The new tuberculosis drug Perchlozone® shows cross-resistance with thiacetazone

Perchlozone® (PCZ), a new thiosemicarbazone developed by JSC Pharmasyntez (Moscow, Russia) for the treatment of tuberculosis (TB), was approved for use against multidrug-resistant disease in Russia in 2012. The mechanism of action of the drug is unknown. A well-studied thiosemicarbazone is the old TB drug thiacetazone (TAC). It has a narrow spectrum and inhibits the FASII dehydratase complex HadABC, which is involved in cell wall biosynthesis in Mycobacterium tuberculosis. TAC is a prodrug, requiring activation by the monooxygenase EthA. In this study, a comparative in vitro analysis of both drugs was performed. The two compounds had an identical spectrum of activity, spontaneous resistant mutants showed cross-resistance, and resistance was mapped to HadABC and EthA. These results suggest that PCZ, like TAC, is a prodrug and that both drugs share EthA as an activating enzyme and HadABC as their principal target.