A novel AR degrader in castrate-resistant prostate cancer

Androgen receptor (AR) plays a critical role in prostate cancer (PCa) in all stages. While a majority of patients with PCa initially respond to androgen deprivation and/or anti-androgen therapies, a significant portion of patients develop castrate-resistant prostate cancer (CRPC). Clinical studies showed that CRPC is often enriched with AR splice variants lacking the ligand binding domain (LBD), thereby being constitutively active in an androgen-independent manner and escaping from the antiandrogen enzalutamide-mediated AR inhibition. The goal of this RO1 application is to develop and characterize novel therapeutics that effectively degrade (remove) AR proteins in PCa. Technical innovations include the development of a novel therapeutic platform for AR protein degradation using autophagy-targeting chimera (AUTOTAC). We successfully generated AR- targeted AUTOTACs, which are bifunctional molecules, composed of enzalutamide (an AR ligand binding domain inhibitor) or VPC-14449 (an AR DNA binding domain inhibitor) as a target binding ligand, linked to YTK-6-2 as a ligand of the autophagic cargo receptor p62/Sequestosome-1/SQSTM1. AR-targeted AUTOTAC brings the target protein AR to p62, forming a ternary complex. YTK-6-2 induces p62 self-oligomerization, resulting in AR-p62 oligomeric complexes. YTK-6-2-activated p62 facilitates AR-p62-LC3 interaction on autophagic membranes and promotes autophagosome biogenesis and degradation of AR proteins. Using clinically relevant animal models that reflect the relevant tumor microenvironment and tumor heterogeneity, we will test our novel hypothesis that AUTOTAC-mediated degradation (removal) of AR and its variants is a more effective approach than the currently available therapeutics including anti-androgen therapy. We also hypothesize that unlike anti-androgens which result in therapy-resistant PCa cells involving activation of noncanonical AR signaling programs, the AR-targeted AUTOTAC platform is unlikely to result in noncanonical AR signaling-associated malignant phenotypes. Aim 1 will characterize the molecular actions of AR LBD- targeted AUTOTAC (Enz-AUTOTAC) and AR DBD-targeted AUTOTAC (VPC-AUTOTAC), and evaluate their therapeutic efficacies in prostate cancer cell models. Aim 2 will evaluate the therapeutic efficacies of Enz- AUTOTAC and VPC-AUTOTAC in vivo using PTEN knockout and patient-derived xenograft (PDX) mouse models of prostate cancer. Activation of potential oncogenic pathways in therapy-resistant tumors will be examined in relation to the expression levels of AR and the status of AR variants. In addition to the transcriptome analysis of tumor cells, tumor heterogeneity, cancer cell plasticity and tumor microenvironments will also be assessed by single cell RNA-seq analysis before and after drug treatments. These data may lead to the identification of additional therapeutic target(s) in castrate-resistant PCa. Successful completion of the proposed study will develop a revolutionary drug platform of AR degraders for patients with CRPC.