Controlled release of recombinant insulin-like growth factor from a novel formulation of polylactide-co-glycolide microparticles

Journal of Controlled Release 70 (2001) 21–28www.elsevier.com/ locate / jconrel

Controlled release of recombinant insulin-like growth factorfrom a novel formulation of polylactide-co-glycolide

microparticles

*Manmohan Singh , Bret Shirley, Kamal Bajwa, Emil Samara, Maninder Hora,Derek O’Hagan

Chiron Corporation, 4560 Horton Street, Emeryville, CA 94608, USA

Received 9 March 2000; accepted 25 July 2000

Abstract

The purpose of the current study was to develop a controlled-release delivery system for recombinant insulin-like growthfactor (rhIGF-I). Polylactide-co-glycolide (PLG) microparticles with entrapped rhIGF-I were prepared by a novel emulsionbased solvent evaporation process. Microparticles with two loading levels of rhIGF-I were prepared (4 and 20% w/w). Theintegrity of released rhIGF-I was characterized by RP-HPLC, SDS–PAGE and a bioactivity assay. In vitro and in vivorelease profiles of rhIGF-I from these microparticles were also evaluated. Reproducible batches of microparticles with 4%and 20% w/w loading of rhIGF-I were prepared, with excellent encapsulation efficiency (81 and 85% of total proteinrespectively entrapped). The protein retained integrity after the microencapsulation process as evaluated by RP-HPLC,SDS–PAGE and bioactivity assay. The in vitro profiles exhibited a significant burst release of rhIGF-I (20–30%), followedby controlled release of protein for up to 28 days. A similar level of burst release was observed in vivo, followed bycontrolled release of protein for 14–18 days. In addition, there was a surprisingly close correlation between in vitro and invivo release rates. PLG microparticles with entrapped rhIGF-I are a promising delivery system which may allow rhIGF-I tobe used for a broad range of therapeutic indications. 2001 Elsevier Science B.V. All rights reserved.

Keywords: Polylactide-co-glycolide; Microparticles; IGF-I; Controlled release

1. Introduction quence, this protein is currently being evaluated for anumber of therapeutic applications in several disease

Insulin-like growth factor I (IGF-I) is a naturally states. The protein has a molecular weight of 7.65 kdoccurring protein which has many important bio- and high aqueous solubility. Like many other pro-logical effects, including stimulating the growth of teins, rhIGF-I has a short biological half-life and isnervous tissue, increasing cellular uptake of glucose cleared rapidly from the circulation after systemicand stimulation of renal function [1]. As a conse- administration [2,3]. Therefore, the development of a

delivery system that could release rhIGF-I overseveral days or weeks is highly desirable, to allow*Corresponding author. Tel.: 11-510-923-7877; fax: 11-510-rhIGF-I to be used for a range of therapeutic923-2586.

E-mail address: manmohan [email protected] (M. Singh). indications [4]. Since the protein has a number of]

0168-3659/01/$ – see front matter 2001 Elsevier Science B.V. All rights reserved.PI I : S0168-3659( 00 )00313-8

22 M. Singh et al. / Journal of Controlled Release 70 (2001) 21 –28

possible indications, the required dose to be de- 2. Materials and methodslivered may differ widely. Therefore, an optimalcontrolled-release delivery system should be capable 2.1. Materialsof being loaded with different levels of protein foruse in different indications. A controlled-release Polylactide-co-glycolide polymers (RG502H, Mw

delivery system for rhIGF-I has previously been 23 kd, intrinsic viscosity 0.2 dl /g) were obtaineddescribed, which was based on multivesicular lipo- from B.I. Chemicals, NJ, USA. rhIGF-I was obtainedsomes [4]. However, this delivery system was able to from the Process Development Department at Chironmaintain plasma levels of rhIGF-I for only a rela- Corporation. The internal reference standard of rhIG-tively limited period of time (5–7 days). To allow F-I used for comparison throughout these studies wasrhIGF-I to be more widely used for a range of a well-characterized protein from a clinical lot usedpossible indications, we were interested in develop- by Chiron Corp. All other chemicals and solventsing a controlled-release formulation with a longer were obtained from Sigma Chemicals, St. Louis,duration of protein release. USA and used as supplied.

