Structural basis for exploring the allosteric inhibition of human kidney type glutaminase

Cancer cells employ glutaminolysis to provide a source of intermediates for their upregulated biosynthetic needs. Glutaminase, which catalyzes the conversion of glutamine to glutamate, is gaining increasing attention as a potential drug target. Small-molecule inhibitors such as BPTES and CB-839, which target the allosteric site of glutaminase with high specificity, demonstrate immense promise as anti-tumor drugs. Here, we report the study of a new BPTES analog, N,N'-(5,5'-(trans-cyclohexane-1,3-diyl)bis(1,3,4-tiadiazole-5,2-diyl))bis(2-phenylacetamide) (trans-CBTBP), and compared its inhibitory effect against that of CB-839 and BPTES. We show that CB-839 has a 30- and 50-fold lower IC50 than trans-CBTBP and BPTES, respectively. To explore the structural basis for the differences in their inhibitory efficacy, we solved the complex structures of cKGA with 1S, 3S-CBTBP and CB-839. We found that CB-839 produces a greater degree of interaction with cKGA than 1S, 3S-CBTBP or BPTES. The results of this study will facilitate the rational design of new KGA inhibitors to better treat glutamine-addicted cancers.