PT  - JOURNAL ARTICLE
AU  - Jinno, Hideto
AU  - Saeki, Mayumi
AU  - Saito, Yoshiro
AU  - Tanaka-Kagawa, Toshiko
AU  - Hanioka, Nobumitsu
AU  - Sai, Kimie
AU  - Kaniwa, Nahoko
AU  - Ando, Masanori
AU  - Shirao, Kuniaki
AU  - Minami, Hironobu
AU  - Ohtsu, Atsushi
AU  - Yoshida, Teruhiko
AU  - Saijo, Nagahiro
AU  - Ozawa, Shogo
AU  - Sawada, Jun-ichi
TI  - Functional Characterization of Human UDP-Glucuronosyltransferase 1A9 Variant, D256N, Found in Japanese Cancer Patients
AID  - 10.1124/jpet.103.051250
DP  - 2003 Aug 01
TA  - Journal of Pharmacology and Experimental Therapeutics
PG  - 688--693
VI  - 306
IP  - 2
4099  - http://jpet.aspetjournals.org/content/306/2/688.short
4100  - http://jpet.aspetjournals.org/content/306/2/688.full
SO  - J Pharmacol Exp Ther2003 Aug 01; 306
AB  - SN-38 (7-ethyl-10-hydroxycamptothecin), an active metabolite of the antitumor prodrug irinotecan, is conjugated and detoxified to SN-38 10-O-β-d-glucuronide by hepatic UDP-glucuronosyltransferase (UGT) 1A1. Recent studies have revealed that other UGT1A isoforms, UGT1A7 and UGT1A9, also participate in SN-38 glucuronidation. Although several genetic polymorphisms are reported for UGT1A1 and UGT1A7 that affect the SN-38 glucuronidation activities, no such polymorphisms have been identified for UGT1A9. In the present study, UGT1A9 exon 1 and its flanking regions were sequenced from 61 Japanese cancer patients who were all treated with irinotecan. A novel nonsynonymous single nucleotide polymorphism was identified in UGT1A9 exon 1, heterozygous 766G>A resulting in the amino acid substitution of D256N. The wild-type and D256N UGT1A9s were transiently expressed at similar protein levels in COS-1 cells, and their membrane fractions were characterized in vitro for the glucuronidation activities toward SN-38. The apparent Km values were 19.3 and 44.4 μM, and the Vmax values were 2.94 and 0.24 pmol/min/mg of membrane protein for the wild-type and D256N variant, respectively. The SN-38 glucuronidation efficiency (normalized Vmax/Km) of D256N was less than 5% that of wild-type UGT1A9. These results clearly indicate that the D256N variant is essentially nonfunctional with regard to SN-38 glucuronidation. These findings highlight the importance of further studies into the potential influence of UGT1A9 D256N variant to irinotecan metabolism in vivo. The American Society for Pharmacology and Experimental Therapeutics