Abstract 388: Acquired sensitivity to ONC201/TIC10 in ER+ breast cancer progressing on the mTOR inhibitor everolimus

Abstract

Abstract The mTOR inhibitor everolimus has become an important component for clinical management of metastatic ER+ breast cancer. Despite the improved patient outcomes, progression and resistance will still develop. Therefore, it is important to research strategies that can increase response durability and effectiveness of this therapy. Here we developed everolimus resistance models and performed pre-clinical evaluation of the small molecule ONC201/TIC10, a drug candidate showing promising results in clinical trials with advanced cancer patients. ONC201/TIC10 targets mitochondrial function and metabolism and activates stress response, however its efficacy has not been studied in everolimus resistant breast cancer. Transcriptomic analysis in everolimus resistant tumors identified sustained mitochondrial oxidative phosphorylation activity suggesting increased sensitivity to ONC201/TIC10. Our results show that combination treatment of ONC201/TIC10 with everolimus inhibits the growth of sensitive as well as everolimus resistant cells in 2D and 3D in vitro studies. The increased response to combination therapy was confirmed in primary cells from patients progressing on endocrine and mTOR therapy, supporting clinical relevance. We further show that the mechanism of ONC201/TIC10 anti-proliferative activity involves disruption of mitochondrial function and increased levels of the pro-apoptotic transcription factors CHOP and ATF4. Importantly, several resistant cell lines demonstrated increased dependency on mitochondrial respiration compared to sensitive cells which contributes to a vulnerability to ONC201/TIC10. In conclusion, we used pre-clinical models to characterize acquired sensitivity to mTOR inhibition. Combining patient derived data with resistant cell line driven experiments, our study provides validated findings in various settings strengthening the potential for clinical applications of ONC201/TIC10. We propose that ONC201/TIC10 and modulation of mitochondrial function is effective in drug resistant cancer cells and can enhance the anti-tumor activity of standard of care therapy in progressing patients. Citation Format: Eleni Farmaki, Rena Emond, Aritro Nath, Vince K. Grolmusz, Patrick A. Cosgrove, Andrea H. Bild. Acquired sensitivity to ONC201/TIC10 in ER+ breast cancer progressing on the mTOR inhibitor everolimus [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 388.