Arthur B. Raitano

Prostate stem cell antigen (PSCA) expression increases with high gleason score, advanced stage and bone metastasis in prostate cancer.

Prostate stem cell antigen (PSCA) is a recently defined homologue of the Thy-1/Ly-6 family of glycosylphosphatidylinositol (GPI)-anchored cell surface antigens. PSCA mRNA is expressed in the basal cells of normal prostate and in more than 80% of prostate cancers. The purpose of the present study was to examine PSCA protein expression in clinical specimens of human prostate cancer. Five monoclonal antibodies were raised against a PSCA-GST fusion protein and screened for their ability to recognize PSCA on the cell surface of human prostate cancer cells. Immunohistochemical analysis of PSCA expression was performed on paraffin-embedded sections from 25 normal tissues, 112 primary prostate cancers and nine prostate cancers metastatic to bone. The level of PSCA expression in prostate tumors was quantified and compared with expression in adjacent normal glands. The antibodies detect PSCA expression on the cell surface of normal and malignant prostate cells and distinguish three extracellular epitopes on PSCA. Prostate and transitional epithelium reacted strongly with PSCA. PSCA staining was also seen in placental trophoblasts, renal collecting ducts and neuroendocrine cells in the stomach and colon. All other normal tissues tested were negative. PSCA protein expression was identified in 105/112 (94%) primary prostate tumors and 9/9 (100%) bone metastases. The level of PSCA expression increased with higher Gleason score (P=0.016), higher tumor stage (P=0.010) and progression to androgen-independence (P=0.021). Intense, homogeneous staining was seen in all nine bone metastases. PSCA is a cell surface protein with limited expression in extraprostatic normal tissues. PSCA expression correlates with tumor stage, grade and androgen independence and may have prognostic utility. Because expression on the surface of prostate cancer cells increases with tumor progression, PSCA may be a useful molecular target in advanced prostate cancer.

The Survival Function of the Bcr-Abl Oncogene Is Mediated by Bad-Dependent and -Independent Pathways: Roles for Phosphatidylinositol 3-Kinase and Raf

ABSTRACT The Bcr-Abl tyrosine kinase constitutively activates cytokine signal transduction pathways that stimulate growth and prevent apoptosis in hematopoietic cells. The antiapoptotic action of interleukin-3 (IL-3) has been linked to a signaling pathway which inactivates the proapoptotic protein Bad by phosphorylation through kinases such as Akt and Raf. Here we report also that expression of Bcr-Abl leads to phosphorylation of Bad in hematopoietic cells. Bad phosphorylation induced by Bcr-Abl is kinase dependent, requires phosphatidylinositol 3-kinase (PI3-kinase), and mitochondrial targeting of Raf, and occurs independently of Erk. The ability of Bcr-Abl to confer cytokine-independent survival to hematopoietic cells was compromised by inhibitors of PI3-kinase, as well as by a dominant negative form of Raf targeted to the mitochondria. Furthermore, when the capacity of Bcr-Abl to phosphorylate Bad was completely blocked by dominant negative Raf, a subpopulation of cells remained viable, providing evidence for Bad-independent survival pathways. This alternative survival pathway remained PI3-kinase dependent. Finally, Bcr-Abl, but not IL-3, inhibited the proapoptotic activity of overexpressed Bad. We conclude that the antiapoptotic function of Bcr-Abl is mediated through pathways involving PI3-kinase and Raf and that survival can occur in the absence of Bad phosphorylation.

Anti-PSCA mAbs inhibit tumor growth and metastasis formation and prolong the survival of mice bearing human prostate cancer xenografts

Prostate stem-cell antigen (PSCA) is a cell-surface antigen expressed in normal prostate and overexpressed in prostate cancer tissues. PSCA expression is detected in over 80% of patients with local disease, and elevated levels of PSCA are correlated with increased tumor stage, grade, and androgen independence, including high expression in bone metastases. We evaluated the therapeutic efficacy of anti-PSCA mAbs in human prostate cancer xenograft mouse models by using the androgen-dependent LAPC-9 xenograft and the androgen-independent recombinant cell line PC3-PSCA. Two different anti-PSCA mAbs, 1G8 (IgG1κ) and 3C5 (IgG2aκ), inhibited formation of s.c. and orthotopic xenograft tumors in a dose-dependent manner. Furthermore, administration of anti-PSCA mAbs led to retardation of established orthotopic tumor growth and inhibition of metastasis to distant sites, resulting in a significant prolongation in the survival of tumor-bearing mice. These studies suggest PSCA as an attractive target for immunotherapy and demonstrate the therapeutic potential of anti-PSCA mAbs for the treatment of local and metastatic prostate cancer.