1. Ivermectin was extensively metabolized by human liver microsomes to at least 10 metabolites. The structure of many of them (mostly hydroxylated and demethylated) was determined by 1H-NMR and LC/MS. 2. To determine which human cytochrome P450 isoform(s) is responsible for the metabolism of ivermectin, chemical inhibitors including sulphaphenazole, quinidine, furafylline, troleandomycin (TAO) and diethyldithiocarbamate (DDC) were used to evaluate their effect on ivermectin metabolism. TAO, a specific inhibitor of cytochrome P4503A4, was the most potent inhibitor, inhibiting the total metabolism as well as formation of each metabolite. Metabolism was also inhibited by an anti-human cytochrome 3A4 antibody by 90%. 3. When ivermectin was incubated with microsomes from cells expressing CYP1A1, 1A2, 2A6, 2B6, 2C8, 2C9, 2C19, 2D6, 2E1 or 3A4 at 4 mg/ml protein concentrations, metabolic activity was only detected with the microsomes containing CYP3A4. The metabolic profile from cDNA-expressed CYP3A4 microsomes was qualitatively similar to that from human liver microsomes. 4. Thus, cytochrome P4503A4 is the predominant isoform responsible for the metabolism of ivermectin by human liver microsomes.

The FDA issued a guidance on the safety testing of metabolites in February 2008, in which they stated that metabolites of concern are those that are detected at levels greater than 10% of the systemic exposure of the parent at steady state. This has presented many challenges in determining the circulating human metabolites at an early stage of development. The intention of this perspective is to address the question of how effective in vitro metabolism and early exploratory clinical data are in predicting the circulating metabolites from both a qualitative and a quantitative perspective. To this end, data were reviewed from 17 molecules in the Lilly portfolio for which there were in vitro data and a radiolabeled study in humans. Twelve example cases are presented in detail to demonstrate trends for when in vitro data adequately predicted in vivo (41%), when in vitro data underpredicted the circulating metabolites (35%), and when in vitro data overpredicted the circulating metabolites (24%). In addition, cases that present special challenges due to very low levels of the circulating parent or long half-lives of the parent and/or metabolites are presented. The trends indicate that the more complex the metabolism, the less likely the in vitro data were to predict the circulating metabolites. The in vitro data were also less predictive for N-glucuronidations and non-P450-mediated cleavage reactions. Although the in vitro data were better at predicting clearance pathways, the data set often failed to predict the quantity of metabolites, which is needed in consideration of whether or not a "disproportionate" metabolite may be circulating in human plasma.

Transmembrane AMPA receptor regulatory proteins (TARPs) are a family of scaffolding proteins that regulate AMPA receptor trafficking and function. TARP γ-8 is one member of this family and is highly expressed within the hippocampus relative to the cerebellum. A selective TARP γ-8-dependent AMPA receptor antagonist (TDAA) is an innovative approach to modulate AMPA receptors in specific brain regions to potentially increase the therapeutic index relative to known non-TARP-dependent AMPA antagonists. We describe here, for the first time, the discovery of a noncompetitive AMPA receptor antagonist that is dependent on the presence of TARP γ-8. Three major iteration cycles were employed to improve upon potency, CYP1A2-dependent challenges, and in vivo clearance. An optimized molecule, compound (-)-25 (LY3130481), was fully protective against pentylenetetrazole-induced convulsions in rats without the motor impairment associated with non-TARP-dependent AMPA receptor antagonists. Compound (-)-25 could be utilized to provide proof of concept for antiepileptic efficacy with reduced motor side effects in patients.

A new series of hPPARalpha agonists containing a 2,4-dihydro-3H-1,2,4-triazol-3-one (triazolone) core is described leading to the discovery of 5 (LY518674), a highly potent and selective PPARalpha agonist.