Ujiie Shuta, Sasaki Takamitsu, Mizugaki Michinao, Ishikawa Masaaki, Hiratsuka Masahiro
Departments of Clinical Pharmacotherapeutics, Tohoku Pharmaceutical University, Sendai, Japan.
Pharmacogenet Genomics. 2008 Oct;18(10):887-93. doi: 10.1097/FPC.0b013e3283097328.
Thiopurine S-methyltransferase (TPMT) is an enzyme responsible for the detoxification of the widely used thiopurine drugs. TPMT is genetically polymorphic and is associated with large interindividual variations in thiopurine drug toxicity and therapeutic efficacy. In this study, we performed an in-vitro analysis of TPMT variant alleles, namely, TPMT*2, *3A, *3B, *3C, *5, *6, *7, *8, *9, *10, *11, *12, *13, *14, *16, *17, *18, *19, *20, *21, *22, *23, and *24.
The wild-type TPMT proteins, TPMT.1 and 23 variants were heterologously expressed in COS-7 cells, and the kinetic parameters Km, Vmax, and intrinsic clearance (Vmax/Km) of 6-thioguanine S-methylation were determined.
The expression levels of TPMT.2, TPMT.3A, TPMT.5, TPMT.12, TPMT.14, and TPMT.22 were considerably lower than that of TPMT.1 (P<0.005), and that of TPMT.18 was slightly reduced (P<0.05). The kinetic parameters of TPMT.3A, TPMT.3B, TPMT.5, TPMT.14, TPMT.18, TPMT.21, and TPMT.22 could not be accurately established because of no activity in 6-thioguanine S-methylation. The Vmax/Km values of TPMT.2, TPMT.7, TPMT.17, and TPMT.24 were displayed less than 10% of the wild-type.
This functional analysis with respect to TPMT variants could provide useful information for individualization of thiopurine drugs therapy.
硫嘌呤甲基转移酶（TPMT）是一种负责对广泛使用的硫嘌呤类药物进行解毒的酶。TPMT具有遗传多态性，与硫嘌呤类药物毒性和治疗效果的个体间巨大差异相关。在本研究中，我们对TPMT变异等位基因，即TPMT*2、*3A、*3B、*3C、*5、*6、*7、*8、*9、*10、*11、*12、*13、*14、*16、*17、*18、*19、*20、*21、*22、23和24进行了体外分析。
野生型TPMT蛋白、TPMT.1和23种变体在COS-7细胞中进行异源表达，并测定6-硫鸟嘌呤S-甲基化的动力学参数Km、Vmax和内在清除率（Vmax/Km）。
TPMT.2、TPMT.3A、TPMT.5、TPMT.12、TPMT.14和TPMT.22的表达水平显著低于TPMT.1（P<0.005），TPMT.18的表达水平略有降低（P<0.05）。由于6-硫鸟嘌呤S-甲基化无活性，TPMT.3A、TPMT.3B、TPMT.5、TPMT.14、TPMT.18、TPMT.21和TPMT.22的动力学参数无法准确确定。TPMT.2、TPMT.7、TPMT.17和TPMT.24的Vmax/Km值显示低于野生型的10%。
这种关于TPMT变体的功能分析可为硫嘌呤类药物治疗的个体化提供有用信息。
