THU544 Prostatic Acid Phosphatase Is Negatively Regulated By Androgens And Persists In Castrate-resistant Metastatic Prostate Cancer

Disclosure: V. Rajagopalan: None. A. Kirschenbaum: None. S. Yao: None. A. Levine: None. Abstract: Prostate cancer (PCa) is the most common cancer and second leading cause of cancer death in American men. Most patients with metastatic PCa respond initially to androgen deprivation therapy (ADT) but the majority will progress to lethal, metastatic, castrate-resistant PCa (mCRPC). The identification of markers of mCRPC that are not regulated or negatively regulated by androgens can serve as markers and therapeutic targets in mCRPC. We hypothesized that prostatic acid phosphatase (PAP), a protein phosphatase and 5’ectonucleotidase that is expressed in both the cytoplasm and transmembrane (TM-PAP) of PCa cells, is negatively regulated by androgen signaling and can serve as a therapeutic target. Methods: Protein expression of PAP was assessed with western blotting in PCa cell lines. TM-PAP is identified by sub-cellular fractionation analysis, confocal microscopy, and flow cytometry. Effects of androgens and anti-androgens on PAP expression were assessed in VCaP cells with dihydrotestosterone (DHT) and Enzalutamide treatment followed by PAP, AR and PSA protein expression determined with Western Blotting. Loss of function analysis of PAP was performed with siRNA-mediated silencing and functional analysis was evaluated with migration and colony formation assays. Transcriptional regulation of PAP was determined by real time qPCR analysis. ChiPseq was done to confirm the binding of AR to PAP promoter. Results: All forms of PAP including TM-PAP are expressed in VCaP cell line. However, we did not detect PAP protein expression in-vitro in the LNCaP, C42B or 22Rv1 cell lines. In VCaP cell lines, we demonstrated that androgens decreased while anti-androgens increased PAP expression in a time and dose dependent fashion. Androgenic regulation of PAP occurred, at least in part, at the transcriptional level. We successfully knocked down TM and secretory PAP expression in VCaP cells using siRNA technology and showed that loss of PAP decreased migration and colony formation. Conclusions: The identification of markers of mCRPC that not regulated or negatively regulated by androgen could help identify recalcitrant tumor cells and mount targeted delivery of therapeutic agents. In the VCaP cell line, derived from a patient with mCRPC, TM and cytosolic PAP is one such protein that is negatively regulated by androgen signaling and may therefore serve as a viable therapeutic target in mCRPC. Presentation: Thursday, June 15, 2023