Abstract 258: Recombinant human TRAIL or a DR5 agonistic antibody convert the response of non-triple negative breast cancer cells to ONC201 from anti-proliferative to apoptotic

ONC201 was initially identified as an inducer of cell death through the tumor necrosis factor related apoptosis inducing ligand (TRAIL) pathway. The compound is being tested in patients with a variety of tumor types, including those of the breast. Both triple negative breast cancer (TNBC) cells and non-TNBC cells are sensitive to ONC201. In a subset of TRAIL-sensitive TNBC cells, ONC201 treatment leads to the induction of apoptosis in a TRAIL-dependent manner. In the majority of TRAIL-resistant non-TNBC cells, ONC201’s effects are anti-proliferative rather than apoptotic. In vivo , the apoptotic response to ONC201 leads to efficacy of the compound while the anti-proliferative response does not (Ralff et al., Mol Cancer Ther ., 2017). Here we worked to identify strategies to convert the response of cancer cells to ONC201 from anti-proliferative to apoptotic. ONC201 treatment primed TRAIL-resistant non-TNBC cells to undergo TRAIL-dependent cell death. Increases in the mRNA and surface protein levels of death receptor 5 (DR5) as well as decreases in the expression of multiple anti-apoptotic proteins occured in ONC201-treated cells. We also observed small but significant increases in TRAIL mRNA and surface protein in non-TNBC cells following treatment with ONC201. Despite apoptotic priming and the induction of TRAIL, the effect of the compound in the non-TNBC cells remains anti-proliferative but not apoptotic. We hypothesized that the level of TRAIL induced by ONC201 in these cells, known to be TRAIL-resistant, was insufficient. Remarkably, the addition of exogenous recombinant human TRAIL (rhTRAIL) converted the response of TRAIL-resistant non-TNBC cells to ONC201 from anti-proliferative to apoptotic. Cleaved PARP, caspase-3, caspase-9, and caspase-8 were observed in cells treated with ONC201 followed by rhTRAIL, but not in cells treated with ONC201 or rhTRAIL alone. Propidium iodide staining and quantification of the subG 1 population via flow cytometry further confirmed these findings. Similar observations about the ability of rhTRAIL to convert the cellular response to ONC201 from anti-proliferative to apoptotic were made in cancer cells from other tumor types. Importantly, rhTRAIL did not convert the response of normal fibroblasts to ONC201 from anti-proliferative to apoptotic. Addition of a DR5 agonistic antibody to ONC201 treated non-TNBC cells also converted the response of the non-TNBC cells to ONC201 from anti-proliferative to apoptotic. Ongoing experiments are currently testing the combination of ONC201 and rhTRAIL in vivo . These findings describe a strategy for potently converting the response of a cancer cell to ONC201 from anti-proliferative to apoptotic. Clinical application of this combination therapy may result in tumor regressions in patients with decreased sensitivity to ONC201 as a single agent. Citation Format: Marie D. Ralff, Jocelyn E. Ray, Avital Lev, Lanlan Zhou, David T. Dicker, Wafik S. El-Deiry. Recombinant human TRAIL or a DR5 agonistic antibody convert the response of non-triple negative breast cancer cells to ONC201 from anti-proliferative to apoptotic [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 258.