Polylactide-co-glycolide (PLG) polymers are at-tractive polymers for development of a controlled 2.2. Pre-formulation screening of rhIGF-I forrelease delivery systems for rhIGF-I, since they have compatibility with microencapsulation process anda well established history of safe use in humans in excipientssimilar situations and have been shown to be usefulfor the controlled release of several protein and rhIGF-I was subjected to pre-formulation screen-peptide drugs [5–9]. However, it is well established ing with various process conditions and excipientsthat entrapment in PLG microparticles often results prior to initiating the microencapsulation process.in degradation or inactivation of the protein [10]. Briefly, 100 mg/ml solution of rhIGF-I was used toTherefore, it is necessary to evaluate the integrity evaluate the effect of homogenization, sonication,and biological activity of proteins following their exposure to solvents (dichloromethane, ethyl acetate,entrapment in PLG microparticles [10]. In addition, ethanol) and exposure to particle stabilisers (Poly-substantial losses of protein may be incurred during vinylalcohol and polyvinyl pyrrolidone).the microencapsulation, resulting in increased manu-facturing costs and unnecessary wastage. Therefore, 2.3. Preparation method for PLG microparticlesnovel formulation processes must be developed toallow efficient and reproducible encapsulation of Three individual batches of rhIGF-I microparticlesproteins in a cost effective manner. The release of were prepared at two different targeted loading levelsproteins from PLG microparticles is a complex (20 and 4% w/w), using a novel solvent evaporationprocess, with many contributing factors, which are based multiple emulsion process. For the preparationoften difficult to predict [11–14]. Consequently, of the high-load microspheres (20% w/w), solubilityalthough both in vitro and in vivo release rates need of rhIGF-I in an aqueous solution (112 mg/ml) atto be evaluated, a good correlation is relatively pH 4.5 was modified by increasing the pH to 5.5–6.0uncommon. by the addition of 0.1 M sodium hydroxide solution.

In the present study, a novel process was de- To 0.89 ml of rhIGF-I solution (determined by BCAveloped for the preparation of PLG microparticles assay), 0.1 ml of 0.1 M NaOH was added. The pHwith entrapped rhIGF-I, following an in vitro evalua- change caused the majority of the rhIGF-I to form ation of the effect of the formulation process on suspended gel (a highly viscous protein solution)protein integrity. Following microencapsulation, the within the aqueous phase. This rhIGF-I gel wasintegrity and biological activity of the released cooled to 48C and was added to 3.125 ml of a 16%protein and the rate of release over time were PLG (RG 502H) solution in methylene chloride. Thedetermined in vitro. Subsequently, the ability of the mixture was homogenized at 10 000 rpm in an ultraformulations to provide sustained levels of protein in turrex homogenizer for 2.5 min at 48C to yield avivo was evaluated in a rat model. viscous w/o emulsion. This emulsion was poured

M. Singh et al. / Journal of Controlled Release 70 (2001) 21 –28 23

into 20 ml of 10% poly vinyl alcohol (PVA) and and 21, were selected to evaluate the integrity of thestirred at 500 rpm on a magnetic stirrer overnight to rhIGF-I released from the microparticles. rhIGF-Iallow the methylene chloride to evaporate. integrity was evaluated as described below.

The multiple emulsion was then centrifuged at30 000 g for 30 min and the pellet consisting of PLG 2.7. Reversed-phase HPLCmicroparticles was recovered and washed twice withdistilled water. Finally, the microparticles were Separation and quantitation of rhIGF-I species wasfreeze dried and stored in a dessicator. accomplished with RP-HPLC. Separations were per-

To prepare microparticles with the lower protein formed on a Zorbax 300SB-CN, 4.6 mm ID315 cm,load (4% w/w) the same starting rhIGF-I solution at 5 m, cyano column with sample detection at 214 nm.a concentration of 112 mg/ml was used and the Approximately 16 mg of IGF-I was injected permicroparticles were prepared by the solvent evapora- sample. Elution was achieved with a gradient oftion process as described above. acetonitrile /water /0.2% TFA from approximately 25

to 34% ACN over 25 min. The internal standard2.4. Measurement of microparticle size sample of rhIGF-I was run comparison for all assays.

