Metformin concentration is a deciding factor of its pro- or anti-tumor function in triple negative breast cancer

Abstract We have previously reported that triple negative (TN) breast cancer (BC), an aggressive subtype of BC, has high dependency for mitochondrial fatty acid oxidation (FAO). We have also reported that FAO activates c-Src, one of the frequently upregulated oncopathways in TNBC. Our mechanism-based mathematical model of cancer metabolism by coupling the master gene regulators (AMPK, HIF-1) suggested that the combination of mitochondrial electron transport chain (ETC) and FAO repressions acquire the highest efficacy in suppressing the bioenergetics (i.e., cellular ATP production) of the TNBC cells. Biguanides such as metformin are one of the most widely administered anti-diabetic agents. Phenformin, a biguanide derivative similar to metformin, has greater potency than metformin. Both these drugs have been widely studied for their antitumor activities but showed only limited clinical advantages in BC. Biguanides can suppress oxidative phosphorylation (OXPHOS) by inhibiting the complex-I activity of mitochondrial ETC. However, biguanides also activate the energy sensor AMPK and phosphorylate its downstream protein ACC. Since ACC inhibits the transport of fatty acids to mitochondria, its phosphorylation can lead to FAO activation. Thus, biguanides can play opposing roles in mitochondrial metabolism (suppression of ETC and activation of FAO). Here we have analyzed the significance of these opposing roles of biguanides in TNBC metabolism and oncopathway activation. Molecular biology and RNASeq analyses suggest that while higher concentrations of biguanides suppress ETC activity and Src pathway despite the activation of AMPK, lower concentrations of biguanides activate FAO-driven ETC and Src pathway in TNBC cells. To understand the translational significance of this observation, we have performed preclinical studies using TNBC organoids and patient-derived xenografts (PDX) models. Combination therapy with metformin and FAO inhibitor, etomoxir significantly improved the antitumor activity compared to the single drug therapy. For a better clinically relevant approach, we did preclinical studies using the combination of metformin and Src inhibitor, dasatinib in TNBC organoids and PDX models. As expected, the combination of metformin and dasatinib synergistically inhibited tumor growth and enhanced the overall survival of the mice. Our observations suggested that the tumor bioavailability of biguanides is critical for its anti-tumor activity, especially in FAO-dependent tumors like TNBC. Using metabolomic, genomic and preclinical experiments, we are currently evaluating the translational potential of this findings in FAO-dependent TNBCs. Citation Format: Jun Hyoung Park, Dongya Jia, Sukjin Yang, Kwang Hwa Jung, Abha Tiwari, Debasmita Dutta, Meron Ghidey, Nagireddy Putluri, Cristian Coarfa, Chad Creighton, José N. Onuchic, Benny A Kaipparettu. Metformin concentration is a deciding factor of its pro- or anti-tumor function in triple negative breast cancer [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P5-05-06.