In vivo implantation of 2,2'-bis(oxazoline)-linked poly-epsilon-caprolactone: proof for enzyme sensitive surface erosion and biocompatibility.

Previously, we have demonstrated that 2,2-bis(2-oxazoline) linked poly-epsilon-caprolactone (PCL-O) is degraded in vitro enzymatically by surface erosion which could enable the novel use of this material for drug delivery and other biomedical applications. In this study, degradation, erosion (weight loss) and toxicity of PCL-O poly(ester-amide)s were evaluated in vivo. PCL and three PCL-O polymers with different PCL block lengths (M(n): 1500, 3900, 7500 g/mol) were melt-pressed in the form of discs and implanted subcutaneously in Wistar rats (dose approximately 340 mg/kg) for 1, 4 and 12 weeks. With implantation for 12 weeks, up to 16.5% weight loss of polymer discs was measured for the most extensively linked PCL-O polymer (block length 1500 g/mol) whereas practically no weight loss was observed with the other polymers. NMR, DSC and SEC studies as well as SEM micrographs before and after implantation and in vitro hydrolysis studies indicate that enzyme based surface erosion of PCL-O polymers occurred in vivo. The in vivo evaluation based on results from hematology, clinical chemistry and histology of the implantation area and main organs (i.e. heart, lung, liver, kidney, spleen and brain) demonstrated that PCL-O polymers are biocompatible and safe, enzyme sensitive biomaterials.

Three-step tumor targeting of paclitaxel using biotinylated PLA-PEG nanoparticles and avidin-biotin technology: Formulation development and in vitro anticancer activity.

Despite recent advances in cancer therapy, many malignant tumors still lack effective treatment and the prognosis is very poor. Paclitaxel is a potential anticancer drug, but its use is limited by the facts that paclitaxel is a P-gp substrate and its aqueous solubility is poor. In this study, three-step tumor targeting of paclitaxel using biotinylated PLA-PEG nanoparticles and avidin-biotin technology was evaluated in vitro as a way of enhancing delivery of paclitaxel. Paclitaxel was incorporated both in biotinylated (BP) and non-biotinylated (LP) PEG-PLA nanoparticles by the interfacial deposition method. Small (mean size approximately 110 nm), spherical and slightly negatively charged (-10 mV) BP and LP nanoparticles achieving over 90% paclitaxel incorporation were obtained. The successful biotinylation of nanoparticles was confirmed in a novel streptavidin assay. BP nanoparticles were targeted in vitro to brain tumor (glioma) cells (BT4C) by three-step avidin-biotin technology using transferrin as the targeting ligand. The three-step targeting procedure increased the anti-tumoral activity of paclitaxel when compared to the commercial paclitaxel formulation Taxol and non-targeted BP and LP nanoparticles. These results indicate that the efficacy of paclitaxel against tumor cells can be increased by this three-step targeting method.

Effects of block length on the enzymatic degradation and erosion of oxazoline linked poly-epsilon-caprolactone.

The aim of the study was to develop enzyme sensitive polymers for pharmaceutical applications. Thus, 2,2'-bis(2-oxazoline)-linked poly-epsilon-caprolactone (PCL-O) polymers were synthesized by using epsilon-caprolactone precursors with different molecular weights (M(n): 1500, 3900, 7500 and 12,000g/mol), and the effects of PCL block length on enzymatic degradation and erosion (weight loss) of PCL-O films were studied. Solvent cast PCL and PCL-O films were incubated (22 days) in the presence of pancreatin (1%, pH 7.5), with and without enzyme inhibitors. In the absence of enzyme inhibitors, surface erosion of the PCL-O films occurred during incubation, and the erosion of the PCL-O films increased in parallel with a decrease in the PCL block length. The presence of the lipase inhibitors, paraoxon-ethyl and tetrahydrolipstatin delayed the weight loss of the PCL-O films. These results indicate that lipase was mainly responsible for the enzymatic erosion of the PCL-O films. In comparison, practically no weight loss of the PCL or the PCL-O films was observed in phosphate buffer (pH 7.4) (28 days incubation). The results demonstrate that the studied epsilon-caprolactone based poly(ester-amide)s are enzyme sensitive polymers whose erosion rate can be controlled by the PCL block length.

Effects of incorporated drugs on degradation of novel 2,2'-bis(2-oxazoline) linked poly(lactic acid) films.

Earlier studies have indicated that the degradation rate of poly(lactic acid) (PDLLA) can be modified by using 2,2'-bis(2-oxazoline) as a chain extender in polymer synthesis to form a lactic acid-based poly(ester-amide) (PEA). In the present study, the effect of an incorporated drug on the degradation rate of the PEA was evaluated. The model drugs, neutral guaifenesin, acidic sodium salicylate (pK(a) 3.0) and basic timolol (pK(a) 9.2), were incorporated into solvent cast PDLLA and PEA films. The drug content in the films was 2% (w/w). The degradation studies were carried out in PBS (pH 7.4, 37 degrees C); the resulting decrease in molecular weight of polymers was determined by size exclusion chromatography and the weight loss of films was measured. In addition, the drug release from the films in PBS (pH 7.4, 37 degrees C) was studied. The model drugs were released from the PDLLA and PEA films in a biphasic or triphasic manner. The final fast release phase of the drugs from both PDLLA and PEA films started when the molecular weight (M(n)) of the polymer had decreased close to 15,000 g/mol. The degradation rate of the PDLLA films was clearly enhanced by incorporated sodium salicylate or timolol. Whereas, the degradation rate of the PEA film was not enhanced by the incorporated drugs. The present results indicate that when compared to the PDLLA film, degradation rate of the PEA film in the presence of the drug is more predictable.

