Mitochondrial protein translation is a heightened dependence and therapeutic vulnerability of chemo-refractory triple negative breast cancer

Triple negative breast cancer (TNBC) patients harboring residual cancer burden following completion of conventional neoadjuvant chemo-immunotherapy regimens have poor relapse-free and overall survival rates despite recent advances in immunotherapies and antibody drug conjugates. We and others have demonstrated the requirement of mitochondrial function for survival of chemo-refractory TNBC, as well as its pervasive association with chemoresistance in human and patient-derived xenograft (PDX) cohorts. We sought to gain new mechanistic insights into the mitochondrial vulnerability of TNBC. Analyses of human and PDX mass spectrometry proteomics datasets revealed that mitochondrial protein translation-related signatures were among the top significantly associated with chemoresistance. Those signatures encompassed many core mitoribosome components as well as the mitoribosome accessory protein, Oxidase (Cytochrome C) Assembly 1-Like (OXA1L), which was consistently enriched in chemoresistant versus chemosensitive TNBCs across datasets. OXA1L, while not yet characterized in cancer, has been reported to be crucial for the termination of translation of the 13 mtDNA-encoded electron transport chain (ETC) proteins and for the insertion of those proteins, as well as nDNA-encoded ETC proteins, into the inner mitochondrial membrane. Together, those functions are crucial for the proper formation and function of the ETC. Therefore, we hypothesized that mitochondrial translation supported by OXA1L supports mitochondrial dependence and chemoresistance in TNBC. Knockdown (KD) of OXA1L in human TNBC cells reduced ETC protein levels, mitochondrial respirasome supercomplex levels, ATP production, and oxidative phosphorylation (oxphos). Of note, OXA1L was required for the characteristic oxphos elevation induced by carboplatin (CRB), and KD significantly enhanced CRB sensitivity. To explore the translational potential of targeting the mitoribosome in TNBC, we leveraged the bacterial ancestry of mitochondria to repurpose the FDA-approved antibiotic tigecycline (TIG) as a chemo-sensitizing drug based on its mitoribosome inhibitory function. Direct measurement of mitochondrial nascent peptide levels revealed that, while CRB elevated mitochondrial translation, TIG potently diminished mitochondrial translation as monotherapy and when combined with CRB or docetaxel (DTX). Further, TIG abolished CRB-induced oxphos, decreased oxphos in combination with DTX, and significantly improved sensitivity to chemotherapies in human TNBC cell lines, PDX-derived spheroids, and in an in vivo PDX trial. These findings identify OXA1L-dependent mitochondrial translation and ETC formation as critical determinants of mitochondrial function that support TNBC chemoresistance, justifying further exploration of the clinical potential of repurposed antibiotics for TNBC. DISCLOSURESGVE is co-founder, Chief Scientific Officer, and an equity stakeholder of Nemea Therapeutics. G.V.E. formerly received sponsored research funding from Chimerix Inc. G.V.E. receives experimental compounds from the Lead Discovery Center of Germany and from Jazz Pharmaceuticals. MLB is a co-inventor at Nemea Therapeutics. MTL is a founder and limited partner in StemMed Ltd. and a manager in StemMed Holdings, its general partner. He is a founder and equity stakeholder in Tvardi Therapeutics Inc. Some PDX models, including BCM-4272 and BCM-7649, are exclusively licensed to StemMed Ltd., resulting in royalty income to MTL when used for commercial purposes. LED is a compensated employee of StemMed Ltd. Some PDX models, none of which are included in this study, are exclusively licensed to StemMed Ltd., resulting in royalty income to LED. All other authors have nothing to disclose.