PT  - JOURNAL ARTICLE
AU  - Xue-Qing Li
AU  - Martin A. Hayes
AU  - Gunnar Grönberg
AU  - Kristina Berggren
AU  - Neal Castagnoli, Jr.
AU  - Lars Weidolf
TI  - Discovery of a Novel Microsomal Epoxide Hydrolase–Catalyzed Hydration of a Spiro Oxetane
AID  - 10.1124/dmd.116.071142
DP  - 2016 Aug 01
TA  - Drug Metabolism and Disposition
PG  - 1341--1348
VI  - 44
IP  - 8
4099  - http://dmd.aspetjournals.org/content/44/8/1341.short
4100  - http://dmd.aspetjournals.org/content/44/8/1341.full
SO  - Drug Metab Dispos2016 Aug 01; 44
AB  - Oxetane moieties are increasingly being used by the pharmaceutical industry as building blocks in drug candidates because of their pronounced ability to improve physicochemical parameters and metabolic stability of drug candidates. The enzymes that catalyze the biotransformation of the oxetane moiety are, however, not well studied. The in vitro metabolism of a spiro oxetane-containing compound AZD1979 [(3-(4-(2-oxa-6-azaspiro[3.3]heptan-6-ylmethyl)phenoxy)azetidin-1-yl)(5-(4-ethoxyphenyl)-1,3,4-oxadiazol-2-yl)methanone] was studied and one of its metabolites, M1, attracted our interest because its formation was NAD(P)H independent. The focus of this work was to elucidate the structure of M1 and to understand the mechanism(s) of its formation. We established that M1 was formed via hydration and ring opening of the oxetanyl moiety of AZD1979. Incubations of AZD1979 using various human liver subcellular fractions revealed that the hydration reaction leading to M1 occurred mainly in the microsomal fraction. The underlying mechanism as a hydration, rather than an oxidation reaction, was supported by the incorporation of 18O from H218O into M1. Enzyme kinetics were performed probing the formation of M1 in human liver microsomes. The formation of M1 was substantially inhibited by progabide, a microsomal epoxide hydrolase inhibitor, but not by trans-4-[4-(1-adamantylcarbamoylamino)cyclohexyloxy]benzoic acid, a soluble epoxide hydrolase inhibitor. On the basis of these results, we propose that microsomal epoxide hydrolase catalyzes the formation of M1. The substrate specificity of microsomal epoxide hydrolase should therefore be expanded to include not only epoxides but also the oxetanyl ring system present in AZD1979.