The microparticles were evaluated on a laser sizer 2.8. Non-reducing SDS–PAGE(Malvern Mastersizer, USA). The samples werediluted to 0.5% w/v in distilled water. Diluted The presence of possible covalent aggregates wassamples of various batches were run in triplicate and detected on 18% Tris–Glycine non-reducing SDS–the mean d value estimated for each batch. PAGE gels (NOVEX Cat [EC6505). Approximately50

3 mg rhIGF-I was loaded per gel lane. Gels were run2.5. Determination of the loading levels of rhIGF-I at constant voltage and stained with colloidalin microparticles Coomassie blue, according to the manufacturer’s

instructions (NOVEX Cat [LC6025). DestainedThe loading level of rhIGF-I in all batches was gels were scanned with a Molecular Dynamics

determined by hydrolyzing 10 mg of microparticles Personal Densitometer SI and bands were convertedin 1 ml of 0.2 N NaOH/5% SDS solution overnight, to peak areas with the accompanying data processingas previously described [15]. The total protein con- software package.The internal standard sample oftent of the samples was determined by micro-BCA rhIGF-I was run for comparison in all assays.assay. The loading level of rhIGF-I was expressed as% w/w of microparticles. In addition, the rhIGF-I 2.9. Mitogenic bioassayloading efficiency of each batch was determined byexpressing the amount of protein entrapped in the The bioactivitity of rhIGF-I was determined usingmicroparticles as a percentage of the total amount of a mitogenic assay with 3-[4,5-dimethylthiazol-2-yl]-protein used to make the formulation. 2,5-diphenyltetrazolium bromide stain (MTT stain,

Sigma M-2128). This assay is based on the dose2.6. In vitro release profile of rhIGF-I dependent induction of cell proliferation by rhIGF-I

[1]. The response is measured with MTT stain,The rate of release of rhIGF-I from high and low which is reduced to a colored product by the

load (20% and 4% w/w) microparticles were evalu- mitochondrial enzymes of live MG-63 cells (Ameri-ated using three individual batches at each loading can Type Culture Collection (ATCC CRL 1427)).level. Several 3-ml vials, each containing 10 mg of The internal standard sample of rhIGF-I was run formicroparticles were weighed and to each vial, 1 ml comparison in all assays.of PBS was added and the vials were kept at 378C.At each time point (days 1, 7, 14, 21 and 28) 1 vial 2.10. In vivo evaluationwas withdrawn and the supernatant assayed forprotein content. Four time points, at days 1, 7, 14 Both the high and the low load batches of


Table 1microparticles (20% and 4% w/w) were evaluatedPre-formulation evaluation of rhIGF-I involving exposure tofor rhIGF-I release in vivo, in Sprague–Dawley rats.relevant excipients and process conditions prior to

Groups of nine animals were used in each of the two amicroencapsulationstudies performed. In the first study with the high-

Condition for pre-formulation % Purity by % Monomer byload formulation (20% w/w), animals were injectedexposure with rhIGF-I RP-HPLC SDS–PAGE

s.c. with a 40-mg/kg dose of rhIGF-I. In the secondIGF-I1Homogenization 77 68study, with the low load formulation (4% w/w), aIGF-I1Sonication 68 70

25-mg/kg dose of rhIGF-I was used. The two dose IGF-I1DCM 87 78levels 40 mg/kg and 25 mg/kg were evaluated based IGF-I1EtAc 94 84on varying dose requirements of rhIGF-I for different IGF-I1Ethanol 90 80

