Abstract 7505: Detection validation of androgen-receptor splice variant 7 in circulating tumor cells of prostate cancer by double-check assays

Abstract Introduction: Androgen-receptor splice variant 7 (AR-V7) is constitutively activated isoform of AR and has been associated with resistance towards AR targeting therapies and development into mCRPC. Confirmation of AR-V7 expression is important step in prostate cancer diagnosis and determining the drug, but the detection of AR-V7 with tissues has limitations such as clinical challenge to poorly accessible tumor tissues before and after treatment. Here, we developed the method of AR-V7 detection in circulating tumor cells (CTC) after isolation with CytoGen’s Smart BiopsyTM CTC isolator by in vitro assays of qPCR and immunofluorescence (IF) with high sensitivity and specificity, overcoming the limitations of tissue biopsy. Method: qPCR and IF methods were developed for high sensitivity and specificity of AR-V7 detection. Sensitivity and specificity were tested using AR-V7 positive cells (VCaP and 22Rv1) and negative cells (PC-3 and Raji). Limit of detection (LOD) test of AR-V7 expression was performed with AR-V7 positive cells (200 cells to 50 cells, 3 points) mixed with Raji cells (1 × 10^5cells). Then, AR-V7 positive cells (200 cells to 50 cells, 3 points) were spiked into peripheral blood mononuclear cells (PBMC) of blood sample (5mL, healthy donor) to mimic CTC after isolation by CytoGen’s Smart BiopsyTM CTC isolator, subsequently AR-V7 expression was tested with qPCR and IF assay. Results: AR-V7 expression was clearly detected by qPCR and IF in the LOD test of AR-V7 positive cells mixed with Raji cells and was not detected at all in the negative controls. The similar clear results were also observed in the spiking test of AR-V7 positive cells into PBMC isolated by CytoGen’s Smart BiopsyTM CTC isolator, suggesting that clinical samples of prostate cancer could be applied with excellent sensitivity and specificity for AR-V7. Conclusions: AR-V7 expresses only a part of cancer tissue, so it is difficult to accurately diagnose with traditional histological assays. Detection of AR-V7 in intact live CTC isolated by CytoGen’s Smart BiopsyTM CTC isolator might overcome limitations of tissue biopsy. In this study, we developed the method to detect AR-V7 in CTC with high sensitivity and specificity with qPCR and IF assay, and presented the results of verifying AR-V7 expression by double check using two kinds of assays. We plan to conduct clinical validation of the developed method through additional study using patient samples. Citation Format: Hoin Kang, Jihyun Lee, Min Hyung Kim, Soee Kim, Hyoyong Kim, Jubi Lee, Hae Ung Lee, Hai-Chon Lee, Jung Won Kim. Detection validation of androgen-receptor splice variant 7 in circulating tumor cells of prostate cancer by double-check assays [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 7505.