Monoclonal antibodies to different epitopes on a prostate tumor-associated antigen. Implications for immunotherapy

Monoclonal antibody to the prostate specific antigen

Somatic cell hybrids were made from mouse myeloma cells and spleen cells derived from BALB/c mice immunized with homogenized epithelial fractions of BPH. The screening by immunoperoxidase staining on human prostate and non-prostate tissue resulted in one monoclonal antibody identifying a prostate specific antigen. Upon SDS-PAGE and Western blot this antigen exhibited a single band at the position of 34 kDa molecular weight. The immunoreactivity of the prostate antigen was found to be localized exclusively in the epithelial lining of ducts and secretions of normal prostate, BPH and prostate cancer. Anti-p34 antibody reacted with an antigenic determinant on the PSA molecule cancer. Anti-p34 antibody reacted with an antigenic determinant on the PSA molecule and inhibited the binding of Anti-PSA antibody to PSA by about 80 to 90% in the RIA.

Binding and internalization of anti-sarcoma IgG and IgM antibodies

A variety of monoclonal antibodies directed against tumor cell surface antigens have been employed for tumor detection and delivery of toxins and radioisotopes to tumors in situ. The sequence of events following antibody binding to tumor cells may be critical to the success or failure of tumor imaging or therapy. Using indirect immunofluorescence, we have examined the binding and internalization of two different monoclonal antibodies (19-24 and MFH 4.10) by HT-1080, a cultured human sarcoma cell line. MAb 19-24 (IgG1) and MAb MFH 4.10 (IgM) are directed against surface antigens on cells from human malignant fibrous histiocytoma (MFH). For both of these antibodies, the initial binding on the surface of HT-1080 cells at 4 degrees C was uniform. After binding secondary fluorescent antibody, monoclonal antibodies underwent rapid internalization at 37 degrees C. Surface-bound antigen-antibody complexes were completely cleared from the cell surface in 30-60 min. In the absence of secondary fluorescent antibody, MAb 19-24 remained bound to the cell surface at 37 degrees C for up to 20 hr without being released or internalized. However, under these same conditions MAb MFH 4.10 was internalized completely within 30 min by HT-1080 cells and did not subsequently return to the cell surface. Such differences in the mechanisms of binding and uptake for these two antibodies may have significant implications for their future clinical or therapeutic uses.

Internalization and shedding of Lym-1 monoclonal antibody following interaction with surface antigens of a cultured human B cell lymphoma

Modulation of surface antigens of Raji Burkitt's lymphoma cells by monoclonal antibody Lym-1 was investigated by flow cytometry and radioimmunoassay (RIA). Raji cells, treated with antibody conjugated with FITC, became bright green as determined by FACS and the FITC-labeled Lym-1 remained associated with target cells for up to 48 hr after incubation at either 4 or 37 degrees C. Lym-1 antibody linked with biotin also bound to Raji cells and rendered these cells highly reactive with avidin-phycoerythrin (APE). However, the APE fluorescence intensity measured by FACS decreased substantially when Raji cells were cultured at 37 degrees C for 1 hr prior to APE exposure but not when incubation was carried out at 4 degrees C, indicating a disappearance of antibody from the surface of the metabolically active cells. This process was time dependent with a total loss of surface-bound biotinylated antibody occurring over a period of approximately 2 hr. Raji cells exposed to both fluoresceinated and biotinylated Lym-1 in a double labeling experiment became positive to both reagents. The flow cytometric profile was not altered when these cells were incubated for 1 hr at 4 degrees C followed by reaction with APE. However, they failed to react with APE when the 1-hr incubation took place at 37 degrees C despite the fact that they remained FITC positive, suggesting that the antibody with its fluorescent label had entered the cells. Utilizing 131I-labeled Lym-1 it was determined that approximately 50% of initially bound antibody had dissociated from the cells within the first 2 hr of incubation at 37 degrees C, although the remainder persisted with targets for up to 48 hr. The HPLC protein profile indicated that the radioactivity found in the culture supernatants and cytoplasm was associated with whole antibody, degradation products, and Ig complexes with antigen. Therefore, the present findings suggest that Lym-1 Ig molecules react with cell surface antigens and are rapidly internalized and shed, resulting in the disappearance of antibody from the surface membrane of Raji cells.

