Abstract 2102: ONC201 targets AR and AR-V7 signaling pathways, reduces PSA and synergizes with everolimus in castration resistant prostate cancer

Abstract

Androgen receptor (AR) signaling plays a key role in prostate cancer progression; thus Androgen Deprivation Therapy (ADT) is a mainstay therapy for patients with advanced prostate cancer. However, in most cases the tumor becomes androgen-independent and resistant to ADT with patients ultimately progressing to metastatic castration resistant prostate cancer (mCRPC). Constitutively activated AR splice variants (AR-Vs) have emerged as major mediators of resistance to AR-targeted therapy and progression of mCRPC, representing an important therapeutic target for mCRPC. Out of at least 15 AR-Vs described thus far, AR-V7 is the most abundant in prostate cancer and its expression correlates with ADT resistance. ONC201 is the founding member of the imipridone class of small molecules that induces apoptosis in a variety of tumor types tested. It is currently in Phase I/II clinical trials for advanced solid tumors and hematological malignancies, including mCRPC with encouraging activity observed in patients in early clinical testing (Stein et al., ASCO, 2016). We demonstrate here that ONC201 treatment induces apoptosis in both castration-resistant and –sensitive human prostate cancer cell lines. Furthermore, an in-vitro synergistic effect is observed with ONC201 and FDA approved drugs for prostate cancer such as enzalutamide, docetaxel and everolimus. Mechanistically, we found that ONC201 inhibits both AR and AR-V7 signaling pathways. Analysis of AR+ cell lines stimulated with DHT showed a significant decrease in both RNA and protein levels of AR, AR-V7, PSA and other AR-target genes following ONC201 treatment. Ongoing experiments are aimed at better understanding the molecular and cellular mechanisms that enable ONC201 to inhibit the AR signaling pathway. In-vivo studies with AR-negative hormone refractory prostate cancer xenografts demonstrate single agent ONC201 anti-tumor efficacy. Ongoing studies are further evaluating the in-vivo efficacy of ONC201 as a single agent or in combination with enzalutamide and everolimus using mouse models of both castration-resistant and -sensitive prostate cancer. These preclinical results indicate that ONC201 is well suited to address mCRPC, including tumors that harbor AR-V7, as a single agent that may be combined synergistically with enzalutamide or everolimus . With these observations we envision further development a combination of ONC201 plus everolimus in CRPC with or without enzalutamide resistance.

Citation Format: Avital Lev, Amriti R. Lulla, David T. Dicker, Wafik S. El-Deiry. ONC201 targets AR and AR-V7 signaling pathways, reduces PSA and synergizes with everolimus in castration resistant prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2102. doi:10.1158/1538-7445.AM2017-2102