Abstract 6384: Morphological and functional plasticity of mitochondria promotes chemotherapy resistance in triple negative breast cancer
Authors: Baek Lily , Lee Junegoo , Berner Mariah J. , Pendleton Katherine E. , Goff Emily B. , Wang Karen , Barrish James P. , Lim Bora , Lorenzi Philip J. , Porter Weston , Lewis Michael T. , Echeverria Gloria V. 
Published: June 2022

Abstract
Mitochondrial metabolism plays a key role in triple negative breast cancer (TNBC) aggressiveness. As TNBC has limited targeted therapy options, chemotherapies remain the mainstay treatment. Nearly 50% of TNBC patients harbor substantial residual cancer following chemotherapy, leading to high rates of recurrence. Using longitudinal biopsies from orthotopic patient-derived xenograft (PDX) models and TNBC patients, we found residual tumors following chemotherapy transitioned to a unique metabolic state characterized by high mitochondrial oxidative phosphorylation (oxphos). This state was transient, with tumors reverting to their baseline glycolysis-high phenotype when they were allowed to regrow in the absence of treatment. Using genomic sequencing and cellular barcode-mediated clonal tracking, we found this mechanism of chemoresistance arose in the absence of clonal selection, suggesting chemotherapy induced plastic (i.e., non-genomic) programs enabling cell survival following treatment. Blocking oxphos with an inhibitor of electron transport chain Complex I (IACS010759; PMID:29892070) was significantly more efficacious against residual than pre-treated tumors (PMID:30996079), providing evidence that dynamic metabolic phenotypes represent targetable therapeutic vulnerabilities for TNBC. Using longitudinal samples collected from PDX models undergoing treatments with anthracyclines, platinums, and/or taxanes, we visualized and quantified mitochondrial structure in two- and three-dimensions by electron microscopy. These studies revealed extensive alteration of mitochondrial structure and number in residual tumor cells, and these changes reverted when residual tumors were allowed to regrow in the absence of treatment. We then administered chemotherapeutics to human TNBC cells, revealing that DNA-damaging chemotherapeutics increased mitochondrial elongation, but microtubule poisons increased mitochondrial fragmentation. These findings suggested chemotherapeutics may alter the dynamics of mitochondrial fission and fusion in TNBC cells. These structural changes were accompanied by increased or decreased oxphos rates, glucose-driven TCA cycle flux, and mitochondrial content, respectively. Driving mitochondrial fusion by genetic or pharmacologic inhibition of the mitochondrial fission factor Drp1 increased oxphos and chemoresistance, whereas driving mitochondrial fission by genetic or pharmacologic inhibition of the mitochondrial fusion protein Opa1 decreased oxphos and chemoresistance. These findings provide evidence that modulating mitochondrial fission and fusion may be a promising strategy to overcome metabolic states contributing to chemoresistance in TNBC. Our ongoing investigations are aimed at rational targeted therapies and scheduling approaches to overcome chemoresistance in in vivo models of TNBC.
Citation Format: Lily Baek, Junegoo Lee, Mariah J. Berner, Katherine E. Pendleton, Emily B. Goff, Karen Wang, James P. Barrish, Bora Lim, Philip J. Lorenzi, Weston Porter, Michael T. Lewis, Gloria V. Echeverria. Morphological and functional plasticity of mitochondria promotes chemotherapy resistance in triple negative breast cancer [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 6384.