ACTIVATION OF THE MITOGEN-ACTIVATED PROTEIN KINASE ERK5 REGULATES THE DEVELOPMENT AND GROWTH OF HEPATOCELLULAR CARCINOMA

POSTERS markers. Metformin induces PTEN expression, which may explain the positive therapeutic effect of metformin in several tumors. 1039 ACTIVATION OF THE MITOGEN-ACTIVATED PROTEIN KINASE ERK5 REGULATES THE DEVELOPMENT AND GROWTH OF HEPATOCELLULAR CARCINOMA G. Di Maira 1 , E. Rovida 1 ,N.Navari 1 , S. Cannito 2 ,B.Fani 1 , P. Dello Sbarba 1 , M. Parola 2 ,F.Marra 1 . 1 University of Florence, Florence, 2 University of Turin, Turin, Italy E-mail: giovanni.dimaira@unifi.it Background and Aims: Current treatment options for hepatocel- lular carcinoma (HCC) are limited. The interference with signaling pathways deregulated in hepatocarcinogenesis could be considered a promising therapeutic strategy. ERK5 is the least studied member of the MAPK family and has been implicated in several biologic actions relevant for tumor development. Moreover, deregulation of the ERK5 pathway has been shown to be associated with cancer. Aim of this study was to understand the role of ERK5 in HCC in vitro and in vivo. Methods: Huh-7 and HepG2 were cultured by standard methods. Liver tissue was obtained from HCC and peritumoral areas. ERK5 was silenced by siRNA transfection or with shRNA and lentiviral vectors. The specific ERK5 inhibitor XMD8–92was also used. In vivo development of HCC was evaluated using the Huh-7 xenograft model in athymic nude mice. Results: Analysis of ERK5 by IHC in human tissues showed more abundant nuclear localization in patients with HCC or cirrhosis than in normal liver, indicating ERK activation. ERK5 silencing in HCC cells or exposure to XMD8–92 blocked the increase in migration and invasion induced by EGF or serum. Similar results were observed in response to hypoxia. Immunofluorescence experiments demonstrated that ERK5 silencing or inhibition caused cytoskeletal remodeling and rearrangement of focal adhesions, consistent with a reduction in cell motility. In addition, ERK5 activation was necessary for the growth of HCC cells, affecting the G1/S transition. In a mouse model of HCC xenograft, administration of XMD8–92 significantly decreased tumor volume by approximately 40% compared to vehicle, 13 days after starting the treatment. Moreover, in mice injected with Huh-7 cells silenced for ERK5 using a lentiviral shRNA vector, the rate of tumor appearance was significantly lower (4/16 mice, 25%) than in animals inoculated with cells transduced with non targeting shRNA (9/15, 60%). In addition, at the end of the experiment, tumor volume was smaller in the presence of ERK5 silencing. Conclusions: The ERK5 pathway plays a critical role in HCC tumor development and growth in vivo. Blocking the ERK5 pathway should be further investigated as a novel approach for the treatment of HCC.