Shikonin enhances Adriamycin antitumor effects by inhibiting efflux pumps in A549 cells

Shikonin (SHK) is a natural naphthoquinone pigment isolated from Lithospermum erythrorhizon, that has been reported to suppress the growth of a number of cancer cell types. Adriamycin (AD) is typically used as an effective anticancer agent; however, it has the propensity to induce drug resistance. The aim of the present study was to investigate the effects of SHK alone and in combination with AD on lung adenocarcinoma cells and the underlying molecular mechanisms of their effects. Colony formation, MTT and propidium iodide staining assays demonstrated that the co-treatment of A549 cells with SHK and AD significantly decreased cell viability and potently induced apoptosis. The mitochondrial membrane potential was assessed using 5,5', 6,6'-tetrachloro-1,1', 3,3' tetraethyl-benzimidazolylcarbo-cyanine iodide staining and fluorescence microscopy. Cells co-treated with SHK and AD exhibited marked mitochondrial membrane damage. In addition, co-treatment with SHK and AD significantly reduced ATP levels in A549 cells compared with the control. Western blot analysis revealed that SHK enhanced the antitumor effects of AD by inhibiting the expression of ATP-binding cassette transporters. These results suggest that the inhibition of glycolysis could be an effective approach for lung cancer treatment. Therefore, SHK has the potential to be used as an anticancer agent in the treatment of lung adenocarcinoma, and thus warrants further investigation and development.