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Hepatocellular carcinoma (HCC) is one of the most common cancers worldwide, and outcome is dismal, due to tumor heterogeneity and lack of effective treatment options for patients with later stage disease. Transcatheter arterial chemoembolization (TACE) is the gold standard of therapy for patients with intermediate to locally advanced tumors. TACE delivers a high dose of chemotherapy directly to the tumor via the hepatic artery, followed by an embolizing agent to restrict tumor blood supply. However, tumor hypoxia is linked to alterations in metabolism, such as increased glycolysis (the Warburg effect), and can lead to enhanced cell survival. Several randomized control trials (RCTs) showed a survival benefit with TACE, but only with strict patient selection criteria. In Asia, TACE is also commonly used as adjuvant therapy after surgical resection, yet RCTs evaluating adjuvant TACE have shown conflicting results, likely due to patient selection and stratification. We hypothesize that tumor gene expression is predictive of response following TACE, and that differential cellular metabolism resembling a hypoxic phenotype prior to treatment is responsible for TACE resistance. We retrospectively analyzed gene expression data in treatment-naive tumor tissue from a cohort of Chinese patients who received TACE. Using hierarchical clustering, followed by class comparison and survival risk prediction, we identified a 14-gene signature that is predictive of response vs. non-response to TACE, as measured by overall survival, independent of other clinical variables. We found that hypoxia- and glycolysis-related genes are enriched among differentially expressed genes in TACE Responders vs. Non-Responders, and that hypoxia master regulator HIF-1α and hypoxia target gene VEGF are significantly up-regulated in Non-Responders. We determined that a key glycolysis gene is up-regulated in Non-Responders, and conversely, two rate-limiting genes involved in gluconeogenesis, the pathway opposing glycolysis, are up-regulated in Responders. We also examined metabolomic data from the TACE cohort, and found an enrichment of glycolysis-related metabolites in Non-Responders, and gluconeogenesis-related metabolites in Responders. Further investigation will be required to connect altered glucose metabolism to TACE resistance and to determine driver genes linking hypoxia and metabolism, which, together with our 14-gene signature, may serve as a stratification tool to guide personalized treatment modalities for HCC patients. Citation Format: Valerie Fako, Joyce Lee, Tan-To Cheung, Irene O. Ng, Xin W. Wang. Hypoxia response signaling is linked to TACE resistance in hepatocellular carcinoma (HCC) patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 544. doi:10.1158/1538-7445.AM2017-544

Fatty acid synthase (FASN), a seven domain enzyme, is the sole protein capable of de novo synthesis of free fatty acids, most commonly 16-carbon palmitate. The fatty acid synthesis cycle begins with the condensation of acetyl-CoA and malonyl-CoA, and continues with the elongation of the fatty acid chain, which is tethered to an acyl carrier protein domain (ACP), via a repeating cycle. At the end of elongation, the thioesterase (TE) domain of FASN, a member of the serine hydrolase family with an Asp-His-Ser catalytic triad, cleaves the bond between palmitate and ACP, and releases free palmitate. FASN has been found to be over-expressed in a wide variety of human cancers, and this over-expression is correlated to a higher metastatic potential and poorer prognosis in cancer patients. FASN over-expression is also associated with increased resistance toward cancer chemotherapeutics. Orlistat, an FDA approved drug for obesity treatment that prevents uptake of dietary fats by inhibiting pancreatic lipases in the gastrointestinal tract, is a compound found to act as a reversible inhibitor of FASN TE. A previous study using the co-crystal structure of the TE domain with orlistat found that orlistat was covalently bound to the active site Ser within the TE domain, indicating that inhibition of FASN by orlistat halts the fatty acid synthesis cycle by blocking the release of free palmitate from the ACP. A hydrolyzed form of orlistat was also observed in the active site of TE, demonstrating that orlistat is not a stable inhibitor of FASN. In this study, we examined the mechanism of orlistat hydrolysis within the TE domain of FASN using molecular dynamics simulations. We found that the hexanoyl tail of orlistat is capable of shifting while covalently bound to the active site Ser, and that this shift is accompanied by the destabilization of a hydrogen bond that exists between a hydroxyl moiety of orlistat and the active site His. Once this hydrogen bond is destabilized, a catalytic water molecule can enter the active site of TE with the proper orientation for catalysis of the covalent bond between orlistat and Ser. These findings suggest that the hexanoyl tail of orlistat plays an important role in its hydrolysis and may guide the future design of new inhibitors that target the TE domain of FASN with greater endurance for potential use in the treatment of cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3978. doi:1538-7445.AM2012-3978