Monoclonal antibody that defines the prostate specific antigen

A monoclonal antibody to a protein with a single band in the 30-kD region was obtained from fusion of Balb/C mouse spleen cells immunized with epithelial fractions of BPH, with the myeloma cell line P3 x 63 Ag8 6.5.3 by standard procedures. This antigen was characterized in immunobinding studies with various cellular and target antigens and in immunoperoxidase staining.

Internalization and re-expression of antigens of human melanoma cells following exposure to monoclonal antibody

Modulation of the surface membrane of human Sk-Mel-28 melanoma cells by monoclonal antibody (MoAb) 96.5 recognizing p97 determinants was examined using direct radioimmunoassay and indirect fluorescent antibody-staining techniques. It was determined that the majority of 111In-labeled antibody that remained associated with cells after a 24-hr incubation at 37 degrees C had been internalized because MoAb 96.5 was no longer visible on the cell surface. A second treatment of these cells with the same antibody 24 hr later not only increased the cell-associated radioactivity, reflecting an increase of total antibody bound, but also rendered these cells membrane immunofluorescent again, indicating the re-expression of surface antigens. Autoradiographs of the electrophoretically analyzed membrane components of Sk-Mel-28 cells further demonstrated the appearance of newly synthesized 97-kDa proteins that were immunoprecipitable with MoAb 96.5. Taken together, the present findings suggest that p97 antigens undergo endocytosis in Sk-Mel-28 cells following exposure to MoAb 96.5. However, the same antigens were regenerated and expressed on the cell surface within a period of 24 hr. The re-expression of tumor cell surface antigen following initial internalization of the MoAb-antigen complex may have implications for diagnosis and therapy.

Characterization of monoclonal antibodies raised against the prostatic cancer cell line PC-82

For production of monoclonal antibodies (McAbs), hybrid cells were prepared by fusion of spleen cells of BALB/c mice immunized with the human prostatic cancer cell line PC-82 and the P3-X6(3)Ag8.653 murine myeloma cell line. Supernatants of approximately 500 hybrid clones were screened for prostate specific antibodies using an ELISA on PC-82 cells. A selection of antibodies was further tested for their specificity on a large series of different tissues. A broad cross reactivity pattern was obtained. Most cross reactivity was with pancreatic tissue, kidney, and bowel. One antibody turned out to react with prostate stromal cells. Two McAbs (ER-Pr 1 and ER-Pr 2) reacted solely with prostatic epithelium. Monoclonal antibody affinity chromatography combined with SDS-PAGE showed that both antibodies were directed against a 35-kD protein. Immunoblotting revealed that this protein is identical to prostatic antigen (PA). The epitope detected by ER-Pr 1 and ER-Pr 2 was largely preserved after formalin-fixation of prostatic tissues which renders these antibodies very suitable for routine examination of tissue sections.

In vitro synergism between hybrid immunotoxins and chemotherapeutic drugs: relevance to immunotherapy of prostate carcinoma

