Detection of AR gene rearrangements and regulation of AR variant-driven prostate cancer models

Abstract

Prostate cancer is one of the leading causes of death for men in the United States. The androgen receptor (AR) plays a central role in normal prostate development and homeostasis, but prostate cancer cells are also dependent on AR signaling for growth and survival. AR is the target for most prostate cancer therapies. Inhibiting this signaling axis is associated with progression to the lethal form of the disease, castration-resistant prostate cancer (CRPC). The development of CRPC is usually due to a variety of AR reactivation mechanisms including AR amplification, AR gene rearrangements, AR ligand binding domain mutations, altered expression of AR coregulatory factors, and the emergence of AR variants (AR-V). These resistance mechanisms allow AR to function in the presence of AR inhibitors, which creates challenges for development of prostate cancer therapies. The studies performed in this dissertation were aimed at expanding our ability to detect AR gene rearrangements that encode AR-Vs and understanding coregulatory proteins that regulate AR-V-driven prostate cancer models. In this thesis, we review AR-Vs, alterations in AR, and alterations in the broader AR pathway examined in the context of primary prostate cancer tissue, metastatic CRPC tissue, circulating tumor cells (CTCs), and circulating cell-free tumor DNA (ctDNA). Additionally, we profile a technique we developed for detection of AR gene rearrangements from CTC DNA. Using this approach, we analyzed matched CTC DNA and ctDNA from a cohort of ten CRPC patients and found that genomic alterations in CTC DNA and ctDNA were discordant. This proves the feasibility and utility of analyzing genomic alterations from a single blood sample. Finally, we characterized the role of TLE3 in AR-V-driven prostate cancer models. We found that TLE3, a transcriptional co-repressor, supports anchorage- independent growth and restricts migration in prostate cancer cell lines that express AR-Vs. Mechanistically, we found that TLE3 restricts cell migration by negatively regulating mTOR. This study enhances our understanding of the cross connectivity of AR, Wnt, and mTOR signaling that occurs in prostate cancer.