Development of Pentablock Copolymer Based Formulations for the Sustained Delivery of Protein Therapeutics in the Treatment of Posterior Segment Ocular Diseases

Title from PDF of title page, viewed on December 14, 2015Dissertation advisor: Ashim K. MitraVitaIncludes bibliographical references (page 235-248)Thesis (Ph.D.)--School of Pharmacy and Department of Chemistry. University of Missouri--Kansas City, 2013We have successfully synthesized pentablock (PB) copolymers comprised of various FDA approved polymer blocks such as polyethylene glycol (PEG), polycaprolactone (PCL), polylactic acid (PLA) and polyglycolic acid (PGA). PB copolymers with different composition, molecular weights and block arrangements were utilized to develop protein-embedded thermosensitive gels or nanoparticles (NPs) for sustained delivery in the treatment of posterior segment ocular diseases. In order to eliminate the burst release effect, we have studied PB composite formulation comprised of protein-encapsulated PB NPs dispersed in PB thermosensitive gel. The composite formulation eliminated burst release effect and exhibited nearly zero-order protein release for significantly longer durations. In this research work, we have utilized various model proteins (lysozyme, IgG-Fab, IgG, BSA, and catalase) and therapeutic proteins (octreotide, insulin and bevacizumab) to optimize the formulation. We have synthesized various triblock (TB) (PCL-PEG-PCL, B-A-B) and PB (PLA-PCL-PEG-PCL-PLA (C-B-A-B-C) and PEG-PCL-PLA-PCL-PEG (A-B-C-B-A)) copolymers based thermosensitive gelling polymers. We have observed distinct effect of block arrangement and molecular weights of block copolymers on the sol-gel transition and on the kinematic viscosity of aqueous solutions. PB copolymers with A-B-C-B-A block arrangement exhibited significantly lower viscosity relative to TB copolymers or other types of PB copolymers (C-B-A-B-C). The difference in viscosity and sol-gel transition behavior has been explained by two different processes of micellization for A-B-C-B-A and B-A-B, or C-B-A-B-C types of copolymers. Moreover, a PB copolymer based formulation sustained the release of IgG up to ~20 days, which is significantly longer relative to TB copolymers based formulations. In order to sustain release for longer duration, we have synthesized various PB copolymers (PLA-PCL-PEG-PCL-PLA and PGA-PCL-PEG-PCL-PGA) with high molecular weight and utilized them for the fabrication of protein-encapsulated NPs. We observed a significant effect of the presence of PLA or PGA on entrapment efficiency (EE), drug loading (DL) and in vitro release behavior. This may be due to the fact that PB copolymers exhibited significantly reduced crystallinity relative to TB copolymers. In addition, we have successfully optimized NP preparation methods to achieve maximum possible DL. This achievement allowed the loading of a large amount of drug which can last for ~6 month in a limited injection volume (100 μL). The optimized methods were successfully utilized to encapsulate a wide variety of peptides and proteins with molecular weights ranging from 1 - 237 kDa in PB NPs. PB NPs alone exhibited significant burst release in the first few days of release study. However, a composite formulation comprised of protein-encapsulated PB-NPs prepared with optimized method and optimized PB copolymers (PB copolymers for NPs and thermosensitive gel) exhibited protein release for significantly longer duration of time (~6 months) with nearly zero-order release rate. We have evaluated the structural integrity of released protein at different time intervals by CD spectroscopy. Moreover, biological activity of bevacizumab was evaluated by cell proliferation and cell migration assays. Enzymatic activity of lysozyme and catalase were confirmed with their respective enzymatic assays. Our results indicated that proteins retained their structural integrity and bioactivity during the preparation of formulation and also during the release process. In vitro cell culture studies such as cell viability, cytotoxicity and biocompatibility studies performed on various ocular cell lines confirmed the safety of PB copolymers for ocular applications. Further, we have performed in vivo ocular tolerability studies with optimized PB formulations which demonstrated no inflammation, retinal toxicity, change in intraocular pressure or cataract even after 16 week of exposure. Moreover, in vivo studies further revealed that PB copolymers based formulations were slowly degraded and dissolved in vitreous humor confirming biodegradability of polymers. Our studies indicated that PB copolymer based composite formulation can serve as a platform technology for the development of sustained release therapy in the treatment of posterior segment ocular diseases such as wet age-related macular degeneration (wet-AMD), diabetic macular edema (DME) and diabetic retinopathy (DR). This technology has a scope beyond ocular treatments and can also be used for the treatment of other chronic diseases.Literature review -- Introduction -- Novel thermosensitive pentablock (PB) copolymers for sustained delivery of proteins in the treatment of posterior segment diseases -- Sustained delivery of proteins employing novel pentablock copolymer based nanoparticlulate systen for the treatment of posterior segment ocular diseases -- Tailor-made pentablock copolymer based composite formulation for sustained ocular delivery of protein therapeutics -- Optimization of novel pentablock copolymer based composite formulation for sustained delivery of protein therapeutics in the treatment of ocular diseases -- In vivo tolerability studies of various pentablock copolymer based formulations: delivered topically or intravitreally -- Summary and recommendations -- Appendi

