RT Journal Article
SR Electronic
T1 Time Course of Aldehyde Oxidase and Why It Is Nonlinear
JF Drug Metabolism and Disposition
JO Drug Metab Dispos
FD American Society for Pharmacology and Experimental Therapeutics
SP 473
OP 483
DO 10.1124/dmd.118.085787
VO 47
IS 5
A1 Armina Abbasi
A1 Erickson M. Paragas
A1 Carolyn A. Joswig-Jones
A1 John T. Rodgers
A1 Jeffrey P. Jones
YR 2019
UL http://dmd.aspetjournals.org/content/47/5/473.abstract
AB Many promising drug candidates metabolized by aldehyde oxidase (AOX) fail during clinical trial owing to underestimation of their clearance. AOX is species-specific, which makes traditional allometric studies a poor choice for estimating human clearance. Other studies have suggested using half-life calculated by measuring substrate depletion to measure clearance. In this study, we proposed using numerical fitting to enzymatic pathways other than Michaelis-Menten (MM) to avoid missing the initial high turnover rate of product formation. Here, product formation over a 240-minute time course of six AOX substrates—O6-benzylguanine, N-(2-dimethylamino)ethyl)acridine-4-carboxamide, zaleplon, phthalazine, BIBX1382 [N8-(3-Chloro-4-fluorophenyl)-N2-(1-methyl-4-piperidinyl)-pyrimido[5,4-d]pyrimidine-2,8-diamine dihydrochloride], and zoniporide—have been provided to illustrate enzyme deactivation over time to help better understand why MM kinetics sometimes leads to underestimation of rate constants. Based on the data provided in this article, the total velocity for substrates becomes slower than the initial velocity by 3.1-, 6.5-, 2.9-, 32.2-, 2.7-, and 0.2-fold, respectively, in human expressed purified enzyme, whereas the Km remains constant. Also, our studies on the role of reactive oxygen species (ROS), such as superoxide and hydrogen peroxide, show that ROS did not significantly alter the change in enzyme activity over time. Providing a new electron acceptor, 5-nitroquinoline, did, however, alter the change in rate over time for mumerous compounds. The data also illustrate the difficulties in using substrate disappearance to estimate intrinsic clearance.