Hexokinase 2 in Liver Cancer

A major focus of cancer biologists is to identify novel therapeutic strategies to improve cancer-patient outcomes. One of the most prevalent cancer-specific phenotypes is glucose addiction, manifest, by the specific upregulation of glycolysis in the presence of oxygen (aerobic glycolysis), and thus, cancer metabolism has been under investigation to learn how to best exploit this vulnerability to selectively eradicate cancer cells. Hexokinase (HK) enzymes catalyze the first, committed step of the glycolysis pathway, phosphorylating glucose to produce the product glucose-6-phosphate (G6P), that is used in a number of ways to support cell viability and proliferation. In liver cancer, an isoform switch is observed, whereby the normal, adult isoform, Glucokinase (GCK), is repressed and the embryonic form, Hexokinase 2 (HK2) is upregulated, and is the only isoform expressed. Therefore, liver cancer could be selectively targeted by HK2 ablation sparing the normal hepatocytes. We found that by targeting HK2 in two independent human HCC cell lines, HepG2 and Huh7, reduced hexokinase activity, proliferation, and tumorigenicity was observed in in-vitro and in-vivo assays. These phenotypes were rescued by exogenous expression of a rat, wt-HK2 orthologue that is resistant to silencing by shRNA used in the cells to target human HK2, but that both catalytic and mitochondrial-binding mutants could not, indicating that both of these functions are required for HK2 to exert tumorigenic potential. GCK could not phenocopy HK2 in rescue experiments either. Cells with HK2 knockdown that exhibited reductions in glycolysis also showed a compensatory upregulation in respiration. By targeting both glycolysis and OXPHOS, with HK2 shRNA and Metformin treatment, respectively, we were able to inhibit tumor growth in mouse tumorigenesis models. Treatment with Metformin in combination with HK2 loss also synergistically downregulates the mTORC1 signaling pathway through the REDD1 protein. Data suggests that targeting HK2 and Metformin co-treatment should be considered for HCC cancer therapy.