New active leads for tuberculosis booster drugs by structure-based drug discovery

The transcriptional regulator EthR from Mycobacterium tuberculosis, a member of the TetR family of prokaryotic homo-dimeric transcriptions factors, controls the expression of the mycobacterial mono-oxygenase EthA. Due to the fact that EthA is responsible for the bio-activation of the second-line tuberculosis pro-drug ethionamide, EthR inhibitors have been shown to boost drug efficacy by increasing EthA levels. Here, we present a comprehensive in-silico structure-based screening protocol that led to the identification of a number of novel scaffolds of EthR inhibitors. We present biophysical characterization of 85 potential leads, 20 of which showed binding by thermal shift assays. The co-crystal structures of EthR with four new ligands at resolution ranging from 2.1 to 1.4 Å confirm the binding and inactivation mode. The crystal structures include ligands with three new chemical scaffolds that will enable future lead development. Five of the lead compounds showed the desired booster effect with the most promising displaying an EC50 value of 0.76 μM.