Engineering temperature-sensitive poly(N-isopropylacrylamide) polymers as carriers of therapeutic proteins

This study was carried out to engineer N-isopropylacrylamide (NiPAM) polyme rs that contain protein-reactive N-acryloxysuccinimide (NASI) and hydrophob ic alkylmethacrylates (AMAs). These thermoreversible, protein-conjugating p olymers hold potential for retention of therapeutic proteins at an applicat ion site where tissue regeneration is desired. The lower critical solution temperatures (LCST) of the polymers were effectively controlled by the AMA mole content. The AMAs with longer side-chains were more effective in lower ing the LCST. Polymers without NASI exhibited a stable LCST in phosphate bu ffer and in serum over a 10-day study period. The LCST of polymers containi ng NASI was found to increase over time in phosphate buffer, but not in ser um-containing medium. The LCST increase in phosphate buffer was proportiona l to the AMA content. The feasibility of localizing a therapeutic protein, recombinant human bone morphogenetic protein-2 (rhBMP-2), to a site of appl ication was explored in a rat intramuscular injection model. The results in dicated that polymers capable of conjugating to rhBMP-2 were most effective in localizing the protein irrespective of the LCST (13-25 degreesC). For p olymers with no NASI groups, a lower LCST resulted in a better rhBMP-2 loca lization. We conclude that thermosensitive polymers can be engineered for d elivery of therapeutic proteins to improve their therapeutic efficacy. (C) 2001 John Wiley & Sons, Inc.