Induction and repair of 4-OHEN-DNA adducts in human breast cancer cells by the metabolites of equine estrogens

激素替代疗法（HRT）被广泛用于减少绝经后妇女的绝经症状。然而，长期HRT会增加乳腺癌、卵巢癌和子宫内膜癌的发病率。4-羟基马雌激素（4-OHEN）是常见HRT制剂（倍美力）中存在的马雌激素的代谢产物，能够产生大量的4-OHEN-DNA加合物。使用我们的加合物特异性抗体的免疫测定显示，4-OHEN-DNA加合物在人乳腺癌细胞中修复效率低下。MTS检测显示，在人正常细胞和修复缺陷细胞之间观察到相似的4-OHEN敏感性。此外，包括人H1在内的组蛋白以浓度依赖性方式竞争性抑制抗体与4-OHEN-DNA加合物的结合，这被认为是损伤识别修复蛋白的模型。因此，DNA加合物的形成可能参与了Premarin诱导的肿瘤的发生过程。

Hormone replacement therapy (HRT) is widely used to decrease menopausal symptoms in post-menopausal women. However, long-term HRT increases the incidence of breast, ovarian and endometrial cancers. 4-Hydroxyequilenin (4-OHEN), a metabolite of equine estrogens present in common HRT formulations (Premarin), is capable of producing bulky 4-OHEN-DNA adducts. An immunological assay using our adduct-specific antibodies revealed that 4-OHEN-DNA adducts are repaired inefficiently in human breast cancer cells. MTS assay revealed that similar 4-OHEN sensitivities are observed between human normal and repair-deficient cells. Moreover, histones including human H1 competitively inhibited the binding of the antibodies to 4-OHEN-DNA adducts in a concentration-dependent manner, which are considered as a model of damage-recognising repair protein. Thus, the formation of DNA adducts with inefficient repair character might be involved in carcinogenesis process of Premarin-induced cancers.