Telaglenastat (CB-839) hydrochloride is a first-in-class, reversible, and orally active inhibitor of glutaminase 1 (GLS1). It selectively inhibits the splice variants of GLS1, specifically KGA (kidney-type glutaminase) and GAC (glutaminase C), as compared to GLS2. Telaglenastat hydrochloride has an IC50 of 23 nM for endogenous glutaminase in mouse kidney and 28 nM in the brain. In addition, it induces autophagy and exhibits antitumor activity.