IGF-I1PVA 95 88indications.IGF-I1PVP 92 76IGF-I1DCM1Homogenization 80 80

2.11. Pharmacokinetic analysis IGF-I1EtAc1Homogenization 86 84Internal standard of rhIGF-I 98 97

The pharmacokinetic parameters were derived a Solvents used were dichloromethane, ethyl acetate and etha-from the average plasma concentration–time data nol. Microparticle stabilisers screened were polyvinylalcoholutilizing the noncompartmental approach. C and (PVA) and polyvinyl pyrrolidone (PVP). CN–RP-HPLC analysismax

and non-reducing SDS–PAGE analysis (colloidal Coomassie). %T were estimated directly from the observed data.maxpurity is based on AUC of the main peak compared to the internalArea under plasma concentration–time curve for thereference standard sample of rhIGF-I.last measurable concentration (AUCt) was estimated

using the linear trapezoidal rule. The AUCt wasextrapolated to infinity (AUC`) by adding the an encapsulation efficiency of 85 and 81%, respec-quotient of the last measurable concentration and the tively. The mean size of the microparticles (d ) was50

linear terminal slope. The initial in vivo burst was 30–40 mm. All batches had a monodisperse sizedetermined as the quotient of day 1 AUC and distribution with (d ) in the range of 70 mm.90

AUC`. The pharmacokinetic (pk) parameters forboth the high- and low-load batches are summarized 3.2. Protein integrityin Table 3.

It was shown that rhIGF-I was released frommicroparticles in vitro in a predominantly intact

3. Results form. Table 2 shows the evaluation of rhIGF-Iintegrity from the three high-load batches of mi-

3.1. Microparticle characterization croparticles, following in vitro release over 21 days.Similar data were also obtained for the low load

Prior to microencapsulation a range of excipients, batches of microparticles (not shown). Figs. 1 and 2solvents and conditions were screened for com- show a representative non-reducing SDS–PAGE gelpatibility with rhIGF-I. Based on this screening, and an RP-HPLC chromatogram of the rhIGF-Idichloromethane (DCM) and polyvinylalcohol (PVA) released from PLG microparticles.were selected for use in the microencapsulationprocess. In addition, we sought to further protect the 3.3. In vitro release of rhIGF-Iprotein from damage by using it in a suspended gelform, which was achieved by pH modification as An evaluation of the in vitro release rate of rhIGF-described above. Table 1 summarizes the pre-formu- I from three separate batches of both high- andlation screening results with various conditions and low-load microparticles was performed at 378C. Theexcipients. burst release from the three high-load batches ranged

The actual load of rhIGF-I in the microparticles between 24 and 31% w/w. Greater than 60% of thewas estimated to be 17 and 3.25% w/w for the high- rhIGF-I was released in about 21 days. The burstand low-load batches, respectively, which indicated release from the low load batches of microparticles


Table 2In vitro release of rhIGF-I from three high load batches character-ized by CN–RP-HPLC analysis, non-reducing SDS–PAGE analy-

asis (colloidal Coomassie) and mitogenic bioassay estimations

Sample % Purity by % Monomer by % ActivityRP-HPLC SDS–PAGE by Bioassay

Internal standard 98.52 100 93.8rhIGF-IBatch I /Day 1 96.18 100 96.9Batch I /Day 7 96.10 100 107.6Batch I /Day14 95.62 100 98.4Batch I /Day 21 95.78 96 106.1Batch II /Day 1 95.70 100 101.53Batch II /Day 7 95.67 100 83.8Batch II /Day 14 95.73 100 112.3Batch II /Day 21 95.74 92 104.6Batch III /Day 1 95.74 100 101.5Batch III /Day 7 95.75 100 108.4Batch III /Day 14 95.62 100 96.9Batch III /Day 21 95.84 96 94.4

a Internal reference standard sample of rhIGF-I used as aninternal control in all three assays. % purity by RP-HPLCcorresponds to AUC of the main peak. % monomer corresponds tofraction of the protein that is monomer versus dimer or trimer incomparison to reference standrad sample. % activity correspondsto % bioactivity of the sample based on the in vitro bioassay.

was lower (|20%) and the total amount of rhIGF-IFig. 1. RP-HPLC analysis of day 7 released IGF-I from high-loadreleased over 21 days was also lower. Fig. 3 showsPLG microparticle formulation. Chromatogram A is referencethe in vitro release rate profiles for the high and therhIGF-I and B is day 7 in vitro released rhIGF-I from high load

low load batches of rhIGF-I microparticles. PLG microparticle formulation.

