Exploring the Pharmacokinetic/Pharmacodynamic Relationship of Relebactam (MK-7655) in Combination with Imipenem in a Hollow-Fiber Infection Model.

Resistance to antibiotics among bacterial pathogens is rapidly spreading, and therapeutic options against multidrug-resistant bacteria are limited. There is an urgent need for new drugs, especially those that can circumvent the broad array of resistance pathways that bacteria have evolved. In this study, we assessed the pharmacokinetic/pharmacodynamic relationship of the novel ß-lactamase inhibitor relebactam (REL; MK-7655) in a hollow-fiber infection model. REL is intended for use with the carbapenem ß-lactam antibiotic imipenem for the treatment of Gram-negative bacterial infections. In this study, we used an in vitro hollow-fiber infection model to confirm the efficacy of human exposures associated with the phase 2 doses (imipenem at 500 mg plus REL at 125 or 250 mg administered intravenously every 6 h as a 30-min infusion) against imipenem-resistant strains of Pseudomonas aeruginosa and Klebsiella pneumoniae Dose fractionation experiments confirmed that the pharmacokinetic parameter that best correlated with REL activity is the area under the concentration-time curve, consistent with findings in a murine pharmacokinetic/pharmacodynamic model. Determination of the pharmacokinetic/pharmacodynamic relationship between ß-lactam antibiotics and ß-lactamase inhibitors is complex, as there is an interdependence between their respective exposure-response relationships. Here, we show that this interdependence could be captured by treating the MIC of imipenem as dynamic: it changes with time, and this change is directly related to REL levels. For the strains tested, the percentage of the dosing interval time that the concentration remains above the dynamic MIC for imipenem was maintained at the carbapenem target of 30 to 40%, required for maximum efficacy, for imipenem at 500 mg plus REL at 250 mg.

Benzimidazole analogs as WTA biosynthesis inhibitors targeting methicillin resistant Staphylococcus aureus.

A series of benzimidazole analogs have been synthesized to improve the profile of the previous lead compounds tarocin B and 1. The syntheses, structure-activity relationships, and selected biochemical data of these analogs are described. The optimization efforts allowed the identification of 21, a fluoro-substituted benzimidazole, exhibiting potent TarO inhibitory activity and typical profile for a wall teichoic acid (WTA) biosynthesis inhibitor. Compound 21 displayed a potent synergistic and bactericidal effect in combination with imipenem against diverse methicillin-resistant Staphylococci.

MK-7128, a novel CB1 receptor inverse agonist, improves scopolamine-induced learning and memory deficits in mice.

Cannabinoid receptors (CBRs) play an important role in a variety of physiological functions and have been considered drug targets for obesity and psychiatric disorders. In particular, the CB1R is highly expressed in brain regions crucial to learning and memory processes, and several lines of evidence indicate that pharmacological blockade of this receptor could have therapeutic applications in the treatment of cognitive disorders. In this study, we investigated whether MK-7128 (0.1, 0.3, and 1 mg/kg, orally), a novel and selective CB1R inverse agonist, could improve learning and memory deficits induced by scopolamine (1 mg/kg, subcutaneously) in mice. The investigators also assessed CB1R occupancy in the brain to ensure target engagement of MK-7128, and showed that MK-7128 significantly improved both Y-maze spontaneous alternation and object habituation performance in scopolamine-treated mice and inhibits the binding of radioiodinated AM251 in murine cortex and hippocampus. These data indicate that MK-7128 improves cognitive performance in a model of cholinergic hypofunction and suggest that efficacy is achieved at relatively low levels of CB1R occupancy in the brain. Our results extend earlier findings suggesting a role of CB1Rs in the modulation of memory processes and a potential therapeutic application for CB1R inverse agonists in cognitive disorders.

Synthesis and evaluation of N-[(1S,2S)-3-(4-chlorophenyl)-2-(3-cyanophenyl)-1-methylpropyl]-2-methyl-2-aminopropanamide as human cannabinoid-1 receptor (CB1R) inverse agonists.

Obesity is a chronic medical condition that is affecting large population throughout the world. CB1 as a target for treatment of obesity has been under intensive studies. Taranabant was discovered and then developed by Merck as the 1st generation CB1R inverse agonist. Reported here is part of our effort on the 2nd generation of CB1R inverse agonist from the acyclic amide scaffold. We replaced the oxygen linker in taranabant with nitrogen and prepared a series of amino heterocyclic analogs through a divergent synthesis. Although in general, the amine linker gave reduced binding affinity, potent and selective CB1R inverse agonist was identified from the amino heterocycle series. Molecular modeling was applied to study the binding of the amino heterocycle series at CB1 binding site. The in vitro metabolism of representative members was studied and only trace glucuronidation was found. Thus, it suggests that the right hand side of the molecule may not be the appropriate site for glucuronidation.

Pharmacological evaluation of LH-21, a newly discovered molecule that binds to cannabinoid CB1 receptor.

