Abstract 5538: Arv7 validation in castrate resistant prostate tumors utilizing Rnascope in situ hybridization assay

Abstract

Abstract Background Androgen receptor splice variant 7 (ARV7) is a ligand-independent transcription factor associated with resistance to androgen deprivation therapy. There are efforts in development to monitor ARV7 expression during the treatment of patients with prostate cancer. Methods We evaluated ARV7 expression in primary and metastatic prostate adenocarcinomas tissues utilizing automated RNAScope (Advanced Cell Diagnostics) ISH assay, Immunohistochemistry (IHC) and quantitative PCR (qPCR). The novel RNAscope ISH assay was used for direct chromogenic visualization of RNA transcripts and to confirm positivity as an orthogonal approach to validate IHC and quantitative qPCR assay findings. We screened a total of 44 CRPC FFPE tumor samples by IHC and a subset of 28 (excluding controls) with the ISH and qPCR assays. Samples for qPCR were enriched for tumor by macrodissection. RNAScope Scoring Criteria was used to score ISH expression and raw Ct values were normalized to the RPL19 housekeeping gene for qPCR. Thresholds for each assay was established by comparing the findings with the other 2 assays. The data was calculated as ARV7 (+) or ARV7 (-) based on thresholds and compared to the other 2 assays to establish assay performance statistics. Results The ISH screening of 28 CRPC tumors resulted in 16 tumors with some level of positivity and approximately 10 tumors with significant positivity. Of the 44 CRPC tumors stained by IHC, 16 tumors showed various levels of ARV7 nuclear positivity and 8 tumors with strong positivity. Conclusions The detection of ARV7 was achieved in three independent assays. The correlation of three orthogonal data sets were used to identify positive and negative tissues. ISH has the potential for greater sensitivity compared to traditional IHC. The development of automated RNAscope ISH assay allows for more samples to run in a standardized manner with minimal inter-operator variably and requires less hands on-time gives consistently reproducible results. Citation Format: Tanesha Cash-Mason, Jackson Wong, Martinez Martinez, Michael Sharp, Jayaprakash Karkera, John D. Alvarez, Gerald C. Chu, Shibu Thomas, Weiman Li, S. Ken Tian. Arv7 validation in castrate resistant prostate tumors utilizing Rnascope in situ hybridization assay [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5538.