SUN-139 Luminescence-Based Drug Screen for Novel Androgen Receptor Antagonists for Prostate Cancer Therapy

Abstract

The development and maintenance of the adult prostate is dependent on the action of androgens, which mediate its effect by binding to the androgen receptor (AR). Dysregulation in the AR signaling axis disrupts transcriptional homeostasis, shifting the balance towards uncontrolled proliferation and driving the progression towards prostate cancer (PCa). The prominent role of AR signaling in prostate carcinogenesis led to the development of androgen deprivation therapy (ADT) as the primary treatment strategy for managing PCa. Despite the success of ADT in early PCa cases, most patients develop resistance to ADT and the cancer ultimately recurs towards a lethal state termed castration-resistant prostate cancer (CRPC). Remarkably, AR signaling is still active in CRPC, suggesting that the progression towards CRPC is still reliant on AR activity. Current treatments are ineffective against CRPC, highlighting the need for alternative therapeutics that can combat the resistant nature of CRPC. To address the need for innovative approaches against CRPC, we used a robust luminescence-based bioassay that can identify novel AR antagonists. We screened plant extracts derived from local fauna by measuring their effect on AR-driven activity using a luciferase-based reporter assay in HeLa cells stably overexpressing hAR (HeLa-hAR). To identify candidate hits, HeLa-hAR cells were treated with DHT to induce AR-dependent luciferase activity, DHT with the AR antagonist bicalutamide as a positive control, and DHT plus the plant extracts. We identified one extract, A32, which showed significant inhibition of AR-dependent luciferase activity without having deleterious effects on cell viability. Secondary validation tests also showed that A32 exhibits a dose-dependent inhibition of AR-driven reporter activity. When testing the effect of A32 on gene expression in LNCaP cells, we observed a down-regulation in the expression of canonical AR target genes such as PSA to degrees similar to bicalutamide. These results suggest that A32 may be an AR antagonist or may target the AR signaling axis. Collectively, this study establishes the use of a luminescence-based reporter assay for the identification of novel AR antagonists from a plant extract library.