Immunocytochemical localization of an immunoconjugate (antibody IgG against prostatic acid phosphatase conjugated to 5-fluoro-2'-deoxyuridine) in human prostate tumors

Current chemotherapeutic and/or endocrine treatments for adenocarcinoma of the prostate (CaP) do not selectively target neoplastic prostate cells. Therefore, new approaches are needed to improve treatment for prostate tumors. We hypothesized that because of the specific binding of antibody immunoglobulin G (IgG) against human prostatic acid phosphatase (PAcP), PAcP-IgG could function as a carrier protein for the conjugated chemotherapeutic drugs and that the immunoconjugate would then selectively localize (bind) to epithelial cells of human prostate tumors, but not to epithelial cells of other organs. Our objective was to test this hypothesis using human prostate, colon, and kidney tissue samples and human prostate pieces incubated in short-term organ culture. We used derivatives of 5-fluorouracil labeled with fluorescein isothiocyanate (FITC) and rabbit anti-PAcP-IgG tagged with CY3/rhodamine alone or as an immunoconjugate. Localization of PAcP-IgG alone and the immunoconjugate in prostate produced similar and specific immunostaining in prostate epithelial cells and their tumors, but not in epithelia of colon and kidney tissue sections or in prostate sections-treated with normal rabbit serum. Confocal microscopy showed co-localization of CY3 and FITC of the immunoconjugate in the same group of prostate epithelial cells and their tumors. Organ culture studies showed that human prostate tissue samples incubated with normal rabbit serum did not show any flourescence whereas those cultured with PAcP-IgG immunoconjugate showed fluorescence in glandular epithelial cells. The later study also showed that in organ culture the immunoconjugate had penetrated and labeled prostate glands internal to the cut surfaces. Drug labeled with FITC did not localize specifically in the prostatic epithelium. Analysis of our data has shown that PAcP-IgG was needed for specific localization of the immnuoconjugate in prostate glands. We conclude that PAcP-IgG was essential for delivery and binding of the drug in human prostate. This is the first report to show that PAcP-IgG-5-Fu-2'-d-based immunoconjugate was selective and specific to epithelial cells of human prostate and its tumors, as revealed by organ culture, immunocytochemical, and confocal microscopic techniques.