Abstract B29: Genetic interactions between AKT/mTOR and Ras/MAPK pathways in liver cancer pathogenesis: from animal models to targeted therapy

Abstract

Abstract Introduction: Hepatocellular carcinoma (HCC) and cholangiocellular carcinoma (CCC) are deadly malignant liver tumors lacking of efficient treatment options. Akt/mTOR and Ras/MAPK pathways have been implicated in hepatic carcinogenesis. Our study is to define the genetic interactions between Akt/mTOR and Ras/MAPK pathways in liver carcinogenesis. Methods: Activation of Akt/mTOR and Ras/MAPK signaling was assayed in 62 human HCC and 25 CCC samples. An activated Akt (myr-Akt) was stably transfected into the mouse liver alone or together with activated N-Ras (RasV12) via hydrodynamic gene delivery. Molecular and biochemical features of liver lesions were analyzed. A primary cell line (Akt/Ras) was isolated from a tumor co-injected with Akt and Ras protooncogenes. Akt/Ras cells and human HCC cell lines were treated with different mTOR inhibitors, including NVP-BEZ235, PP242 and Rapamcyin, as well as the MEK inhibitor AZD6244. Results: Using human HCC samples, we demonstrated the coordinated activation of Akt/mTOR and Ras/MAPK pathways in subsets of HCC and CCC characterized by poor prognosis. We found that coexpression of myr-Akt with RasV12 synergizes to promote liver tumor development in mice, leading to HCC and CCC formation within 4 to 6 weeks post injection. At cellular level, tumors from Akt/N-Ras co-injection cells are characterized by high proliferation and low apoptotic index, and disrupted expression of genes involved in cell cycle regulation. At the molecular level, liver tumors show high levels of activated Akt/mTOR and Erk cascades. A primary cell line (Akt/Ras) was isolated from a tumor and used to test the response to different mTOR and MEK inhibitors. We found that dual PI3K/mTOR inhibitor NVP-BEZ235 has superior activity inhibiting Akt/Ras cell proliferation with IC50 around 2nM. It also efficiently inhibits phospho-S6, phospho-4EBP1 and cyclin D1 expression in Akt/Ras cells. Furthermore, NVP-BEZ235 synergizes with the MEK inhibitor AZD6244 to dramatically reduce the growth of the Akt/Ras cell line. Equivalent results were obtained in human HCC cell lines with the same inhibitors. Conclusion: Coordinated activation of Akt/mTOR and Ras/MAPK signaling is the hallmark of aggressive subtypes of human HCC and CCC. Activated Akt cooperates with activated Ras/MAPK to rapidly promote liver tumor formation in mice. The Akt/Ras mouse model is a useful pre-clinical system to test anti-neoplastic therapeutic approaches against HCC and CCC in vivo. In addition, our preliminary studies suggest that the combination of a dual PI3K/mTOR inhibitor with a MEK inhibitor may represent a promising novel targeted therapy for treating human HCC harboring activated Akt/mTOR and Ras/MAPK pathways. Citation Information: Clin Cancer Res 2010;16(14 Suppl):B29.