Abstract LB-A16: Novel Small Molecule ONC201 Induces Cell Death in Triple Negative and Non-triple Negative Breast Cancer Cells (2015)

Abstract Breast cancer is a major cause of cancer related death in United States women, and there is an urgent need for novel targeted therapies with low toxicity and increased efficacy. The TRAIL pathway has been of interest in the field of oncology, but resistance has been identified in cancer cell lines and primary tumors including those of the breast. Only a subset of triple negative breast cancers (TNBC) is sensitive to TRAIL, with other breast cancer molecular subtypes being resistant (Rahman et al., Breast Cancer Res. Treat., 2008). Clinical translation of these findings has been limited, as TRAIL receptor agonistic antibodies have shown minimal effects. We identified a small molecule inducer of the TRAIL pathway, ONC201/TIC10 (Allen et al., Sci. Trans. Med., 2013) that functions through dual inhibition of AKT/ERK, induction of the ATF4/CHOP pathway (Kline et al., Submitted, 2015) and cytotoxic effects dependent on TRAIL/DR5 upregulation. Recently, ONC201 completed its first-in-man phase 1 clinical trial in advanced solid tumors that defined its safety, pharmacokinetics and recommended phase II dose (Stein et al., Abstract C138, 2015 AACR-EORTC meeting). The objective of this work was to investigate ONC201 efficacy in TNBC (TRAIL-sensitive) and non-TNBC (TRAIL-resistant) cells. Using cell viability assays, we demonstrate IC50 values for ONC201 in the low micromolar range for both TNBC (n = 6) and non-TNBC cells (n = 5). These doses are achievable based on human PK. The evaluated non-TNBC cell lines, including those with estrogen receptor positivity and HER2 amplifications, have been shown to be highly resistant to TRAIL therapy. Propidium iodide staining and analysis of SubG1 DNA content indicates that ONC201 induces apoptosis in both TNBC and non-TNBC cells. We also show that a single dose of ONC201 is well tolerated and efficacious in vivo against the MDA-MB-231 triple negative human breast cancer xenograft model. The effects of ONC201 on well-known mechanisms of TRAIL-resistance, such as increases in inhibitor of apoptosis (IAP) family proteins, were investigated to explain sensitivity of TRAIL-resistant breast cancer cells to ONC201. We observed that ONC201 mediates a decrease in expression of IAP family proteins XIAP, c-IAP1, and c-IAP2 across TNBC and non-TNBC cell lines. We have shown that XIAP levels correlate with sensitivity to ONC201-induced apoptosis (Kline et al., Submitted, 2015). We also examined levels of death receptors DR4 and DR5 using flow cytometry, as a known mechanism of TRAIL resistance involves constitutive death receptor endocytosis from the cell surface (Zhang et al., Mol. Cancer Res., 2008). Interestingly, increases in cell surface DR4 and DR5 levels are greater in TNBC cell lines when compared with non-TNBC cell lines. Overall, our findings suggest that ONC201 exerts cytotoxic effects against a broad range of breast cancer cells, including TNBC and non-TNBC subtypes. These effects are observed regardless of the TRAIL sensitivity of the cells, and may be mediated through mechanisms involving downregulation of anti-apoptotic proteins and upregulation of cell surface death receptors. Our work will further understanding of these mechanisms and contribute to development of a preclinical rationale for the use of ONC201 as a treatment for breast cancers. Citation Format: Marie D. Baumeister, Jessica Wagner, Christina L.B. Kline, Joshua E. Allen, David T. Dicker, Wafik S. El-Deiry. Novel Small Molecule ONC201 Induces Cell Death in Triple Negative and Non-triple Negative Breast Cancer Cells. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr LB-A16.