Genetically mandated alterations in the fundamental metabolic pathways of tumors often cause a dramatic rise in the uptake of the nutrients glucose and glutamine. Removal of glutamine leads to a substantial reduction in cell growth or induces cell death in certain types of cancer cells, indicating that these cells are dependent on, or “addicted” to, glutamine. Normal cells do not show this pronounced dependence on glutamine. The enzyme glutaminase, which converts glutamine to glutamate, has been identified as a critical choke point in the utilization of glutamine by cancer cells. CB-839 is a potent, selective, reversible and orally bioavailable inhibitor of human glutaminase.