3.4. In vivo release of rhIGF-Ilower load formulation can be attributed to a higher

After SC administration of rhIGF-I in high- and particle number that is being injected per animal withlow-load PLG formulations, plasma concentrations this formulation, due to different load and differentof rhIGF-I increased rapidly, reaching maxima with- dose level.in 2 h. The concentrations rapidly declined reachingpredose levels within 24 h. A second slower releasephase occurred at a later time, reaching new maxima 4. Discussionaround day 5 for the high load formulation andaround day 10 for the low load formulation. The Due to the economics of the production andslow release in vivo continued for at least 14–18 purification of many recombinant proteins, improveddays. The initial burst of rhIGF-I was calculated at encapsulation efficiency and high loading levels in30 and 18% for the high and low-load formulations, PLG microparticles is an important objective. Torespectively (Table 3). These numbers were in close increase the rhIGF-I concentration in the internalaccordance with the amount released in vitro during aqueous phase during microparticle preparation, wethe first 24 h. The C for the low-load formulation considered the possibility of concentrating the pro-max

was 2867 (ng/ml) at 90 min whereas the C for tein by a well-established ultrafiltration technique.max

the high-load formulation was 1882 (ng/ml) at 30 However, the use of such a method would involve anmin. (Fig. 4). The higher AUC observed with the extra manufacturing step with associated losses of


Table 3Pharmacokinetic parameters from the in vivo evaluation of thehigh- and low-load formulation in Sprague–Dawley rats

Parameters High-load IGF Low-load IGFDose 40 mg/kg 25 mg/kg

C (ng/ml) 1882 2867max

T (h) 0.5 1.5max

AUC (ng*h/ml) 59,973 130,680Cl /F (ml /h) 667 191Initial Burst (%) 30 18

least soluble form and minimizes the loss of proteinto the larger volume of the external aqueous phaseduring microparticle preparation.

The novel microparticle preparation process de-scribed in this paper resulted in high encapsulationefficiency for rhIGF-I in both high- and low-loadbatches of PLG microparticles, 85 and 81%, respec-tively. In addition, the encapsulation process wasshown to be highly reproducible for repeat batches,prepared under identical conditions. Most important-Fig. 2. Non-reducing SDS–PAGE gel of day 1 released IGF-I

from high-load PLG microparticle formulation. Lane A is molecu- ly, rhIGF-I maintained structural integrity after en-lar weight markers, lane B is internal standard rhIGF-I, lanes C capsulation, as indicated by both gel and HPLCand D are day 1 released IGF-I from the microparticle formulation analysis. Furthermore, the protein also retained fullin duplicate.

bioactivity and integrity during release in vitro over21 days. It appears likely that an important con-the expensive rhIGF-I protein. Instead, we havetributor to the stability of rhIGF-I in microparticlesestablished a novel in situ protein gel formation stepwas the physical condition of the protein duringin the encapsulation process itself, which achievesmicroencapsulation. rhIGF-I exhibits markedthe necessary concentration of rhIGF-I and obviateschanges in solubility with pH and a minor pHthe need for an extra manufacturing step. The in situadjustment was made during the formulation processgel formation also maximizes the efficiency of the

encapsulation process by presenting the protein in its

Fig. 3. In vitro release profile of both high- and low-load PLG– Fig. 4. In vivo release profile of both high- and low-loadrhIGF-I formulations at various days at 378C. The figure repre- formulations after SC administration in Sprague–Dawley rats. Thesents geometric mean6s.e. for all time points. figure represents geometric mean6s.e. for all time points.


