Clinical Utility of Radiolabeled Monoclonal Antibodies in Prostate Cancer

Prostate cancer represents an ideal target for radioimmunotherapy based on the pattern of spread, including bone marrow and lymph nodes, sites that typically receive high levels of circulating antibody, and the small volume of disease, ideally suited for antibody delivery and antigen access. This review explores possible antibody targets in prostate cancer and focuses on the potential role for radioimmunotherapy by highlighting several clinical trials involving radiolabeled anti–prostatespecific membrane antigen monoclonal antibody J591. Prostate-specific membrane antigen, a highly prostate-restricted transmembrane glycoprotein with increased expression in high-grade, metastatic, and hormone-refractory disease, represents an ideal target for monoclonal antibody therapy in prostate cancer. Radiolabeled anti–prostate-specific membrane antigen monoclonal antibody J591 trials using the radiometals yttrium-90 and lutetium-177 have demonstrated manageable myelotoxicity, no significant nonhematologic toxicity, excellent targeting of soft-tissue and bone metastases, and preliminary efficacy including prostate-specific antigen and measurable disease responses. Additional studies are under way to better define the activity of radiolabeled antibody therapy as well as the role for fractionated therapy and combination approaches with taxane-based chemotherapy.