Androgen Receptor Variant 7 (AR-V7) Protein Detection in Circulating Tumor Cells by Immunocytostaining

Precision medicine prostate cancer drug development, which targets patient-specific molecular alterations in prostate cancer cells, is rapidly progressing. Traditionally, tissue samples are used to screen for and study molecular alterations, but liquid biopsies are emerging as practical and potentially superior methodologies to longitudinally characterize cancer cell biology and evolution. The expression of androgen receptor variants correlates with the development of castrate resistance prostate cancer (CRPC), and the most studied variant 7 (AR-V7) is associated with CRPC, disease progression, and resistance to certain AR-pathway targeted treatments and is readily detectable in circulating tumor cells (CTCs). While mainly detected at the transcript level, subcellular localization of the protein defines its activity as a transcription factor, and emerging evidence suggests that detection of nuclear AR-V7 in CTCs is central to its utility as a poor-prognosis biomarker. Thus, transcript and protein detection of the AR-V7 biomarker in CTCs may complement each other to achieve the highest sensitivity and specificity. Here, we describe a method of AR-V7 protein detection in CTCs using immunocytostaining.