Enhancement of in vitro and in vivo tumor cell radiosensitivity by the DNA methylation inhibitor zebularine
Enhancement of in vitro and in vivo tumor cell radiosensitivity by the DNA methylation inhibitor zebularine
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DOI：
10.1158/1078-0432.ccr-05-0050
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发表时间：
2005-06-15
影响因子：
11.5
通讯作者：
Tofilon, PJ
中科院分区：
文献类型：
--
作者：
Dote, H;Cerna, D;Tofilon, PJ
异常的DNA高甲基化是肿瘤细胞中常见的现象，这表明抑制DNA甲基化可能是一种有效的癌症治疗策略。由于DNA甲基化影响基因表达和染色质结构，被认为是影响放射反应的参数，我们研究了DNA甲基化抑制剂zebularine对人肿瘤细胞放射敏感性的影响。本研究中使用了三种人肿瘤细胞系（MiaPaCa、DU 145和U251），并确定了肿瘤细胞中三种经常高甲基化的基因（RASSF 1A、HIC-1和14-3-3 sigma）的甲基化状态与zebularine暴露量的关系。Zebularine以时间依赖性方式导致DNA去甲基化，在48小时检测到最大甲基化损失。用zebularine处理细胞48小时也导致放射敏感性增加，剂量增强因子> 1.5。作为辐射诱导的DNA损伤的量度，测定γ H2 AX表达。尽管zebularine在1小时时对辐射诱导的γ H2 AX焦点没有影响，但在照射后24小时时，在zebularine处理的细胞中，每个细胞的γ H2 AX焦点的数量显著更大，表明存在未修复的DNA损伤。给小鼠注射Zebularine可重新激活U251异种移植瘤的基因表达;用zebularine照射小鼠U251肿瘤可导致放射诱导的肿瘤生长延迟增加。这些结果表明zebularine可增强肿瘤细胞在体外和体内的放射敏感性，并提示这种作用可能涉及抑制DNA修复。
Aberrant DNA hypermethylation is a frequent finding in tumor cells, which has suggested that inhibition of DNA methylation may be an effective cancer treatment strategy. Because DNA methylation affects gene expression and chromatin structure, parameters considered to influence radioresponse, we investigated the effects of the DNA methylation inhibitor zebularine on the radiosensitivity of human tumor cells. Three human tumor cell lines were used in this study (MiaPaCa, DU145, and U251) and the methylation status of three genes frequently hypermethylated in tumor cells (RASSF1A, HIC-1, and 14-3-3 sigma) was determined as a function of zebularine exposure. Zebularine resulted in DNA demethylation in a time-dependent manner, with the maximum loss of methylation detected by 48 hours. Treatment of cells with zebularine for 48 hours also resulted in an increase in radiosensitivity with dose enhancement factors of > 1.5. As a measure of radiation-induced DNA damage, gamma H2AX expression was determined. Whereas zebularine had no effect on radiation-induced gamma H2AX foci at 1 hour, the number of gamma H2AX foci per cell was significantly greater in the zebularine-treated cells at 24 hours after irradiation, suggesting the presence of unrepaired DNA damage. Zebularine administration to mice reactivated gene expression in U251 xenografts; irradiation of U251 tumors in micetreated with zebularine resulted in an increase in radiation -induced tumor growth delay.These results indicate that zebularine can enhance tumor cell radiosensitivity in vitro and in vivo and suggest that this effect may involve an inhibition of DNA repair.