Optimization of LpxC Inhibitors for Antibacterial Activity and Cardiovascular Safety.

UDP-3-O-(R-3-hydroxymyristoyl)-N-acetylglucosamine deacetylase (LpxC) is a Zn2+ deacetylase that is essential for the survival of most pathogenic Gram-negative bacteria. ACHN-975 (N-((S)-3-amino-1-(hydroxyamino)-3-methyl-1-oxobutan-2-yl)-4-(((1R,2R)-2-(hydroxymethyl)cyclopropyl)buta-1,3-diyn-1-yl)benzamide) was the first LpxC inhibitor to reach human clinical testing and was discovered to have a dose-limiting cardiovascular toxicity of transient hypotension without compensatory tachycardia. Herein we report the effort beyond ACHN-975 to discover LpxC inhibitors optimized for enzyme potency, antibacterial activity, pharmacokinetics, and cardiovascular safety. Based on its overall profile, compound 26 (LPXC-516, (S)-N-(2-(hydroxyamino)-1-(3-methoxy-1,1-dioxidothietan-3-yl)-2-oxoethyl)-4-(6-hydroxyhexa-1,3-diyn-1-yl)benzamide) was chosen for further development. A phosphate prodrug of 26 was developed that provided a solubility of >30 mg mL-1 for parenteral administration and conversion into the active drug with a t1/2 of approximately two minutes. Unexpectedly, and despite our optimization efforts, the prodrug of 26 still possesses a therapeutic window insufficient to support further clinical development.

A Phase 1 Study of Intravenous Plazomicin in Healthy Adults to Assess Potential Effects on the QT/QTc Interval, Safety, and Pharmacokinetics.

Plazomicin is an aminoglycoside with in vitro activity against multidrug-resistant Enterobacteriaceae. A phase 1, randomized, double-blind, crossover study assessed the potential effects of plazomicin on cardiac repolarization (NCT01514929). Fifty-six healthy adults (24 men, 32 women) received a single therapeutic dose of plazomicin (15 mg/kg administered by 30-minute intravenous infusion), a single supratherapeutic dose of plazomicin (20 mg/kg administered by 30-minute intravenous infusion), placebo, or oral moxifloxacin (400 mg). The primary end point was the baseline-adjusted, placebo-corrected QTc interval using the Fridericia formula (ΔΔQTcF). Assay sensitivity was concluded if the lower limit of a 1-sided 95%CI (adjusted for multiplicity using the Hochberg procedure) for moxifloxacin ΔΔQTcF was >5 milliseconds at ≥1 prespecified time points. No QT prolongation effect for plazomicin was concluded if the largest mean effect was <5 milliseconds, and the upper limit of a 2-sided 90%CI for plazomicin ΔΔQTcF was <10 milliseconds at all time points. Assay sensitivity was demonstrated based on moxifloxacin ΔΔQTcF. No QT prolongation effect for plazomicin was concluded because the largest mean ΔΔQTcF for plazomicin was 3.5 milliseconds, and the highest upper limit was 5.6 milliseconds. No clinically relevant changes were observed in electrocardiograms. For the 15- and 20-mg/kg dose levels of plazomicin, mean peak plasma concentration values were 76.0 and 96.6 mg/L, and mean values of the area under the concentration-time curve over 24 hours were 263 and 327 mg·h/L, respectively. Model-derived pharmacokinetic parameters and safety findings were generally consistent with previously reported plazomicin studies. In conclusion, therapeutic and supratherapeutic doses of plazomicin had no clinically significant effect on cardiac repolarization and were generally well tolerated.

No Effect of Plazomicin on the Pharmacokinetics of Metformin in Healthy Subjects.

Plazomicin is an aminoglycoside that was engineered to overcome aminoglycoside-modifying enzymes, which are the most common aminoglycoside resistance mechanism in Enterobacteriaceae. Because plazomicin is predominantly eliminated via renal pathways, an in vitro study was conducted to determine whether plazomicin inhibits the organic cation transporter 2 (OCT2) and the multidrug and toxin extrusion (MATE1 and MATE2-K) transporters, using metformin as a probe substrate. Plazomicin inhibited OCT2, MATE1, and MATE2-K transporters with half-maximal inhibition of the transporter values of 5120, 1300, and 338 µg/mL, respectively. To determine whether this in vitro inhibition translates in vivo, an open-label, randomized, 2-period, 2-treatment crossover study (NCT03270553) was carried out in healthy subjects (N = 16), who received a single oral dose of metformin 850 mg alone and in combination with a single intravenous infusion of plazomicin 15 mg/kg. Geometric least-squares mean ratios of the test treatment (combination) vs the reference treatment (metformin alone) and 90% confidence intervals were within the equivalence interval of 80% to 125% (peak plasma concentration, 104.5 [95.1-114.9]; area under the plasma concentration-time curve from time zero to time of last quantifiable concentration, 103.7 [93.5-115.0]; area under the plasma concentration-time curve from time zero to infinity, 104.0 [94.2-114.8]). The results demonstrate that there is no clinically significant drug-drug interaction resulting from coadministration of single doses of intravenous plazomicin 15 mg/kg and oral metformin 850 mg in healthy subjects. Coadministration of plazomicin and metformin was well tolerated in healthy subjects.

Biodistribution of the multidentate hydroxypyridinonate ligand [(14) C]-3,4,3-LI(1,2-HOPO), a potent actinide decorporation agent.

