Smart polymer-based controlled-release drug-delivery systems for peptide and protein

An in situ gel forming injectable smart polymer-based drug delivery system was investigated for delivering therapeutic peptide and protein at a controlled rate in their conformationally stable and biologically active form. Lysozyme and bromelain were used as model proteins and leuprolide acetate as a model peptide, which widely vary in size. Polyols were investigated for their protective role against various protein/peptide degradation mechanisms. DSC was used to determine the conformational stability of lysozyme. The biological activity of lysozyme and bromelain was studied by enzyme activity assay. Three types of the thermosensitive triblock copolymers based on PEG and PLA/PLGA were synthesized. Critical gelling concentrations were found in the range of 20–25% at 37°C by the inverted tube method. GPC was used to characterize the weight average and the number average molecular weight of polymers. NMR was used to identify various protons from different groups of triblock polymers. In vitro release studies from phase-sensitive formulations showed a greater burst, release rate, conformational stability, and biological activity of proteins in formulations with a greater proportion of hydrophilic component of solvent mixture. The presence of mannitol in lysozyme formulations further increased the conformational stability and biological activity, and decreased the burst and release rate. In vitro release studies of protein/peptide from the thermosensitive polymer formulations indicated that a greater concentration of polymer can be used for a longer duration of release. The in vivo absorption study showed prolonged absorption of LA from phase as well as the thermosensitive formulations in comparison to the absorption of leuprolide acetate from solution form. A decline in serum testosterone concentration to castration level beginning from the 3rd week and its maintenance at or below castration level until the end of study (i.e., 91 days) with formulation 1 and until 63 days with formulation 2 corroborated the protection of structural integrity of leuprolide acetate by formulation components. In vitro biocompatibility studies with CRFK cell lines showed significantly greater (p < 0.05) viability in cell lines containing growth media diluted with polymer extract than diluted with PBS. Light micrographs of tissue samples from injection sites did not reveal the presence of foreign body giant cells. In conclusion, smart polymers can be used for delivering protein/peptide at a controlled rate in conformationally stable and biologically active form. They were found to be biocompatible and biodegradable.