Gastric adenocarcinoma is highly lethal with a 5-year survival of only 31.5%, largely due to late presentation of disease and ineffective chemotherapy options. ONC201 is a first-in-class small molecule anti-cancer therapy that induces cell death in many different types of malignant tumors via a multitude of mechanisms including up-regulation of TNF-related apoptosis-inducing ligand (TRAIL) by Foxo3a and death receptor 5 (DR5) via activation of the integrated stress response. We investigated the efficacy of ONC201 in inducing cell death in gastric adenocarcinoma cells as monotherapy and in combination with recombinant human TRAIL (rhTRAIL).

AGS (caspase 8 and PIK3CA mutant, HER2 amplified) and SNU-16 (p53 mutant) gastric adenocarcinoma cell lines were treated with ONC201 and rhTRAIL and viability assays were performed to determine cell line sensitivities. Both cell lines were then treated with combination therapy based on sensitivities and viability assays were performed in order to determine combination indices. Cell death was verified with sub-G1 analysis via flow cytometry and protein expression was established via western blotting.

SNU-16 cells were sensitive to ONC201, while AGS cells were shown to be resistant to monotherapy. Both cell lines were sensitive to rhTRAIL and exhibited synergy when treated in combination with ONC201, resulting in combination indices of less than 0.5 at doses that did not induce cell death in fibroblasts. The proportion of cells in sub-G1 phase of the cell cycle increased in a dose-dependent manner with combination treatment. PARP cleavage increased in a dose-dependent manner after combination therapy, indicating apoptosis and ATF4 and CHOP expression also increased with increasing doses of combination therapy, indicating activation of the integrated stress response.

These results suggest that ONC201 may be an effective therapeutic agent for gastric adenocarcinoma in combination with rhTRAIL by inducing apoptosis via the integrated stress response. We are currently expanding the in vitro model to include additional cell lines SNU-1(Ras mutant, microsatellite instability) and SNU-5 (p53

and CDH1 mutant). We are further exploring the role of ONC201 in priming cells via up-regulation of DR5 receptors such that they have increased sensitivity to rhTRAIL when pretreated with ONC201 as a potential source for the established synergy in gastric adenocarcinoma cells. We will also apply this study regimen to an organoid and in vivo model.

Citation Format: Cassanda Susan Parker, Lanlan Zhou, Wafik S. El-Deiry. ONC201 induces apoptosis in gastric adenocarcinoma and exhibits synergy with rhTRAIL [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 3012.