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Background:  We previously demonstrated that a Danshensu-Tetramethylpyrazine conjugate DT-010 enhanced anticancer effect of doxorubicin (Dox) in Dox-sensitive human breast cancer cells, and protected against Dox-induced cardiotoxicity. This work was designed to see whether DT-010 overcomes Dox resistance in resistant human breast cancer cells.    Methods:  The effects of DT-010, Dox or their combination on cell viability of Dox-resistant human breast cancer MCF-7/ADR cells were conducted using 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Apoptosis was examined by flow cytometry after Annexin V-FITC/PI co-staining. Dox accumulation in MCF-7/ADR cells was detected by flow cytometry and fluorescence microscopy. A fluorometric multidrug resistance (MDR) assay kit was used to evaluate the effect of DT-010 on MDR transporter activity. P-glycoprotein (P-gp) expression and activity were analyzed by Western blot and rhodamine 123 (Rh123) efflux assay, respectively. The effects of DT-010 on glycolysis and mitochondrial stress were detected using an Extracellular Flux Analyzer. A Succinate Dehydrogenase Activity Assay kit was used to measure mitochondrial complex II activity.    Results:  At non-cytotoxic concentrations, DT-010 in combination with Dox led to a significant growth inhibition of MCF-7/ADR cells, suggesting a synergy between DT-010 and Dox to reverse Dox resistance. DT-010 restored Dox-mediated apoptosis and p53 induction in MCF-7/ADR cells. DT-010 increased Dox accumulation in MCF-7/ADR cells  via  inhibiting P-gp activity, but without changing P-gp expression. Further studies showed that DT-010 significantly inhibited glycolysis and mitochondrial function of MCF-7/ADR cells. Mitochondrial complex II activity was inhibited by DT-010 or DT-010/Dox combination, but not by Dox. The DT-010-mediated suppression of metabolic process may render cells more vulnerable to Dox treatment and thus result in enhanced efficacy.    Conclusions:  The results indicate that DT-010 overcomes Dox resistance in human breast cancer cells through a dual action  via  simultaneously inhibiting P-gp-mediated drug efflux and influencing metabolic process.

A Danshensu-Tetramethylpyrazine Conjugate DT-010 Overcomes Multidrug Resistance in Human Breast Cancer