Leukemia is a common malignancy affecting humans worldwide. Pirarubicin (Pira) is one of the anticancer agents used for the treatment of leukemia. Although Pira is effective, drug resistance may develop in cancer cells exposed to this drug, whereas the combination of natural products with Pira may help to overcome this problem. The aim of the present study was to focus on the effect of gallic acid (GA) on the anticancer activity of Pira in K562 leukemia cells and K562/doxorubicin (Dox)-resistant leukemia cells in order to investigate the possible underlying mechanisms. The cell viability, mitochondrial activity, mitochondrial membrane potential (ΔΨm) and ATP levels were assessed in living K562 and K562/Dox cancer cells following treatment with GA/Pira combination, GA alone or Pira alone. P-glycoprotein-mediated efflux of Pira was determined in GA-treated K562/Dox cancer cells. The results demonstrated that GA/Pira combination decreased cell viability, mitochondrial activity, ΔΨm and ATP levels in K562 and K562/Dox cancer cells in a GA concentration-dependent manner compared with non-treated or Pira-treated cells. GA inhibited P-glycoprotein-mediated efflux of Pira in GA-treated K562/Dox cancer cells. Therefore, GA enhanced the anticancer effect of Pira on K562 and K562/Dox cancer cells through cellular energy status impairment, and was able to reverse drug resistance in living K562/Dox cancer cells by inhibiting the function of P-glycoprotein.

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