Tanshinone IIA sensitizes TRAIL-induced apoptosis in glioblastoma through inducing the expression of death receptors (and suppressing STAT3 activation).

Objective: This work was designed to explore whether the combination of Tanshinone IIA (T-IIA) and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has a direct anti-cancer effect in glioblastoma (GBM) and the possible mechanisms.

Methods: GBM cells (U-87 and U-251 MG) were treated with T-IIA or/and TRAIL, or the expression of death receptors (DRs), DR4 and DR5, was suppressed in GBM cells. The activity of GBM cells was determined by MTT, and the apoptosis was assessed by Hoechst33342 staining and flow cytometry. The expression levels of cleaved caspase-3/8/9, phosphorylated (p)-STAT3 as well as DR4 and DR5 in GBM cells were assessed by Western blotting. A nude mouse xenograft model was constructed to evaluate the effects of T-IIA and TRAIL cotreatment on tumor growth and apoptosis in vivo.

Results: After T-IIA treatment, GBM cells resumed the sensitivity to TRAIL-induced apoptosis dependent on inhibition of p-STAT3 and activation of DR4, DR5 and caspases. DR4 or/and DR5 knockdown significantly abated the co-effect of T-IIA and TRAIL on GBM cell apoptosis and proliferation. Furthermore, T-IIA and TRAIL cotreatment markedly inhibited the growth of transplanted tumor and activated U87 cell apoptosis in nude mice.

Conclusion: T-IIA increases TRAIL-induced apoptosis by downregulating STAT3 and upregulating DR4 and DR5, indicating T-IIA therapy as a novel treatment strategy for TRAIL-resistant GBM.