Abstract 2252: Mechanism of thymoquinone-induced cell death in glioblastoma multiforme.

Abstract

Abstract Glioblastoma (GBM) is the most aggressive and common type of brain tumor in humans. Surgical resection followed by radiation and chemotherapy is the current standard treatment; however, due to the upregulation of several survival pathways, tumor recurrence is quite common with a median survival of 12 to 15 months. Therefore, there is an urgent need for more effective therapeutic strategies for the treatment of glioblastoma. Naturally occurring phytochemicals have steadily received much scientific attention, owing to the fact that many of these compounds have potent action against tumors. Thymoquinone (TQ) is the bioactive compound of the volatile oil extracted from the black seed, Nigella sativa. TQ has shown anti-oxidant, anti-inflammatory and anti-neoplastic actions with a selective cytotoxicity for human cancer cells compared to several normal cells. Here, we show that TQ can dose-dependently inhibit colony formation in three distinct glioblastoma cell lines, with the highly tumorigenic Gli36ΔEGFR displaying the greatest sensitivity to the anti-proliferative effects of TQ. Moreover, normal human astrocytes are far less sensitive to TQ-induced cell kill. The absence of both DNA fragmentation and PARP cleavage in U87 and Gli36ΔEGFR cells suggests that TQ does not activate apoptosis. We show that TQ does not change the levels of Beclin-1 expression, but does cause accumulation of LC3-II and p62 protein levels. This suggests that TQ blocks the late stages of autophagy. TQ-induced cell death can be partially rescued by co-treatment with a lysosomal cathepsin hydrolase inhibitor III. We also show that TQ induces persistent γ-H2AX activation and causes G2/M cell cycle arrest in GBM cells to a degree that correlates with the cells’ relative clonogenic sensitivity. Moreover, co-treatment with TQ and N-acetyl cysteine, a simple thiol nucleophile and antioxidant, prevented cell death, DNA double strand breaks, and cell cycle arrest. Citation Format: Ira O. Racoma, Robert M. Snapka, Altaf A. Wani. Mechanism of thymoquinone-induced cell death in glioblastoma multiforme. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2252. doi:10.1158/1538-7445.AM2013-2252