Discovery of substituted benzyloxy-benzylamine inhibitors of acetyltransferase Eis and their anti-mycobacterial activity

A clinically significant mechanism of tuberculosis resistance to the aminoglycoside kanamycin (KAN) is its acetylation catalyzed by upregulated Mycobacterium tuberculosis (Mtb) acetyltransferase Eis. In search for in-hibitors of Eis, we discovered an inhibitor with a substituted benzyloxy-benzylamine scaffold. A structure -activity relationship study of 38 compounds in this structural family yielded highly potent (IC50 similar to 1 mu M) Eis inhibitors, which did not inhibit other acetyltransferases. Crystal structures of Eis in complexes with three of the inhibitors showed that the inhibitors were bound in the aminoglycoside binding site of Eis, consistent with the competitive mode of inhibition, as established by kinetics measurements. When tested in Mtb cultures, two in-hibitors (47 and 55) completely abolished resistance to KAN of the highly KAN-resistant strain Mtb mc(2) 6230 K2O4, likely due to Eis inhibition as a major mechanism. Thirteen of the compounds were toxic even in the absence of KAN to Mtb and other mycobacteria, but not to non-mycobacteria or to mammalian cells. This, yet unidentified mechanism of toxicity, distinct from Eis inhibition, will merit future studies along with further development of these molecules as anti-mycobacterial agents.

Automated summary

Eis acetyltransferase is a clinically significant mechanism of tuberculosis resistance to kanamycin. Inhibitors of Eis have been discovered, which can effectively abolish resistance to kanamycin in highly resistant strains. Additionally, several compounds with toxic effects on mycobacteria have been identified, with a mechanism of toxicity distinct from Eis inhibition.