title: Vorinostat and sorafenib synergistically kill tumor cells via FLIP suppression and CD95 activation.
abstract: OBJECTIVE
  Mechanism(s) by which the multikinase inhibitor sorafenib and the histone deacetylase inhibitor vorinostat interact to kill hepatic, renal, and pancreatic adenocarcinoma cells has been defined.
  
  
  RESULTS
  Low doses of sorafenib and vorinostat interacted in vitro in a synergistic fashion to kill hepatic, renal, and pancreatic adenocarcinoma cells in multiple short-term viability (24-96 h) and in long-term colony formation assays. Cell killing was suppressed by inhibition of cathepsin proteases and caspase-8 and, to a lesser extent, by inhibition of caspase-9. Twenty-four hours after exposure, the activities of extracellular signal-regulated kinase 1/2, AKT, and nuclear factor-kappaB were only modestly modulated by sorafenib and vorinostat treatment. However, 24 h after exposure, sorafenib- and vorinostat-treated cells exhibited markedly diminished expression of c-FLIP-s, full-length BID, BCL-2, BCL-XL, MCL-1, XIAP, increased expression of BIM, and increased activation of BAX, BAK, and BAD. Expression of eIF2alpha S51A blocked sorafenib- and vorinostat-induced suppression of c-FLIP-s levels and overexpression of c-FLIP-s abolished lethality. Sorafenib and vorinostat treatment increased surface levels of CD95 and CD95 association with caspase-8. Knockdown of CD95 or FADD expression significantly reduced sorafenib/vorinostat-mediated lethality.
  
  
  CONCLUSIONS
  These data show that combined exposure of epithelial tumor cell types to sorafenib and vorinostat diminishes expression of multiple antiapoptotic proteins and promotes activation of the CD95 extrinsic apoptotic and the lysosomal protease pathways, and that suppression of c-FLIP-s expression represents a critical event in transduction of the proapoptotic signals from CD95 to promote mitochondrial dysfunction and death.
authors.affiliation: Department of Biochemistry, Virginia Commonwealth University, Richmond, Virginia 23298-0035, USA.
authors.forename: Guo
authors.initials: G
authors.lastname: Zhang
authors.forename: Margaret A
authors.initials: MA
authors.lastname: Park
authors.forename: Clint
authors.initials: C
authors.lastname: Mitchell
authors.forename: Hossein
authors.initials: H
authors.lastname: Hamed
authors.forename: Mohamed
authors.initials: M
authors.lastname: Rahmani
authors.forename: Aditi Pandya
authors.initials: AP
authors.lastname: Martin
authors.forename: David T
authors.initials: DT
authors.lastname: Curiel
authors.forename: Adly
authors.initials: A
authors.lastname: Yacoub
authors.forename: Martin
authors.initials: M
authors.lastname: Graf
authors.forename: Ray
authors.initials: R
authors.lastname: Lee
authors.forename: John D
authors.initials: JD
authors.lastname: Roberts
authors.forename: Paul B
authors.initials: PB
authors.lastname: Fisher
authors.forename: Steven
authors.initials: S
authors.lastname: Grant
authors.forename: Paul
authors.initials: P
authors.lastname: Dent