Efficacy of a Novel Tricyclic Topoisomerase Inhibitor in a Murine Model of Neisseria gonorrhoeae Infection.

There is an urgent need for new antibiotics to treat multidrug-resistant Neisseria gonorrhoeae In this report, the microbiology, in vivo pharmacokinetics, and efficacy of REDX05931, a representative novel tricyclic topoisomerase inhibitor, were evaluated. REDX05931 demonstrated high oral bioavailability in mice and reduced N. gonorrhoeae infection after a single dose in a mouse model of gonorrhea. These data support the potential of this series of small molecules as a new treatment for drug-resistant gonorrheal infections.

Biological profiling of novel tricyclic inhibitors of bacterial DNA gyrase and topoisomerase IV.

OBJECTIVES: The objective of this study was to characterize the in vitro and in vivo biological properties of a novel series of small-molecule bacterial type IIA topoisomerase inhibitors. METHODS: Bacterial susceptibility testing was performed by broth microdilution. Resistance frequencies were determined by plating bacteria onto agar containing test compound and enumerating mutants. Bacteria were passaged using subinhibitory concentrations of antibacterials to generate resistance. Target enzyme inhibition was determined by exposure to antibacterials and DNA; topoisomers were visualized by gel electrophoresis. Oral and intravenous pharmacokinetic profiles were determined in mice. In vivo efficacy was determined using a mouse model of septicaemia and thigh infection with MSSA and MRSA, respectively. RESULTS: Representative compounds REDX04139, REDX05604 and REDX05931 demonstrated in vitro potency against a range of Gram-positive and fastidious Gram-negative pathogens. Clinical isolate testing revealed REDX04139 and REDX05931 had MIC90 values of 0.25 and 0.5 mg/L, respectively, for MRSA and MIC90 values of 2 mg/L for streptococci. REDX04139 was bactericidal in vitro against Staphylococcus aureus at 8× MIC over 6 h. Pharmacokinetic profiling of REDX04139 and REDX05604 in mice revealed low clearance and excellent bioavailability (≥71%). REDX04139 provided 100% survival against S. aureus in a mouse septicaemia model, while REDX05604 reduced bacterial load by up to 3.7 log units in the MRSA mouse thigh infection model. CONCLUSIONS: Redx Pharma has discovered a novel series of topoisomerase inhibitors that are being further developed for drug-resistant bacteria.

The binding of drugs to hepatocytes and its relationship to physicochemical properties.

The binding of 17 drugs to rat hepatocytes has been determined using equilibrium dialysis in combination with metabolic inhibitors and a kinetic model for the binding and dialysis processes. Metabolic inhibitors were used to retard the main routes of metabolism such that the half-life for turnover of the drugs was comparable to or greater than the time scale of the equilibrium dialysis process. Further experiments were carried out to determine the kinetics of diffusion of the compounds across the dialysis membrane and the observed extent of binding to hepatocytes. Knowledge of the rate of metabolism of the drugs in the presence of the inhibitors, the kinetics of the dialysis process, and the observed extent of binding was then used with a kinetic model of the system to give true free fractions of the drugs in live hepatocytes. Further studies show that, for this set of compounds, there is no significant difference in the extent of binding to live or dead hepatocytes. The extent of hepatocyte binding is correlated with lipophilicity, and the best model for binding uses log P for basic compounds and log D(7.4) for acidic and neutral compounds. Hepatocyte binding is also demonstrated to be highly correlated with microsome binding.