MicroRNA‑22 mediates the cisplatin resistance of osteosarcoma cells by inhibiting autophagy via the PI3K/Akt/mTOR pathway.

Osteosarcoma (OS) is the most common primary malignant tumor of the bone affecting children and adolescents. Chemotherapy is now considered as a standard component of OS treatment, not only for children, but also for adults. However, chemoresistance continues to pose a challenge to therapy. Inhibition of autophagy has been demonstrated to decrease chemoresistance in OS. Moreover, microRNA‑22 (miR‑22) inhibits autophagy, leading to an improvement in the sensitivity of cisplatin (CDDP) in OS. The aim of the present study was therefore to investigate whether miR‑22 could mediate the CDDP resistance of OS cells by inhibiting autophagy via the phosphoinositide 3‑kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) pathway. Cell proliferation assay, LC3 flow cytometry assay and monodansylcadaverine staining in MG63 cells and CDDP resistance cells (MG63/CDDP) were performed to explore to role of miR‑22 and CDDP in OS chemoresistance. Inoculation of tumor cells in an in vivo model, reverse transcription‑quantitative PCR (RT‑qPCR) assay, western blot analysis, and immunohistochemistry analysis were performed to investigate the role of miR‑22 and CDDP in the PI3K/Akt/mTOR pathway as it is affected by autophagy. The results revealed that miR‑22 inhibited the proliferation of MG63 and MG63/CDDP cells, and enhanced the anti‑proliferative ability of CDDP in vivo and in vitro. miR‑22 mediated the CDDP resistance of OS cells by inhibiting autophagy and decreasing CDDP‑induced autophagy via downregulation of the expression of PI3K, Akt, and mTOR at the mRNA level, and the expression of PI3K, phosphorylated (p)‑Akt, and p‑mTOR at the protein level. It was also convincingly demonstrated that miR‑22 mediates the CDDP resistance of OS by inhibiting autophagy via the PI3K/Akt/mTOR pathway. Furthermore, in the MG63 cells that were affected by CDDP, the role of miR‑22 was shown to be similar to that of the investigated inhibitor of PI3K (wortmannin) in terms of regulating the PI3K/Akt/mTOR pathway, and wortmannin could also promote the effect of miR‑22. Interestingly, CDDP was demonstrated to induce autophagy by inhibiting the PI3K/Akt/mTOR pathway, whereas the pathway was upregulated in the state of chemoresistance. In conclusion, downregulation of the PI3K/Akt/mTOR pathway was shown to assist in the process of preventing chemoresistance.