Regulation of mitochondrial ROS by C15ORF48 in a basal cell subpopulation contributes to chemotherapy resistance in TNBC.

Systemic neoadjuvant chemotherapy, often combined with immunotherapy, is the standard of care for early-stage, non-breast cancer susceptibility gene (BRCA)-mutant triple negative breast cancer (TNBC). However, up to 70% of patients retain residual disease after treatment, which is linked to recurrence and mortality within 5 years. To define mechanisms of resistance, we performed single-cell RNA sequencing on orthotopic TNBC patient-derived xenografts during a cycle of treatment with doxorubicin and cyclophosphamide (AC). Clustering identified four tumor epithelial cell populations, with basal cells enriched in residual tumors. These basal cells up-regulated C15ORF48, a paralog of the mitochondrial cytochrome c oxidase associated subunit FA4 (NDUFA4), while exhibiting reciprocal down-regulation of NDUFA4. Functionally, C15ORF48 knockdown sensitized breast cancer cells to AC, increasing reactive oxygen species (ROS) and apoptosis. Thus, the up-regulation of C15ORF48 blunts ROS accumulation and induces resistance to chemotherapy in the basal cell subpopulations. Our findings identify C15ORF48 as a potential therapeutic target for overcoming AC resistance in TNBC.