Tumor-Targeting Ability of Novel Anti-Prostate-Specific Membrane Antigen Antibodies

Patients with prostate-specific membrane antigen (PSMA)-positive tumors can benefit from PSMA-targeted therapy; thus, we have constructed a phage-displayed synthetic antibody library for the production of novel PSMA antibodies with superior PSMA-targeting ability, favoring clinical management. The binding affinities of anti-PSMA antibodies were verified by an enzyme-linked immunosorbent assay (ELISA). Several in vitro and in vivo experiments, including cellular uptake, internalization, and cytotoxicity studies, micro single photon emission computed tomography (microSPECT)/CT, and biodistribution studies, were performed to select the most promising antibody among six different antibodies. The results showed the target affinities of our antibodies in the ELISA assays (7A, 8C, 8E, and 11A) were comparable to the existing antibodies (J591). The half-maximal effective concentrations of 7A, 8C, 8E, 11A, and J591 were 2.95, 6.64, 5.50, 2.08, and 4.79, respectively. The radiochemical yield of 111In-labeled antibodies ranged from 30% to 50% with high radiochemical purity (>90%). In the cellular uptake studies, the accumulated radioactivity of 111In-J591, 111In-7A, and 111In-11A increased over time. The internalized percentage of 111In-11A was the highest (32.14% ± 2.06%) at 48 h after incubation, whereas that of 111In-J591 peaked at 22.43% ± 4.38% at 24 h and dropped to 13.52% ± 3.03% at 48 h postincubation. Twenty-four hours after injection, radioactivity accumulation appeared in the LNCaP xenografts of the mice injected with 111In-11A, 111In-8E, 111In-7A, and 111In-J591 but not in the xenografts of the 111In-8C-injected group. Marked liver uptake was noticed in all groups except the 111In-11A-injected group. Moreover, the killing effect of 177Lu-11A was superior to that of 177Lu-J591 at low concentrations. In conclusion, we successfully demonstrated that 11A IgG owned the most optimal biological characteristics among several new anti-PSMA antibodies and it can be an excellent PSMA-targeting component for the clinical use.