RT Journal Article
SR Electronic
T1 <em>N</em>-Isopropyl-<em>p</em>-iodoamphetamine Hydrochloride Is Predominantly Metabolized by CYP2C19
JF Drug Metabolism and Disposition
JO Drug Metab Dispos
FD American Society for Pharmacology and Experimental Therapeutics
SP 843
OP 846
DO 10.1124/dmd.111.043893
VO 40
IS 5
A1 Ken-ichi Fujita
A1 Minako Sugiyama
A1 Yuko Akiyama
A1 Kazuhito Hioki
A1 Munetaka Kunishima
A1 Kodai Nishi
A1 Masato Kobayashi
A1 Keiichi Kawai
A1 Yasutsuna Sasaki
YR 2012
UL http://dmd.aspetjournals.org/content/40/5/843.abstract
AB [123I]N-Isopropyl-p-iodoamphetamine hydrochloride ([123I]IMP) is clinically used to evaluate blood flow in the brain on single photon emission-computed tomography. This is a rare radiopharmaceutical that undergoes metabolism. The first step is reported to be [123I]p-iodoamphetamine formation. The drug-metabolizing enzyme(s) involved remain(s) unclear. This study examined the roles of human cytochrome P450 (P450) in the metabolism of nonradiolabeled IMP with the use of human liver microsomes (HLM) and recombinant human CYP1A1, -1A2, -1B1, -2A6, -2B6, -2C8, -2C9, -2C19, -2D6, -2E1, -3A4, and -3A5. Disappearance of IMP was examined because p-iodoamphetamine was not available. IMP (0.5 μM) time-dependently disappeared when HLM and NADPH-generating system were added to the reaction mixture. (S)-Mephenytoin (1 mM) inhibited the IMP disappearance by approximately 90%. The disappearance of IMP was predominantly catalyzed by recombinant CYP2C19, with Km and Vmax of 8.6 μM and 9.7 nmol · min−1 · nmol P450−1, respectively. IMP disappearance in CYP2C19-deficient HLM (CYP2C19*2/*2) was approximately 30% of that in the presence of HLM harboring wild-type CYP2C19, indicating that IMP is polymorphically metabolized by CYP2C19. High-performance liquid chromatography of the incubation mixture of IMP and CYP2C19 revealed an unidentified peak. As the area of the IMP peak decreased, the area of this unidentified peak increased in a time-dependent fashion. The peak was also detectable on incubation of IMP with HLM. Mass spectrometry revealed that the molecular weight of a compound in this unidentified peak was the same as that of p-iodoamphetamine. Thus, we demonstrated that IMP was predominantly metabolized by CYP2C19 to form p-iodoamphetamine.