Mechanism of action of the novel aminomethylcycline antibiotic omadacycline

Abstract

Omadacycline is a novel first-in-class aminomethylcycline with potent activity against important skin and pneumonia pathogens, including community-acquired methicillin-resistant Staphylococcus aureus (MRSA), β-hemolytic streptococci, penicillin-resistant Streptococcus pneumoniae, Haemophilus influenzae, and Legionella. In this work, the mechanism of action for omadacycline was further elucidated using a variety of models. Functional assays demonstrated that omadacycline is active against strains expressing the two main forms of tetracycline resistance (efflux and ribosomal protection). Macromolecular synthesis experiments confirmed that the primary effect of omadacycline is on bacterial protein synthesis, inhibiting protein synthesis with a potency greater than that of tetracycline. Biophysical studies with isolated ribosomes confirmed that the binding site for omadacycline is similar to that for tetracycline. In addition, unlike tetracycline, omadacycline is active in vitro in the presence of the ribosomal protection protein Tet(O).

FIG 1

Chemical structure of omadacycline.

FIG 2

Effect of Tet(O) protein on the protein synthesis activity of omadacycline in vitro. Poly(U)-dependent Poly(Phe) synthesis (in vitro translation) was carried out in the presence or absence of purified Tet(O) added in a 1:1 molar ratio with ribosomes and various concentrations of either omadacycline or tetracycline. Percent activity relative to the control reaction (no omadacycline or tetracycline) is plotted.

FIG 3

Ribosomal binding competition studies with [³H]tetracycline and unlabeled minocycline (A) or omadacycline (B). A series of tubes were prepared containing purified 70S ribosomes and increasing concentrations of the competitor test compound and a fixed concentration (3 μM) of [³H]tetracycline. Data are plotted as the log of the unlabeled competitor concentration in nM versus the percent binding relative to the reaction mixture containing no competitor. IC₅₀ values were calculated by nonlinear curve fitting to a one-site competitive binding model and were determined to be 1.63 ± 0.01 μM (standard error) for minocycline and 1.96 ± 0.01 μM for omadacycline.