Abstract 3709: Synergistic activity of ABT-263 and ONC201 against solid tumor cell lines is associated with suppression of BAG3, Mcl-1, pAkt, and upregulation of Noxa along with Bax cleavage during apoptosis
Authors: Cristofano Francesca R. Di , Fong Mara , Zhou Lanlan , El-Deiry Wafik S. 
Published: June 2022

Abstract
There is an urgent need for the development of novel therapeutic approaches that can address the complex nature of cancer, including resistance to therapy. A major underlying cause of the resistance is the evasion of cell death following anti-cancer drug treatment. A great deal of progress has been made in the discovery and early development of cancer therapeutics that target cell death via the intrinsic or extrinsic cell death pathways. Two such drugs are ABT-263 and ONC201. ABT-263 is a small molecule that targets the pro-apoptotic cell death of tumor cells by blocking the anti-apoptotic function of BCL-XL and BCL-2; ONC201/TIC10 is a first-in-class small molecule originally discovered as a TRAIL-inducing compound. Previous studies have found that a mechanism of resistance to ABT-263 involves upregulation of anti-apoptotic Mcl-1 in ABT-263-treated tumors, while the efficacy of ONC201 is limited by BCL-2 overexpression. Given that ONC201 is known to downregulate Mcl-1 expression and that BCL-2 is a target of ABT-263, the combination of the two drugs has great synergistic potential. ONC201 and ABT-263 been tested in glioblastoma; however, ABT-263 is not able to cross the blood-brain barrier, and the combination of ONC201 and ABT-263 has not been tested in other solid tumors. It remains a gap in the field to test this combination therapy in tissues to which ONC201 and ABT-263 are bioavailable. We explored the combination of TRAIL-inducing compound ONC201/TIC10 and BCL-xl/BCL-2 inhibitor ABT-263 to target the extrinsic and intrinsic apoptotic pathways, respectively, in solid tumor cell lines (N=13) derived from different tissues (colon, prostate, lung, breast, ovary, bladder). We found an IC50 range of 0.83-20.10 μM for ONC201 and 0.06-14.75 μM for ABT-263 among the 13 cell lines. We show that combination of ONC201 and ABT-263 produces a strong synergistic effect leading to tumor cell death across the 1cell line panel, with maximum synergy scores ranging from 13.56-52.23 (scores were calculated using SynergyFinder; scores 0-10 indicate additive effects, while scores &gt;10 indicate synergism), and that the combination is not toxic to human fibroblast cells. We also found that the combination of these two agents resulted in caspase activation and PARP cleavage consistent with induction of apoptosis, and that these effects where over and above individual drug effects. Combination therapy-induced cell death correlated with decreased levels of Mcl-1, BAG3, pAkt, and upregulation of Noxa along with Bax cleavage during apoptosis. Our data provide evidence for synergy from the combination of ONC201 and ABT-263 against human solid tumor cell lines associated with alterations in cell death and pro-survival mediators. The combination of ONC201 and ABT-263 merits further exploration in vivo in a variety of solid malignancies.
Citation Format: Francesca R. Di Cristofano, Mara Fong, Lanlan Zhou, Wafik S. El-Deiry. Synergistic activity of ABT-263 and ONC201 against solid tumor cell lines is associated with suppression of BAG3, Mcl-1, pAkt, and upregulation of Noxa along with Bax cleavage during apoptosis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3709.