to minimize the solubility of the protein. rhIGF-I was previously described by our group [4], theforms a thick viscous gel at pH 5.5–6.0, and this duration of release in vivo (5–7 days) was relativelycharacteristic feature of the protein was used to short compared to the duration of release achieved inminimize the diffusion of the protein to the outer the current study (14–18 days). Furthermore, sinceaqueous phase of the double emulsion, resulting in the polymers used in the current study were ofhigh encapsulation efficiency (80–85%). Using an relatively low molecular weight and had a co-poly-alternative approach, human growth hormone has mer ratio of 50/50, it would be relatively easy tobeen efficiently encapsulated into PLG microparti- change the polymer to extend the duration of release.cles after the formation of insoluble complexes with The longer duration of release of rhIGF-I from PLGdivalent metal ions [8,9]. Recent work by Lam et al. microparticles and the greater total dose that can be[19] has shown that rhIGF-I can also be encapsulated administered significantly broadens the range ofefficiently in PLG microparticles using the ‘Prolease’ potential therapeutic indications for this importantcryogenic process, involving spraying of suspended protein drug. In addition, the ability to efficientlydried protein into liquid nitrogen and solvent ex- achieve both high and low loading levels in thetraction. While this process may be suitable for some microparticles allows significantly dose flexibility, toproteins, the current studies indicate that complex- accommodate a range of possible indications foration or freeze drying of rhIGF-I is not necessary to rhIGF-I.achieve high encapsulation efficiency and the releaseof biologically active protein from PLG microparti-cles. Both the current process and the process Acknowledgementspreviously described for microencapsulation of rhIG-F-I [19] appear to result in the preparation of We would like to acknowledge the help ofcontrolled release microparticles with about 20–30% Maylene Briones in the protein estimation and inburst release of rhIGF-I, and release of active vitro assays and Chiron’s Analytical Operationsprotein. It seems likely that the physical state of the group for bioassay determinations.protein during encapsulation in the current process(entrapped as a viscous gel), may be an importantcontributor to the stability of entrapped rhIGF-I.

ReferencesThe extent of burst release of rhIGF-I from both

high- and low-load formulations was very similar in[1] J. Zapf, E.R. Froesch, Insulin-like growth factors

vitro and in vivo. As too was the presence and the somatomedins; structure, secretion biological actions andduration of the lag phases in vitro and in vivo, which physiological role, Hormone Res. 24 (1986) 121–130.was followed by a second peak of protein release in [2] D.R. Clemmons, H.P. Guler, M.A. Bach, M. Skarulius,

Clinical uses of insulin-like growth factor, Ann. Intern. Med.both situations. The only major difference from in120 (1994) 593–601.vitro and in vivo was the duration of release, which

[3] H.P. Guler, J. Zapf, E.R. Froesch, Short term metabolicwas longer in vitro than in vivo. It is possible that effects of recombinant human insulin-like growth factor inthe insensitivity of the assay for in vivo released healthy adults, N. Engl. J. Med. 317 (1989) 137–140.rhIGF-I may have contributed to the apparent shorter [4] N.V. Katre, J. Asherman, H. Schaefer, M. Hora, Multivesicu-

lar liposome (Depofoam) technology for the sustained deliv-duration of release in vivo. The bi-phasic releaseery of insulin-like growth factor 1 (IGF-I), J. Pharm. Sc. 87profile for rhIGF-I in vitro is a typical finding and(1998) 1341–1346.

has been seen previously with many alternative [5] H. Okada, One- and three-month release injectable micro-proteins [14–18]. However, the observation that the spheres of the LH-RH superagonist leuprorelin acetate, Adv.in vivo release also showed a very similar profile is Drug Del. Rev. 28 (1997) 43–70.

