Dexamethasone enhances trichosanthin-induced apoptosis in the HepG2 hepatoma cell line

Aims: Trichosanthin (TCS) is a type I ribosome-inactivating protein (RIP) with antitumor activities for various cancers. In this paper, we aimed to investigate whether dexamethasone, an important synthetic member of the glucocorticoid steroids, in combination with TCS can be a potential therapy in treating hepatoma. Main methods: Cell viability was investigated using MTT assay, and apoptosis was evaluated with Hoechst 33258 staining. Western blot analysis was used to examine the changes in the expression levels Of I kappa B-alpha, NF-kappa B p65 subunit and Cox-2. Additionally, we took advantage of dominant-negative I kappa B (I kappa B-DM) overexpression and chemical inhibitor PDTC to inhibit NF-kappa B activation. Key findings: Our results demonstrated that dexamethasone could enhance TCS-induced apoptosis in the hepatoma cell line HepG2, decreasing IC50 values from in excess of 200 mu g/ml to 50 mu g/ml. In addition, our results demonstrated that TCS could induce rapid degradation Of I kappa B-alpha, nuclear translocation of NF-kappa B and decrease of COX-2 expression in HepG2 cells. Inhibition of NF-kappa B by biological (I kappa B-DM) or chemical inhibitor (PDTC) increased HepG2 cells' sensitivity to TCS, resulting in cell viability rate decreasing and apoptotic rate increasing. Simultaneously, dexamethasone increased the level Of I kappa B-alpha protein and effectively inhibited TCS-induced degradation Of I kappa B-alpha. Significance: These results suggest that dexamethasone could enhance trichosanthin-induced apoptosis in the HepG2, at least in part, by inhibiting the NF-kappa B signaling pathway and thus strengthening the antitumor effects of TCS, which highlights the possibility of combined drug application of TCS and dexamethasone in the clinical treatment of hepatoma. (C) 2009 Elsevier Inc. All rights reserved.