Molecular Epidemiology and Cancer Control, Penn State University College of Medicine, Hershey, Pennsylvania 17033, USA.
Pharmacogenet Genomics. 2010 Oct;20(10):575-85. doi: 10.1097/FPC.0b013e32833b04af.
Exemestane is a third-generation aromatase inhibitor used in the treatment of breast cancer in postmenopausal women. Reduction to form 17-dihydroexemestane and subsequent glucuronidation to exemestane-17-O-glucuronide is a major pathway for exemestane metabolism. The goal of this study was to analyze 17-dihydroexemestane anti-aromatase activity, characterize the 17-dihydroexemestane glucuronidation pathway, and determine whether the functional polymorphisms in active UGTs could play a role in altered 17-dihydroexemestane glucuronidation.
Homogenates from a HEK293 aromatase-overexpressing cell line (HEK293-aro) were used to examine exemestane versus 17-dihydroexemestane anti-aromatase activities. UGT-overexpressing cell lines and a panel (n=110) of human liver microsome (HLM) were screened for glucuronidation activity against 17-dihydroexemestane. UGT2B17 genotyping and liver mRNA expression were performed by real-time PCR.
The inhibition of estrone formation from androst-4-ene-3,17-dione in HEK293-aro cell homogenates was similar for 17-dihydroexemestane (IC(50)=2.3±0.83 μmol/l) and exemestane (IC(50)=1.4±0.42 μmol/l). UGTs 2B17 and 1A4 were high-expression hepatic UGTs that exhibited activity against 17-dihydroexemestane, with UGT2B17 exhibiting a 17-fold higher V(max)/K(M) than UGT1A4. The rate of exemestane-17-O-glucuronide formation was shown to be significantly (P<0.001) decreased (14-fold) in HLMs exhibiting the UGT2B17(*2/*2) deletion genotype versus wild-type UGT2B17(*1/*1) HLMs; a 36-fold lower V(max)/K(M) (P=0.023) was observed in UGT2B17(*2/*2) versus UGT2B17(*1/*1) HLMs. A significant (P<0.0001, R(2)=0.72) correlation was observed between HLM exemestane-17-O-glucuronide formation and liver UGT2B17 expression.
These data suggest that 17-dihydroexemestane is an active metabolite of exemestane and that the UGT2B17 deletion polymorphism could play an important role in determining levels of excretion of 17-dihydroexemestane and overall exemestane metabolism.
依西美坦是一种第三代芳香酶抑制剂，用于治疗绝经后妇女的乳腺癌。还原为 17-二氢依西美坦并随后与葡萄糖醛酸结合形成依西美坦-17-O-葡萄糖醛酸苷是依西美坦代谢的主要途径。本研究的目的是分析 17-二氢依西美坦的抗芳香酶活性，研究 17-二氢依西美坦的葡萄糖醛酸化途径，并确定活性 UGT 中的功能性多态性是否在改变 17-二氢依西美坦的葡萄糖醛酸化中发挥作用。
使用过表达芳香酶的 HEK293 细胞系（HEK293-aro）的匀浆来研究依西美坦与 17-二氢依西美坦的抗芳香酶活性。用 UGT 过表达细胞系和一个（n=110）人肝微粒体（HLM）筛选针对 17-二氢依西美坦的葡萄糖醛酸化活性。通过实时 PCR 进行 UGT2B17 基因分型和肝 mRNA 表达。
HEK293-aro 细胞匀浆中，17-二氢依西美坦对雄烯二酮-3,17-二酮形成雌酮的抑制作用与依西美坦相似（IC（50）=2.3±0.83μmol/L）和依西美坦（IC（50）=1.4±0.42μmol/L）。UGT2B17 和 1A4 是高表达的肝 UGT，对 17-二氢依西美坦具有活性，UGT2B17 的 V（max）/K（M）比 UGT1A4 高 17 倍。与野生型 UGT2B17（*1/*1）相比，HLM 中表现出 UGT2B17（*2/*2）缺失基因型的依西美坦-17-O-葡萄糖醛酸苷形成率显著（P<0.001）降低（14 倍）；与 UGT2B17（*1/*1）相比，UGT2B17（*2/*2）HLM 的 V（max）/K（M）降低了 36 倍（P=0.023）。HLM 中依西美坦-17-O-葡萄糖醛酸苷的形成与肝 UGT2B17 表达之间存在显著（P<0.0001，R（2）=0.72）相关性。
这些数据表明，17-二氢依西美坦是依西美坦的一种活性代谢物，UGT2B17 缺失多态性可能在决定 17-二氢依西美坦和依西美坦整体代谢物的排泄水平方面发挥重要作用。
