RT Journal Article
SR Electronic
T1 Functional Characterization of Human UDP-Glucuronosyltransferase 1A9 Variant, D256N, Found in Japanese Cancer Patients
JF Journal of Pharmacology and Experimental Therapeutics
JO J Pharmacol Exp Ther
FD American Society for Pharmacology and Experimental Therapeutics
SP 688
OP 693
DO 10.1124/jpet.103.051250
VO 306
IS 2
A1 Jinno, Hideto
A1 Saeki, Mayumi
A1 Saito, Yoshiro
A1 Tanaka-Kagawa, Toshiko
A1 Hanioka, Nobumitsu
A1 Sai, Kimie
A1 Kaniwa, Nahoko
A1 Ando, Masanori
A1 Shirao, Kuniaki
A1 Minami, Hironobu
A1 Ohtsu, Atsushi
A1 Yoshida, Teruhiko
A1 Saijo, Nagahiro
A1 Ozawa, Shogo
A1 Sawada, Jun-ichi
YR 2003
UL http://jpet.aspetjournals.org/content/306/2/688.abstract
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