Abstract B070: Myc synthetic lethality as a therapeutic strategy for resistance: Insights into the targetability of mitochondrial complex I in Myc-high TNBC

Abstract

Abstract Patients with advanced triple-negative breast cancer (TNBC) frequently develop chemoresistance, emphasizing an urgent need for novel therapeutic strategies able to eradicate treatment resistant tumor cells. Recent studies have highlighted MYC as a common oncogenic alteration and a driver of stem-like TNBC phenotype, which commonly features high mitochondrial respiratory activity instated through OXPHOS system and chemoresistance. Interestingly, emerging evidence suggests that residual tumors from chemo treatment remain susceptible to OXPHOS inhibition through inhibition of respiratory complex I. Our previous studies have revealed a specific MYC-dependent and tumor suppressive synthetic lethal action for combination of metformin and BH3 mimetics in cells, ex vivo and in vivo models of aggressive breast cancer (PMID: 30728358). Metformin is a systemic and local metabolic modulator, which acts as a weak complex I inhibitor and promoter of AMPK activation. Here, we have explored the role of MYC in OXPHOS regulation, to address the question if metformin specifically and lethally targets MYC-modulated OXPHOS in MYC-high TNBC. We found that a selective c-MYC inhibitor (EN4) leads to a significant decrease in complex I activity despite only a modest drop in complex I mass in endogenously MYC-high TNBC cell lines. Conversely, engineered MYC overexpression in these cells upregulated complex I activity. Our current work explores transcriptomic, proteomic, and functional approaches to the mechanisms through which MYC regulates complex I activity, structure, and dynamics, ultimately hoping to define a biological rationale for therapeutic targeting of OXPHOS in Myc-high TNBC. Citation Format: Antti O Hiltunen, Linda J Id, Juha Klefström. Myc synthetic lethality as a therapeutic strategy for resistance: Insights into the targetability of mitochondrial complex I in Myc-high TNBC [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Breast Cancer Research; 2023 Oct 19-22; San Diego, California. Philadelphia (PA): AACR; Cancer Res 2024;84(3 Suppl_1):Abstract nr B070.