Assessing the Dual Mechanism of MZA antitubercular activity
Tuberculosis (TB), caused by Mycobacterium tuberculosis (MTB), is a global threat which has an estimated annual case rate of 10 million resulting in over 1 million deaths each year. Although therapeutic strategies for treating TB exist, these approaches are limited by the protracted 6 month treatment time required to cure drug susceptible infections. Moreover, the rising prevalence of drug resistant strains of MTB have led to more extended treatment times with lower success rates. Thus, investigation of antitubercular agents with bactericidal activity against drug resistant isolates is a paramount goal for antimicrobial drug discovery. Pyrazinamide (PZA) is a cornerstone drug of TB therapy due to its ability to kill non-replicating populations of drug-tolerant MTB and has shortened treatment times and reduced disease relapse rates. Since PZA is a prodrug that must be activated by the MTB pyrazinamidase, loss-of-function mutations account for the majority of PZA resistance. This has led us to investigate PZA analogues that may have antitubercular activity against PZA resistant strains. One PZA analog candidate that our lab is interested in is morphazinamide (MZA, N-(4-morpholinyl methyl)-2-pyrazinecarboxamide). MZA exhibits particularly potent antitubercular activity in addition to activity against pncA null strains of MTB. Despite these promising results, the antitubercular mechanism of MZA activity remains unknown. In a preliminary study seeking to characterize mutations that confer resistance to MZA via whole-genome sequencing, we observed that pncA null mutant strains that acquired spontaneous MZA resistance had acquired mutations in the promoter region of an aldehyde reductase (MscR). This observation led us to hypothesize that the formation of aldehyde upon the metabolism of the morpholine MZA ring might be an important contributor to the anti-tubercular mechanism. We also predict that mutations that upregulate the production of aldehyde reductase may confer resistance to MZA. In turn my research involved generating MICs of WT M. Bovis and mscR mutant M. Bovis strains in several aldehyde producing drugs; using these MICs as a means of comparing formaldehyde susceptibility of the two M. Bovis strains.