Culturing MCF7 and Doxorubicin-Resistant Cells

The MCF7 and doxorubicin-resistant MCF7 cell lines were originally obtained from the Cell Bank of the Type Culture Collection of the Chinese Academy of Sciences (Shanghai, China) and cultured as previously described (Wang et al., 2021 (link)). Briefly, the cells were maintained in monolayer cultures in Dulbecco’s Modified Eagle’s medium (KEL Biotech, China) supplemented with 2 mM L-Glutamine (Gibco, USA), 100 mM sodium pyruvate (Gibco, USA), 10% FBS (KEL Biotech, China), 50 units/mL penicillin and 50 μg/ml streptomycin (Sigma-Aldrich, USA). Both MCF7 and MCF7-DR cells were grown in a humidified atmosphere of 5% CO₂ at 37°C in 10-cm dishes. Thereafter, the medium was renewed every 2–3 days until ready for sub-culturing. At about 80% confluence, cells were serially passaged by 1:4 dilution after trypsinization. The resistant-derived cells were maintained in 1 μM doxorubicin hydrochloride (MedChem Express, USA), and the parental MCF7 cells were grown in a drug-free medium for comparison. The MCF7-DR cells were maintained in the doxorubicin-free medium for about one week prior to further experiments.