Thymoquinone reversed doxorubicin resistance in <scp>U87</scp> glioblastoma cells via targeting <scp>PI3K</scp>/Akt/<scp>mTOR</scp> signaling

Natural compounds such as thymoquinone (TQ) have recently gained increasing attention in treating glioblastoma (GBM). However, the effects of TQ in reversing drug resistance are not completely understood. Therefore, we aimed to examine TQ impacts on GBM cells with doxorubicin (DOX) resistance and the involvement of the PI3K/Akt/mTOR pathway. GBM cancer U87 and U87/DOX (resistant cells) cells were exposed to DOX and TQ, and cell proliferation was assessed by the MTT assay. ELISA was applied to evaluate cell apoptosis. The expression of apoptotic mediators such as Caspase-3, Bax, Bcl-2 and PI3K, Akt, mTOR, P-gp, and PTEN was assessed via qRT-PCR and western blot. We found that a combination of TQ and DOX suppressed dose-dependent cell growth capacity in cells and increased the cytotoxic effects of DOX in resistant cells. In addition, TQ treatment increased DOX-mediated apoptosis in U87/DOX cell lines via modulating the pro- and anti-apoptotic markers. A combination of TQ and DOX upregulated PTEN and downregulated PI3K, Akt, and mTOR, suppressing this signal transduction in resistant cells. In conclusion, we showed TQ potentiated doxorubicin-mediated antiproliferative and pro apoptotic function DOX-resistant glioblastoma cells, which is mediated by targeting and suppressing PI3K/Akt/mTOR signal transduction.