Abstract 5840: Normal fibroblasts, cancer-associated fibroblasts, and their senescent counterparts exert varying effects on tumorigenic potential and ABT-263 sensitivity of gastric cancer cells

It has become increasingly apparent that cancer is not a tumor cell-centric disease. Elements of the tumor microenvironment (TME), including fibroblasts and senescent cells, have been shown to contribute to tumor cell proliferation, metastasis, and therapy resistance, and are therefore major contributors to disease progression. However, this has been complicated by accumulating evidence suggesting that the function of fibroblasts is heterogeneous, with normal fibroblasts (NFs) and cancer-associated fibroblasts (CAFs) both promoting or suppressing tumorigenesis and drug sensitivity within different contexts. Moreover, although senescent fibroblasts have been shown to accelerate tumor growth and contribute to therapy resistance, whether phenotypic differences exist between different senescent fibroblasts remains poorly understood. It is clear that additional work must be done to unravel the precise mechanisms by which NFs, CAFs, and their senescent counterparts interact within the tumor microenvironment to modulate tumor cell growth and sensitivity to therapy. Here, we show different NF and CAF lines exert varying effects on AGS gastric cancer cells. We found that when AGS cells are co-cultured with IMR90 lung fibroblasts, they form fewer and smaller colonies (total colony area = 5.14E3 pixels^2) than when cultured alone (total colony area = 2.57E4 pixels^2). On the other hand, colony formation ability is enhanced when AGS cells are co-cultured with GF1 primary gastric fibroblasts (total colony area = 3.56E4 pixels^2), and to a greater extent when cultured with CK4520 (total colony area = 4.59E4 pixels^2) and CK8612 (total colony area = 4.88E4 pixels^2) primary gastric CAFs. We next sought to determine whether these cells modulate AGS sensitivity to ABT-263, a BH3 mimetic that activates the intrinsic apoptotic pathway by targeting and inhibiting Bcl-2 and Bcl-xl. We treated AGS cells with ABT-263 with or without the addition of fibroblast-conditioned medium. We showed that IMR90 cells sensitize AGS cells to ABT-263, with an IC50 shift from 109 nM to 54 nM in AGS cells treated with IMR90-conditioned medium. On the other hand, AGS cells were more resistant to ABT-263 when treated with GF1, CK4520, or CK8612-conditioned medium, with IC50s of 270 nM, 520 nM, and 540 nM, respectively. Ongoing efforts involve expanding these experiments to senescent fibroblasts and conducting cytokine profiles to begin investigating the mechanisms underlying these phenotypes. These results contribute to our understanding of tumorigenesis and drug resistance.

Citation Format: Francesca R. Di Cristofano, Shengliang Zhang, Kelsey E. Huntington, Wafik S. El-Deiry. Normal fibroblasts, cancer-associated fibroblasts, and their senescent counterparts exert varying effects on tumorigenic potential and ABT-263 sensitivity of gastric cancer cells. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5840.

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

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 >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.