This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Tatebe, H. Articles by Moriwaki, H. PubMed PubMed Citation Articles by Tatebe, H. Articles by Moriwaki, H.

Synergistic Growth Inhibition by 9-cis-Retinoic Acid Plus Trastuzumab in Human Hepatocellular Carcinoma Cells

Authors' Affiliation: Department of Medicine, Gifu University Graduate School of Medicine, Gifu, Japan

Requests for reprints: Masahito Shimizu, Department of Medicine, Gifu University Graduate School of Medicine, 1-1 Yanagido, Gifu 501-1194, Japan. Phone: 81-58-230-6313; Fax: 81-58-230-6310; E-mail: shimim-gif{at}umin.ac.jp.

Purpose: A malfunction of retinoid X receptor- (RXR) due to phosphorylation by the Ras/mitogen-activated protein kinase signaling pathway is associated with the development of hepatocellular carcinoma (HCC). The humanized anti-HER2 monoclonal antibody trastuzumab inhibits the activation of HER2 and its multiple downstream signaling pathways, including the Ras/mitogen-activated protein kinase pathway. In this study, the effects of phosphorylation of RXR on the ability of RXR ligand 9-cis-retinoic acid (9cRA) and trastuzumab to inhibit growth of HCC cells was examined.

Experimental Design: The effects of a combination of 9cRA plus trastuzumab on the inhibition of cell growth in HLF human HCC cells which express constitutive activation of HER2 protein were examined.

Results: The combination of 9cRA plus trastuzumab synergistically inhibited the growth of HLF cells without affecting the growth of Hc normal human hepatocytes. Combined treatment with these agents acted synergistically to induce apoptosis in HLF cells. The treatment of HLF cells with trastuzumab alone inhibited the phosphorylation of HER2, RXR, ERK, Akt, and Stat3 proteins and these effects were enhanced when the cells were cotreated with 9cRA. Reporter assays indicated that the combination of 9cRA plus trastuzumab markedly increased both the retinoic acid responsive element and retinoid X responsive element promoter activities in HLF cells.

Conclusion: 9cRA and trastuzumab cooperatively inhibit the activation of HER2 and its downstream signaling pathways, subsequently inhibiting the phosphorylation of RXR and the growth of HCC cells. This combination might therefore be effective for the chemoprevention and chemotherapy of HCC.