Epetraborole, a leucyl-tRNA synthetase inhibitor, demonstrates murine efficacy, enhancing the in vivo activity of ceftazidime against Burkholderia pseudomallei, the causative agent of melioidosis

by Jason E. Cummings, Christopher S. Lunde, M. R. K. Alley, Richard A. Slayden

Burkholderia pseudomallei is the causative agent of melioidosis, which is increasingly being reported worldwide. Mortality rates as high as 40% have been reported based on clinical patient outcomes in the endemic areas of Australia and Thailand. Novel therapies are needed to reduce treatment duration and adverse effects and improve treatment outcomes. Epetraborole, a novel antibiotic, targets leucyl-tRNA synthetase (LeuRS), an essential enzyme that catalyzes the attachment of leucine to transfer RNA. Epetraborole was evaluated for in vitro activity and efficacy in a murine model to assess clinical relevance against Burkholderia pseudomallei infections for possible treatment of melioidosis. Epetraborole was tested against 13 clinically derived and three reference B. pseudomallei strains that have a broad spectrum of susceptibilities to the standard-of-care (SoC) drugs for melioidosis, which showed that epetraborole exhibited minimal inhibitory concentrations of 0.5–4 μg/mL. Ex vivo studies using THP-1 macrophages confirmed the potency of epetraborole and demonstrated synergy between epetraborole and ceftazidime. In the acute pulmonary murine infection model of melioidosis, epetraborole demonstrated equivalent efficacy when delivered orally or subcutaneously, which compared well with the standard-of-care drug ceftazidime. In addition, adding epetraborole to ceftazidime significantly improved antimicrobial activity in this animal model. This work warrants further exploration of epetraborole as a candidate for treating melioidosis and substantiates LeuRS as a clinically relevant drug target in B. pseudomallei.