BCL-2 Family Inhibitors Enhance Histone Deacetylase Inhibitor and Sorafenib Lethality via Autophagy and Overcome Blockade of the Extrinsic Pathway to Facilitate Killing

• Published in: Molecular pharmacology 2009-08, Vol.76 (2), p.327-341
• Main Authors: Martin, Aditi Pandya, Park, Margaret A., Mitchell, Clint, Walker, Teneille, Rahmani, Mohamed, Thorburn, Andrew, Häussinger, Dieter, Reinehr, Roland, Grant, Steven, Dent, Paul
• Format: Article
• Language: English
• Subjects: Adenoviridae - genetics; Antineoplastic Agents - pharmacology; Autophagy - drug effects; Benzenesulfonates - pharmacology; CASP8 and FADD-Like Apoptosis Regulating Protein - metabolism; Cell Line, Transformed; Cell Line, Tumor; Cell Survival - drug effects; Drug Synergism; Enzyme Inhibitors - metabolism; fas Receptor - metabolism; Histone Deacetylase Inhibitors; Humans; Immunohistochemistry; Niacinamide - analogs & derivatives; Phenylurea Compounds; Proto-Oncogene Proteins c-bcl-2 - antagonists & inhibitors; Pyridines - pharmacology; RNA, Small Interfering - metabolism; Transfection
• ISSN: 0026-895X; 1521-0111
• DOI: 10.1124/mol.109.056309

We examined whether the multikinase inhibitor sorafenib and histone deacetylase inhibitors (HDACI) interact to kill pancreatic carcinoma cells and determined the impact of inhibiting BCL-2 family function on sorafenib and HDACI lethality. The lethality of sorafenib was enhanced in pancreatic tumor cells in a synergistic fashion by pharmacologically achievable concentrations of the HDACIs vorinostat or sodium valproate. Overexpression of cellular FLICE-like inhibitory protein (c-FLIP-s) or knockdown of CD95 suppressed the lethality of the sorafenib/HDACI combination (sorafenib + HDACI). In immunohistochemical analyses or using expression of fluorescence-tagged proteins, treatment with sorafenib and vorinostat together (sorafenib + vorinostat) promoted colocalization of CD95 with caspase 8 and CD95 association with the endoplasmic reticulum markers calnexin, ATG5, and Grp78/BiP. In cells lacking CD95 expression or in cells expressing c-FLIP-s, the lethality of sorafenib + HDACI exposure was abolished and was restored when cells were coexposed to BCL-2 family inhibitors [ethyl [2-amino-6-bromo-4-(1-cyano-2-ethoxy-2-oxoethyl)]-4H-chromene-3-carboxylate (HA14-1), obatoclax (GX15-070)]. Knockdown of BCL-2, BCL-XL, and MCL-1 recapitulated the effects of GX15-070 treatment. Knockdown of BAX and BAK modestly reduced sorafenib + HDACI lethality but abolished the effects of GX15-070 treatment. Sorafenib + HDACI exposure generated a CD95- and Beclin1-dependent protective form of autophagy, whereas GX15-070 treatment generated a Beclin1-dependent toxic form of autophagy. The potentiation of sorafenib + HDACI killing by GX15-070 was suppressed by knockdown of Beclin1 or of BAX + BAK. Our data demonstrate that pancreatic tumor cells are susceptible to sorafenib + HDACI lethality and that in tumor cells unable to signal death from CD95, use of a BCL-2 family antagonist facilitates sorafenib + HDACI killing via autophagy and the intrinsic pathway.