Mary Lou Beckett

Expression of prostate-specific membrane antigen in normal, benign, and malignant prostate tissues.

Prostate-specific membrane antigen (PSMA) is a trans-membrane glycoprotein recognized by the murine monoclonal antibody (MAb) 7EII-C5.3 both in its native (CYT-351) and immunoconjugate form (CYT-356). Previous studies have shown that tissue expression of PSMA is highly restricted to prostate tissues. In this study, a definitive immunohistochemistry evaluation was performed to assess PSMA expression in prostate tissues. A stain index was established by multiplying the percentage of stained cells by the intensity of the stained cells to provide a quantitative measurement of PSMA expression in the various tissue types. The cellular location of PSMA, its correlation with clinical status, and its comparison with the expression of prostate-specific antigen (PSA) were evaluated. Prostate-specific membrane antigen was found to be highly expressed in most of the normal intraepithelial neoplasia, and the primary and metastatic prostate tumor specimens evaluated. In contrast to PSA, PSMA expression was often heterogeneous with variable staining patterns, ranging from a low-level diffuse cytoplasmic staining in normal prostate epithelium to very intense cytoplasmic and focal membrane staining in high-grade primary carcinomas and metastatic tissues. The predominant cytoplasmic staining was expected because the antigenic epitope of the PSMA transmembrane glycoprotein recognized by MAb 7EII-C5.3 is located in the cytoplasmic domain. Benign prostate tumors, ie, hypertrophy, showed the lowest expression of PSMA with a stain index of 52, compared with stain indexes of 146 and 258 for normal prostate and bone metastatic tissues, respectively. The reason for the apparent down-regulation of PSMA in benign prostate tissue is unknown but may be related to a splicing variant or post-translational modification of PSMA. Expression of PSMA was observed to increase with increasing pathologic grade, but not with clinical stage. Although PSMA was overexpressed in poorly differentiated and metastatic prostate tumors, expression in the primary tumor did not correlate with nodal status, extracapsular penetration, or seminal vesicle invasion. These results suggest that PSMA is not a useful biomarker of disease progression; however, high expression does appear to be associated with the more aggressive prostate carcinoma phenotype. The restricted specificity, differential prostate tissue expression, and overexpression of PSMA in metastatic tissues support the continued study of this unique prostate tumor-associated biomarker for developing new strategies for diagnostic and therapy of prostate cancer.

Location of prostate-specific membrane antigen in the LNCaP prostate carcinoma cell line

Prostate‐specific membrane antigen (PSMA) is a novel prostate biomarker overexpressed in poorly differentiated and metastatic prostate carcinomas and apparently upregulated following hormone‐ablation therapy. PSMA appears to be a satisfactory target for antibody‐directed 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 [Troyer et al.: Urol Oncol 1:29–37, 1995]. This finding prompted the present investigation to precisely define the cellular location of PSMA in the LNCaP prostate carcinoma cell line, the line used to generate MAb 7E11‐C5.

Biochemical characterization and mapping of the 7E11-C5.3 epitope of the prostate-specific membrane antigen

The expression of the prostate-specific membrane antigen (PSMA) glycoprotein recognized by the murine monoclonal antibody (MAb) 7E11-C5.3 has been shown to be highly restricted to prostate epithelium. Although the conjugated form of this MAb (CYT-356) may soon be used clinically for in vivo imaging of extraprostatic disease, few details regarding the nature of the antigenic epitope of PSMA have been reported. This study was carried out to analyze the MAb 7E11-C5.3 epitope on PSMA using standard biochemical techniques, and the antigenic epitope was mapped with synthetic peptides. The MAb 7E11-C5.3 epitope was susceptible to both periodic acid oxidation and proteolytic digestion, which indicated that the antigen consisted of a glycoprotein. However, additional biochemical assays such as sodium borohydride, tunicamycin treatment, and digestion with glycosidases failed to abrogate MAb 7E11-C5.3 binding. Epitope mapping with synthetic peptides demonstrated the epitope to be localized to the intracellular domain at the N-terminus of the PSMA molecule with a minimal reactive peptide consisting of six amino acids (MWNLLH). The synthetic peptides were treated with periodic acid, which resulted in inhibition of antibody binding, suggesting that treatment of the PSMA antigen resulted in damage to the peptide chain. These data suggest that the MAb 7E11-C5.3 does not recognize a glycopeptide as was initially thought, but recognizes an intracellular epitope consisting of only the primary polypeptide chain. Further studies are needed to determine how CYT-356 is able to image tumors in vivo when the antigenic epitope is intracellular.

Identification of a superimmunoglobulin gene family member overexpressed in benign prostatic hyperplasia .

Benign prostate hyperplasia (BPH), a nonmalignant disease with an increasing rate of occurrence associated with advancing age, requires auxiliary markers to help identify its presence and distinguish its progression from prostate cancer.

Binding of Human IgG to Cultured Urogenital Tumor Cells

Binding of human IgG by the Fc portion of the immunoglobulin molecule was detected on established human tumor cell lines by indirect immunofluorescence microscopy, cytofluorography, quantitative absorption, and rosette formation with the use of antibody-coated erythrocytes. Of the nonlymphoid tumors tested, IgG binding was restricted to the cell membranes of certain prostate and urinary bladder tumor cell lines. Although most cell lines tested shared a common antigenic determinant with monocytes and granulocytes, these cells did not express T- and B-cell antigens, the complement 3b receptor, or bind a monoclonal antibody specific for the Fc receptor expressed on human neutrophils. The facts that IgG binding was present on long-term established tumor lines and was not influenced by in vitro passage provide evidence that these properties are intrinsic to the tumor cells and may play some role in the pathophysiology of these tumors.