Abstract 4972: Detection of PSMA on circulating tumor cells from blood of prostate cancer patients using anti-PSMA Centyrin

Prostate specific membrane antigen (PSMA), a transmembrane glycoprotein, is a clinically validated marker of prostate cancer. PSMA is overexpressed in primary and metastatic prostate cancer when compared to normal prostate tissue which makes it an attractive target for immunotherapy. Several antibodies are being considered to target PSMA for the development of an anticancer drug. The expression levels of PSMA on tumor cells may play a role in response to treatment with anti PSMA drugs. Therefore, it is important to monitor PSMA expression on tumor cells before and during treatment. We used CellSearch® CTC assay to determine the presence of PSMA on circulating tumor cells (CTCs) using anti PSMA Centyrin as a biomarker. Centyrins are a class of alternative scaffold molecules which are proteins of small size (∼ 10 kDa). They are engineered to bind to target molecules with high specificity and sensitivity. The anti PSMA Centyrin was tested for specificity and sensitivity using tissue cultured tumor cell lines spiked into normal healthy blood and then compared to anti PSMA antibody. The anti PSMA Centyrin showed 100% positivity with the high PSMA expressing cell line (LNCap), 25% positivity with the low PSMA expressing cell line (22Rv1) and 0% positivity with the PSMA negative cell line (PC3-9). The anti PSMA Centyrin was further tested with prostate patient blood samples to determine the expression levels of PSMA on CTCs. The patient samples which contain CTCs are positive for anti PSMA Centyrin and the percentage of CTCs positive for PSMA ranged from 25-100%. Thus, PSMA expression on CTCs can be determined using CellSearch® system and anti PSMA Centyrin as a biomarker in a clinical trial. Citation Format: Bhavesh Vaidya, Peter Vulfson, Renouard Sanders, Donna Klein, Shalom Goldberg, Steve Jacobs, Chandra Rao. Detection of PSMA on circulating tumor cells from blood of prostate cancer patients using anti-PSMA Centyrin. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4972.