Treatment of endotoxin-induced uveitis by topical application of cyclosporine a-loaded PolyGel™ in rabbit eyes.

The main objective of this study was to investigate the potential of poly(α-carboxylate-co-α-benzylcarboxylate-ε-caprolactone)-block-poly(ethylene glycol)-block-poly(α-carboxylate-co-α-benzylcarboxylate-ε-caprolactone) (PCBCL-b-PEG-b-PCBCL; denoted as PolyGel™) as an in situ gel system for ocular delivery of CyA. The newly developed formulation was systematically assessed and its profile was compared to Restasis®, 0.5% CyA extemporaneous preparation, and CyA-loaded poly(ethylene oxide)-block-poly(ε-caprolactone) (PEO-b-PCL) a non-gelling micelle formulation. In vivo Draize test showed that CyA-loaded PolyGel™ was well tolerated with only moderate irritation that resolved within 24 h. Both ex vivo corneal permeation and in vivo pharmacokinetics in aqueous humor (AqH) showed sustained release of CyA from PolyGel™. Non-compartmental analysis of CyA concentrations in AqH showed significant changes in pharmacokinetic parameters of CyA among different formulations. The highest Cmax and AUC0-∞ in AqH were achieved with Restasis® followed by PolyGel™. Nonetheless, CyA-loaded PolyGel™ had approximately 87% longer t1/2 for CyA compared to Restasis®. Pharmacological and histopathological studies were performed on an endotoxin-induced uveitis rabbit model, where CyA-loaded PolyGel™ showed a comparable profile to Restasis®. Our results point to a great potential of PolyGel™ as ocular drug delivery carrier.

Thermoreversible hydrogels based on triblock copolymers of poly(ethylene glycol) and carboxyl functionalized poly(ε-caprolactone): The effect of carboxyl group substitution on the transition temperature and biocompatibility in plasma.

In this study we report on the development, characterization and plasma protein interaction of novel thermoresponsive in situ hydrogels based on triblock copolymers of poly(ethylene glycol) (PEG) and poly(α-carboxyl-co-benzyl carboxylate)-ε-caprolactone (PCBCL) having two different degrees of carboxyl group substitution on the PCBCL block. Block copolymers were synthesized through ring-opening polymerization of α-benzyl carboxylate-ε-caprolactone by dihydroxy PEG, leading to the production of poly(α-benzyl carboxylate-ε-caprolactone)-PEG-poly(α-benzyl carboxylate-ε-caprolactone) (PBCL-PEG-PBCL). This was followed by partial debenzylation of PBCL blocks under controlled conditions, leading to the preparation of PCBCL-PEG-PCBCL triblock copolymers with 30 and 54mol.% carboxyl group substitution. Prepared PCBCL-PEG-PCBCL block copolymers have been shown to have a concentration-dependent sol to gel transition as a result of an increase in temperature above ∼29°C, as evidenced by the inverse flow method, differential scanning calorimetry and dynamic mechanical analysis. The sol-gel transition temperature/concentration and dynamic mechanical properties of the gel were found to be dependent on the level of carboxyl group substitution. Both hydrogels (30 and 54mol.% carboxyl group substitution) showed similar amounts of protein adsorption but striking differences in the profiles of the adsorbed proteome. Additionally, the two systems showed similarities in their clot formation kinetics but substantial differences in clot endpoints. The results show great promise for the above-mentioned thermoreversible in situ hydrogels as biocompatible materials for biomedical applications.

Polymeric micelles for pH-responsive delivery of cisplatin.

Methoxy poly(ethylene oxide)-block-poly-(α-carboxylate-ε-caprolactone) (PEO-b-PCCL) was used to develop pH-responsive polymeric micelles for the delivery of cisplatin (CDDP). Micelles were prepared through complexation of CDDP with the pendant carboxyl groups on the poly(ε-caprolactone) core, perhaps through coordinate bonding. The obtained micelles were characterized using dynamic light scattering (DLS) measurement for size and stability. The in vitro release of CDDP at different pHs (7.4, 6.0 and 5.0) was evaluated. The in vitro cell uptake as well as cytotoxicity of developed micelles against two breast cancer cell lines, i.e. MDA-MB-435 and MDA-MB-231, were also assessed and compared to free CDDP as control. DLS results showed PEO-b-PCCL to form stable micelles with an average diameter of <50 nm upon complexation with CDDP. Developed polymeric micelles were capable of slowly releasing CDDP in physiological pH. However, CDDP release from polymeric micelles was triggered upon exposure to electrolytes and/or acidic pHs mimicking that of extracellular tumor microenvironment or intracellular organelles. Consistent with the slow release of CDDP from its polymeric micellar formulation, polymeric micellar CDDP exhibited lower cytotoxicity and CDDP intracellular uptake compared to free drug. The results indicate a great potential for the developed formulation in platinum therapy of breast cancer.

Characterization of the thermo- and pH-responsive assembly of triblock copolymers based on poly(ethylene glycol) and functionalized poly(ε-caprolactone).

A series of novel triblock copolymers composed of poly(ethylene glycol) (PEG) and poly(ε-caprolactone)-bearing benzyl carboxylate on the α-carbon of ε-caprolatone were synthesized through ring opening polymerization of α-benzyl carboxylate-ε-caprolactone by dihydroxylated PEG. The debenzylation of the synthesized copolymer, i.e., poly(α-benzyl carboxylate-ε-caprolactone)-b-PEG-b-poly(α-benzyl-carboxylate-ε-caprolactone) (PBCL-b-PEG-b-PBCL), in the presence of hydrogen gas using different levels of catalyst, was carried out to achieve copolymers with various degrees of free α-carboxyl to α-benzyl-ε-carboxylate groups on the hydrophobic block. Incomplete reduction of PBCL led to the formation of poly(α-carboxyl-co-benzyl caboxylate-ε-caprolactone) PCBCL in the lateral blocks at 27%, 50% and 75% carboxyl group substitution. The molecular weight and polydispersity of the resultant copolymers were estimated by (1)H NMR and MALDI-TOF. Synthesized triblock copolymers formed stable micelles at low concentrations (critical micellar concentrations (CMC) of 0.34-12.5 µg ml(-1)). Polymers containing carboxyl groups in their structure showed a pH-dependent increase in CMC. As the pH was raised from 4.0 to 9.0, CMC increased from 0.76 to 1.06 µg ml(-1), for 27% debenzylated polymer, and from 1.30 to 2.20 µg ml(-1), for 50% debenzylated polymers. In contrast, the CMC in polymers without carboxyl group was independent of pH (0.55 µg ml(-1)). Different changes in micellar size as a function of temperature was observed depending on the degree of debenzylation on the PCBCL block: polymers with 27% degree of debenzylation illustrated a rise in micelle size from ~38 to 55 nm as the temperature increased above 29°C, while polymers with 50% debenzylation showed a decrease in micelle size, from ~52 to 38 nm, with increase in temperature. A similar trend was observed at pH 4.5, 7.0 and 9.0 for polymers containing carboxyl groups on their hydrophobic block. The temperature for the onset of size change and/or the extent of aggregate size change was found to be dependent on the pH of the medium and the polymer concentration. The results point to a potential for the formation of thermo- and pH-responsive micelles from triblock copolymers of PEG and carboxyl substituted caprolactone. The results also imply a potential for the 27% debenzylated PCBCL-b-PEG-b-PCBCL copolymers to form a biodegradable thermoreversible gel with a transition temperature a few degrees below 37°C.