Discovery of Novel Oral Protein Synthesis Inhibitors of Mycobacterium tuberculosis That Target Leucyl-tRNA Synthetase

Abstract

The recent development and spread of extensively drug-resistant and totally drug-resistant resistant (TDR) strains of Mycobacterium tuberculosis highlight the need for new antitubercular drugs. Protein synthesis inhibitors have played an important role in the treatment of tuberculosis (TB) starting with the inclusion of streptomycin in the first combination therapies. Although parenteral aminoglycosides are a key component of therapy for multidrug-resistant TB, the oxazolidinone linezolid is the only orally available protein synthesis inhibitor that is effective against TB. Here, we show that small-molecule inhibitors of aminoacyl-tRNA synthetases (AARSs), which are known to be excellent antibacterial protein synthesis targets, are orally bioavailable and effective against M. tuberculosis in TB mouse infection models. We applied the oxaborole tRNA-trapping (OBORT) mechanism, which was first developed to target fungal cytoplasmic leucyl-tRNA synthetase (LeuRS), to M. tuberculosis LeuRS. X-ray crystallography was used to guide the design of LeuRS inhibitors that have good biochemical potency and excellent whole-cell activity against M. tuberculosis. Importantly, their good oral bioavailability translates into in vivo efficacy in both the acute and chronic mouse models of TB with potency comparable to that of the frontline drug isoniazid.

Targeting Toxoplasma gondii CPSF 3 as a new approach to control toxoplasmosis

“…Human foreskin fibroblasts (HFFs) were infected with tachyzoites of the virulent RH strain and treated with benzoxaboroles, pyrimethamine, the standard of care to treat toxoplasmosis, or vehicle (DMSO). We screened a group of 20 representative benzoxaboroles that were previously shown to have activity against bacteria, fungi or other eukaryotic parasites (Rock et al , ; Xia et al , ; Hernandez et al , ; Zhang et al , ; Palencia et al , ). Some of these compounds were known to target leucyl‐tRNA synthetase (LeuRS).…”

“…Notably, Kerydin is an FDA‐approved benzoxaborole that inhibits fungal leucyl‐tRNA synthetase (LeuRS) and is used for the treatment of onychomycosis. Related compounds are being developed as LeuRS inhibitors of other human pathogens (Hernandez et al , ; Palencia et al , ,b). Other benzoxaboroles inhibit phosphodiesterase‐4 (Freund et al , ), Rho kinase (Akama et al , ) and bacterial β‐lactamases (Xia et al , ).…”

Roles of aminoacyl-tRNA synthetases in immune regulation and immune diseases

“…Besides their antiparasitic effects, ARS inhibitors also played an important role in the antibacterial and antifungal processes [45][46][47][48] . By evaluating the inhibitory effect of a series of 3-aminomethyl 4-halogen benzoxaboroles on Mtb leucyl-tRNA synthetase (LeuRS), Li et al 49 found that one of the compounds, GSK656, was highly selective for Mtb LeuRS and had good antitubercular activity and tolerability in the mid-nanomolar range.…”

A continuous assay for monitoring the synthetic and proofreading activities of multiple aminoacyl-tRNA synthetases for high-throughput drug discovery

“…AN2690 inactivates the enzyme by reacting with the vicinal diol at the 3′ end of the tRNA to form a covalent adduct that is irreversibly bound to the enzyme [12]. The success of this latter compound prompted development of similar drugs using a benzoxaborole core (containing an RNA-reactive boronic acid group) to target the LeuRS from M. tuberculosis and Pseudomonas aeruginosa , as well as other parasites such as Cryptosporidium and Toxoplasma [13-15]. …”