Injectable controlled release formulations incorporating protein crystals

Development of ready-to-inject in situ formable controlled release gel systems for proteins is extremely challenging due to poor stability of proteins in the organic solvents typically used to fabricate these systems and because of the need of initial drying of proteins. The focus of the present study was to develop and characterize injectable controlled release systems composed of crystals of amylase, a model protein, suspended in solutions of polymeric and non-polymeric matrix materials in organic solvents. In this study, α-amylase derived from Aspergillus oryzae was crystallized and crystals were suspended in a poly( dl-lactide-co-glycolide) (PLGA) solution in acetonitrile (PLGA/acetonitrile), or in sucrose acetate isobutyrate (SAIB) plasticized with ethanol (SAIB/ethanol) systems. The results indicate that the protein crystals could be incorporated in these in situ formable gels without the need for initial drying. The crystals withstand organic solvents and water/organic solvent interfaces, and provide high protein loading (>30%) in these systems. Moreover, changing the morphology of the amylase crystals successfully modulated amylase release profiles. Study of long-term stability at 4 °C revealed a greater stability of crystalline protein compared to amorphous amylase. The abovementioned data suggest that protein crystals might offer greater feasibility in developing sustained release injectable in situ formable protein depot systems.