MicroRNA-21 inhibitor sensitizes human glioblastoma cells U251 (PTEN-mutant) and LN229 (PTEN-wild type) to taxol

Background: Substantial data indicate that the oncogene microRNA 21 (miR-21) is significantly elevated in glioblastoma multiforme (GBM) and regulates multiple genes associated with cancer cell proliferation, apoptosis, and invasiveness. Thus, miR-21 can theoretically become a target to enhance the chemotherapeutic effect in cancer therapy. So far, the effect of downregulating miR-21 to enhance the chemotherapeutic effect to taxol has not been studied in human GBM. Methods: Human glioblastoma U251 (PTEN-mutant) and LN229 (PTEN wild-type) cells were treated with taxol and the miR-21 inhibitor (in a poly (amidoamine) (PAMAM) dendrimer), alone or in combination. The 50% inhibitory concentration and cell viability were determined by the MTT assay. The mechanism between the miR-21 inhibitor and the anticancer drug taxol was analyzed using the Zheng-Jun Jin method. Annexin V/PI staining was performed, and apoptosis and the cell cycle were evaluated by flow cytometry analysis. Expression of miR-21 was investigated by RT-PCR, and western blotting was performed to evaluate malignancy related protein alteration. Results: IC(50) values were dramatically decreased in cells treated with miR-21 inhibitor combine with taxol, to a greater extent than those treated with taxol alone. Furthermore, the miR-21 inhibitor significantly enhanced apoptosis in both U251 cells and LN229 cells, and cell invasiveness was obviously weakened. Interestingly, the above data suggested that in both the PTEN mutant and the wild-type GBM cells, miR-21 blockage increased the chemosensitivity to taxol. It is worth noting that the miR-21 inhibitor additively interacted with taxol on U251 cells and synergistically on LN229 cells. Thus, the miR-21 inhibitor might interrupt the activity of EGFR pathways, independently of PTEN status. Meanwhile, the expression of STAT3 and p-STAT3 decreased to relatively low levels after miR-21 inhibitor and taxol treatment. The data strongly suggested that a regulatory loop between miR-21 and STAT3 might provide an insight into the mechanism of modulating EGFR/STAT3 signaling. Conclusions: Taken together, the miR-21 inhibitor could enhance the chemo-sensitivity of human glioblastoma cells to taxol. A combination of miR-21 inhibitor and taxol could be an effective therapeutic strategy for controlling the growth of GBM by inhibiting STAT3 expression and phosphorylation.