Novel lead generation of an anti-tuberculosis agent active against non-replicating mycobacteria: exploring hybridization of pyrazinamide with multiple fragments

The key to shortening tuberculosis (TB) drug regimen lies in eliminating the reservoir of non-replicating persistent (NRP) Mycobacterium tuberculosis (Mtb). Pyrazinamide (PZA) is the only known drug used as part of a combination therapy that is believed to kill NRP Mtb and achieve sterilization. PZA is active only under low pH screening conditions. Screening and identification of NRP-active anti-TB compounds are severely limited because compounds are usually inactive under regular assay conditions. In an effort to design novel NRP-active anti-TB compounds, we used pyrazinamide as a core and hybridized it with the fragments derived from marketed drugs. One of these designs, compound 8, was a hybrid with fluoroquinolone. This compound exhibited > 10 fold improvement in NRP activity under low pH condition as compared to pyrazinamide and a modest activity (0.8 log(10) kill) under nutritionally starved NRP condition. Furthermore, compound 8 was active against fluoroquinolone-resistant strains and did not show any activity in a DNA supercoiling assay (gyrase inhibition), suggesting that its mechanism of action is not that of the parent fluoroquinolone. These results provide a novel avenue in the exploration of new chemotypes that are active against non-replicating Mtb.