Measurement of prostate-specific membrane antigen in the serum with a new antibody

Work to date has identified prostate-specific membrane antigen (PSMA) as a membrane-bound glycoprotein with high specificity for prostatic epithelial cells. PSMA reacts with the monoclonal antibody 7E11.C5, which is present in serum, seminal fluid, and prostatic epithelial cells, and is increased in its expression in the presence of a hormone refractory state associated with prostatic cancer. This report confirms these results and further documents the presence of the monoclonal antibody 3F5.4G6, which reacts with the extracellular domain of PSMA. This region of PSMA is also an element present in a truncated version of the protein, so-called PSM'. Immune precipitation with either 7E11.C5 or 3F5.4G6 yields an isolated protein species that are reactive with the reciprocal antibody in Western blot analysis. Thus, 3F5.4G6 recognizes the same PSMA protein as does 7E11.C5, but at different epitopes on essentially opposite ends of the molecule. These two antibodies are well suited for use in a sandwich immunoassay, either one as a capture or detection antibody. Current work on this is underway. This report also confirms that 7E11.C5 Western blots for PSMA are negative with normal human brain tissue. The monoclonal antibody 9H10 does not react with 3F5.4G6 or with 7E11.C5 in studies conducted herein. Moreover, 3F5.4G6 reacts with PSMA found in the LNCaP cell line, but not DU-145 or PC3, which lack PSMA.