ABSTRACT
Prostate-specific membrane antigen (PSMA) is a cell membrane glycoprotein that is selectively expressed in prostate cells, with expression levels increasing dramatically in prostatic adenocarcinoma. PSMA-based radioligand therapy (RLT) has emerged as a viable therapeutic modality for the treatment of progressive metastatic prostate cancer. One commonly employed combination involves lutetium-177 conjugated to the ligand PSMA-617 (177Lu-PSMA-617). In this meta-analysis, we examine therapeutic responses in patients with metastatic disease who have received 177Lu-PSMA-617 therapy. We conducted a literature search with the following inclusion criteria: clinical trials involving more than 10 patients and solely utilizing 177Lu-PSMA-617. Seventeen studies were included in the final analysis. Variables documented included the number of patients, the total therapeutic dose administered, the percentage of any prostate-specific antigen (PSA) decline, the percentage with PSA decline exceeding 50% baseline, and toxicities. Overall, a majority of patients responded to therapy, and in the prospective studies, survival was found to be upwards of one year. Significant toxicities included cytopenias, which were infrequent. Patients who had PSA declines in response to therapy had longer survival. Performance status and tumor grade were also key predictors of outcome.
ABSTRACT
Prostate cancer is the most common non-cutaneous cancer in men in the United States and is the second most common cause of cancer deaths after lung cancer in men. Despite all advances in the field of prostate cancer imaging and treatment, currently, it is sub-optimally responsive to all available treatment options. Radioimmunotherapy with a monoclonal antibody (mAb), J591, has shown promising results in the treatment of prostate cancer. J591 is a deimmunized mAb that targets the extracellular domain of prostate-specific membrane antigen (PSMA), a surface-bound and internalizing glycoprotein that is upregulated in prostate cancer. Phase I/II clinical trials have shown accurate tumor targeting, biochemical and radiographic responses, and increased overall survival in patients with mCRPC with tolerable, predictable, and reversible myelotoxicity. Ongoing studies focus on improving the therapeutic index of radiolabeled J591. Herein, the literature on published clinical trials involving therapeutic J591 conjugated to b-emitter, lutetium-177 for mCRPC, is sequentially reviewed.
ABSTRACT
Cancer cells can be selectively targeted by identifying and developing antibodies to specific antigens present on the cancer cell surface. Cytotoxic agents can be conjugated to these antibodies that bind to these cell surface antigens in order to significantly increase the therapeutic index of whichever cytotoxic agent is utilized. This approach of conjugating the cytotoxic drugs to antibodies to target specific surface antigens enhances the anti-tumor activity of antibodies and improves the tumor-to-normal tissue selectivity of chemotherapy. Critical parameters in the development of these antibody-drug conjugates include: 1) selection of most appropriate antigen, 2) the ability of an antibody to be internalized after binding to the antigen, 3) cytotoxic drug potency and 4) stability of the antibody-drug conjugate. For prostate cancer, prostate-specific membrane antigen (PSMA, also known as folate hydrolase-1) is the most validated theragnostic target to date. PSMA is overexpressed on the prostate cancer cell surface, which makes it an even better target for selective drug delivery through conjugated antibodies. Here, we review the PSMA-based antibody-drug conjugates for metastatic castration-resistance prostate cancer (mCRPC).
