A serologic approach to the definition of human prostatic carcinoma antigens

Application of mass spectrometry to the discovery of biomarkers for detection of prostate cancer

There has been an impressive emergence of mass spectrometry based technologies applied toward the study of proteins. Equally notable is the rapid adaptation of these technologies to biomedical approaches in the realm of clinical proteomics. Concerted efforts toward the elucidation of the proteomes of organ sites or specific disease state are proliferating and from these efforts come the promise of better diagnostics/prognostics and therapeutic intervention. Prostate cancer has been a focus of many such studies with the promise of improved care to patients via biomarkers derived from these proteomic approaches. The newer technologies provide higher analytical capabilities, employ automated liquid handling systems, fractionation techniques and bioinformatics tools for greater sensitivity and resolving power, more robust and higher throughput sample processing, and greater confidence in analytical results. In this prospects, we summarize the proteomic technologies applied to date in prostate cancer, along with their respective advantages and disadvantages. The development of newer proteomic strategies for use in future applications is also discussed.

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.

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

Mouse monoclonal antibodies alpha Pro3 and alpha Pro5 bind to different epitopes on an antigen (p54) of 54 kD reduced and 175 kD nonreduced MW. p54 antigen has been characterized previously with regard to tissue distribution using alpha Pro3 monoclonal antibody; the p54 antigen is present in substantially greater quantities in malignant prostatic tissue extracts than in benign prostatic and nonmalignant nonurogenital tissue extracts. In this report, we have established that alpha Pro5 and alpha Pro3 monoclonal antibodies exhibit same molecule-different epitope recognition. That both antibodies recognize the same molecular entity has been established by partial physiochemical characterization of the antigen recognized by the two antibodies and by sequential immunoprecipitation experiments. Different determinant recognition was established by lack of competitive surface binding between alpha Pro3 and alpha Pro5 to a prostatic carcinoma cell line. The p54 antigen can be labeled with glucosamine and immunoprecipitated from urea-solubilized membrane proteins; however, p54 cannot be detected by immunoprecipitation in a glycosylated form in spent culture medium removed from glucosamine-labeled cells. Experiments using indirect cellular immunoassays and directly radioiodinated monoclonal antibody have shown that both alpha Pro3 and alpha Pro5 form stable complexes with p54 antigen on the prostatic carcinoma cell surface. To the extent that modulation occurs upon interaction of p54 with alpha Pro3 and alpha Pro5; endocytosis of the immune complex appears to be the primary route of modulation. Furthermore, modulation by endocytosis is more intense when alpha Pro3 and alpha Pro5 are used in combination than when either monoclonal antibody is used alone. Although in vivo biologic behavior does not invariably correlate with in vitro behavior, careful in vitro analysis of monoclonal antibodies with respect to cell surface behavior, nevertheless, should precede in vivo evaluation. The data presented in this report indicate that preliminary in vitro analyses will expedite the effectiveness of in vivo immunotherapeutic trials; preliminary in vitro evaluations are absolutely essential if monoclonal-toxic agent (e.g., ricin A) conjugates, which must be internalized by the tumor cell to achieve cytotoxicity, are employed as immunotherapeutic agents.

Spontaneous metastasis of cells of the human prostate carcinoma cell line PC-3 in athymic nude mice

Spontaneous metastasis and extensive invasiveness were observed in athymic nude mice injected with human prostatic carcinoma cells of the PC-3 line or heterotransplants of nude mouse supported PC-3 tumor. In 3 experimental series, 60, 63 and 50 per cent of the nude mice receiving subcutaneous inoculations of PC-3 cells or tumor heterotransplants developed 1 or more lymphatic tumor metastases. Examination of metaphase-arrested cells recovered from the metastatic sites confirmed the tumor origin as human in each case. Cells recovered from 1 nude mouse supported subline, MPC-3-10, frequently exhibited double minute chromosomes in addition to the typical PC-3 chromosomal profile. These observations provide the foundation for a study of the relationship between prostate carcinoma cell characteristics and lymphatic metastasis in the nude mouse.