Identification of Fumarate Hydratase Inhibitors with Nutrient-Dependent Cytotoxicity

Development of cell-permeable small molecules that target enzymes involved in energy metabolism remains important yet challenging. We describe here the discovery of a new class of compounds with a nutrient-dependent cytotoxicity profile that arises from pharmacological inhibition of fumarate hydratase (also known as fumarase). This finding was enabled by a high-throughput screen of a diverse chemical library in a panel of human cancer cell lines cultured under different growth conditions, followed by subsequent structure-activity optimization and target identification. While the highest cytotoxicity was observed under low glucose concentrations, the antiproliferative activities and inhibition of oxygen consumption rates in cells were distinctly different from those displayed by typical inhibitors of mitochondrial oxidative phosphorylation. The use of a photoaffinity labeling strategy identified fumarate hydratase as the principal pharmacological target. Final biochemical studies confirmed dose-dependent, competitive inhibition of this enzyme in vitro, which was fully consistent with the initially observed growth inhibitory activity. Our work demonstrates how the phenotypic observations combined with a successful target identification strategy can yield a useful class of pharmacological inhibitors of an enzyme involved in the operation of tricarboxylic acid cycle.