Pancreatin enhanced erosion of and macromolecule release from 2,2-bis(2-oxazoline)-linked poly(epsilon-caprolactone).

The degradation and erosion of solvent cast films and injection molded bars prepared from poly(epsilon-caprolactone) (PCL) and 2,2'-bis(2-oxazoline) linked poly(epsilon-caprolactone) (PCL-O) were evaluated in simulated gastric fluid (SGF) (pH 1.2, pepsin present) and in simulated intestinal fluid (SIF) (pH 7.5, pancreatin present). After incubation of the polymer films (10 mg) and bars (70 mg) in the medium, the resulting decrease in molecular weight (degradation) was determined by size exclusion chromatography and the weight loss of the preparations was measured. In addition, the effect of pancreatin on FITC-dextran (MW 4400) release from PCL and PCL-O microparticles, prepared by w/o/w double emulsion technique, was studied. No degradation or weight loss was observed for either PCL or PCL-O films in SGF (12 h incubation, 37 degrees C). When compared to PBS pH 7.4, pancreatin hardly enhanced the weight loss of PCL films and bars. In contrast, pancreatin enhanced substantially erosion of PCL-O films and bars. Unlike PCL preparations, the PCL-O preparations showed surface erosion in SIF. Pancreatin increased considerably FITC-dextran release from both PCL and PCL-O microparticles. In conclusion, the present results demonstrate the enzyme sensitivity of the novel PCL-O polymer. In addition, the results show that pancreatin present in intestinal fluid may substantially affect drug release from PCL based preparations.

Drug release profiles from and degradation of a novel biodegradable polymer, 2,2-bis(2-oxazoline) linked poly(epsilon -caprolactone).

In the present study, poly (epsilon -caprolactone) (PCL) was modified by introducing oxamide groups into PCL (PCL-O). The degradation (decrease in molecular weight) and erosion (weight loss) of PCL and PCL-O films were studied in PBS (pH 7.4, USP XXIV, 37 degrees C, 26 weeks incubation). The release rates of guaifenesin (M(w) 198.2), griseofulvin (M(w) 352.8), timolol (M(w) 332.4), sodium salicylate (M(w) 160.1) and FITC-dextran (M(w) 4400) from PCL and PCL-O preparations (solvent cast films, compression-molded plates, midi injection-molded rods and microparticles) were examined in PBS (pH 7.4, 37 degrees C). The degradation rate of PCL-O film was faster than that of PCL film while no erosion was observed for either film. When compared to the corresponding drug release from PCL films, the release rates of low molecular weight drugs (M(w)< or =352.8) from PCL-O films were comparable, their releases from both films following closely square-root-of-time kinetics. These results indicate that the oxamide groups had no substantial effect on the release of the low molecular weight drugs. The exception was sodium salicylate which was released faster from PCL-O film. However, FITC-dextran release was notably faster from PCL-O microparticles than from those made of PCL. FITC-dextran release was a combination of diffusion and polymer degradation and thus, the faster degradation of PCL-O enhanced the release of FITC-dextran. In conclusion, the effects of the oxamide groups on drug release profiles were dependent on the drug release mechanisms.

Degradation of and drug release from a novel 2,2-bis(2-oxazoline) linked poly(lactic acid) polymer.

The degradation rate of poly(lactic acid) (PLA) is typically modified by copolymerization of the glycolide with lactide. In the present study, the degradation rate of PDLLA was modified by a novel linking of PLA with 2,2'-bis(2-oxazoline). This modification resulted in formation of a more rapidly degrading poly(ester amide) (PEA) for controlled drug release. The hydrolytic degradation of PDLLA and PEA films was studied in PBS (pH 7.4, USP XXIV, 37 degrees C); the resulting decrease in molecular weight was determined by size exclusion chromatography and the weight loss of films was measured. Drug releases of guaifenesin (mw 198.2), timolol (mw 332.4), sodium salicylate (mw 160.1) and FITC-dextran (mw 4400) from PDLLA and PEA films and microspheres were examined in PBS (pH 7.4, 37 degrees C). The degradation rate of PEA was substantially greater than that of PDLLA. The release profiles of all small model drugs (mw <332.4) from PDLLA films were biphasic or triphasic, while the release profiles of small model drugs from PEA films varied extensively. Due to the faster weight loss of PEA, FITC-dextran (mw 4400) was released substantially more rapidly from PEA microspheres than from PDLLA microspheres. In conclusion, all model drugs, except guaifenesin, were released faster from PEA preparations than from PDLLA preparations.