PLGA Depots for Controlled Release of Bevacizumab.

Abstract

The advent of monoclonal antibody (mAb)-based anti-vascular endothelial growth factor (VEGF) therapy for treatment of wet age-related macular degeneration (AMD) has significantly improved the clinical outcomes in patients. However, monthly intravitreal injection of the anti-VEGF agents is inconvenient for patients and introduce the risks of infection, inflammation, and hemorrhage. Therefore, the development of intravitreal sustained release formulations of anti-VEGF agents would be beneficial to patients. The work in this dissertation investigated poly(lactic-co-glycolic acid) (PLGA) depot formulations to address this unmet need. Active self-encapsulating PLGA microspheres with high molecular weight dextran sulfate (HDS) as a trapping agent and ZnCO3 as an antacid demonstrated continuous 8-week in vitro release of the immunoreactive bevacizumab Fab fragments, however, loading and encapsulation efficiency were low. Adjusting loading parameters did not significantly improve those values. PLGA millicylindrical implants suitable for intravitreal injection were next employed as sustained release formulations of the anti-VEGF full-length mAb, bevacizumab. To stabilize the encapsulated mAb against the acidic microenvironment inside the PLGA implants during release period, MgCO3 was co-encapsulated. To prevent aggregation of bevacizumab during powder preparation, trehalose was co-lyophilized with the mAb above a critical level. The presence of osmotically active excipients necessary to stabilize the mAb also caused a rapid uncontrolled release due to polymer swelling. To offset this effect, the lateral surface of implants was coated with pure PLGA. The optimized coated implants demonstrated continuous release kinetics in vitro over six weeks with high (>80%) total cumulative release. The released bevacizumab over this entire period retained > 90 % monomer content as well as excellent preservation of immunoreactivity and secondary structure. Although there have been several attempts to develop sustained release formulations of the anti-VEGF mAbs, one or more desirable but unmet characteristics have hindered their clinical development. The data presented in this work provide a new paradigm for controlled release of stable bevacizumab from PLGA with the desired characteristics in various aspects, which both supports further development of this approach for wet AMD treatment and a generalizable application to site-specific controlled release of therapeutic mAbs.