title: Vorinostat and sorafenib increase CD95 activation in gastrointestinal tumor cells through a Ca(2+)-de novo ceramide-PP2A-reactive oxygen species-dependent signaling pathway.
abstract: The targeted therapeutics sorafenib and vorinostat interact in a synergistic fashion to kill carcinoma cells by activating CD95, and this drug combination is entering phase I evaluation. In this study, we determined how CD95 is activated by treatment with this drug combination. Low doses of sorafenib and vorinostat, but not the individual drugs, rapidly increased reactive oxygen species (ROS), Ca(2+), and ceramide levels in gastrointestinal tumor cells. The production of ROS was reduced in Rho zero cells. Quenching ROS blocked drug-induced CD95 surface localization and apoptosis. ROS generation, CD95 activation, and cell killing was also blocked by quenching of induced Ca(2+) levels or by inhibition of PP2A. Inhibition of acidic sphingomyelinase or de novo ceramide generation blocked the induction of ROS; however, combined inhibition of both acidic sphingomyelinase and de novo ceramide generation was required to block the induction of Ca(2+). Quenching of ROS did not affect drug-induced ceramide/dihydro-ceramide levels, whereas quenching of Ca(2+) reduced the ceramide increase. Sorafenib and vorinostat treatment radiosensitized liver and pancreatic cancer cells, an effect that was suppressed by quenching ROS or knockdown of LASS6. Further, sorafenib and vorinostat treatment suppressed the growth of pancreatic tumors in vivo. Our findings show that induction of cytosolic Ca(2+) by sorafenib and vorinostat is a primary event that elevates dihydroceramide levels, each essential steps in ROS generation that promotes CD95 activation.
authors.affiliation: Department of Biochemistry, Virginia Commonwealth University, Richmond, Virginia 23298-0035, USA.
authors.forename: Margaret A
authors.initials: MA
authors.lastname: Park
authors.forename: Clint
authors.initials: C
authors.lastname: Mitchell
authors.forename: Guo
authors.initials: G
authors.lastname: Zhang
authors.forename: Adly
authors.initials: A
authors.lastname: Yacoub
authors.forename: Jeremy
authors.initials: J
authors.lastname: Allegood
authors.forename: Dieter
authors.initials: D
authors.lastname: Häussinger
authors.forename: Roland
authors.initials: R
authors.lastname: Reinehr
authors.forename: Andrew
authors.initials: A
authors.lastname: Larner
authors.forename: Sarah
authors.initials: S
authors.lastname: Spiegel
authors.forename: Paul B
authors.initials: PB
authors.lastname: Fisher
authors.forename: Christina
authors.initials: C
authors.lastname: Voelkel-Johnson
authors.forename: Besim
authors.initials: B
authors.lastname: Ogretmen
authors.forename: Steven
authors.initials: S
authors.lastname: Grant
authors.forename: Paul
authors.initials: P
authors.lastname: Dent
mesh_terms: D000818:Animals; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology*; D001557:Benzenesulfonates / Q000008:administration & dosage / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D002265:Carboxylic Ester Hydrolases / Q000037:antagonists & inhibitors / Q000378:metabolism; D045744:Cell Line, Tumor; D002518:Ceramides / Q000378:metabolism; D005770:Gastrointestinal Neoplasms / Q000188:drug therapy* / Q000378:metabolism; D006801:Humans; D006877:Hydroxamic Acids / Q000008:administration & dosage / Q000494:pharmacology*; D009536:Niacinamide / Q000031:analogs & derivatives; D010671:Phenylurea Compounds; D011725:Pyridines / Q000008:administration & dosage / Q000494:pharmacology*; D017382:Reactive Oxygen Species / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D000077157:Sorafenib; D000077337:Vorinostat; D019014:fas Receptor / Q000378:metabolism*
chemical_list: D001557:Benzenesulfonates; D002518:Ceramides; D006877:Hydroxamic Acids; D010671:Phenylurea Compounds; D011725:Pyridines; D017382:Reactive Oxygen Species; D019014:fas Receptor; D009536:Niacinamide; D000077337:Vorinostat; D000077157:Sorafenib; D002265:Carboxylic Ester Hydrolases; C119357:protein phosphatase methylesterase-1; D002118:Calcium