ABSTRACT
HZ-166 has previously been characterized as an α2,3-selective GABAA receptor modulator with anticonvulsant, anxiolytic, and anti-nociceptive properties but reduced motor effects. We discovered a series of ester bioisosteres with reduced metabolic liabilities, leading to improved efficacy as anxiolytic-like compounds in rats. In the present study, we evaluated the anticonvulsant effects KRM-II-81 across several rodent models. In some models we also evaluated key structural analogs. KRM-II-81 suppressed hyper-excitation in a network of cultured cortical neurons without affecting the basal neuronal activity. KRM-II-81 was active against electroshock-induced convulsions in mice, pentylenetetrazole (PTZ)-induced convulsions in rats, elevations in PTZ-seizure thresholds, and amygdala-kindled seizures in rats with efficacies greater than that of diazepam. KRM-II-81 was also active in the 6â¯Hz seizure model in mice. Structural analogs of KRM-II-81 but not the ester, HZ-166, were active in all models in which they were evaluated. We further evaluated KRM-II-81 in human cortical epileptic tissue where it was found to significantly-attenuate picrotoxin- and AP-4-induced increases in firing rate across an electrode array. These molecules generally had a wider margin of separation in potencies to produce anticonvulsant effects vs. motor impairment on an inverted screen test than did diazepam. Ester bioisosters of HZ-166 are thus presented as novel agents for the potential treatment of epilepsy acting via selective positive allosteric amplification of GABAA signaling through α2/α3-containing GABA receptors. The in vivo data from the present study can serve as a guide to dosing parameters that predict engagement of central GABAA receptors.
Subject(s)
Anticonvulsants/pharmacology , GABA-A Receptor Agonists/pharmacology , Oxazoles/pharmacology , Seizures/drug therapy , Action Potentials/drug effects , Animals , Anticonvulsants/chemistry , Anticonvulsants/pharmacokinetics , Benzodiazepines/chemistry , Benzodiazepines/pharmacokinetics , Benzodiazepines/pharmacology , Biological Availability , Child , Diazepam/pharmacology , Disease Models, Animal , Drug Resistant Epilepsy/drug therapy , Drug Resistant Epilepsy/physiopathology , Female , GABA-A Receptor Agonists/chemistry , GABA-A Receptor Agonists/pharmacokinetics , Humans , Imidazoles/chemistry , Imidazoles/pharmacokinetics , Imidazoles/pharmacology , Male , Mice , Oxazoles/chemistry , Oxazoles/pharmacokinetics , Random Allocation , Rats, Sprague-Dawley , Seizures/physiopathology , Tissue Culture TechniquesABSTRACT
Assessment of the pharmacokinetics of [14C]2-[3-[3-[(5-ethyl-4'-fluoro-2-hydroxy[1,1'-biphenyl]-4-yl)oxy]propoxy]-2-propylphenoxy-]benzoic acid ([14C]LY293111), an experimental anti-cancer agent, suggested long-lived circulating metabolites in rats. In vivo metabolites of LY293111 were examined in plasma, bile, urine, and feces of Fischer 344 (F344) rats after oral administration of [14C]LY293111. Metabolites were profiled by high-performance liquid chromatography-radiochromatography, and identified by liquid chromatography (LC)/mass spectrometry and LC/NMR. The major in vivo metabolites of LY293111 identified in rats were phenolic (ether), acyl, and bisglucuronides of LY293111. Measurement of radioactivity in rat plasma confirmed that a fraction of LY293111-derived material was irreversibly bound to plasma protein and that this bound fraction increased over time. This was consistent with the observed disparity in half-lives between LY293111 and total radioactivity in rats and monkeys, and is likely due to covalent modification of proteins by the acyl glucuronide. In vitro metabolism of [14C]LY293111 in liver slices from CD-1 mice, F344 rats, rhesus and cynomolgus monkeys, and humans indicates that glucuronidation was the primary metabolic pathway in all species. The acyl glucuronide was the most prevalent radioactive peak (16% of total 14C) produced by F344 rat slices, whereas the ether glucuronide was the major metabolite in all other species (26-36% of total 14C). Several minor hydroxylated metabolites were detected in F344 rat slice extracts but were not observed in other species. The data presented suggest that covalent modification of proteins by LY293111 acyl glucuronide is possible in multiple species, although the relative reactivity of this metabolite appears to be low compared with those known to cause adverse drug reactions.
Subject(s)
Benzoates/blood , Benzoates/pharmacokinetics , Animals , Benzoates/chemistry , Drug Evaluation, Preclinical/methods , Female , Humans , Liver/drug effects , Liver/metabolism , Macaca fascicularis , Macaca mulatta , Male , Mice , Middle Aged , Rats , Rats, Inbred F344 , Species SpecificityABSTRACT
1. Studies were conducted in the Fischer 344 rat and beagle dog to determine the disposition of LY333531 and its equipotent active des-methyl metabolite, LY338522, both potent and selective inhibitors of the beta-isozyme of protein kinase C. 2. Male Fischer 344 rats and female beagle dogs received a single 5-mg kg(-1) oral dose of (14)C-LY333531. Urine, faeces, bile and plasma were collected and analysed for (14)C, LY333531 and LY338522. 3. LY333531 was eliminated primarily in the faeces (91% by 120 h in rat, 90% by 96 h in dog). Bile contributed the majority of the radioactivity excreted in the faeces in rat (66% in the cannulated bile duct study) and a variable but significant proportion in dog. 4. Pharmacokinetics following a single 5 mg kg(-1) oral dose of (14)C-LY333531 to the male rat produced C(max) and AUC(0-infinity ) for LY333531 of 14.7 ng ml(-1) and 60.8 ng h ml(-1), respectively, with a half-life of 2.5 h. LY338522 and total radioactivity showed similar profiles. 5. In the female dog at the same dose, C(max) and AUC(0-infinity ) of LY333531 were higher, producing 245 +/- 94 ng ml(-1) and 1419 +/- 463 ng h ml(-1), respectively, with a half-life of 5.7 h. 6. The data indicate that the disposition of LY333531 is similar in rat and dog.
