Divergent transcriptional programs and constrained metabolic states reveal selective metabolic dependencies in chemoresistant luminal breast cancer.

Aim: Resistance to neoadjuvant chemotherapy remains a major challenge in hormone receptor-positive/human epidermal growth factor receptor 2-negative (HR+/HER2-) breast cancer (BC). Although anthracyclines and taxanes constitute the standard sequential regimen, the metabolic adaptations accompanying resistance to these agents remain poorly defined. We investigated whether chemoresistance is associated with shared or drug-specific metabolic alterations. Methods: Parental MCF-7 and ZR-75-1 cells and their anthracycline-, and taxane-resistant derivatives, were characterized through multi-omics, Seahorse-based metabolic flux, and pharmacological inhibition analyses, alongside validation in patient transcriptomic datasets. Results: Chemoresistant cells displayed reduced drug sensitivity and improved recovery following treatment withdrawal. Transcriptomic profiling revealed extensive yet largely distinct gene expression changes among resistant models, whereas metabolomics showed limited divergence. Functional studies demonstrated concurrent reductions in mitochondrial respiration and glycolytic capacity, indicating a low-bioenergetic phenotype without compensatory metabolic rewiring. Lipidomic changes were heterogeneous and model-dependent. Despite this overall metabolic constraint, spermidine and spermine levels were increased across all resistant models, whereas upregulation of the polyamine-related genes ATP13A4 and SAT1 was specific to anthracycline-resistant cells. Chemoresistant phenotypes conferred reduced sensitivity to mitochondrial inhibitors. In contrast, sensitivity to polyamine pathway inhibition varied across models. Clinical datasets corroborated key experimental features, showing increased ATP binding cassette subfamily B member 1 (ABCB1) expression and significant post-treatment suppression of oxidative phosphorylation and glycolysis signatures. Polyamine pathway enrichment trends were less uniform, reflecting clinical heterogeneity. Conclusion: Chemoresistance in HR+/HER2- BC is characterized by heterogeneous transcriptional remodeling but relative metabolic constraint. Clinical dataset validation confirms post-chemotherapy bioenergetic suppression, while polyamine alterations represent context-dependent adaptations rather than universal vulnerabilities.