Down-regulation of phospho-Akt is a major molecular determinant of bortezomib-induced apoptosis in hepatocellular carcinoma cells

• Published in: Cancer research (Chicago, Ill.) Vol. 68; no. 16; pp. 6698 - 6707
• Main Authors: Chen, Kuen-Feng, Yeh, Pei-Yen, Yeh, Kun-Huei, Lu, Yen-Shen, Huang, Shang-Yi, Cheng, Ann-Lii
• Format: Journal Article
• Language: English
• Published: United States 15.08.2008
• Subjects: Animals; Antineoplastic Agents - pharmacology; Apoptosis - drug effects; Blotting, Western; Boronic Acids - pharmacology; Bortezomib; Carcinoma, Hepatocellular - drug therapy; Carcinoma, Hepatocellular - metabolism; Carcinoma, Hepatocellular - pathology; Cell Cycle - drug effects; Down-Regulation; Flow Cytometry; Humans; Liver Neoplasms - drug therapy; Liver Neoplasms - metabolism; Liver Neoplasms - pathology; Male; Mice; Mice, Nude; NF-kappa B - genetics; NF-kappa B - metabolism; Proteasome Inhibitors; Proto-Oncogene Proteins c-akt - metabolism; Pyrazines - pharmacology; Tumor Cells, Cultured; Xenograft Model Antitumor Assays
• DOI: 10.1158/0008-5472.CAN-08-0257
• ISSN: 0008-5472

Bortezomib, a proteasome inhibitor, has been clinically approved for the treatment of myeloma and lymphoma. Here, we report a differential effect of bortezomib on apoptosis in four hepatocellular carcinoma (HCC) cell lines and identify the major molecular event that determines sensitivity. Although bortezomib inhibited proteasome activity to a similar extent in all HCC cell lines, it showed differential effects on their viability: Huh-7 (IC(50) 196 nmol/L), Sk-Hep1 (IC(50) 180 nmol/L), Hep3B (IC(50) 112 nmol/L), and resistant PLC5 (IC(50) >1,000 nmol/L). Bortezomib caused cell cycle arrest at G(2)-M phase in all HCC cells tested whereas apoptotic induction was found only in sensitive cells but not in PLC5 cells. No significant bortezomib-induced NF-kappaB changes were noted in Huh-7 and PLC5. Bortezomib down-regulated phospho-Akt (P-Akt) in a dose- and time-dependent manner in all sensitive HCC cells whereas no alterations of P-Akt were found in PLC5. Down-regulation of Akt1 by small interference RNA overcame the apoptotic resistance to bortezomib in PLC5 cells, but a constitutively activated Akt1 protected Huh-7 cells from bortezomib-induced apoptosis. Furthermore, bortezomib showed suppression of tumor growth with down-regulation of P-Akt in Huh-7 tumors but not in PLC5 tumors. Down-regulation of P-Akt represents a major molecular event of bortezomib-induced apoptosis in HCC cell lines and may be a biomarker for predicting clinical response to HCC treatment. Targeting Akt signaling overcomes drug resistance to bortezomib in HCC cells, which provides a new approach for the combinational therapy of HCC.