A Leucyl-tRNA Synthetase Inhibitor with Broad-Spectrum Antimycobacterial Activity

Abstract

Global infections by non-tuberculous mycobacteria (NTM) are steadily rising. New drugs are needed to treat NTM infections, but the NTM drug pipeline remains poorly populated and focused on repurposing or reformulating approved antibiotics. We sought to accelerate de novo NTM drug discovery by testing advanced compounds with established activity against Mycobacterium tuberculosis. 3-aminomethyl 4-halogen benzoxaboroles, a novel class of leucyl-tRNA synthetase inhibitors, were recently discovered as active against M. tuberculosis. Here, we report that the benzoxaborole EC/11770 is not only a potent anti-tubercular agent but is active against the M. abscessus and M. avium complexes. Focusing on M. abscessus, which causes the most difficult-to-cure NTM disease, we show that EC/11770 retained potency against drug-tolerant biofilms in vitro and was effective in a mouse lung infection model. Resistant mutant selection experiments showed a low frequency of resistance and confirmed leucyl-tRNA synthetase as the target. This work establishes the benzoxaborole EC/11770 as a novel preclinical candidate for the treatment of NTM lung disease and tuberculosis and validates leucyl-tRNA synthetase as an attractive target for the development of broad-spectrum anti-mycobacterials.

Epetraborole Is Active against Mycobacterium abscessus

“…Recently, we reported that the antituberculosis 4-halogen benzoxaborole EC/11770 ( Fig. 1 ) is active against M. abscessus in vitro and in vivo in a mouse infection model ( 14 ). Here, we asked whether the anti-Gram-negative, nonhalogenated benzoxaborole epetraborole ( Fig.…”

“…We first measured the MIC of this compound against our screening strain M. abscessus subsp. abscessus Bamboo ( 15 ) in Middlebrook 7H9 medium using 96-well plates, as previously described ( 14 ). Surprisingly, epetraborole showed activity similar to that of the antitubercular EC/11770 ( Table 1 ).…”

“…CLR, clarithromycin; EPB, epetraborole. b EC/11770 MIC values are from published literature ( 14 ) and are included for comparison. …”

“…To confirm that epetraborole indeed exerts its antimycobacterial activity by targeting M. abscessus LeuRS, we selected for epetraborole-resistant M. abscessus mutants ( Table 2 ). Adapting our previously described method ( 14 ), M. abscessus ATCC 19977 culture was plated on Middlebrook 7H10 agar containing 16.5 μM epetraborole, the lowest concentration suppressing the emergence of wild-type colonies. After 5 days of incubation, apparent resistant colonies were confirmed by restreaking on epetraborole-containing agar.…”

Current Molecular Therapeutic Agents and Drug Candidates for Mycobacterium abscessus

“…Furthermore, EC/11770 inhibited the growth of the Mab biofilm in vitro model and showed effective in vivo efficacy in the NOD SCID mice lung infection model. Fortunately, EC/11770 showed low-resistant mutant frequency, and leucyl-tRNA synthetase was confirmed as its target ( Ganapathy et al, 2021 ).…”