Abstract 1932: Bortezomib sensitizes malignant human glioma cells to histone deacetylase inhibitors depends on reactive oxygen species production, mitochondrial dysfunction, Noxa upregulation and Mcl-1 cleavage

Abstract

Abstract Glioblastomas are invasive tumors with poor prognosis despite current therapies. Unfortunately, individual targeted therapies have failed to offer long-term survival benefit. Histone deacetylase inhibitors (HDACIs) represent a class of agents that can modulate gene expression to reduce tumor growth. Suberoylanalide hydroxamic acid (SAHA, vorinostat) and LBH-589 are inhibitors of several members of the HDAC family, and we and others have noted some antiglioma activity, although insufficient to warrant use as single-agent therapy. Proteasome inhibitors represent a promising class of anticancer agents, already in clinical use, as bortezomib (PS-341/Velcade) has been approved for the treatment of multiple myeloma with inactivation of NF-κB signaling pathway. We have recently demonstrated that bortezomib exhibited potent anti-glioma activity and dramatically sensitized highly resistant glioma cells to TRAIL cytotoxicity, suggesting that proteasomal inhibition may be a promising combination strategy for glioma therapeutics. In this study, we examined whether bortezomib could enhance response to HDAC inhibition in glioma cells. These studies showed that bortezomib enhanced vorinostat and LBH-589-induced apoptosis in malignant glioma cells. Although vorinostat or LBH-589 treatment alone did not induce apoptosis in glioma cells, efficacy was enhanced by addition of bortezomib, which promoted activation of proapoptotic mitochondrial injury, generation of ROS, and inhibition of the prosurvival NF-κB signaling pathway. Our results also revealed that cotreatment with bortezomib and vorinostat enhanced apoptosis by increasing Mcl-1, Noxa cleavage and other pro-apoptotic protein expression. The significantly enhanced antitumor activity that results from the combination of bortezomib and HDACIs offers promise as a novel treatment for glioma patients. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1932. doi:10.1158/1538-7445.AM2011-1932