title: Sorafenib enhances proteasome inhibitor-induced cell death via inactivation of Akt and stress-activated protein kinases.
abstract: BACKGROUND
  Advanced hepatocellular carcinoma (HCC) responds poorly to conventional systemic therapies. Therefore, new effective therapy strategies are urgently needed. Molecular targeted therapies have entered the field of anti-neoplastic treatment and are being used on their own and in combination with other drugs. Sorafenib inhibits proliferation and angiogenesis of HCC by suppressing the Raf serine/threonine kinases and the receptor tyrosine kinases. The proteasome inhibitor bortezomib has shown activity in a variety of solid tumors, including HCC. However, the precise anti-proliferative mechanisms of these agents remain unclear.
  
  
  METHODS
  We treated human hepatoma cell lines (Huh7 and Hep3B) and immortalized human hepatocyte (OUMS29) with sorafenib and/or proteasome inhibitors, including epoxomicin and acetyl-leucyl-leucyl-norleucinal. Cytotoxic effects were examined by morphometric analyses of apoptosis and necrosis. Apoptosis was also evaluated by Western blotting of keratin18, PARP and caspase3. The activity of Akt and stress-activated protein kinases was examined by Western blotting.
  
  
  RESULTS
  Both sorafenib and proteasome inhibitors induced apoptosis in Huh7 and OUMS29. However, sorafenib attenuated proteasome inhibitor-induced apoptosis. Sorafenib induced necrosis, especially in combination with proteasome inhibitors. Sorafenib induced down-regulation of Akt synergistically in combination with proteasome inhibitors in Huh7. Sorafenib inhibited both the JNK and p38 pathways in a time- and dose-dependent manner. In addition, sorafenib also inhibited proteasome inhibitor-mediated JNK and p38 activation in both Huh7 and OUMS29.
  
  
  CONCLUSIONS
  Sorafenib enhances the anti-proliferative effect of proteasome inhibitors in part by inactivating the Akt signaling pathway and modulating stress-activated protein kinases. The combination of these agents could be an ideal molecular targeted therapy for HCC.
authors.affiliation: Third Department of Internal Medicine, School of Medicine, University of Occupational and Environmental Health, 1-1 Iseigaoka, Yahatanishi-ku, Kitakyushu, 807-8555, Japan.
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Honma
authors.forename: Satoshi
authors.initials: S
authors.lastname: Shimizu
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Takehara
authors.forename: Masaru
authors.initials: M
authors.lastname: Harada
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects; D006528:Carcinoma, Hepatocellular / Q000188:drug therapy* / Q000473:pathology; D016923:Cell Death / Q000187:drug effects; D045744:Cell Line, Tumor; D015536:Down-Regulation / Q000187:drug effects; D004357:Drug Synergism; D006801:Humans; D007976:Leupeptins / Q000494:pharmacology; D008113:Liver Neoplasms / Q000188:drug therapy* / Q000473:pathology; D058990:Molecular Targeted Therapy; D009536:Niacinamide / Q000031:analogs & derivatives* / Q000494:pharmacology; D009842:Oligopeptides / Q000494:pharmacology; D010671:Phenylurea Compounds / Q000494:pharmacology*; D061988:Proteasome Inhibitors / Q000494:pharmacology; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011494:Protein Kinases / Q000187:drug effects / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000187:drug effects* / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D000077157:Sorafenib
chemical_list: D000970:Antineoplastic Agents; D007976:Leupeptins; D009842:Oligopeptides; D010671:Phenylurea Compounds; D061988:Proteasome Inhibitors; D047428:Protein Kinase Inhibitors; C063261:acetylleucyl-leucyl-norleucinal; D009536:Niacinamide; D000077157:Sorafenib; D011494:Protein Kinases; D051057:Proto-Oncogene Proteins c-akt; C078846:epoxomicin
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