LH-21 (5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-3-hexyl-1H-1,2,4-triazole) was previously reported as a neutral antagonist at the cannabinoid CB1 receptor which, despite its reported poor ability to penetrate into the brain, suppressed food intake and body weight in rats by intraperitoneal administration. In the present study, we studied the mechanism of action of LH-21 by characterizing its in vitro pharmacological properties and in vivo efficacy. LH-21 inhibited the binding of [3H]CP55940 to cloned human and rat CB1 receptors with IC50 values of 631+/-98 nM, and 690+/-41 nM, respectively, and acted as an inverse agonist in a cAMP functional assay using cultured cells expressing human, rat or mouse CB1 receptor. The compound was shown to be brain-penetrant in rats by intravenous administration. Importantly, a single dose of LH-21 (60 mg/kg, i.p.) caused a similar suppression of overnight food intake and body weight gain in wild-type and CB1 receptor knockout mice. Our results suggest that LH-21 is a low affinity inverse agonist for the CB1 receptor and does not act on the CB1 receptor to inhibit food intake in mice.

Effects of mutations at conserved TM II residues on ligand binding and activation of mouse 5-HT6 receptor.

An aspartate residue (Asp-72) in the transmembrane helix II of mouse 5-hydroxytryptamine-6 receptor (5-HT6) is conserved among most G protein-coupled receptors. We have examined the functional significance of this residue by site-directed mutagenesis. A single Asp --> Ala (D72A) mutation resulted in an 8-fold decrease in apparent affinity for 5-HT, and a 60-fold reduction in EC50 value of agonist-induced stimulation of adenylyl cyclase. A F69L/T70I/D72A triple mutant showed a 2-fold reduction in apparent affinity for 5-HT but complete loss of adenylyl cyclase stimulation. Binding of SB-258585 (4-iodo-N-[4-methoxy-3-(4-methylpiperazin-1-yl)phenyl]benzene-sulfonamide), a selective 5-HT6 antagonist, was mildly affected (2- to 4-fold decrease in affinity) in the two mutants. Our data suggest that Asp-72 and additional residues toward the intracellular side of TM II have a limited role in ligand binding but are critical for functional activation of the 5-HT6 receptor.

1-Sulfonyl-4-acylpiperazines as selective cannabinoid-1 receptor (CB1R) inverse agonists for the treatment of obesity.

A novel series of 1-sulfonyl-4-acylpiperazines as selective cannabinoid-1 receptor (CB1R) inverse agonists was discovered through high throughput screening (HTS) and medicinal chemistry lead optimization. Potency and in vivo properties were systematically optimized to afford orally bioavailable, highly efficacious, and selective CB1R inverse agonists that caused food intake suppression and body weight reduction in diet-induced obese rats and dogs. It was found that the receptor binding assay predicted in vivo efficacy better than functional antagonist/inverse agonist activities. This observation expedited the structure-activity relationship (SAR) analysis and may have implications beyond the series of compounds presented herein.

Antiobesity efficacy of a novel cannabinoid-1 receptor inverse agonist, N-[(1S,2S)-3-(4-chlorophenyl)-2-(3-cyanophenyl)-1-methylpropyl]-2-methyl-2-[[5-(trifluoromethyl)pyridin-2-yl]oxy]propanamide (MK-0364), in rodents.

The cannabinoid-1 receptor (CB1R) has been implicated in the control of energy balance. To explore the pharmacological utility of CB1R inhibition for the treatment of obesity, we evaluated the efficacy of N-[(1S,2S)-3-(4-chlorophenyl)-2-(3-cyanophenyl)-1-methylpropyl]-2-methyl-2-[[5-(trifluoromethyl)pyridin-2-yl]oxy]propanamide (MK-0364) and determined the relationship between efficacy and brain CB1R occupancy in rodents. MK-0364 was shown to be a highly potent CB1R inverse agonist that inhibited the binding and functional activity of various agonists with a binding K(i) of 0.13 nM for the human CB1R in vitro. MK-0364 dose-dependently inhibited food intake and weight gain, with an acute minimum effective dose of 1 mg/kg in diet-induced obese (DIO) rats. CB1R mechanism-based effect was demonstrated for MK-0364 by its lack of efficacy in CB1R-deficient mice. Chronic treatment of DIO rats with MK-0364 dose-dependently led to significant weight loss with a minimum effective dose of 0.3 mg/kg (p.o.), or a plasma C(max) of 87 nM. Weight loss was accompanied by the loss of fat mass. Partial occupancy (30-40%) of brain CB1R by MK-0364 was sufficient to reduce body weight. The magnitude of weight loss was correlated with brain CB1R occupancy. The partial receptor occupancy requirement for efficacy was also consistent with the reduced food intake of the heterozygous mice carrying one disrupted allele of CB1R gene compared with the wild-type mice. These studies demonstrated that MK-0364 is a highly potent and selective CB1R inverse agonist and that it is orally active in rodent models of obesity.