Quercetin sensitizes human glioblastoma cells to temozolomide in vitro via inhibition of Hsp27

Aim: Quercetin is an effective Hsp27 inhibitor and has been reported to facilitate tumor cell apoptosis. The aim of this study was to investigate whether quercetin could sensitize human glioblastoma cells to temozolomide (TMZ) in vitro. Methods: Both U251 and U87 human glioblastoma cells were treated with quercetin and/or TMZ for 48 h. Cell viability was detected using the MU assay. Cell apoptosis was analyzed with caspase-3 activity kits and flow cytometry. Hsp27 expression and phosphorylation were examined using Western blot analysis. RNA interference using Hsp27 siRNA oligos was performed to knock down the gene expression of Hsp27. Results: TMZ (200 or 400 mu mol/L) alone effectively inhibited the viability of U251 and U87 cells. When combined with quercetin (30 mu mol/L), TMZ (100 mu mol/L) significantly inhibited the cell viability, and the inhibition of TMZ (200 and 400 mu mol/L) was enhanced. TMZ or quercetin anole did not affect caspase-3 activity and cell apoptosis, while TMZ combined with quercetin significantly increased caspase-3 activity and induced cell apoptosis. TMZ anole significantly increased Hsp27 phosphorylation in U251 and U87 cells, while quercetin or Hsp27 siRNA oligos combined with TMZ attenuated TMZ-induced Hsp27 phosphorylation and significantly inhibited Hsp27 expression. Conclusion: Combined treatment with TMZ and quercetin efficiently suppressed human glioblastoma cell survival in vitro.