Pivotal Role of mTOR Signaling in Hepatocellular Carcinoma

Gastroenterology, 2008 Dec;135(6):1972-83. Published: 2008.08.21

Augusto Villanueva, Derek Y. Chiang, Pippa Newell, Judit Peix, Swan Thung, Clara Alsinet, Victoria Tovar, Sasan Roayaie, Beatriz Minguez, Manel Sole, Carlo Battiston, Stijn van Laarhoven, Maria I Fiel, Analisa Di Feo, Yujin Hoshida, Steven Yea, Sara Toffanin, Alex Ramos, John A. Martignetti, Vincenzo Mazzaferro, Jordi Bruix, Samuel Waxman, Myron Schwartz, Matthew Meyerson, Scott L. Friedman, Josep M. Llovet


BACKGROUND: The advent of targeted therapies in hepatocellular carcinoma (HCC) has underscored the importance of pathway characterization to identify novel molecular targets for treatment. Based on its role in cell growth and differentiation, we evaluated mTOR signaling activation in human HCC, as well as the anti-tumoral effect of a duallevel blockade of the mTOR pathway. METHODS: The mTOR pathway was assessed using integrated data from mutation analysis (direct sequencing), DNA copy number changes (SNP-array), mRNA levels (qRT-PCR and gene expression microarray), and protein activation (immunostaining) in 351 human samples, including HCC (n=314), and non-tumoral tissue (n=37). Effects of dual blockade of mTOR signaling using a rapamycin analog (everolimus) and an EGFR/VEGFR inhibitor (AEE788) were evaluated in liver cancer cell lines, and in a tumor xenograft model. RESULTS: Aberrant mTOR signaling (phosphorylated-RPS6) was present in half of the cases, associated with IGF pathway activation, EGF upregulation, and PTEN dysregulation. PTEN and PI3KCA-B mutations were rare events. Chromosomal gains in RICTOR (25% of patients) and positive pRPS6 staining correlated with recurrence. RICTOR-specific siRNA downregulation reduced tumor cell viability in vitro. Blockage of mTOR signaling with everolimus in vitro and in a xenograft model decelerated tumor growth and increased survival. This effect was enhanced in vivo after EGFR blockade. CONCLUSIONS: MTOR signaling has a critical role in the pathogenesis of HCC, with evidence for the role of RICTOR in tumor oncogenesis. MTOR blockade with everolimus is effective in vivo. These findings establish a rationale for targeting mTOR pathway in clinical trials in HCC.