Quantitative study of cellular heterogeneity in doxorubicin uptake and its pharmacological effect on cancer cells

Cellular heterogeneity in doxorubicin (DOX) uptake and its relationship with pharmacological effect on cancer cells were quantitatively investigated for the first time. An in vitro experimental model was established by treating human leukemia K562 and breast cancer MCF-7 cells with different schedules of DOX with or without surface P-glycoprotein (P-gp) inhibitor verapamil (VER). The cellular heterogeneity in DOX uptake was quantitatively examined by single-cell analysis using capillary electrophoresis coupled with laser-induced fluorescence detection. The corresponding cytotoxic effect was tested by cellular morphology, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium and flow cytometry assays. The expression of cellular membrane surface P-gp was determined by flow cytometry. Results showed that the cellular heterogeneity exists in DOX uptake. The single-high DOX schedule leads to lower uptake heterogeneity and higher mean drug uptake. The cellular heterogeneity in DOX uptake was found to be negatively correlated with drug cytotoxicity and surface P-gp expression, with r = -0.7680 to ~ -0.9587. VER reduces the cellular variation in DOX uptake, suggesting that surface P-gp may be one of the causes of the cellular heterogeneity in DOX uptake. This research demonstrates the importance of quantitative study of cellular heterogeneity in drug uptake and its potential application in drug schedule design, response prediction and therapy modulation.