Abstract 5139: Development of AR-V7 blood-based detection test by digital PCR in castration-resistant prostate cancer patients undergoing hormonal therapy
Authors: Cho William C. , Fung King Y. , Fong Alvin H. , Chan Timothy T. 
Published: June 2022

Abstract
Introduction: Androgen receptor splice variant 7 (AR-V7) is found to be associated with resistance to hormonal therapy in castration-resistant prostate cancer (CRPC). This study aims to develop a minimally-invasive approach for the direct quantification of AR-V7 in blood and evaluates whether AR-V7 can act as a predictor of progression in CRPC patients undergoing hormonal therapy.
Materials and Methods: A prostate cancer cell line (VCaP) was used to test the assay’s limit of detection. The detection of AR-V7 was then evaluated in 126 serial plasma samples and 77 serial platelet samples, prospectively collected from 30 patients with CRPC before and during hormonal therapy (abiraterone or enzalutamide) using reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and droplet digital polymerase chain reaction (ddPCR).
Results: RT-qPCR and ddPCR were first performed on VCaP to measure a range of 20 fg to 20 ng VCaP cDNA. ddPCR was able to detect down to 2 pg while RT-qPCR was only able to detect 200 pg for AR-V7 and total AR. RT-qPCR and ddPCR were then performed on the plasma samples of CRPC patients. Our results observed that RT-qPCR was unable to detect AR-V7 from these plasma samples, whereas ddPCR yielded a higher detection rate of 13%. Plasma with 22Rv1 and VCaP RNA spike-in revealed that RNase in plasma degraded spike-in RNA. We further detected AR-V7 in platelet samples, our results found that RT-qPCR was able to detect AR-V7 from 56% of the platelet samples and ddPCR yielded a much higher detection rate of 97%. Finally, we quantified the AR-V7 levels of 22 available platelet samples taken at the point closest to the patients’ progression time to evaluate the correlation of AR-V7 with the patient’s progression records. In receiver operating characteristic curve analysis, the area under the curve was 0.656.
Conclusion: Our results showed that platelet samples had higher detection sensitivity than plasma samples, this might be due to the possibility of RNA degradation by RNase during processing in plasma samples. Performing RT-qPCR and ddPCR on platelet samples, a higher detection rate was observed in ddPCR when compared with RT-qPCR. We successfully develop a detection test to assess AR-V7 by highly sensitive ddPCR in the platelet of CRPC patients, with a high detection rate of 97%. We also reveal that there is a certain correlation between the ddPCR detection for AR-V7 in patients’ platelet samples with the patients’ progression status, indicating that AR-V7 may act as a potential predictor of progression in CRPC patients undergoing hormonal therapy.
Citation Format: William C. Cho, King Y. Fung, Alvin H. Fong, Timothy T. Chan. Development of AR-V7 blood-based detection test by digital PCR in castration-resistant prostate cancer patients undergoing hormonal therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5139.