Development of Methionyl-tRNA Synthetase Inhibitors as Antibiotics for Gram-Positive Bacterial Infections

Abstract

Antibiotic-resistant bacteria are widespread and pose a growing threat to human health. New antibiotics acting by novel mechanisms of action are needed to address this challenge. The bacterial methionyl-tRNA synthetase (MetRS) enzyme is essential for protein synthesis, and the type found in Gram-positive bacteria is substantially different from its counterpart found in the mammalian cytoplasm. Both previously published and new selective inhibitors were shown to be highly active against Gram-positive bacteria with MICs of ≤1.3 μg/ml against ,, and strains. Incorporation of radioactive precursors demonstrated that the mechanism of activity was due to the inhibition of protein synthesis. Little activity against Gram-negative bacteria was observed, consistent with the fact that Gram-negative bacterial species contain a different type of MetRS enzyme. The ratio of the MIC to the minimum bactericidal concentration (MBC) was consistent with a bacteriostatic mechanism. The level of protein binding of the compounds was high (>95%), and this translated to a substantial increase in MICs when the compounds were tested in the presence of serum. Despite this, the compounds were very active when they were tested in a murine thigh infection model. Compounds 1717 and 2144, given by oral gavage, resulted in 3- to 4-log decreases in the bacterial load compared to that in vehicle-treated mice, which was comparable to the results observed with the comparator drugs, vancomycin and linezolid. In summary, the research describes MetRS inhibitors with oral bioavailability that represent a class of compounds acting by a novel mechanism with excellent potential for clinical development.

Toward a structome of Acinetobacter baumannii drug targets

“…MetRS is not only crucial for elongation in protein synthesis but also the initiation of all mRNA translation through a tRNA (fMet) aminoacylation. While work on MetRS has yielded successful inhibitors for gram‐positive pathogens, like S. aureus and antibiotic resistant Enterococcus species, little success has been had on gram‐negative bacterial species, due to differences between the two in the MetRS enzyme …”

“…While work on MetRS has yielded successful inhibitors for gram-positive pathogens, like S. aureus and antibiotic resistant Enterococcus species, little success has been had on gram-negative bacterial species, due to differences between the two in the MetRS enzyme. 35 The active site of A. baumannii MetRS contains residue differences compared to the human ortholog which may be used to develop selective inhibitors. For example, Pro256 in A. baumannii MetRS is a threonine in human MetRS which offers different substrate interactions as well as structural rigidity associated (Figure 1).…”

Methionyl-tRNA synthetase inhibitor has potentin vivoactivity in a novelGiardia lamblialuciferase murine infection model

“…26 Chemical synthesis, pharmacokinetics, cytotoxicity, and inhibitory activity of compound 1717 on the wild type G. lamblia WBC6 strain and the Gl MetRS enzyme were previously described. 26, 32, 33 Analysis of 1717 ’s pharmacokinetic profile showed that a single 50 mg/kg oral dose in mice would have sufficient gut and systemic levels to be effective for treatment of mouse giardiasis. 33 The compound is about 8 times more potent than metronidazole, which has an EC 50 of 5 µM.…”

Aminoacyl-tRNA Synthetases as Valuable Targets for Antimicrobial Drug Discovery

“…Despite possessing excellent antibiotic potency, the poor oral bioavailability of REP8839 has restricted its application to the topical treatment of skin infections. Massive efforts have been made by Buckner [ 101 ] et al to further optimize this scaffold to improve its oral bioavailability, pharmacokinetic properties, antibacterial potency, and selectivity versus the human ortholog, thus making better candidates for antibiotic development. The best compounds 1717 and 2144 ( Figure 7 a) were shown to have broad-spectrum antibacterial activities against Gram-positive pathogens Staphylococcus , Enterococcus , and Streptococcus strains and to be highly active against the S. aureus strain ATCC 29213 with MICs of 0.16 and 0.01 μg/mL, respectively.…”