[6] S.D. Putney, P.A. Burke, Improving protein therapeutics withmore surprising.sustained-release formulations, Nature Biotechnol. 16 (1998)The results from the current study clearly highlight153–157.

the potential of using PLG microparticles to develop [7] J.P. McGee, M. Singh, L.I. Xuan-Mao, H. Qui, D.T.a sustained-release delivery system for rhIGF-I. O’Hagan, The encapsulation of a model protein in polyAlthough a controlled-release formulation of rhIGF-I (lactide-co-glycolide) microparticles of various sizes; an


evaluation of process reproducibility, J. Microencap. 14 [13] D. Bodmer, T. Kissel, E. Traechslin, Factors influencing the(1997) 197–210. release of peptides and proteins from biodegradable parenter-

[8] O.L. Johnson, J.L. Cleland, H.J. Lee, M. Charnis, E. Duenas, al depot systems, J. Control. Rel. 21 (1992) 129–138.W. Jaworowicz, D. Shepard, A. Shahzamani, A.J.S. Jones, [14] G. Crotts, H. Sah, T.G. Park, Adsorption determines in-vitroS.D. Putney, A month-long effect from a single injection of protein release rate from biodegradable microspheres: quan-microencapsulated human growth hormone, Nat. Med. 2 titative analysis of surface area during degradation, J.(1996) 795–798. Control. Rel. 47 (1997) 101–111.

[9] J.L. Cleland, E. Duenas, A. Daughety, M. Marian, J. Yang, [15] S. Sharif, D.T. O’Hagan, A comparison of alternativeM. Wilson, A.C. Celniker, A. Shahzamani, V. Quarmby, H. methods for the determination of the levels of proteinsChu, V. Mukku, A. Mac, M. Roussakis, N. Gillette, B. Boyd, entrapped in poly(lactide-co-glycolide) microparticles, Int. J.D. Yeung, D. Brooks, Y.F. Maa, C. Hsu, A.J.S. Jones, Pharm. 115 (1995) 259–263.Recombinant human growth hormone poly(lactic-co-glycolic [16] M.S. Hora, R.K. Rana, J.H. Numberg, T.R. Tice, R.M.acid) (PLGA) microspheres provide a long lasting effect, J. Gilley, M.E. Hudson, Release of human serum albumin fromControl. Rel. 49 (1997) 193–205. poly(lactide-co-glycolide) microspheres, Pharm. Res. 7

[10] T.G. Park, W. Lu, G. Crotts, Importance of in vitro ex- (1990) 1190–1194.perimental conditions on protein release kinetics, stability [17] S. Cohen, T. Yoshioka, M. Lucarelli, L.H. Hwang, R.and polymer degradation in protein encapsulated poly (D,L- Langer, Controlled delivery systems for proteins based onlactic acid-co-glycolic acid) microspheres, J. Control. Rel. 33 poly(lactic /glycolic acid) microspheres, Pharm. Res. 8(1995) 211–222. (1991) 713–720.

[11] G. Crotts, T.G. Park, Stability and release of bovine serum [18] D.T. O’Hagan, H. Jeffery, S.S. Davis, The preparation andalbumin encapsulated within poly(D,L-lactide-co-glycolide) characterization of poly(lactide-co-glycolide) microparticlesmicroparticles, J. Control. Rel. 44 (1997) 123–134. III: Microparticle /polymer degradation rates and the in vitro

[12] J.L. Cleland, A. Mac, B. Boyd, J. Yang, E.T. Duenas, D. release of a model protein, Int. J. Pharm. 103 (1994) 37–45.Yeung, D. Brooks, C. Hsu, V. Mukku, A.J.S. Jones, The [19] M.L. Xanthe, E.T. Duenas, A.L. Daugherty, N. Levin, J.L.stability of recombinant human growth hormone in poly- Cleland, Sustained release of recombinant human insulin-like(lactic-co-glycolic acid) (PLGA) microspheres, Pharm. Res. growth factor-I for treatment of diabetes, J. Control. Rel. 6714 (1997) 420–426. (2000) 281–292.

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Controlled release of recombinant insulin-like growth factor from a novel formulation of polylactide-co-glycolide microparticles