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

// Sarath Ramachandran 1 , Catherine Qiurong Pan 2 , Sarah C. Zimmermann 3 , Bridget Duvall 3 , Takashi Tsukamoto 3 , Boon Chuan Low 1, 2 , J. Sivaraman 1 1 Department of Biological Sciences, National University of Singapore, 117543, Singapore 2 Mechanobiology Institute Singapore, National University of Singapore, 117411, Singapore 3 Department of Neurology and Johns Hopkins Drug Discovery Program, Johns Hopkins University, Baltimore, Maryland 21205, USA Correspondence to: J. Sivaraman, email: dbsjayar@nus.edu.sg Keywords: glutaminase, cancer target, BPTES, CB-839, allosteric inhibitors Received: November 30, 2015     Accepted: June 17, 2016     Published: July 22, 2016 ABSTRACT 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 IC 50 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 1 S , 3 S -CBTBP and CB-839. We found that CB-839 produces a greater degree of interaction with cKGA than 1 S , 3 S -CBTBP or BPTES. The results of this study will facilitate the rational design of new KGA inhibitors to better treat glutamine-addicted cancers.