Phillips D H, Hewer A, White I N, Farmer P B
Haddow Laboratories, Institute of Cancer Research, Sutton, Surrey, UK.
Carcinogenesis. 1994 May;15(5):793-5. doi: 10.1093/carcin/15.5.793.
Tamoxifen is a potent liver carcinogen in rats and has been shown to form covalent DNA adducts in the livers of several species of rodent. We have shown previously by 32P-postlabeling (Carcinogenesis, 13, 2197-2203) that > 85% of the total adducts detected and resolved by multi-directional TLC migrate as a single spot. In the present study, this material was further analysed by reverse-phase HPLC and resolved into two approximately equal components. Tamoxifen 1,2-epoxide, a postulated metabolite of tamoxifen, was reacted with DNA and polydeoxyribonucleotides and the products analysed. 32P-Postlabeling revealed three major adduct spots on TLC which comigrated with the three major adduct spots seen with DNA from livers of tamoxifen-treated rats. Moreover, the major epoxide adduct, which contained guanine as the modified base, eluted on HPLC as a single major peak coincident with one of the major peaks derived from the liver DNA of tamoxifen-treated rats. These results demonstrate that approximately 40% of the tamoxifen-DNA adducts formed in vivo are chromatographically indistinguishable with the major product of the reaction of tamoxifen epoxide with guanine residues in DNA and provide important clues to the mechanism of activation of tamoxifen to a genotoxic carcinogen.
他莫昔芬是大鼠体内一种强效的肝脏致癌物，并且已证实在几种啮齿动物的肝脏中会形成共价DNA加合物。我们之前通过³²P后标记法（《癌变》，13卷，2197 - 2203页）表明，通过多向薄层层析法检测和分离出的总加合物中，超过85%以单一斑点形式迁移。在本研究中，该物质通过反相高效液相色谱法进一步分析，并分离成两个大致相等的组分。他莫昔芬1,2 - 环氧化物是他莫昔芬的一种假定代谢产物，使其与DNA和多脱氧核糖核苷酸反应并分析产物。³²P后标记法在薄层层析上显示出三个主要加合物斑点，它们与用他莫昔芬处理过的大鼠肝脏DNA所观察到的三个主要加合物斑点共迁移。此外，以鸟嘌呤作为修饰碱基的主要环氧化物加合物，在高效液相色谱上洗脱为一个单一的主峰，与源自他莫昔芬处理过的大鼠肝脏DNA的主要峰之一重合。这些结果表明，体内形成的他莫昔芬 - DNA加合物中约40%在色谱上与他莫昔芬环氧化物与DNA中鸟嘌呤残基反应的主要产物无法区分，这为他莫昔芬激活成为遗传毒性致癌物的机制提供了重要线索。
