miR‐15b modulates multidrug resistance in human osteosarcoma in vitro and in vivo

The development of multidrug resistance (MDR) in cancer cells to chemotherapy drugs continues to be a major clinical problem. MicroRNAs (miRNA, miR) play an important role in regulating tumour cell growth and survival; however, the role of miRs in the development of drug resistance in osteosarcoma cells is largely uncharacterized. We sought to identify and characterize human miRs that act as key regulators of MDR in osteosarcoma. We utilized a miR microarray to screen for differentially expressed miRs in osteosarcoma MDR cell lines. We determined the mechanisms of the deregulation of expression of miR‐15b in osteosarcoma MDR cell lines, and its association with clinically obtained tumour samples was examined in tissue microarray (TMA). The significance of miR‐15b in reversing drug resistance was evaluated in a mouse xenograft model of MDR osteosarcoma. We identified miR‐15b as being significantly (P < 0.01) downregulated in KHOS(MR) and U‐2OS(MR) cell lines as compared with their parental cell lines. We found that Wee1 is a target gene of miR‐15b and observed that transfection with miR‐15b inhibits Wee1 expression and partially reverses MDR in osteosarcoma cell lines. Systemic in vivo administration of miR‐15b mimics sensitizes resistant cells to doxorubicin and induces cell death in MDR models of osteosarcoma. Clinically, reduced miR‐15b expression was associated with poor patient survival. Osteosarcoma patients with low miR‐15b expression levels had significantly shorter survival times than patients with high expression levels of miR‐15b. These results collectively indicate that MDR in osteosarcoma is associated with downregulation of miR‐15b, and miR‐15b reconstitution can reverse chemotherapy resistance in osteosarcoma.