Cultured prostate carcinoma cells incubated in the presence of a novel hybrid immunotoxin and ricin A chain exhibited synergy with the chemotherapeutic drugs vinblastine, methotrexate, and bleomycin. No cooperative effect was noted with adriamycin. Under conditions where individual components of immunotoxin or chemotherapeutic drug mixtures were nontoxic or minimally toxic the immunotoxin-drug mixture exhibited marked impact on 14C amino acid incorporation into prostate carcinoma cells. Analysis of drug-treated cells by flow cytometry indicated that cells exposed to vinblastine and bleomycin bound hybrid immunotoxin antibody to a greater extent than cells not exposed to these drugs. Adriamycin did not exhibit synergistic cytotoxicity with hybrid immunotoxin. Also, adriamycin did not enhance antibody binding as evaluated by flow cytometry. The fact that hybrid monoclonal antibody-ricin A chain (HIT-RAC) conjugates inhibited uptake of 14C amino acids 3 to 10-fold within 48 h of incubation with target cells and that this inhibition was further increased 2 to 3-fold in conjunction with three out of four chemotherapeutic drugs tested may be attributed to the unique cytotoxicity imposed by the hybrid immunotoxins. The RAC moiety is not chemically coupled to antibody but instead occupies one of the antigen-combining sites of the molecule. In this manner, RAC is closely juxtaposed to the cell membrane of the target cell and is anchored in this position via binding of the remaining antigen-combining site to p40 prostate restricted antigen.

1,10-Phenanthroline reversibility inhibits proliferation of two human prostate carcinoma cell lines (PC-3 and DU145)

The metal chelator 1,10-phenanthroline reversibly inhibits proliferation of two human prostate carcinoma cell lines, PC-3 and DU145. Inhibition is dose-dependent, and persists for several days after removal of the chelator. The ability to induce reversible quiescence in human prostate carcinoma cells in vitro may facilitate the study of their growth cycle biochemistry.

A human monoclonal antibody reactive with human prostate

A human immunoglobulin M monoclonal antibody secreting hybridoma, termed MHG7, has been isolated and characterized for its reactivity against human prostate cells. Lymphocytes isolated from a regional draining lymph node of a patient with prostate carcinoma were fused with murine P3-NS1-Ag4-1 myeloma cells. Supernatants from the generated mouse-human somatic cell hybrids were first screened for human immunoglobulin production by an enzyme immunoassay. The identified human immunoglobulin-secreting hybridomas were expanded for further analysis and their supernatants screened by enzyme immunoassay against a panel of prostate cell lines. The human immunoglobulin M monoclonal antibody MHG7, in addition to reacting with prostate cell lines, also reacted with prostate carcinoma cells and benign prostatic hypertrophy cells on both frozen and paraffin embedded tissue sections. These data suggest that regional draining lymph nodes of prostate carcinoma patients can be used as a source of human lymphocytes for generating human immunoglobulin-secreting hybridomas reactive with human prostate cells.

Characterization of prostate-tissue-directed monoclonal antibody, alpha-Pro 13

The alpha-Pro 13-secreting hybridoma was produced by immunizing mice with an equal mixture of PC-3, DU145, and LNCaP established prostatic carcinoma cell lines. The specificity of alpha-Pro 13 monoclonal antibody was evaluated by the criteria of differential binding to cultured cells; differential binding to extracts of malignant prostate, nonmalignant prostate, and malignant and nonmalignant tissues of various histiotypes in solid phase radioimmunoassay; and by immunoperoxidase staining of primary surgical tissues of varied histiotypes. The data generated by multiple assay investigation indicate that alpha-Pro 13 exhibits preferential binding to the ductal epithelium of prostate tissue; immunoperoxidase evaluation indicates a considerable heterogeneity of staining of ductal epithelial cells. The most prevalent cross-reactivity of alpha-Pro 13 monoclonal antibody with non-prostate tissue occurs with blood vessel endothelium of restricted tissues. Electrophoretic analysis of immunoprecipitates from radioiodinated prostatic tumor extracts indicates that the molecule recognized by alpha-Pro 13 is of 120,000 dalton apparent nonreduced molecular weight. Under reducing conditions, the antigen (p40) consists of a major component of 40,000 dalton apparent MW and a minor component of 17,000 dalton MW. p40 has an isoelectric point of 3.5-4.5. The antigen is intrinsically stable on the PC-3 cell surface; its release into spent culture medium is negligible. p40 is also stable upon complexation with alpha-Pro 13 antibody in that it is not shed from the cell surface as an immune complex nor is it endocytosed to any extent as an immune complex.