Identification of arylamine N-acetyltransferase inhibitors as an approach towards novel anti-tuberculars

Abstract

New anti-tubercular drugs and drug targets are urgently needed to reduce the time for treatment and also to identify agents that will be effective against Mycobacterium tuberculosis persisting intracellularly. Mycobacteria have a unique cell wall. Deletion of the gene for arylamine N-acetyltransferase (NAT) decreases mycobacterial cell wall lipids, particularly the distinctive mycolates, and also increases antibiotic susceptibility and killing within macrophage of Mycobacterium bovis BCG. The nat gene and its associated gene cluster are almost identical in sequence in M. bovis BCG and M. tuberculosis. The gene cluster is essential for intracellular survival of mycobacteria. We have therefore used pure NAT protein for high-throughput screening to identify several classes of small molecules that inhibit NAT activity. Here, we characterize one class of such molecules-triazoles-in relation to its effects on the target enzyme and on both M. bovis BCG and M. tuberculosis. The most potent triazole mimics the effects of deletion of the nat gene on growth, lipid disruption and intracellular survival. We also present the structure-activity relationship between NAT inhibition and effects on mycobacterial growth, and use ligand-protein analysis to give further insight into the structure-activity relationships. We conclude that screening a chemical library with NAT protein yields compounds that have high potential as anti-tubercular agents and that the inhibitors will allow further exploration of the biochemical pathway in which NAT is involved.

New Approaches to Target the Mycolic Acid Biosynthesis Pathway for the Development of Tuberculosis Therapeutics

“…The Sim lab performed an extensive screen for selective prokaryotic aNAT inhibitors against five purified aNAT isoforms including hamster, human, M. smegmatis , S. typhimurium and P. aeruginosa [113]. Compounds, tested at 30 μM, were deemed active and selective if they achieved ≥50% inhibition of no less than two bacterial aNAT enzymes and ≤20% inhibition of both eukaryotic aNAT enzymes [113].…”

“…Compounds, tested at 30 μM, were deemed active and selective if they achieved ≥50% inhibition of no less than two bacterial aNAT enzymes and ≤20% inhibition of both eukaryotic aNAT enzymes [113]. From this screen they identified a variety of inhibitors and have followed up on three unique scaffolds.…”

The role of lysine100 in the binding of acetylcoenzyme A to human arylamine N-acetyltransferase 1: Implications for other acetyltransferases

“…Moreover, recent studies have shown a relationship between NAT1 and cancer cell proliferation and survival suggesting that this protein is a potential drug target [7,8]. There have also been a number of reports on the development of small molecule inhibitors for human and non-human NATs [9][10][11][12].…”

Probing the architecture of the Mycobacterium marinum arylamine N-acetyltransferase active site

“…NAT inhibitors were demonstrated to have similar effects to that of deleting the gene (Westwood, 2005;Westwood et al, 2006), suggesting the validity of NAT as a potential anti-tubercular target. Interestingly, as prokaryotic NATs show a different substrate profile compared to eukaryotic enzymes (Westwood et al, 2006), it should be possible to design NAT inhibitors that are selectively toxic to mycobacteria and screen protocols have allowed such specificity to be incorporated (Westwood et al, 2010).…”