The pharmacokinetics and biodistribution of the (14) C-labeled actinide decorporation agent 3,4,3-LI(1,2-HOPO) were investigated in young adult Swiss Webster mice and Sprague Dawley rats, after intravenous, intraperitoneal, and oral dose administration. In all routes investigated, the radiolabeled compound was rapidly distributed to various tissues and organs of the body. In mice, the 24 h fecal elimination profiles suggested that the biliary route is the predominant route of elimination. In contrast, lower fecal excretion levels were observed in rats. Tissue uptake and retention of the compound did not differ significantly between sexes although some differences were observed in the excretion patterns over time. The male mice eliminated a greater percentage of (14) C through the renal pathway than the female mice after receiving an intravenous or intraperitoneal dose, while the opposite trend was seen in rats that received an intravenous dose. Metabolite profiling performed on selected rat samples demonstrated that a putative major metabolite of [(14) C]-3,4,3-LI(1,2-HOPO) is formed, accounting for approximately 10% of an administered oral dose. Finally, to improve its oral bioavailability, 3,4,3-LI(1,2-HOPO) was coformulated with a proprietary permeability enhancer, leading to a notable increase in oral bioavailability of the compound.

Hydroxypyridinonate complex stability of group (IV) metals and tetravalent f-block elements: the key to the next generation of chelating agents for radiopharmaceuticals.

The solution thermodynamics of the water-soluble complexes formed between 3,4,3-LI(1,2-HOPO) and Zr(IV) or Pu(IV) were investigated to establish the metal coordination properties of this octadentate chelating agent. Stability constants log ß110 = 43.1 ± 0.6 and 43.5 ± 0.7 were determined for [Zr(IV)(3,4,3-LI(1,2-HOPO))] and [Pu(IV)(3,4,3-LI(1,2-HOPO))], respectively, by spectrophotometric competition titrations against Ce(IV). Such high thermodynamic stabilities not only confirm the unparalleled Pu(IV) affinity of 3,4,3-LI(1,2-HOPO) as a decorporation agent but also corroborate the great potential of hydroxypyridinonate ligands as new (89)Zr-chelating platforms for immuno-PET applications. These experimental values are in excellent agreement with previous estimates and are discussed with respect to ionic radius and electronic configuration, in comparison with those of Ce(IV) and Th(IV). Furthermore, a liquid chromatography assay combined with mass spectrometric detection was developed to probe the separation of the neutral [M(IV)(3,4,3-LI(1,2-HOPO))] complex species (M = Zr, Ce, Th, and Pu), providing additional insight into the coordination differences between group IV and tetravalent f-block metals and on the role of d and f orbitals in bonding interactions.

In vitro metabolism and stability of the actinide chelating agent 3,4,3-LI(1,2-HOPO).

The hydroxypyridinonate ligand 3,4,3-LI(1,2-HOPO) is currently under development for radionuclide chelation therapy. The preclinical characterization of this highly promising ligand comprised the evaluation of its in vitro properties, including microsomal, plasma, and gastrointestinal fluid stability, cytochrome P450 inhibition, plasma protein binding, and intestinal absorption using the Caco-2 cell line. When mixed with active human liver microsomes, no loss of parent compound was observed after 60 min, indicating compound stability in the presence of liver microsomal P450. At the tested concentrations, 3,4,3-LI(1,2-HOPO) did not significantly influence the activities of any of the cytochromal isoforms screened. Thus, 3,4,3-LI(1,2-HOPO) is unlikely to cause drug-drug interactions by inhibiting the metabolic clearance of coadministered drugs metabolized by these enzymes. Plasma protein-binding assays revealed that the compound is protein-bound in dogs and less extensively in rats and humans. In the plasma stability study, the compound was stable after 1 h at 37°C in mouse, rat, dog, and human plasma samples. Finally, a bidirectional permeability assay demonstrated that 3,4,3-LI(1,2-HOPO) is not permeable across the Caco-2 monolayer, highlighting the need to further evaluate the effects of various compounds with known permeability enhancement properties on the permeability of the ligand in future studies.

(238)Pu elimination profiles after delayed treatment with 3,4,3LI(1,2HOPO) in female and male Swiss-Webster mice.

PURPOSE: To characterize the dose-dependent and sex-related efficacy of the hydroxypyridinonate decorporation agent 3,4,3-LI(1,2-HOPO) at enhancing plutonium elimination when post-exposure treatment is delayed. MATERIALS AND METHODS: Six parenteral dose levels of 3,4,3-LI(1,2-HOPO) from 1-300 µmol/kg were evaluated for decorporating plutonium in female and male Swiss-Webster mice administered a soluble citrate complex of (238)Pu and treated 24 hours later. Necropsies were scheduled at four time-points (2, 4, 8, and 15 days post-contamination) for the female groups and at three time-points (2, 4, and 8 days post-contamination) for the male groups. RESULTS: Elimination enhancement was dose-dependent in the 1-100 µmol/kg dose range at all necropsy time-points, with some significant reductions in full body and tissue content for both female and male animals. The highest dose level resulted in slight toxicity, with a short recovery period, which delayed excretion of the radionuclide. CONCLUSIONS: While differences were noted between the female and male cohorts in efficacy range and recovery times, all groups displayed sustained dose-dependent (238)Pu elimination enhancement after delayed parenteral treatment with 3,4,3-LI(1,2-HOPO), the actinide decorporation agent under development.

Inhibitory effect of oxygenated cholestan-3ß-ol derivatives on the growth of Mycobacterium tuberculosis.

A variety of cholestan-3ß-ol derivatives, which are oxygenated at different positions of the steroid ring system, were prepared and tested for their inhibition of the Mycobacterium tuberculosis H37Rv strain. Several compounds showed significant antitubercular activities with MIC90 values in the range 4-8 µM and low or non-detectable toxicity against mammalian cells.