Anti-PSMA/CD3 Bispecific Antibody Delivery and Antitumor Activity Using a Polymeric Depot Formulation

Abstract

Small therapeutic proteins represent a promising novel approach to treat cancer. Nevertheless, their clinical application is often adversely impacted by their short plasma half-life. Controlled long-term delivery of small biologicals has become a challenge because of their hydrophilic properties and in some cases their limited stability. Here, an <i>in situ</i> forming depot-injectable polymeric system was used to deliver BiJ591, a bispecific T-cell engager (BiTE) targeting both prostate-specific membrane antigen (PSMA) and the CD3 T-cell receptor in prostate cancer. BiJ591 induced T-cell activation, prostate cancer-directed cell lysis, and tumor growth inhibition. The use of diblock (DB) and triblock (TB) biodegradable polyethylene glycol-poly(lactic acid; PEG-PLA) copolymers solubilized in tripropionin, a small-chain triglyceride, allowed maintenance of BiJ591 stability and functionality in the formed depot and controlled its release. In mice, after a single subcutaneous injection, one of the polymeric candidates, TB1/DB4, provided the most sustained release of BiJ591 for up to 21 days. Moreover, the use of BiJ591-TB1/DB4 formulation in prostate cancer xenograft models showed significant therapeutic activity in both low and high PSMA-expressing tumors, whereas daily intravenous administration of BiJ591 was less efficient. Collectively, these data provide new insights into the development of controlled delivery of small therapeutic proteins in cancer. <i>Mol Cancer Ther; 17(9); 1927-40. ©2018 AACR</i>.