| Summary: | 碩士 === 中華醫事科技大學 === 生物科技研究所 === 98 === Tamoxifen (TAM) is an antiestrogen widely used in the treatment and prevention of breast cancer in women. One of the major mechanisms of metabolism of TAM and one of its major active metabolites, 4-hydroxytamoxifen (4-OH-TAM), and endoxifen, is by glucuronidation via the UDP-glucuronosyltransferase (UGT) family of enzymes. The UGT superfamily of enzymes catalyzes the glucuronidation of a variety of compounds including endogenous compounds like bilirubin and steroid hormones, as well as xenobiotics including drugs and environmental carcinogens.
To examine whether polymorphisms in the UGT enzymes responsible for the glucuronidation of active TAM metabolites play an important role in interindividual differences in TAM metabolism, cell lines overexpressing wild-type or variant UGTs were examined for their activities against TAM metabolites in vitro.
In this study, the glucuronidating activities by the human UGT1A4 genetic polymorphisms were examined against TAM. HPLC was used to detect metabolism activity in UGT1A4-overexpressing HEK293 cells. The UGT1A443Asn/45Arg、UGT1A443Ser/45Gln、UGT1A443Asn/45Gln variants were generated by site-directed mutagenesis of the p3xflag-cmv10 plasmid expressing wild-type UGT1A443Ser/45Arg .The aim of the present study was to characterize UGT1A4- induced glucuronidation of 4-OH-TAM and to examine whether missense variants in the UGT1A4 gene alter activity against 4-OH-TAM in vitro. We demonstrated that UGT1A4 exhibited a significantly higher glucuronidation rate against 4-hydroxytamoxifen than not UGT1A4 enzymes in vitro using whole-cell homogenates of UGT1A4-overexpressing HEK293 cells. The polymorphic UGT1A443Asn/45Arg、UGT1A443Ser/45Gln、UGT1A443Asn/45Gln variants exhibited of 0.904 fold、0.977 fold、0.951 fold , respectively. Decrease in glucuronidation activity against 4-hydroxytamoxifen , as compared with the wild-type UGT1A443Ser/45Arg isoform.These data suggest that the UGT1A443Asn/45Arg、UGT1A443Ser/45Gln、UGT1A443Asn/45Gln polymorphism do not significantly alters glucuronidation rates against TAM and its active hydroxylated metabolites but that this UGT1A4 still play an important role in individual pharmacological response to TAM therapy.
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