Transmembrane prostatic acid phosphatase: a therapeutic target in advanced prostate cancer.

Prostate cancer (PCa) is the most common cancer and second leading cause of cancer death in American men. Most patients with metastatic disease respond initially to androgen deprivation therapy (ADT), but almost inevitably progress to castration resistant prostate cancer (CRPC). Identification of markers and drivers of mCRPC that (a) represent a progenitor-type cancer cell population (b) persist in castration resistant disease (c) are actionable targets expressed on the cell surface, and (d) are induced by hypoxia, is required to facilitate the development of novel targeted therapies. We identified prostatic acid phosphatase (PAP), particularly the transmembrane form (TMPAP), as one such potential target. PAP is both a phosphatase and a 5'ectonucleotidase that generates adenosine. We herein demonstrate that PAP is expressed early on during fetal development and persists in castration-resistant disease. The VCaP and VCaP-enzalutamide-resistant PCa cell lines express secretory (sPAP) and TMPAP. Androgens downregulate while hypoxia upregulates PAP expression. In vivo, PAP persists in hypoxic areas of castration-resistant tumors. Knockdown of PAP decreases VCaP migration and colony formation. Finally, treatment of VCaP tumor-bearing mice with inhibitors of adenosine receptors reduces tumor growth. This data demonstrates that TMPAP is a novel therapeutic target in advanced prostate cancer.