Targeting energy metabolism in colorectal cancer

A switch to aerobic glycolysis regardless of oxygen tension is a metabolic phenotype observed in a variety of tumors, known as the Warburg effect, and is a possible target in cancer therapy. The abnormal tumor vasculature leads to a heterogeneous microenvironment with areas of hypoxia, acidity, and low nutrient supply. This thesis investigated the effects of the tumor microenvironment on the expression of glycolytic enzymes and on the efficacy of compounds targeting them. The first set of experiments examined the molecular and metabolic changes associated with dichloroacetate-induced cytoprotection in different human colorectal cancer (CRC) cell lines under anoxic conditions. There was evidence of differential regulation of pyruvate dehydrogenase phosphorylation between different cells leading to altered mitochondrial activity following dichloroacetate exposure. Hexokinase II (HKII) is a glycolytic enzyme often upregulated in tumors. 3-bromopyruvate (3BP) is an alkylating agent that shows promising anti-cancer effects in various cancer models and HKII has been suggested to be one of its principal targets. The efficacy of 3BP against CRC cells was assessed under different media glucose concentrations, and it was determined that 3BP was effective in reducing cell growth through alterations in AKT signaling and that media glucose availability played a role in cytotoxic sensitivity to 3BP. However, knockdown in HKII expression did not alter 3BP sensitivity in different CRC cell lines. Finally, HKII expression was assessed in colorectal cancer tissues and correlated with clinical parameters and patient outcome. Dual immunofluorescence was used to co-localize HKII with a marker of ischemia, carbonic anhydrase IX in 60 cases of human CRC. HKII expression was found only in non-ischemic areas of the tumors. While HKII expression did not correlate with any measured clinicopathlogical characteristics, patients with low HKII-expressing tumors had a worse prognosis than those with high HKII-expressing tumors. Overall, this thesis presents the effects of the tumor microenvironment on both glycolytic enzyme expression and therapeutic efficacy. This research promises to improve our understanding of tumor metabolism in the heterogeneous microenvironment in order to better apply this field of cancer biology for therapeutic use.