiting toxicity;

MTD, maximum-tolerated dose. MTD, maximum-tolerated dose.

What is in the pipeline?What is in the pipeline?Anti-angiogenic molecules fall into 5 categories Anti-angiogenic molecules fall into 5 categories inhibitors of pro-angiogenic growth factorsinhibitors of pro-angiogenic growth factors, e.g. , e.g. VEGFVEGF, , bFGFbFGF, ,

PDGFPDGF protease inhibitorsprotease inhibitors that prevent the breakdown of the that prevent the breakdown of the

surrounding matrix, which is needed for blood-vessel growth; surrounding matrix, which is needed for blood-vessel growth; Analogs ofAnalogs of endogenous inhibitors endogenous inhibitors of angiogenesis e.g. of angiogenesis e.g.

endostatin; endostatin; inhibitors of cellular adhesion moleculesinhibitors of cellular adhesion molecules; and ; and molecules with molecules with undefined mechanismsundefined mechanisms

Anti-VEGFR2 Anti-VEGFR2 therapytherapy

(c,d) Anti-VEGFR2 prunes immature vessels, leading to a progressively 'normalized' vasculature(e) Further treatment leads to a vasculature that is inadequate to sustain tumour growth by day 5. (f) Perivascular cells expressing GFP (under the control of the VEGF promoter) envelope some vessels in the tumour interior. (g) A perivascular cell, presumably a fibroblast, leading the endothelial sprout (arrow).

Before treatment after treatment

Imaging studies to monitor tumour angiogenesis Imaging studies to monitor tumour angiogenesis (blood flow)(blood flow)

Blood-flow maps a | before treatment and b | six months aftertreatment of a patient with metastatic renal-cell carcinoma with thalidomide.

Haematological malignancies!Haematological malignancies!

These images are confocal microscopic sections of bone-marrow biopsies that have These images are confocal microscopic sections of bone-marrow biopsies that have been stained with antibody to von Willebrand factor, which highlights blood been stained with antibody to von Willebrand factor, which highlights blood vessels. In the left panel, normal bone marrow (from a child with a non-vessels. In the left panel, normal bone marrow (from a child with a non-neoplastic disease) shows normal microvasculature of uniform-sized vessels. In neoplastic disease) shows normal microvasculature of uniform-sized vessels. In the right panel, bone marrow from a child with newly diagnosed acute the right panel, bone marrow from a child with newly diagnosed acute lymphoblastic leukaemia reveals intense neovascularization, with microvessels lymphoblastic leukaemia reveals intense neovascularization, with microvessels of variable diameters.of variable diameters.

matrix metalloproteinase inhibitors matrix metalloproteinase inhibitors MMPIsMMPIs Phase III clinical trials with MMPIs (Phase III clinical trials with MMPIs (Marimastat – British Marimastat – British

BiotechBiotech) in several solid tumours) in several solid tumours

Disappointing results. Reasons may beDisappointing results. Reasons may be Early initiation of advanced testing (Phase III) without

the appropriate safety and efficacy indications from Phase I/II trials.

side-effects (mainly musculoskeletal pain) associated with patient non-compliance in trials.

inappropriate model (advanced-stage refractory diseases) in spite of preclinical testing in animal models that had indicated an advantage at an early stage of disease.

Poor survival rate in phase III clinical trials against renal cell Poor survival rate in phase III clinical trials against renal cell carcinomacarcinoma

ReferencesReferences

1) Angiogenesis modulation in cancer research:Novel clinical 1) Angiogenesis modulation in cancer research:Novel clinical approaches by approaches by M Cristofanilli, C Charnsangavej‡ M Cristofanilli, C Charnsangavej‡ and GN.Hortobagyiand GN.Hortobagyi

Nature reviews drug discovery VOL 1 JUNE pp 415 (2002)Nature reviews drug discovery VOL 1 JUNE pp 415 (2002)

2) Angiogenesis in cancer and other diseases by 2) Angiogenesis in cancer and other diseases by P Carmeliet P Carmeliet & RK. Jain& RK. JainNature vol 407 14 september 2000 pp 249

3) Chapter 17 : Knowles and SelbyChapter 17 : Knowles and Selby