Bispecific PSMA antibodies and CAR-T in metastatic castration-resistant prostate cancer.

ABSTRACT

Prostate cancer is the most common cancer among men and the second leading cause of cancer-related deaths in men in the United States. The treatment paradigm for prostate cancer has evolved with the emergence of a variety of novel therapies which have improved survival; however, treatment-related toxicities are abundant and durable responses remain rare. Immune checkpoint inhibitors have shown modest activity in a small subset of patients with prostate cancer and have not had an impact on most men with advanced disease. The discovery of prostate-specific membrane antigen (PSMA) and the understanding of its specificity to prostate cancer has identified it as an ideal tumor-associated antigen and has revived the enthusiasm for immunotherapeutics in prostate cancer. T-cell immunotherapy in the form of bispecific T-cell engagers (BiTEs) and chimeric antigen receptor (CAR) T-cell therapy have shown exceptional success in treating various hematologic malignancies, and are now being tested in patients with prostate cancer with drug design centered on various target ligands including not just PSMA, but others as well including six-transmembrane epithelial antigen of the prostate 1 (STEAP1) and prostate stem cell antigen (PSCA). This summative review will focus on the data surrounding PSMA-targeting T-cell therapies. Early clinical studies with both classes of T-cell redirecting therapies have demonstrated antitumor activity; however, there are multiple challenges with this class of agents, including dose-limiting toxicity, 'on-target, off-tumor' immune-related toxicity, and difficulty in maintaining sustained immune responses within a complex and overtly immunosuppressive tumor microenvironment. Reflecting on experiences from recent trials has been key toward understanding mechanisms of immune escape and limitations in developing these drugs in prostate cancer. Newer generation BiTE and CAR T-cell constructs, either alone or as part of combination therapy, are currently under investigation with modifications in drug design to overcome these barriers. Ongoing innovation in drug development will likely foster successful implementation of T-cell immunotherapy bringing transformational change to the treatment of prostate cancer.

New therapies utilizing T-cell immunotherapy for patients with metastatic prostate cancer There are ongoing developments in therapeutic strategies for the treatment of patients with metastatic castrate-resistant prostate cancer. Many of these developments involve the activation of the immune system to target neoplastic prostate cells and tumors. Conventional immunotherapy modalities such as checkpoint inhibitors did not provide robust response in clinical study to warrant a change to the prostate cancer treatment paradigm. However, we are now seeing various agents in the form of bispecific antibodies and chimeric antigen receptor's which influence T-cell activity and are leading to interesting and promising pre-clinical and clinical results. This review article highlights the biologic rationale for employment of T-cell redirecting therapies for the treatment of prostate cancer, and reviews much of the exciting data emerging within the field.