Research ArticleCancer

Squalene epoxidase drives NAFLD-induced hepatocellular carcinoma and is a pharmaceutical target

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Science Translational Medicine  18 Apr 2018:
Vol. 10, Issue 437, eaap9840
DOI: 10.1126/scitranslmed.aap9840

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Antifungal drug may help fight cancer

The rates of nonalcoholic fatty liver disease are increasing with the rising prevalence of obesity and are associated with an increase in the incidence of hepatocellular carcinoma. By studying the mechanism of hepatocellular carcinoma arising in the setting of nonalcoholic fatty liver disease, Liu et al. discovered a role for squalene epoxidase, a metabolic enzyme involved in cholesterol biosynthesis. Using a combination of human cancer cells and mouse models of disease, the authors examined the pathway by which squalene epoxidase promotes the development of hepatocellular carcinoma and identified terbinafine, a clinically approved antifungal drug, as a potential intervention.

Abstract

Nonalcoholic fatty liver disease (NAFLD)–induced hepatocellular carcinoma (HCC) is an emerging malignancy in the developed world; however, mechanisms that contribute to its formation are largely unknown, and targeted therapy is currently not available. Our RNA sequencing analysis of NAFLD-HCC samples revealed squalene epoxidase (SQLE) as the top outlier metabolic gene overexpressed in NAFLD-HCC patients. Hepatocyte-specific Sqle transgenic expression in mice accelerated the development of high-fat, high-cholesterol diet–induced HCC. SQLE exerts its oncogenic effect via its metabolites, cholesteryl ester and nicotinamide adenine dinucleotide phosphate (NADP+). Increased SQLE expression promotes the biosynthesis of cholesteryl ester, which induces NAFLD-HCC cell growth. SQLE increased the NADP+/NADPH (reduced form of NADP+) ratio, which triggered a cascade of events involving oxidative stress–induced DNA methyltransferase 3A (DNMT3A) expression, DNMT3A-mediated epigenetic silencing of PTEN, and activation of AKT-mTOR (mammalian target of rapamycin). In human NAFLD-HCC and HCC, SQLE is overexpressed and its expression is associated with poor patient outcomes. Terbinafine, a U.S. Food and Drug Administration–approved antifungal drug targeting SQLE, markedly inhibited SQLE-induced NAFLD-HCC cell growth in NAFLD-HCC and HCC cells and attenuated tumor development in xenograft models and in Sqle transgenic mice. Suppression of tumor growth by terbinafine is associated with decreased cholesteryl ester concentrations, restoration of PTEN expression, and inhibition of AKT-mTOR, consistent with blockade of SQLE function. Collectively, we established SQLE as an oncogene in NAFLD-HCC and propose that repurposing SQLE inhibitors may be a promising approach for the prevention and treatment of NAFLD-HCC.

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