Human serum binding and its effect on the pharmacodynamics of the lantibiotic MU1140.

The degree of MU1140 binding to human serum was measured and the effect of serum on MU1140 pharmacodynamics against Streptococcus pneumoniae and Staphylococcus aureus was investigated. 92.7% ± 2.0% of total MU1140 was bound to serum components as determined by ultrafiltration when tested in the concentration range 6.25-200 µg/ml. MIC and time-kill studies were used to study the effect of serum on the dynamics of MU1140. Serum inhibited MU1140 activity against S. pneumoniae but was found to enhance its activity against S. aureus. This phenomenon has not been reported for any other lantibiotic. Time-kill studies of MU1140 against S. aureus in various concentrations of serum revealed that the greatest bactericidal effect was observed at the lowest serum concentration. Mathematical modeling was used to quantify serum augmentation of MU1140 activity against S. aureus. Serum, at the lowest concentration, was shown to decrease MU1140 EC(50) against S. aureus by an order of magnitude. The data suggests that unbound MU1140 comprise the pharmacologically active fraction. Further, these findings suggest the possible existence of a complex dual inhibition and augmentation effect of serum on MU1140's activity against S. aureus. The molecular mechanism responsible for the synergistic action of human serum on MU1140's activity against S. aureus remains to be elucidated.

Pharmacokinetic and pharmacodynamic evaluation of the lantibiotic MU1140.

Presented are the pharmacokinetics (PK), exposure-response relationship, and the PK/pharmacodynamic (PD) index predictive of maximum therapeutic efficacy for the lantibiotic MU1140. MU1140, at a dose of 12.5 or 25 mg/kg, was administered intravenously, to characterize its PK parameters in rat. The recently developed in vitro PD model of MU1140 activity was enhanced by incorporation of the PK of MU1140 in rat. The linked PK/PD model was used in a simulation study to determine the PK/PD index predictive of in vivo efficacy. MU1140 total plasma concentration-time profiles declined biexponentially with elimination terminal half-life of 1.6 +/- 0.1 h. Rapid injection of MU1140 was associated with a hypersensitivity reaction that can be blocked by premedication with diphenhydramine. The simulation study revealed that Staphylococcus aureus concentrations correlated with T > MIC making it the PK/PD index best predictive of efficacy. Collectively, these findings suggest that the best route of administration of MU1140 is slow infusion which will increase the time its concentration remains above the MIC, thus maximizing the therapeutic effect and minimizing the observed toxicity.

Development and validation of a LC-MS quantification method for the lantibiotic MU1140 in rat plasma.

This study reports the first ever development and validation of a quantification method for a lantibiotic in plasma. This method was developed for the quantification of total MU1140 in Sprague Dawley rat plasma. The procedure involved acidification of plasma samples with formic acid followed by precipitation of plasma proteins using isopropanol, filtration, and analysis by RPLC-MS. The lantibiotic gallidermin was used as an internal standard (ISTD). The analyte and ISTD were eluted using a gradient of isopropanol and water, both acidified with 0.3% formic acid (v/v), at a flow rate of 250 microl/min. Positive electrospray ionization was utilized at the ion source and the analyte and ISTD were both detected by selected-ion monitoring (SIM). Total run time was 15 min. This method was validated for selectivity, sensitivity, linearity, recovery, accuracy, and precision. The method was shown to be selective, with a quantitative linear range of 0.39-100 microg/ml using 25 microl samples. The bias, intra- and inter-day percent relative standard deviation at all concentrations tested was lower than 15%. MU1140 mean extraction recovery was 96.1%. The analyte was shown to be stable to freeze/thaw and for short- and long-term storage. Extracted MU1140 was stable at 4 degrees C for over 5 days. This method was successfully applied to a preliminary pharmacokinetic study of intravenously administered MU1140 in Sprague Dawley rats. Overall, this method was shown to be applicable for quantification of MU1140 in plasma samples for the purpose of further MU1140 ADME or bioequivalence studies.

Pharmacodynamic activity of the lantibiotic MU1140.

This study evaluated the pharmacodynamics of the lantibiotic MU1140 and the ability of selected organisms to develop resistance to this antibiotic. MU1140 demonstrated activity against all Gram-positive organisms tested, including oxacillin- and vancomycin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecalis (VREF). No activity was observed against Gram-negative bacteria or yeast. Time-kill studies revealed that MU1140 was rapidly bactericidal against Streptococcus pneumoniae and multidrug-resistant S. aureus, whilst it was bacteriostatic against VREF. In vitro resistance development to MU1140, tested by sequential subculturing in subinhibitory concentrations of MU1140, revealed a stable threefold increase in the minimum inhibitory concentration (MIC) for S. aureus and S. pneumoniae. Subsequent subculturing of the strains with elevated MICs in antibiotic-free media for 7 days did not result in a reduction of their MIC values for MU1140. Collectively, our findings illustrate the therapeutic potential of MU1140 for management of Gram-positive infections.