Abstract P6-11-10: Investigating the role of mitochondrial protein translation in the metabolic adaptation of chemoresistant triple negative breast cancer

BACKGROUND: Nearly 50% of patients with triple negative breast cancer (TNBC) treated with neoadjuvant chemotherapy (NACT) retain residual tumors resulting in high rates of metastatic relapse and poor overall survival. Residual tumors surviving NACT (Adriamycin plus cyclophosphamide; AC) were found to undergo a metabolic transition to heightened mitochondrial oxidative phosphorylation (oxphos; PMID: 30996079). Pharmacologic inhibition of mitochondrial electron transport chain (ETC) complex I with IACS-010759 (PMID: 29892070) had enhanced efficacy in residual, rather than treatment-naïve, tumors of orthotopic patient-derived xenograft (PDX) models. Our analyses of mitochondrial structure and function in human TNBC cell lines revealed differing adaptations in residual cells surviving treatment with conventional NACT agents. While DNA-damaging chemotherapies (e.g.Adriamycin, carboplatin) induced mitochondrial fusion and oxphos, taxanes (e.g.paclitaxel, docetaxel) induced mitochondrial fragmentation and reduced oxphos (Baek et al., Biorxiv Doi 10.1101/2022.02.25.481996). The mechanistic basis of these mitochondrial adaptations is not yet understood. The mitochondrial ETC consists of 92 proteins, 13 of which are encoded in the mitochondrial genome (mtDNA) and translated by the mitoribosome, while the remaining are encoded by the nuclear genome (nDNA), translated by the cytoribosome, and inserted into the inner mitochondrial membrane by accessory proteins, namely Oxidase (Cytochrome C) Assembly 1-Like (OXA1L). Disruption of OXA1L in mammalian cells has been shown to affect the levels and activity of ETC complexes I, III, IV, and V, and thus diminish oxphos. We aim to determine whether mitochondrial translation and OXA1L activity represent therapeutic vulnerabilities to overcome pro-survival metabolic adaptations in chemoresistant TNBC thereby augmenting treatment response. METHODS: Weare evaluating the effects of conventional TNBC chemotherapies singly, and in standard combinations, on mitochondrial translation and ETC formation in human TNBC cells and PDX models(PIM001-P, WHIM14, BCM15116) using metabolomic and proteomic profiling. To perturb these processes genetically, we knocked down (KD) OXA1Lwith siRNA. We are complementing these studies pharmacologically using conventional antibiotics, such as tigecycline, as previous studies showed they inhibit mitochondrial translation in breast and other cancers (PMID: 25625193). These studies will reveal whether OXA1L and mitochondrial translation are required for metabolic adaption and chemotherapy resistance of residual TNBC cells. PDX preclinical trials based on our published residual tumor testing schema (PMID: 30996079), will reveal whether the sequential combination of NACT followed by tigecycline can effectively perturb residual tumor relapse. RESULTS: Proteomic profiling of longitudinally harvested PDX tumors demonstrates substantial disruption of mitochondria-and nuclear-encoded ETC components in residual vs. treatment-naïve tumors. Interestingly, these patterns are distinct between different chemotherapy treatments, with an increase of ETC components in carboplatin-treated residual tumors compared to a decrease in docetaxel-treated residual tumors. Western blot analyses of human cell lines show OXA1LKD perturbs levels of both nuclear-and mitochondria-encoded ETC components. Preliminary findings suggest OXA1LKD increases sensitivity to chemotherapies in human TNBC cell lines. Finally, tigecycline effectively inhibits TNBC cell growth. We next will evaluate whether residual cells not killed by conventional chemotherapies have enhanced tigecycline susceptibility. CONCLUSION: These data suggest targeting mitochondrial translation may be a promising approach to overcome pro-survival metabolic adaptations in residual TNBC cells not killed by conventional chemotherapies.

Citation Format: Mariah J. Berner, Lily Baek, Junegoo Lee, Philip L. Lorenzi, Mei Leng, Alexander B. Saltzman, Anna Malovannaya, Lacey E. Dobrolecki, Christina Sallas, Michael T. Lewis, Gloria V. Echeverria. Investigating the role of mitochondrial protein translation in the metabolic adaptation of chemoresistant triple negative breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P6-11-10.

Abstract P6-11-14: Mitochondrial structure and function adaptation in residual triple negative breast cancer cells surviving chemotherapy treatment

