Oral squamous cell carcinoma cells are resistant to doxorubicin through upregulation of miR-221

Oral squamous cell carcinoma (OSCC) cells are usually resistant to doxorubicin, resulting in limited application of doxorubicin in OSCC treatment. MicroRNA (miR)-221 has been reported to be involved in the development of OSCC; however, it remains unclear if and how miR-221 is implicated in modulating the sensitivity of OSCC cells to doxorubicin. In the present study, reverse transcription-quantitative polymerase chain reaction (RT-qPCR) was used to assess miR-221 expression in OSCC cells in response to doxorubicin treatment. In addition, the SCC4 and SCC9 OSCC cell lines were transfected with anti-miR-221 oligonucleotides and cell viability and apoptosis following doxorubicin treatment were evaluated using an MTT assay and Annexin V-fluorescein isothiocyanate/Hoechst double staining, respectively. The mRNA and protein expression levels of tissue inhibitor of metalloproteinase-3 (TIMP3) in anti-miR-221-transfected cells were assessed using RT-qPCR and western blot analysis, respectively. Furthermore, a luciferase reporter assay was performed to investigate whether TIMP3 may be a direct target gene of miR-221. To explore the roles of TIMP3 in miR-221-mediated cell responses, TIMP3 expression was silenced following transfection with TIMP3-targeting small interfering (si)RNA in cells overexpressing miR-221, and cell viability and apoptosis in response to doxorubicin treatment were measured. The results of the present study demonstrated that miR-221 expression was upregulated in SCC4 and SCC9 cells following treatment with doxorubicin. However, inhibiting the doxorubicin-induced upregulation of miR-221 through transfection with anti-miR-221 oligonucleotides led to an increase in the sensitivity of OSCC cells to doxorubicin. In addition, the results indicated that TIMP3 was a direct target of miR-221 in OSCC cells, as determined by a 3'-untranslated region luciferase reporter assay. Co-transfection of cells with anti-miR-221 oligonucleotides and TIMP3-specific small interfering RNA resulted in reduced sensitivity to doxorubicin compared with the cells transfected with the miR-221 inhibitor alone. In conclusion, these results indicated that OSCC cells are resistant to doxorubicin through upregulation of miR-221, which in turn downregulates TIMP3. Therefore, silencing miR-221 or upregulating TIMP3 may be considered promising therapeutic approaches to enhance the sensitivity of OSCC to doxorubicin.