ONC201 is a well-tolerated, orally active small molecule in the novel imipridone class that has anti-tumorigenic properties in a number of solid tumors, but not in non-neoplastic cells. ONC201 has demonstrated promising activity as a single agent in patients with advanced endometrial cancer in the first-in-human clinical trial with Phase II trials in endometrial cancer patients now underway. Although the mechanism of action in endometrial cell pathology has not been well studied, ONC201’s anti-tumor effect has been shown in other model systems to be p53-independent and mediated through activation of the integrated stress response (ISR) leading to DR5 activation and through induction of cell death or growth arrest. ONC201 inhibits ERK and AKT leading to upregulation of TRAIL in many systems. We hypothesized that ONC201 upregulation of DR5 could sensitize tumor cells to TRAIL and that TRAIL could convert growth arrest to cell death in ONC201-treated cells. Three endometrial cancer cell lines AN3CA, HEC1A and KLE were treated with ONC201 alone or in combination with TRAIL, or a DR5 agonist. Effects on cell viability were assessed by the Cell Titer-Glo cell viability assay, colony formation assays and cell cycle analysis by propidium iodide staining. QPCR and Western blot analysis were used to evaluate mRNA and protein expression, respectively. Assessment of TRAIL and DR5 cell surface expression was evaluated by surface staining using flow cytometry and FlowJo data analysis. ONC201 decreased the cell viability of all three endometrial cancer cell lines at clinically achievable low micro-molar concentrations. ONC201 activated the ISR and an anti-proliferative effect involving a G1 phase arrest and little cell death as indicated by increased Sub-G1 analysis and PARP cleavage. DR5 mRNA and protein expression at the cell surface were induced by ONC201. All three endometrial cancer cell lines were resistant to TRAIL alone, however, pre-treatment with ONC201 sensitized the AN3CA and KLE to TRAIL and a DR5 agonist, leading to potent cell death induction. The combination of ONC201 plus TRAIL did not cause appreciable cell death in normal human fibroblast. ONC201 decreases cell viability in endometrial cancer cells lines primarily through growth arrest while the combination of ONC201 and TRAIL or a DR5 agonist promotes cell death in AN3CA and KLE cells but not in HEC1A endometrial cancer cells. Our results suggest a novel cancer therapeutic strategy that can be exploited in the clinic.

Citation Format: Jocelyn Ray, Marie Ralff, David Dicker, Wafik El-Deiry. Anti-tumorigenic effect of ONC201 is enhanced by combination treatment with TRAIL or a DR5 agonist in endometrial cancer in vitro [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 262.