Background: Neoadjuvant chemotherapy (NACT) used for triple-negative breast cancer (TNBC) eradicates tumors in only 45% of patients. TNBC patients with substantial residual cancer burden have poor metastasis-free and overall survival rates. Our previous studies demonstrated mitochondrial oxidative phosphorylation (OXPHOS) was elevated, suggesting a unique therapeutic dependency of residual tumor cells that survived after NACT. However, mechanisms underlying this enhanced reliance on OXPHOS are yet unknown. Mitochondria are morphologically plastic organelles that cycle between fission and fusion to maintain mitochondrial integrity and metabolic homeostasis. Methods: We modeled residual disease in human TNBC cells by treating with chemotherapeutic agents at the IC50 of cell killing, then evaluating surviving cells after 48 hours of treatment. We modeled residual TNBC in orthotopic patient-derived xenograft (PDX) model (PIM001p) by treating with standard front-line NACT (Adriamycin + cyclophosphamide; AC), then longitudinally harvesting tumors prior to treatment, residual, and upon regrowth. We analyzed mitochondrial morphology, mtDNA content and integrity, mitochondrial oxygen consumption rate, and metabolomic flux. We developed a U-Net based deep learning model that automatically detects and quantifies mitochondrial features in transmission electron micrographs. To test the functional dependency of mitochondrial structure in TNBC, we perturbed mitochondrial fusion genetically (by knocking down the fusion-driving protein Optic Atrophy 1, OPA1) and pharmacologically (using the first-in-class small molecule OPA1 inhibitor, MYLS22). Results: Pharmacologic or genetic disruption of mitochondrial fusion and fission resulted in decreased or increased OXPHOS rate, respectively, in TNBC cells, revealing for the first time that mitochondria morphology regulates OXPHOS in TNBC. Upon comparing mitochondrial effects of conventional chemotherapies, we found that DNA-damaging agents (adriamycin, carboplatin) increased mitochondrial elongation, mitochondrial content, flux of glucose through the TCA cycle, and OXPHOS, whereas taxanes (paclitaxel, docetaxel) instead decreased mitochondrial elongation and OXPHOS rate. Increased levels of the short protein isoform of OPA1 were observed in residual cells that not killed by DNA-damaging chemotherapy treatment. Treatment of cells with adriamycin followed by MYLS22 or given concurrently with MYLS22 drastically decreased cell growth. Conversely, cells treated with adriamycin, inducing fusion, followed by the DRP1 inhibitor Mdivi-1, further inducing fusion, were less sensitive to adriamycin than were vehicle-treated cells. Further, we observed heightened OXPHOS, OPA1 protein levels, and mitochondrial elongation in residual tumors of the PDX model following AC treatment. We found that sequential treatment first with AC, thus inducing mitochondrial fusion and OXPHOS, followed by MYLS22 to inhibit OPA1 in residual tumors, was able to suppress mitochondrial fusion and OXPHOS and significantly inhibited residual tumor regrowth. Our deep-learning algorithm identified distinct changes in mitochondrial phenotypes in residual tumors of multiple PDX models. Treatment of non-chemotherapy-treated mice with the OPA1 inhibitor MYLS22 as a single agent had no effect on tumor growth, revealing that post-AC residual tumors have an enhanced dependency on mitochondrial fusion compared to treatment-naïve tumors. Taken together, our findings establish a functional role for mitochondrial structure in chemotherapeutic response and metabolic reprogramming, which may confer survival advantage to TNBC cells. These results suggest that pharmacologic perturbation of mitochondrial structure can overcome chemoresistance in TNBC cells when administered rationally based on our understanding of chemotherapy-induced mitochondrial adaptations.

Citation Format: Lily Baek, Junegoo Lee, Katherine E. Pendleton, Mariah J. Berner, Emily Goff, Lin Tan, Sara Martinez, Iqbal Mahmud, Argenis Arriojas, Alexander Zhurkevich, Tao Wang, Matthew Meyer, Bora Lim, James P. Barrish, Weston Porter, Kourosh Zarringhalam, Philip L. Lorenzi, Gloria V. Echeverria. Mitochondrial structure and function adaptation in residual triple negative breast cancer cells surviving chemotherapy treatment [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P6-11-14.

Mitochondrial structure and function adaptation in residual triple negative breast cancer cells surviving chemotherapy treatment

Neoadjuvant chemotherapy (NACT) used for triple negative breast cancer (TNBC) eradicates tumors in ~45% of patients. Unfortunately, TNBC patients with substantial residual cancer burden have poor metastasis free and overall survival rates. We previously demonstrated mitochondrial oxidative phosphorylation (OXPHOS) was elevated and was a unique therapeutic dependency of residual TNBC cells surviving NACT. We sought to investigate the mechanism underlying this enhanced reliance on mitochondrial metabolism. Mitochondria are morphologically plastic organelles that cycle between fission and fusion to maintain mitochondrial integrity and metabolic homeostasis. The functional impact of mitochondrial structure on metabolic output is highly context dependent. Several chemotherapy agents are conventionally used for neoadjuvant treatment of TNBC patients. Upon comparing mitochondrial effects of conventional chemotherapies, we found that DNA-damaging agents increased mitochondrial elongation, mitochondrial content, flux of glucose through the TCA cycle, and OXPHOS, whereas taxanes instead decreased mitochondrial elongation and OXPHOS. The mitochondrial effects of DNA-damaging chemotherapies were dependent on the mitochondrial inner membrane fusion protein optic atrophy 1 (OPA1). Further, we observed heightened OXPHOS, OPA1 protein levels, and mitochondrial elongation in an orthotopic patient-derived xenograft (PDX) model of residual TNBC. Pharmacologic or genetic disruption of mitochondrial fusion and fission resulted in decreased or increased OXPHOS, respectively, revealing longer mitochondria favor oxphos in TNBC cells. Using TNBC cell lines and an in vivo PDX model of residual TNBC, we found that sequential treatment with DNA-damaging chemotherapy, thus inducing mitochondrial fusion and OXPHOS, followed by MYLS22, a specific inhibitor of OPA1, was able to suppress mitochondrial fusion and OXPHOS and significantly inhibit regrowth of residual tumor cells. Our data suggest that TNBC mitochondria can optimize OXPHOS through OPA1-mediated mitochondrial fusion. These findings may provide an opportunity to overcome mitochondrial adaptations of chemoresistant TNBC.

Abstract 6384: Morphological and functional plasticity of mitochondria promotes chemotherapy resistance in triple negative breast cancer

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.