Search

Introduction: Given the rising trend in medicinal chemistry strategy to reduce cytochrome P450-dependent metabolism, aldehyde oxidase (AOX) has recently gained increased attention in drug discovery programs and the number of drug candidates that are metabolized by AOX is steadily growing. Areas covered: Despite the emerging importance of AOX in drug discovery, there are certain major recognized problems associated with AOX-mediated metabolism of drugs. Intra- and inter-species variations in AOX activity, the lack of reliable and predictive animal models using the common experimental animals, and failure in the predictions of in vivo metabolic activity of AOX using traditional in vitro methods are among these issues that are covered in this article. A comprehensive review of computational human AOX (hAOX) related studies are also provided. Expert opinion: Following the recent progress in the stem cell field, the authors recommend the application of organoids technology as an effective tool to solve the fundamental problems associated with the evaluation of AOX in drug discovery. The recent success in resolving the hAOX crystal structure can too be another valuable data source for the study of AOX-catalyzed metabolism of new drug candidates, using computer-aided drug discovery methods.

Aldehyde oxidase (AO), an important enzyme in the biotransformation of drugs and xenobiotics, is inhibited by flavonoids. This enzyme can metabolize both aldehydes and N-heterocycles. In this work, a set of 15 flavonoids was assessed for inhibitory activity on the AO oxidation of vanillin as an aldehyde substrate. Spectrophotometrically determined IC50 values showed that myricetin, quercetin, and epicatechin were the most potent inhibitors. The results also revealed that the inhibition of vanillin oxidation by flavonoids was stronger than that of phenanthridine oxidation (an N-heterocyclic substrate) as reported previously. In order to investigate the important structural features responsible for the inhibitory effects of the studied flavonoids, a quantitative structure-activity relationship (QSAR) analysis was performed. This study showed that the size of the flavonoids was the most important factor inversely affecting their potencies. The QSAR model can be used more broadly to predict the AO inhibitory activity of flavonoid-like structures for application in food-drug and drug-drug interaction studies., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Metabolism by aldehyde oxidase (AO) has been responsible for a number of drug failures in clinical trials. The main reason is the clearance values for drugs metabolized by AO are underestimated by allometric scaling from preclinical species. Furthermore, in vitro human data also underestimates clearance. We have developed the first in silico models to predict both in vitro and in vivo human intrinsic clearance for 8 drugs with just two chemical descriptors. These models explain a large amount of the variance in the data using two computational estimates of the electronic and steric features of the reaction. The in vivo computational models for human metabolism are better than in vitro preclinical animal testing at predicting human intrinsic clearance. Thus, it appears that AO is amenable to computational prediction of rates, which may be used to guide drug discovery, and predict pharmacokinetics for clinical trials.

Aldehyde oxidases are molybdoflavoenzymes with broad substrate specificity, oxidizing different types of aldehydes, and heterocyclic rings. The physiological function of aldehyde oxidases is largely unknown, although the enzymes play an important role in the metabolism of numerous compounds of medicinal and toxicological interest, as they oxidize a wide range of aldehydes and heterocyclic compounds. In this article, we review the significance of aldehyde oxidases for the design and development of new drugs and discuss associated problems. These include species-specific differences in the complement of isoenzymes synthesized and general difficulties in studying the enzymatic characteristics of purified or recombinant aldehyde oxidases. We highlight the potential offered by human aldehyde oxidase targeting for the development of new pharmacological agents, limiting our attention to the realms of antiobesity and anti-cancer drugs. The last point is discussed in the context of the design of novel anticancer drugs, selectively activated or inactivated by this enzyme, with the final aim of achieving organ and/or tumor selectivity.