MiR-221 Expression Level Correlates with Insulin-Induced Doxorubicin Resistance in MCF-7 Breast Cancer Cells

Insulin induces anti-cancer drugs resistance in tumor cells. However, the mechanism by which insulin induces its drug resistance effects is not clear. In the present study, the expression of miR-221 in insulin-treated MCF-7 cells in response to the anti-cancer drug doxorubicin, was investigated.

In this experimental study, cell viability was evaluated using MTT (3-[4,5 dimethylthiazol-2- yl]-2,5-diphenyl tetrazolium bromide) assay. The expression level of miR-221 was determined by real time polymerase chain reaction (RT-PCR). Furthermore, the expression of insulin receptor (IR) and cleaved caspase-3 protein was assessed by Western blotting.

The results showed that treatment of the MCF-7 cells with insulin reduced the anti-cancer effects of doxorubicin. Viability of naive and insulin-treated cells following doxorubicin (DOX) treatment was 62.9 ± 5.7% and 79 ± 7.2%, respectively. Furthermore, the expression of miR-221 in insulin-treated cells was significantly increased (2.6 ± 0.37-fold change) as compared with the control group. A significant decrease (26%) in the expression of caspase-3 protein and a significant increase (24%) in IR were observed in insulin-induced drug resistant MCF-7 cells as compared to the naive cells.

Together, the data showed a positive correlation between the expression of miR-221 and IR expression, but a negative correlation with caspase3 expression, in insulin-induced drug resistant MCF-7 breast cancer cells. This could suggest a new mechanism for the role of miR-221 in cancer drugs resistance induced by insulin.