GLS1 Inhibitor-1 (Compound 27) is an orally active inhibitor for glutaminase 1 ( GLS1 ) with an IC 50 of 0.021 μM. GLS1 Inhibitor-1 inhibits the proliferation of PC-3 with an IC 50 of 0.3 nM. GLS1 Inhibitor-1 exhibits antitumor efficacy against NCI-H1703 with GI 50 of 0.011 μM. GLS1 Inhibitor-1 exhibits moderate pharmacokinetic characteristics.