An orally bioavailable inhibitor of glutaminase, with potential antineoplastic activity. Upon oral administration, CB-839 selectively and irreversibly inhibits glutaminase, a mitochondrial enzyme that is essential for the conversion of the amino acid glutamine into glutamate. By blocking glutamine utilization, proliferation in rapidly growing cells is impaired. Glutamine-dependent tumors rely on the conversion of exogenous glutamine into glutamate and glutamate metabolites to both provide energy and generate building blocks for the production of macromolecules, which are needed for cellular growth and survival.