TrxR1 to promote adriamycin resistance in MCF-7 breast cancer cells by upregulating both gene expression level and enzyme activity: Reversed by shikonin.

e15070 Background: Adriamycin is one of the effective drugs commonly used in the treatment of advanced breast cancer, but its high incidence of drug resistance and cardiotoxicity limit the application of doxorubicin. Recent evidence shows that increased antioxidant capacity of cancer cells is associated with resistance to chemotherapy. Shikonin, a derivative of Lithospermum erythrorhizon Sieb.et Zucc, displays broad antitumor activity and direct cytotoxicity on various tumor cells. Our previous study shows that shikonin was enabled to directly binding and inhibiting TrxR1, which significantly downregulates intracellular ROS in cancer cells, suggesting that shikonin might be a promising drug candidate. In this study, we identified the relationship between TrxR1 and chemotherapeutic drug resistance in cancer cells and effects of shikonin with and without adriamycin on adriamycin-resistance cells. Methods: The direct DTNB reduction assay was employed to test the enzyme activity of TrxR1. Cultured ADR-resistant MCF-7 cells were assayed for their half maximal inhibitory concentration (IC50) values and apoptosis using an CCK8 assay and Annexin V-FITC/PI-labeled flow cytometry. Drug resistance was evaluated by inhibitory concentration (IC50) values and immunoblotting multidrug resistance protein 1 (MDR1) and breast cancer resistance protein (BCRP). TrxR1 knockdown was silenced by siRNA, leading to reducing the IC50 value of ADR-resistant MCF-7 cells. Dysfunctional endoplasmic reticulum was measured by western blot analysis of endoplasmic reticulum (ER) stress signaling pathways and observation of morphology using a transmission electron microscope. Results: We found that the TrxR1 was significantly enhanced in adriamycin-resistant (ADR/MCF7) cells.Furthermore, the decreased TrxR1 function by TrxR1-knockdown or TrxR1 inhibitor piperlongumine increased MCF-7 cells sensitivity to adriamycin. Treatment of ADR/MCF7 cells with shikonin (2.5,5,10,20,40 μM) dose-dependently inhibited TrxR1 enzyme activity and the clearance of dysfunctional endoplasmic reticulum, and induced cell apoptosis. Conclusions: Our results suggest that TrxR1 is critical for adriamycin resistance in breast cancer cells(ADR/MCF7),and shikonin or other inhibitors of TrxR1 would be potential in the treatment of cancer cells with adriamycin resistance.