High-performance MPEG-2 software decoder on the Cell broadband engine

The Sony-Toshiba-IBM Cell Broadband Engine is a heterogeneous multicore architecture that consists of a traditional microprocessor (PPE) with eight SIMD coprocessing units (SPEs) integrated on-chip. While the Cell/B.E. processor is designed with multimedia applications in mind, there are currently no open-source, optimized implementations of such applications available. In this paper, we present the design and implementation behind the creation of an optimized MPEG-2 software decoder for this unique parallel architecture, and demonstrate its performance through an experimental study. This is the first parallelization of an MPEG-2 decoder for a commodity heterogeneous multicore processor such as the IBM Cell/B.E. While Drake et al. have recently parallelized MPEG-2 using StreamIt for a streaming architecture, our algorithm is quite different and is the first to address the new challenges related to the optimization and tuning of a multicore algorithm with DMA transfers and local store memory. Our design and efficient implementation target the architectural features provided by the heterogeneous multicore processor. We give an experimental study on Sony PlayStation 3 and IBM QS20 dual-Cell Blade platforms. For instance, using 16 SPEs on the IBM QS20, our decoder runs 3.088 times faster than a 3.2 GHz Intel Xeon and achieves a speedup of over 10.545 compared with a PPE-only implementation. Our source code is freelyavailable through SourceForge under the CellBuzz project. 1

Polyester–Polydopamine Copolymers for Intravitreal Drug Delivery: Role of Polydopamine Drug-Binding Properties in Extending Drug Release

This work reports on a novel polyester copolymer containing poly(dopamine), a synthetic analogue of natural melanin, evaluated in a sustained-release drug delivery system for ocular intravitreal administration of drugs. More specifically, a graft copolymer of poly(ε-caprolactone)-graft-poly(dopamine) (PCL-g-PDA) has been synthesized and was shown to further extend the drug release benefits of state-of-the-art biodegradable intravitreal implants composed of poly(lactide) and poly(lactide-co-glycolide). The innovative biomaterial combines the documented drug-binding properties of melanin naturally present in the eye, with the established ocular tolerability and biodegradation of polyester implants. The PCL-g-PDA copolymer was obtained by a two-step modification of PCL with a final PDA content of around 2–3 wt % and was fully characterized by size exclusion chromatography, NMR, and diffusion ordered NMR spectroscopy. The thermoplastic nature of PCL-g-PDA allowed its simple processing by hot-melt compression molding to prepare small implants. The properties of unmodified PCL and PCL-g-PDA implants were studied and compared in terms of thermal properties (differential scanning calorimetry), thermal stability (thermogravimetry analysis), degradability, and in vitro cytotoxicity. PCL and PCL-g-PDA implants exhibited similar degradation properties in vitro and were both stable under physiological conditions over 110 days. Likewise, both materials were non-cytotoxic toward L929 and ARPE-19 cells. The drug loading and in vitro release properties of the new materials were investigated with dexamethasone (DEX) and ciprofloxacin hydrochloride (CIP) as representative drugs featuring low and high melanin-binding affinities, respectively. In comparison to unmodified PCL, PCL-g-PDA implants showed a significant extension of drug release, most likely because of specific drug–catechol interaction with the PDA moieties of the copolymer. The present study confirms the advantages of designing PDA-containing polyesters as a class of biodegradable and biocompatible thermoplastics that can modulate and remarkably extend the drug release kinetics thanks to their unique drug-binding properties, especially, but not limited to, for ocular applications