LOCATION OF PROSTATE-SPECIFIC MEMBRANE ANTIGEN IN THE LNCAP PROSTATE CARCINOMA CELL-LINE

BACKGROUND. Prostate-specific membrane antigen (PSMA) is a novel prost ate biomarker overexpressed in poorly differentiated and metastatic pr ostate carcinomas and apparently upregulated following hormone-ablatio n therapy. PSMA appears to be a satisfactory target for antibody-direc ted imaging of prostate carcinomas despite the recent finding that the antigenic epitope recognized by monoclonal antibody (MAb) 7E11-C5 is found in the cytoplasmic domain of this transmembrane glycoprotein [Tr oyer et al.: Urol Oncol 1:29-37, 1995]. This finding prompted the pres ent investigation to precisely define the cellular location of PSMA in the LNCaP prostate carcinoma cell line, the line used to generate MAb 7E11-C5. METHODS. Subcellular fractionation, immunofluorescence and i mmunoperoxidase staining of live and fixed cells, and immunoelectron m icroscopy were used to determine the localization of PSMA in LNCaP cel ls. RESULTS. PSMA was found to be localized at the inner face of the p lasma membrane as well as being associated with mitochondria. Staining of LNCaP cells, heated by serum starvation followed by serum stimulat ion, showed no changes in the typical cytoplasmic staining pattern. CO NCLUSIONS. The data suggest that the PSMA target epitope for antibody- directed imaging with MAb 7E11-C5 only becomes accessible upon apoptos is or necrosis. This further suggests that antibodies directed at the extracellular domain may enhance the sensitivity of antibody-directed imaging and therapy of prostate carcinomas by recognizing surface epit opes of PSMA on living cancer cells. (C) 1997 Wiley-Liss, Inc.