The novel UGT1A9 intronic I399 polymorphism appears as a predictor of 7-ethyl-10-hydroxycamptothecin glucuronidation levels in the liver.
Polymorphisms in UGT1A9 were associated with reduced toxicity and increased response to irinotecan in cancer patients. UDP-glucuronosyltransferase (UGT) protein expression, glucuronidation activities for 7-ethyl-10-hydroxycamptothecin (SN-38), and probe substrates of the UGT1A9 and UGT1A1 were measured in 48 human livers to clarify the role of UGT1A9 variants on the in vitro glucuronidation of SN-38. Genotypes were assessed for UGT1A9 (-2152C>T, -275T>A, and -118T(9>10)), three novel UGT1A9 variants (-5366G>T, -4549T>C, and I399C>T), and UGT1A1 (-53TA(6>7), -3156G>A, and -3279T>G). Of all the variants, the UGT1A9 I399C>T was associated with the most dramatic change in SN-38-glucuronide (SN-38G) (2.64-fold; p = 0.0007). Compared with UGT1A9 I399C/C, homozygous I399T/T presented elevated UGT1A1 and UGT1A9 proteins and higher glucuronidation of UGT1A9 and UGT1A1 substrates (p < 0.05). The very low linkage disequilibrium (r(2) < 0.19) between UGT1A9 I399 and all the other UGT1A1 and UGT1A9 variants suggests a direct effect or linkage to unknown functional variant(s) relevant to SN-38 glucuronidation. The UGT1A9 -118T(9/10) was also linked to alteration of SN-38 glucuronidation profiles in the liver (p < 0.05) and was associated with higher UGT1A1 protein (p = 0.03). However, UGT1A9 -118T(10) appears to have low functional impact as a result of the lack of correlation with UGT1A9 protein levels and a modest 1.4-fold higher reporter gene expression associated with the -118T(10) allele in HepG2 cells (p = 0.004). In contrast, the UGT1A9 -5366T, -4549C, -2152T, and -275A, associated with higher UGT1A9 protein (2-fold; p < 0.05), have no influence on SN-38G. Despite limitations resulting from sample size, results indicate that UGT1A9 I399 and -118T(9/10) may represent additional candidates in combination with UGT1A1 promoter haplotypes for the prediction of SN-38 glucuronidation profile in vivo.
Girard
Hugo
H
Laboratory of Pharmacogenomics, Centre Hospitalier de l'Université Laval, Quebec, QC, Canada G1V 4G2.
Villeneuve
Lyne
L
Court
Michael H
MH
Fortier
Louis-Charles
LC
Caron
Patrick
P
Hao
Qin
Q
von Moltke
Lisa L
LL
Greenblatt
David J
DJ
Guillemette
Chantal
C
D002166:Camptothecin / Q000031:analogs & derivatives* / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic; D020719:Glucuronides / Q000378:metabolism*; D014453:Glucuronosyltransferase / Q000235:genetics / Q000378:metabolism*; D006239:Haplotypes; D006801:Humans; D007438:Introns; D000077146:Irinotecan; D015810:Linkage Disequilibrium; D008099:Liver / Q000201:enzymology*; D010597:Pharmacogenetics; D011110:Polymorphism, Genetic; D011237:Predictive Value of Tests; D000090264:UDP-Glucuronosyltransferase 1A9; D000099148:UGT1A1 Enzyme
D002166:Camptothecin; D020719:Glucuronides; D014453:Glucuronosyltransferase; D000077146:Irinotecan; D000090264:UDP-Glucuronosyltransferase 1A9; D000099148:UGT1A1 Enzyme; C441475:7-ethyl-10-hydroxycamptothecin glucuronide; C000715591:UGT1A9 protein, human