Anthracyclines such as doxorubicin (DOX) remain central components of breast cancer (BC) chemotherapy, although their efficacy is frequently limited by drug resistance. Myoglobin (MB), an oxygen-binding heme protein expressed in breast tumors, has been implicated in the detoxification of DOX in cardiomyocytes, but its role in BC remains unclear. Using MB-expressing and MB-knockout (MBKO) MDA-MB-468 BC cells, we demonstrate that MB confers hypoxia-dependent resistance to DOX. Under hypoxia, MB-expressing cells exhibited reduced intracellular DOX-associated fluorescence, enhanced superoxide generation, and decreased sensitivity to DOX, findings consistent with altered redox cycling and oxidative processing of the drug. Re-expression of MB in MBKO cells restored resistance, whereas pharmacological modulation of MB function using carbon monoxide-releasing molecule-3 and tert-butoxycarbonyl-alanine reversed MB-dependent reductions in intracellular DOX accumulation. In contrast, aclarubicin, an anthracycline lacking the hydroquinone moiety required for efficient redox cycling, failed to reproduce MB-dependent effects. Analyses of four independent neoadjuvant BC cohorts further demonstrated that elevated MB expression was consistently associated with reduced probability of achieving pathological complete response following anthracycline-containing chemotherapy. Collectively, these findings identify MB as a previously unrecognized modulator of BC response to redox-active anthracyclines and support its potential utility as both a predictive biomarker and therapeutic target.
Rybińska et al. (Sat,) studied this question.