title: Synergistic interactions between sorafenib and bortezomib in hepatocellular carcinoma involve PP2A-dependent Akt inactivation.
abstract: OBJECTIVE
  Previously we reported that Akt inactivation determines the sensitivity of hepatocellular carcinoma (HCC) cells to bortezomib. Here we report that combined treatment with sorafenib and bortezomib shows synergistic effects in HCC.
  
  
  METHODS
  HCC cell lines (PLC/PRF/5, Huh-7, and Hep3B) were treated with sorafenib and/or bortezomib and analyzed in terms of apoptosis signal transduction. In vivo efficacy was determined in nude mice with PLC/PRF/5 xenografts.
  
  
  RESULTS
  Pretreatment with sorafenib enhanced bortezomib-induced apoptotic cell death by restoring bortezomib's ability to inactivate Akt in PLC/PRF/5 cells. Knocking down Akt1 by RNA-interference overcame apoptotic resistance to bortezomib in PLC/PRF/5 cells and ectopic expression of active Akt in HCC cells abolished the bortezomib sensitizing effect of sorafenib, indicating Akt inactivation plays a key role in mediating the combinational effects. Moreover, okadaic acid, a protein phosphatase 2A (PP2A) inhibitor, reversed down-regulation of phospho-Akt (P-Akt) expression induced by co-treatment with sorafenib and bortezomib, and 1, 9 di-deoxy-forskolin, a PP2A agonist, restored bortezomib's effect on P-Akt and apoptosis. Importantly, silencing of PP2A by RNA-interference reduced the apoptotic effect induced by sorafenib-bortezomib co-treatment, indicating that PP2A is indispensable for mediating the effects of these drugs. Notably, sorafenib with bortezomib increased PP2A activity in PLC/PRF/5 cells without altering protein levels of PP2A complex or the interaction between PP2A and Akt proteins. Finally, sorafenib plus bortezomib significantly suppressed PLC/PRF/5 xenograft tumor growth, down-regulated P-Akt expression, and up-regulated PP2A activity.
  
  
  CONCLUSIONS
  The combination of sorafenib and bortezomib shows synergy in HCC through PP2A-dependent Akt inactivation.
authors.affiliation: Department of Medical Research, National Taiwan University Hospital, Taiwan.
authors.forename: Kuen-Feng
authors.initials: KF
authors.lastname: Chen
authors.forename: Hui-Chuan
authors.initials: HC
authors.lastname: Yu
authors.forename: Tsung-Hao
authors.initials: TH
authors.lastname: Liu
authors.forename: Shoei-Sheng
authors.initials: SS
authors.lastname: Lee
authors.forename: Pei-Jer
authors.initials: PJ
authors.lastname: Chen
authors.forename: Ann-Lii
authors.initials: AL
authors.lastname: Cheng
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology / Q000627:therapeutic use*; D017209:Apoptosis / Q000187:drug effects; D001557:Benzenesulfonates / Q000494:pharmacology / Q000627:therapeutic use*; D001897:Boronic Acids / Q000494:pharmacology / Q000627:therapeutic use*; D000069286:Bortezomib; D006528:Carcinoma, Hepatocellular / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D045744:Cell Line, Tumor; D004195:Disease Models, Animal; D004357:Drug Synergism; D006801:Humans; D008113:Liver Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D008297:Male; D051379:Mice; D008819:Mice, Nude; D009536:Niacinamide / Q000031:analogs & derivatives; D019319:Okadaic Acid / Q000494:pharmacology; D010671:Phenylurea Compounds; D054648:Protein Phosphatase 2 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D011719:Pyrazines / Q000494:pharmacology / Q000627:therapeutic use*; D011725:Pyridines / Q000494:pharmacology / Q000627:therapeutic use*; D000077157:Sorafenib; D016896:Treatment Outcome; D023041:Xenograft Model Antitumor Assays
chemical_list: D000970:Antineoplastic Agents; D001557:Benzenesulfonates; D001897:Boronic Acids; D010671:Phenylurea Compounds; D011719:Pyrazines; D011725:Pyridines; D019319:Okadaic Acid; D009536:Niacinamide; D000069286:Bortezomib; D000077157:Sorafenib; D051057:Proto-Oncogene Proteins c-akt; D054648:Protein Phosphatase 2