An orally available inhibitor of isocitrate dehydrogenase type 2 (IDH2), with potential antineoplastic activity. Upon administration, AG-221 specifically inhibits IDH2 in the mitochondria, which inhibits the formation of 2-hydroxyglutarate (2HG). This may lead to both an induction of cellular differentiation and an inhibition of cellular proliferation in IDH2-expressing tumor cells. IDH2, an enzyme in the citric acid cycle, is mutated in a variety of cancers; It initiates and drives cancer growth by blocking differentiation and the production of the oncometabolite 2HG.