An orally bioavailable inhibitor of the metabolic enzyme glutaminase-1 (GLS1), with potential antineoplastic and immunostimulating activities. Upon oral administration, IACS-6274 selectively targets, binds to and inhibits human GLS1, an enzyme that is essential for the conversion of the amino acid glutamine into glutamate. Blocking glutamine metabolism inhibits proliferation in rapidly growing tumor cells and leads to an induction of cell death. Unlike normal healthy cells, glutamine-dependent tumors heavily rely on the intracellular conversion of exogenous glutamine into glutamate and glutamate metabolites to provide energy and generate building blocks for the production of macromolecules, which are needed for cellular growth and survival.