769 - Cyclin E1 Suppression Contributes to Sorafenib-Induced Apoptosis in Hepatocellular Carcinoma (HCC)

Abstract

ABSTRACT Background We have found that sorafenib can inhibit cyclin E1 expression in HCC cells, which is independent of the inhibitory effects of sorafenib on mitogen-activated protein kinase-extracellular signal-regulated kinase/extracellular signal-regulated kinase signaling. The present study sought to clarify the role of cyclin E1 in sorafenib-induced apoptosis in HCC. Methods A panel of HCC cell lines, including sorafenib-sensitive (Huh-7, HepG2) and sorafenib-resistant (Hep3B, Huh-7R and HepG2R) HCC cells, was tested. Apoptosis was measured by flow cytometry. Knockdown of cyclin E1 expression were used by RNA-interference. Over-expression of cyclin E1 was done by transient transfection of pCMV6-AC-GFP-CCNE1 vector (RG204289; Origene Technologies). The activity of pertinent signaling pathways, cell cycles-related proteins and expression of apoptosis-related proteins were measured by Western blotting. Results Cyclin E1 mRNA and protein expressions were suppressed after sorafenib treatment in sorafenib-sensitive but not in sorafenib-resistant HCC cells. The changes in cyclin E2 or cyclin D1 expression after sorafenib treatment were not correlated with sorafenib sensitivity of HCC cells. Knockdown of cyclin E1 expression reversed the resistance of HCC cells to sorafenib in terms of cell growth and apoptosis induction, whereas over-expression of cyclin E1 increased the resistance of HCC cells to sorafenib. Combination of sorafenib and the cyclin-dependent kinase (CDK) inhibitor flavopiridol synergistically inhibited cell growth and induced apoptosis in HCC cells. The synergistic efficacy was associated with suppression of Bcl-XL expression in HCC cells. Conclusion Cyclin E1 expression in HCC cells may serve a predictive biomarker for treatment efficacy. Combination of sorafenib and CDK inhibitors may improve the therapeutic efficacy of sorafenib in HCC. (Supported by grants: NSC100-2314-B-002-058-MY3, NSC101-2325-B-002-039, and NHRI-EX101-9911BC) Disclosure C. Hsu: Dr Chiun Hsu is a member of the speaker's bureau of Bayer-Schering Pharma. A. Cheng: Dr Ann-Lii Cheng is a consultant for Sanofi-Aventis Inc.; Pfizer, Bayer Schering Pharma; Bristol-Myers Squibb (Taiwan) Ltd.; Boehringer Ingelheim Taiwan Limited; Novartis Inc. All other authors have declared no conflicts of interest.