Sun Dongxiao, Sharma Arun K, Dellinger Ryan W, Blevins-Primeau Andrea S, Balliet Renee M, Chen Gang, Boyiri Telih, Amin Shantu, Lazarus Philip
Cancer Prevention and Control, Penn State Cancer Institute, Department of Pharmacology, Penn State University College of Medicine, Hershey, PA 17033, USA.
Drug Metab Dispos. 2007 Nov;35(11):2006-14. doi: 10.1124/dmd.107.017145. Epub 2007 Jul 30.
Tamoxifen (TAM) is an antiestrogen that has been widely used in the treatment and prevention of breast cancer in women. One of the major mechanisms of metabolism and elimination of TAM and its major active metabolites 4-hydroxytamoxifen (4-OH-TAM) and 4-OH-N-desmethyl-TAM (endoxifen; 4-hydroxy-N-desmethyl-tamoxifen) is via glucuronidation. Although limited studies have been performed characterizing the glucuronidation of 4-OH-TAM, no studies have been performed on endoxifen. In the present study, characterization of the glucuronidating activities of human UDP glucuronosyltransferases (UGTs) against isomers of 4-OH-TAM and endoxifen was performed. Using homogenates of individual UGT-overexpressing cell lines, UGTs 2B7 approximately 1A8 > UGT1A10 exhibited the highest overall O-glucuronidating activity against trans-4-OH-TAM as determined by Vmax/K(M), with the hepatic enzyme UGT2B7 exhibiting the highest binding affinity and lowest K(M) (3.7 microM). As determined by Vmax/K(M), UGT1A10 exhibited the highest overall O-glucuronidating activity against cis-4-OH-TAM, 10-fold higher than the next-most active UGTs 1A1 and 2B7, but with UGT1A7 exhibiting the lowest K(M). Although both N- and O-glucuronidation occurred for 4-OH-TAM in human liver microsomes, only O-glucuronidating activity was observed for endoxifen; no endoxifen-N-glucuronidation was observed for any UGT tested. UGTs 1A10 approximately 1A8 > UGT2B7 exhibited the highest overall glucuronidating activities as determined by Vmax/K(M) for trans-endoxifen, with the extrahepatic enzyme UGT1A10 exhibiting the highest binding affinity and lowest K(M) (39.9 microM). Similar to that observed for cis-4-OH-TAM, UGT1A10 also exhibited the highest activity for cis-endoxifen. These data suggest that several UGTs, including UGTs 1A10, 2B7, and 1A8 play an important role in the metabolism of 4-OH-TAM and endoxifen.
他莫昔芬（TAM）是一种抗雌激素药物，已广泛应用于女性乳腺癌的治疗和预防。TAM及其主要活性代谢产物4-羟基他莫昔芬（4-OH-TAM）和4-羟基-N-去甲基他莫昔芬（内昔芬；4-羟基-N-去甲基他莫昔芬）的主要代谢和消除机制之一是通过葡萄糖醛酸化作用。尽管对4-OH-TAM葡萄糖醛酸化作用的研究有限，但尚未对内昔芬进行相关研究。在本研究中，对人尿苷二磷酸葡萄糖醛酸基转移酶（UGTs）针对4-OH-TAM和内昔芬异构体的葡萄糖醛酸化活性进行了表征。使用单个UGT过表达细胞系的匀浆，通过Vmax/K(M)测定，UGT2B7、UGT1A8和UGT1A10对反式4-OH-TAM表现出最高的总体O-葡萄糖醛酸化活性，其中肝酶UGT2B7表现出最高的结合亲和力和最低的K(M)（3.7 microM）。通过Vmax/K(M)测定，UGT1A10对顺式4-OH-TAM表现出最高的总体O-葡萄糖醛酸化活性，比下一个活性最高的UGT1A1和UGT2B7高10倍，但UGT1A7表现出最低的K(M)。虽然在人肝微粒体中4-OH-TAM同时发生N-和O-葡萄糖醛酸化，但内昔芬仅观察到O-葡萄糖醛酸化活性；在所测试的任何UGT中均未观察到内昔芬-N-葡萄糖醛酸化。通过Vmax/K(M)测定，UGT1A10、UGT1A8和UGT2B7对反式内昔芬表现出最高的总体葡萄糖醛酸化活性，其中肝外酶UGT1A10表现出最高的结合亲和力和最低的K(M)（39.9 microM）。与顺式4-OH-TAM的情况类似，UGT1A10对顺式内昔芬也表现出最高活性。这些数据表明，包括UGT1A10、UGT2B7和UGT1A8在内的几种UGT在4-OH-TAM和内昔芬的代谢中起重要作用。
