STEM-04. NICARDIPINE SENSITIZES APOPTOSIS OF GLIOMA STEM CELLS INDUCED BY TEMOZOLOMIDE THROUGH INHIBITING AUTOPHAGY

Abstract

Abstract BACKGROUND Glioma stem cells (GSCs) play an important role in tumor progression and recurrence. Currently, treatments of glioma are limited mainly due to strong tolerance of GSCs against conventional chemotherapeutic drugs such as temozolomide. Nicardipine, a calcium antagonist, is commonly used in the therapy of hypertension, which is recently repurposed in the comprehensive strategies against gliomas in our previous studies. Here, we explored the cytotoxic sensitization effect of nicardipine combining temozolomide and the underlying mechanisms. METHODS Two human glioma stem cell lines were applied and treated with nicardipine, temozolomide, and combination of both, respectively. Cell viability was detected by CCK-8, cell apoptosis was analyzed by flow cytometry, and immunoblot was used to detect autophagic-releated proteins including p62, LC3 and mTOR. The mTOR agonists and inhibitors were applied to further evaluate whether nicardipine inhibits autophagy via mTOR pathway. RESULTS GSCs had strong tolerance against temozolomide while nicardipine could significantly inhibit the viaibility of GSCs and promote cell apoptosis when acting together with temozolomide, indicating that nicardipine could sensitize the toxicity of temozolomide. Furthermore, both temozolomide and nicardipine could inhibit autophagy, and the effects of nicardipine was more prominent, suggesting that nicardipine might enhance GSCs apoptosis induced by temozolomide through inhibiting autophagy. Further molecular studies showed that the cytotoxic sensitization effects of nicardipine was induced through activation of the phosphorylation level of mTOR, which was abolished with the treatment of rapamycin, a mTOR inhibitor. CONCLUSION Our results suggested that nicardipine could sensitize apoptosis of glioma stem cells induced by temozolomide through inhibiting autophagy, which was mediated by activation of mTOR activity.