Exploiting Metabolic Changes in HCC for Cancer Therapy

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Project Summary: Hepatocellular carcinoma (HCC) is the 10th most common cancer but the fourth leading cause of cancer-related death in the United States. To date, the only FDA-approved molecular therapy, sorafenib, has not been effective. This grant is aimed at determining the role of hexokinase 2 (HK2) in HCC development and progression, and whether or not HK2 is a viable drug target for HCC treatment. Normal healthy adult hepatocytes express glucokinase, a low affinity hexokinase. However, during pathological transition to cirrhosis and HCC, transformed hepatocytes silence glucokinase and induce HK2. We have shown this isoform transition in both human HCC cell lines and in a tumor microarray of 312 samples from 153 patients. This transition also represents a more general metabolic alteration whereby cancer cells increase glucose utilization and lactate secretion despite ample oxygen being present, also known as the Warburg Effect. HK2 is a “mitochondrial” hexokinase, meaning it is capable of binding to the voltage dependent ion channel on the mitochondria, and we have data suggesting this interaction is essential for both tumorigenesis and efficient glucose utilization. Part of this grant will determine by what mechanism the mitochondrial interaction of HK2 promotes tumorigenesis and more generally why mitochondrial binding is necessary for full glycolytic capacity. We have shown that knockdown of HK2 beyond 70% is lethal to HCC cells, and indeed another group has shown that having either HK1 or HK2 is essential for cancer cell viability using a CRISPR/Cas9 knockout screen. Since HCC cells only express HK2, we believe HK2 is an ideal drug target for HCC. We will determine the feasibility of this therapeutic strategy using established mouse models of HCC to determine the cell autonomous necessity of HK2 in HCC initiation and progression. We will emulate drug therapy by using a doxycycline-inducible shRNA targeting HK2 in human HCC cells following subcutaneous implantation in nude mice. We will also determine if targeting mitochondrial glutamine metabolism synergizes with HK2 inhibition. Preliminary data suggests that production of NADPH, an important electron source for fatty acid synthesis and redox balance in cancer cells, is completely dependent on malic enzyme 1 and glutamine metabolism in HCC cells. We will exploit this dependency with a glutaminase-1 inhibitor, BPTES, or a complex-1 inhibitor, metformin in concert with HK2 inhibition. HK2 deletion should prevent compensatory activation of the pentose phosphate pathway and compensatory flux of glycolytic pyruvate into the mitochondria for TCA-flux, creating synergism with BPTES or metformin.