Molecular Mechanisms of Fructose-induced Colorectal Cancer Cell Survival

Project Summary Clear associations have been established between the food we eat and the development and progression of colorectal cancer (CRC). For example, the consumption of fructose increases the risk for CRC development and CRC-specific mortality. However, the mechanism underlying this association is unknown. We have shown that moderate daily exposure to oral high fructose corn syrup (HFCS, a mix of fructose and glucose) leads to larger and more aggressive intestinal adenomas in mice. These effects were absent in mice with genetic deficiency of ketohexokinase (KHK), the enzyme that converts fructose to fructose 1-phosphate (F1P). A metabolomic analysis of these tumors showed that F1P is highly abundant following HFCS exposure, and this increase correlates with a reduction in pyruvate kinase (PK) activity. Therefore, we hypothesize that F1P, the product of KHK, enhances tumor growth by acting as an allosteric inhibitor of PK to promote anabolic metabolism and cell survival. We will test this hypothesis using mouse physiology and organ metabolism, cell and human organoid culture, and recombinant protein biochemistry. In Aim 1, we will genetically and pharmacologically manipulate the M2 isozyme of PK (PKM2) in mice to interrogate its role as a mediator of HFCS-induced tumor growth. In Aim 2, we will define the mechanistic linkage between fructose exposure and cancer cell survival. We have found that cells in culture do not grow faster when exposed to fructose, however we observed a significant improvement in cell viability, especially under conditions of high cell density and hypoxia with fructose in the media. Therefore, we hypothesize that F1P inhibits PKM2 to promote hypoxic cell survival. We will test this hypothesis using cell and organoid culture models exposed to fructose and hypoxia. We will genetically and pharmacologically manipulate KHK and PKM2 expression and activity in these models to determine the specific effects of these proteins on cell metabolism and survival. In Aim 3, we will assess the effects of F1P on recombinant PK isoforms with a particular focus on PKM2. We hypothesize that fructose- derived F1P binds to and inhibits PKM2. We will perform biochemical activity and structural assays to determine the kinetic parameters and oligomeric state of PK isoforms in the presence of F1P. These experiments will reveal the molecular mechanisms of how F1P binds and inhibits PKM2. Together, these aims will change our fundamental understanding of how fructose alters tumor cell metabolism, define the fructose/F1P/PKM2 axis as a metabolic vulnerability of CRC, and provide pre-clinical evidence for PKM2 activators as a novel therapeutic modality to combat CRC.