Abstract 1836: ONC201 shows synergistic effect with the androgen receptor AR-inhibitor darotulamide in prostate cancer models
Authors: Tavora Fabio , Zhou Lanlan , Amin Ali , Howard Safran , Arunasalam Navaraj , de Souza Andre , Mega Anthony , Golijanin Dragan , El-Deiry Wafik , Carneiro Benedito 
Published: September 2020

Abstract
Prostate cancer (PC) is the most frequently diagnosed cancer among men in the United States and is the 3rd cause of cancer mortality. Despite advances in the treatment and understanding of pathogenesis, patients with metastatic PC invariably progress to a lethal stage of castration-resistant prostate cancer (CRPC). Inhibition of androgen signaling remains crucial for the treatment of CRPC, but novel treatment strategies are urgently needed. ONC201 is a first-in-class, selective inhibitor of dopamine receptor D2 that upregulates death-receptor 5 and induces apoptosis. ONC201 induced apoptosis in PC cell lines and showed synergy with enzalutamide, docetaxel and everolimus (Lev A Mol Cancer Res 2018). Darolutamide (DARO) is a novel androgen receptor (AR) antagonist approved for treatment of patients with non-metastatic CRPC. DARO has higher affinity to AR and preclinical activity against enzalutamide-resistant PC cell lines including AR variants associated with enzalutamide agonism (Borgmann H Eur Urol 2018). We treated human PC cell lines (LNCAP [castration sensitive, AR wild-type], 22Rv1 [castration-resistant cell line that expresses AR splice variant AR-V7], DU145 [AR negative], PC3 [AR negative]) with DARO alone and combined with ONC201. Single-agent DARO decreased PC cell viability in Cell-Titer-Glo assays (IC50s of 10 and 693 nM for LNCAP and DU145, respectively). ONC201 showed strong synergism with DARO in LNCAP cells (combination indices &lt; 1 at concentrations of 156, 312, 625 nM, and 1.25 µM of DARO with 2.5 μM ONC201). ONC201 induced robust apoptosis in 22Rv1 as measured by PARP cleavage, which was partially amplified by DARO. PARP cleavage was also observed in LNCAP cells with less intensity and not potentiated by DARO. ONC201 reduced the expression of phospho-AR (p-AR) in both 22Rv1 and LNCAP. The combination of ONC201 and DARO had a significant additive effect in reducing p-AR in 22Rv1, but not in LNCAP. ONC201 reduced PSA protein levels in LNCAP cells while DARO alone did not cause any significant change in PSA. Immunofluorescence experiments showed that DARO caused significant reduction of AR nuclear translocation in both 22rV1 and LNCAP cells. The combination with ONC201 potentiated this inhibition of AR translocation in both cell lines. ONC201 showed strong antiproliferative activity against PC cells lines independent of AR status. Combination of ONC201 with DARO demonstrated synergy in enzalutamide resistant 22Rv1 cells expressing AR-V7 with marked reduction of nuclear localization of AR. Our studies provide preclinical rationale for combination of ONC201 with DARO as a novel therapy of PC.
Citation Format: Fabio Tavora, Lanlan Zhou, Ali Amin, Safran Howard, Navaraj Arunasalam, Andre de Souza, Anthony Mega, Dragan Golijanin, Wafik El-Deiry, Benedito Carneiro. ONC201 shows synergistic effect with the androgen receptor AR-inhibitor darotulamide in prostate cancer models [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1836.