Journal of Controlled Release 72 (2001) 203���215 www.elsevier.com/locate/jconrel Biodegradable block copolymers for delivery of proteins and water-insoluble drugsq a , a a a *, Gaylen M. Zentner Ramesh Rathi , Chung Shih , James C. McRea , b b b c c, Min-Hyo Seo , Hunseung Oh , B.G. Rhee , Jiri Mestecky , Zina Moldoveanu d Michael Morgan , Steve Weitmane a MacroMed Inc., 9520 South State Street, Sandy, UT 84070, USA b Samyang, Inc., 263 Yeonji-Dong, Chongno-Gu, Seoul 110-725, South Korea c University of Alabama at Birmingham, Birmingham, AL, USA d PDEF, University of Utah, Salt Lake City, UT, USA e IDD, San Antonio, TX, USA Received 12 April 2000 accepted 24 January 2001 Abstract ���, Release of several drugs from new ABA-type biodegradable thermal gels, ReGel including proteins and conventional molecules, are presented. These are biodegradable, biocompatible polymers that demonstrate reverse thermal gelation properties. Organic solvents are not used in the synthesis, purification, or formulation of these polymers. The unique ��� ��� characteristics of ReGel hinge on the following two key properties: (1) ReGel is a water soluble, biodegradable polymer ��� at temperatures below the gel transition temperature (2) ReGel forms a water-insoluble gel once injected. This is consistent with a hydrophobically bonded gel state where all interactions are physical, with no covalent crosslinking. An increase in viscosity of approximately 4 orders of magnitude accompanies the sol���gel transition. The gel forms a controlled release drug ������s depot with delivery times ranging from 1 to 6 weeks. ReGel inherent ability to solubilize (400 to .2000-fold) and stabilize poorly soluble and sensitive drugs, including proteins is a substantial benefit. The gel provided excellent control of ��� the release of paclitaxel for approximately 50 days. Direct intratumoral injection of ReGel /paclitaxel (OncoGelE) results in a slow clearance of paclitaxel from the injection site with minimal distribution into any organ. Efficacies equivalent to maximum tolerated systemic dosing were observed at OncoGelE doses that were 10-fold lower. Data on protein release (pGH, G-CSF, insulin, rHbsAg) and polymer biocompatibility are discussed. ��� 2001 Published by Elsevier Science B.V. Keywords: Copolymers Thermal gels Biodegradable Controlled release Proteins Paclitaxel 1. Introduction q All procedures involving animals were performed according to The need for controlled release injectable dosage a protocol approved by the Institutional Animal Care and Use forms for the delivery of protein and poorly soluble Committee. conventional drug molecules over a 1���6-week period *Corresponding author. Tel.: 11-801-565-8561 fax: 11-801- is established. Usable systems will show properties 565-8562. consistent with high level compatibility with sensi- E-mail address: macromed@macromed.com (G.M. Zentner). 0168-3659/01/$ ��� see front matter ��� 2001 Published by Elsevier Science B.V. PII: S0168-3659( 01 )00276-0

204 G.M. Zentner et al. / Journal of Controlled Release 72 (2001) 203 ���215 tive drugs, and facile manufacture and administra- vaccines, and particularly those prepared by modern tion. Clearance of the dosage form from the injection molecular biology approaches, are weakly immuno- site, obviating the need to surgically retrieve the genic. These expensive recombinant proteins and exhausted depot, requires the use of biodegradable peptides often require multiple immunizations to polymers. Reverse thermal gelation of biodegradable induce a protective response. Although the mecha- polymers has been reported [1���5]. These polymers nisms for the adjuvant effects of individual sub- were triblock copolymers consisting of A-blocks and stances are poorly understood, empirical experience B-blocks arranged as BAB or ABA, where A is suggests that factors such as slow and sustained poly(lactide-co-glycolide) (PLGA) and B is poly- release of antigens, enhanced antigen presentation, or (ethylene glycol). The polymers are soluble in water, release of cytokines that promote humoral and/or forming a free-flowing solution that spontaneously cell-mediated immune responses may be responsible gels at body temperature (378C) to create a water- for their effects. insoluble gel [5,6]. These thermal gels remain at the In this paper the drug release profiles of several injection site for approximately 1 month [5,7] in drugs from new ABA-type biodegradable thermal ���, contrast to non-biodegradable thermal gels, poloxam- gels, ReGel including proteins and conventional ers, that are water soluble and dissolve from the molecules, are presented. These are biodegradable injection site within a few days [5]. These bio- polymers that demonstrate reverse thermal gelation degradable, thermally reversible drug delivery sys- properties where a free-flowing aqueous solution of tems are based on custom designed polymers/pro- the polymer spontaneously gels at physiological cesses that control drug release and offer substantial temperatures. Organic solvents are not used in the advantages in administration and manufacture. They synthesis, purification, or formulation of these poly- hold particular promise to provide solutions to the mers. Data on drug solubility, stability, in vivo parenteral delivery problems of protein drugs and efficacy and biocompatibility of these new biodegra- poorly soluble drugs. Thus, the biodegradable ther- dable thermal gels is discussed. mal gels hold high potential as injectable, long-term drug delivery systems. A variety of poloxamer gels, and poloxamer gels 2. Materials and methods modified with additives such as methylcellulose, hydroxypropyl methylcellulose, and polycaprolac- tone have been reported as delivery vehicles for 2.1. Chemicals drugs such as IL-2, urease, mitomycin C, and bovine serum albumin [8���12]. Low-molecular weight poly- Polyethylene glycols (PEG1000 and PEG1450) orthoester [13], and vegetable oil-based gels [14], were purchased from Union Carbide (US). DL-Lac- have shown controlled release properties for tetra- tide and glycolide were purchased from PURAC cycline and levonorgestrel, respectively, for periods (The Netherlands) and used without further purifica- of 2���3 weeks. Injectable forms of poly(DL-lactide- tion. Stannous 2-ethylhexanoate and insulin were co-glycolide) dissolved in N-methyl pyrrolidone that obtained from Sigma (US) and were used as re- ��� precipitate upon contact with aqueous biological ceived. Paclitaxel (Genexol Samyang Genex) was fluids have been reported for delivery of naltrexone .99% pure and used as received. Radiolabelled 14C] [15]. Drug release from biodegradable gels follow paclitaxel (paclitaxel-[2-benzoyl ring-UL- 60 the typical profile of an initial diffusion-controlled mCi per mmol ethyl acetate removed prior to use) mechanism that transitions into a combined mecha- was purchased from Sigma. Porcine growth hormone nism of diffusion/degradation as the polymer prop- (pGH) and G-CSF (glycosylated) were formulated erties deteriorate upon hydrolysis of the PLGA by Samyang. Recombinant hepatitis B surface an- blocks [16���19]. tigen (rHBsAg) was obtained from Genzyme. ��� The need for acceptable vaccine adjuvants for Engerix-B commercial hepatitis B vaccine was humans is accentuated by the fact that several new purchased and used as received.