Identification and human exposure prediction of two aldehyde oxidase-mediated metabolites of a methylquinoline-containing drug candidate

Abstract

1. Aldehyde oxidase (AO enzymes)-mediated oxidation predominantly occurs at a carbon atom adjacent to the nitrogen on aromatic azaheterocycles. In the current report, we identified that AO enzymes oxidation took place at both the C-2 and C-4 positions of the methylquinoline moiety of Compound A based on data from mass spectrometric analysis, AO enzymes "litmus" test, and comparison with authentic standards. 2. To assess the potential for inadequate coverage for these two AO enzyme-mediated metabolites in nonclinical safety studies, given concerns due to differences in AO enzymes expression between preclinical species and humans, the human circulating levels of the two AO enzyme-mediated metabolites were predicted prospectively using in vitro and in vivo models. Both formation clearance and elimination clearance of the two metabolites were predicted based on in vitro to in vivo correlation and comparison with in vivo data from rats. 3. The result showed that the 4-OH metabolite of Compound A would account for less than 3% of the total drug-related exposure in human plasma, while the exposure to the 2-oxo metabolite would be relatively high (∼70%). 4. The predicted human exposure levels for the two metabolites are in similar ranges as those observed in monkeys. These data taken together support the advancement to clinical development of Compound A.

Metabolism by Aldehyde Oxidase: Drug Design and Complementary Approaches to Challenges in Drug Discovery

“…Although prevalence of AO structural alerts was not fully investigated, 56% of Pfizer’s kinase-targeted compounds, and 36% of all ChEMBL-reported drugs (authors’ unpublished observations; , last accessed in June 2018) were predicted to be potential substrates for AO. The sites of oxidations are predominantly carbons adjacent to nitrogen, although important exceptions are quinoline, pyridazine (authors’ observations), cinnoline, acridine, and cryptoleptine motifs, where oxidations are also observed at distant carbons (Figure ). The susceptibility to oxidations by AO generally increases with nitrogen count, especially if the affected carbon is between two nitrogens; for instance, pyrimidine oxidations are more commonly reported than pyridine oxidations.…”

“…Oxidations of azaheterocycles were historically perceived mainly as a risk for high metabolic clearance in humans. Recent examples have significantly broadened this view to include evidence for renal toxicity due to the formation of insoluble crystalline metabolites, , metabolites in safety testing (MIST)-related issues, , interspecies differences, , as well as AO-derived metabolites leading to time-dependent inactivation of CYP3A4 (vide infra) . Despite these discouraging examples, AO should not be perceived as an enemy of drug design teams.…”

Preparation of 18F-Labeled Tracers Targeting Fibroblast Activation Protein via Sulfur [18F]Fluoride Exchange Reaction

“…These transformations might include hydroxylation at the piperazine ring and probably also N -oxygenation at the tertiary amine by FMOs, which are also present in microsome preparations [ 61 ]. As the quinoline system is a known substrate motif for aldehyde oxidase (AO), which can lead to oxidation in ortho - and/or para -position to the nitrogen, we studied stability in liver cytosols, which are a source of AO [ 62 ]. Interestingly, [ 18 F] 12 was found not to be a substrate of AO.…”

Biotransformation: Impact and Application of Metabolism in Drug Discovery

“…One consequence of the current practice of selection of molecules during the discovery phase that have high metabolic stability in liver microsome systems is that alternative non-CYP pathways are now becoming more prevalent as clearance mechanisms, such as those mediated by aldehyde oxidase, and which can result in some unwelcome surprises in the clinic due to unexpectedly high clearance of the drug. , Aldehyde oxidase (AO) is not only present in the liver but is extensively expressed extrahepatically with wide differences in expression across animal species. To alleviate concerns about differences in AO enzyme expression between species used for preclinical assessment and humans, one recent study examining two AO-mediated metabolites of a methylquinoline-containing drug candidate used early in vitro and in vivo models to ensure adequate animal species coverage to predict relatively high exposure of one of the AO metabolites in human plasma …”

“…To alleviate concerns about differences in AO enzyme expression between species used for preclinical assessment and humans, one recent study examining two AOmediated metabolites of a methylquinoline-containing drug candidate used early in vitro and in vivo models to ensure adequate animal species coverage to predict relatively high exposure of one of the AO metabolites in human plasma. 34 AO has broad substrate specificity and is particularly adept at oxidizing azaheterocycles, which are now commonly used in medicinal chemistry programs to lower lipophilicity. However, scientists at UCB propose that AO should not be perceived as an enemy of medicinal chemistry, as oxidized metabolites formed by AO are reported as metabolically stable and, if pharmacologically active, may provide valuable inspiration for novel scaffolds and improved drug design.…”