Villeneuve Lyne, Girard Hugo, Fortier Louis-Charles, Gagné Jean-Francois, Guillemette Chantal
Pharmacogenomics Laboratory, Oncology and Molecular Endocrinology Research Center, CHUL Research Center, Faculty of Pharmacy, Laval University, Québec, Canada.
J Pharmacol Exp Ther. 2003 Oct;307(1):117-28. doi: 10.1124/jpet.103.054072. Epub 2003 Aug 27.
In vitro metabolic studies revealed that along with UDP-glucuronosyltransferase (UGT) 1A1, the hepatic UGT1A9 and the extrahepatic UGT1A7 are involved in the biotransformation of the active and toxic metabolite of irinotecan, 7-ethyl-10-hydroxycamptothecin (SN-38). Variant UGT1A1 and UGT1A7 alleles have been reported but the polymorphic nature of the UGT1A9 gene has not been revealed yet. To further clarify the molecular determinants of irinotecan-induced toxicity, we have identified and characterized the functionality of novel UGT1A9 polymorphisms and determined whether additional missense polymorphisms exist in UGT1A7. Using direct DNA sequencing, four single nucleotide polymorphisms (SNPs) were identified in the first exons of UGT1A7 and UGT1A9. One of the two amino acid substitutions found in the UGT1A9 gene, UGT1A93 (M33T), results in a dramatic decrease in SN-38 glucuronide formation, with 3.8% of the activity of the UGT1A91 allele. In turn, the glucuronidation of flavopiridol, an anticancer drug biotransformed predominantly by UGT1A9, remains unaffected, indicating a substrate-dependent impact of this variant. UGT1A9*3 is detected only in Caucasians and 4.4% of the population tested was found heterozygous (*1/3). Two additional UGT1A7 SNPs were found exclusively in African-American subjects and generate five alleles (UGT1A75 to 9) when combined to the four known SNPs present in UGT1A72, *3, and 4. Upon functional analysis with SN-38, five out of nine UGT1A7 allozymes exhibited much lower SN-38 glucuronidation activities compared with UGT1A71, all having in common the mutational changes at codons 115 or 208. Results suggest that these low SN-38 glucuronidating alleles may represent additional molecular determinants of irinotecan-induced toxicity and warrant further investigations.
体外代谢研究表明，除了尿苷二磷酸葡萄糖醛酸基转移酶（UGT）1A1外，肝脏中的UGT1A9和肝外的UGT1A7也参与了伊立替康的活性和有毒代谢物7-乙基-10-羟基喜树碱（SN-38）的生物转化。已报道了UGT1A1和UGT1A7的变异等位基因，但UGT1A9基因的多态性性质尚未揭示。为了进一步阐明伊立替康诱导毒性的分子决定因素，我们鉴定并表征了新型UGT1A9多态性的功能，并确定UGT1A7中是否存在其他错义多态性。通过直接DNA测序，在UGT1A7和UGT1A9的第一个外显子中鉴定出四个单核苷酸多态性（SNP）。在UGT1A9基因中发现的两个氨基酸替代之一，UGT1A93（M33T），导致SN-38葡萄糖醛酸苷形成急剧减少，其活性仅为UGT1A91等位基因的3.8%。反过来，主要由UGT1A9生物转化的抗癌药物氟吡汀的葡萄糖醛酸化不受影响，表明该变体对底物有依赖性影响。UGT1A93仅在白种人中检测到，在测试人群中4.4%被发现为杂合子（1/3）。另外两个UGT1A7 SNP仅在非裔美国受试者中发现，与UGT1A72、3和4中存在的四个已知SNP组合时产生五个等位基因（UGT1A75至9）。在用SN-38进行功能分析时，九个UGT1A7同工酶中的五个与UGT1A7*1相比表现出低得多的SN-38葡萄糖醛酸化活性，它们都在密码子115或208处有共同的突变变化。结果表明，这些低SN-38葡萄糖醛酸化等位基因可能代表伊立替康诱导毒性的其他分子决定因素，值得进一步研究。
