Abstract 294: Tumor concentration of metformin is a determinant factor of its regulation of fatty acid β-oxidation and c-Src pathway in triple-negative breast cancer
Authors: Park Junhyoung , Jung Kwang Hwa , Jia Dongya , Yang Sukjin , Attri Kuldeep S. , Ahn Songyeon , Murthy Divya , Ghidey Meron , Chatterjee Somik , Pedroza Diego A. , Tiwari Abha , Kim Suna , Creighton Chad C. , Putluri Nagireddy , Rosen Jeffrey M. , Onuchic José N. , Goga Andrei , Kaipparettu Benny A. 
Published: April 2023

Abstract
Biguanides such as metformin are one of the most widely administered anti-diabetic drugs. Biguanides can suppress OXPHOS by inhibiting the complex-I activity of the mitochondrial electron transport chain (ETC). Though metformin recently generated lots of hope in cancer therapy, several clinical trials showed only limited advantages for metformin in breast cancer patients. Considering its long-term observed and widely accepted safety parameters, we investigated the possible mechanisms of the lack of in vivo anticancer effect of metformin and its potential combination therapies. While metformin is an ETC inhibitor, metformin can activate AMPK, leading to ACC phosphorylation, independently of ETC inhibition. Since ACC is the upstream regulator of mitochondrial fatty acid β-oxidation (FAO), lower concentrations of biguanides can also activate FAO. Thus, biguanides can play opposing roles in mitochondrial metabolism by FAO activation, and ETC inhibition. Considering the hybrid metabolic phenotype and increased dependency of TNBC on FAO, we analyzed the effect of biguanides in TNBC progression and metastasis. While higher concentrations of biguanides suppress ETC complex-1 function, their lower concentrations activate AMPK-FAO pathway-driven ETC activity in TNBC. When the mice with TNBC tumors were treated with a clinically relevant dose of metformin, the tumor concentration of metformin after a few hours of treatment was much lower to inhibit ETC effectively. Since low concentrations of metformin can activate FAO, we did in vitro analysis of the combination of metformin and FAO inhibitor, etomoxir, in TNBC cell lines. As expected, this combination synergistically inhibited tumor properties in TNBC cells. We have published that FAO activates c-Src, one of the frequently upregulated oncopathways in TNBC. Thus, we analyzed the role of metformin concentration in Src activation in TNBC. In alignment with FAO, lower metformin concentrations activate, and high concentrations inhibit Src phosphorylation. We then investigated the significance of the combination of Src inhibitor dasatinib with metformin. As observed with FAO inhibitor, Src inhibitor synergistically enhanced the anticancer effect of metformin. To understand the translational significance of this combination, we performed ex vivo studies using TNBC organoids and PDX models. Interestingly, the combination of metformin and dasatinib synergistically inhibited the tumor growth, and metastasis and enhanced survival potential. Our results suggest that the combination of metformin and dasatinib significantly inhibits lung metastasis and modulates the immune microenvironment of the lungs. Since both dasatinib and metformin are clinically approved drugs, our findings provide a clinically translatable option for treating TNBC patients who currently lack targeted therapy.
Citation Format: Junhyoung Park, Kwang Hwa Jung, Dongya Jia, Sukjin Yang, Kuldeep S. Attri, Songyeon Ahn, Divya Murthy, Meron Ghidey, Somik Chatterjee, Diego A. Pedroza, Abha Tiwari, Suna Kim, Chad C. Creighton, Nagireddy Putluri, Jeffrey M. Rosen, José N. Onuchic, Andrei Goga, Benny A. Kaipparettu. Tumor concentration of metformin is a determinant factor of its regulation of fatty acid β-oxidation and c-Src pathway in triple-negative breast cancer [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 294.