New Insights into the Mechanism of Action of the Thienopyrimidine Antitubercular Prodrug TP053

The thienopyrimidine TP053 is an antitubercular prodrug
active
against both replicating and nonreplicating Mycobacterium
tuberculosis (M. tuberculosis) cells,
which requires activation by the mycothiol-dependent nitroreductase
Mrx2. The investigation of the mechanism of action of TP053 revealed
that Mrx2 releases nitric oxide from this drug both in the enzyme
assays with purified Mrx2 and in mycobacterial cultures, which can
explain its activity against nonreplicating bacilli, similar to pretomanid
activated by the nitroreductase Ddn. In addition, we identified a
highly reactive metabolite, 2-(4-mercapto-6-(methylamino)-2-phenylpyrimidin-5-yl)­ethan-1-ol,
which can contribute to the antimycobacterial effects on replicating
cells as well as on nonreplicating cells. In summary, we explain the
mechanism of action of TP053 on both replicating and nonreplicating M. tuberculosis and report a novel activity for Mrx2,
which in addition to Ddn, represents another example of nitroreductase
releasing nitric oxide from its substrate. These findings are particularly
relevant in the context of drugs targeting nonreplicating M. tuberculosis, which is shown to be killed by increased
levels of nitric oxide.