Camphausen Kevin, Burgan William, Cerra Michael, Oswald Kelli A, Trepel Jane B, Lee Min-Jung, Tofilon Philip J
Radiation Oncology Branch and Molecular Radiation Therapeutics Branch, Radiation Oncology Sciences Program, Medicine Branch, National Cancer Institute, Bethesda, Maryland 20892, USA.
Cancer Res. 2004 Jan 1;64(1):316-21. doi: 10.1158/0008-5472.can-03-2630.
Histone deacetylase (HDAC) inhibitors are undergoing clinical evaluation for cancer therapy. Because HDAC modulates chromatin structure and gene expression, parameters considered to influence radioresponse, we have investigated the effects of the HDAC inhibitor MS-275 on the radiosensitivity of two human tumor cell lines (DU145 prostate carcinoma and U251 glioma). Acetylation status of histones H3 and H4 was determined as a function of time after MS-275 addition to and removal from culture medium. Histone acetylation increased by 6 h after MS-275 addition, reaching a maximum between 24 and 48 h of exposure; providing fresh drug-free medium then resulted in a decrease in histone acetylation that began by 6 h and approached untreated levels by 16 h. Treatment of cells with MS-275 for 48 h followed by irradiation had little or no effect on radiation-induced cell death. However, exposure to MS-275 before and after irradiation resulted in an increase in radiosensitivity with dose enhancement factors of 1.9 and 1.3 for DU145 and U251 cells, respectively. This MS-275 treatment protocol did not result in a redistribution of the cells into a more radiosensitive phase of the cell cycle or in an increase in apoptosis. However, MS-275 did modify the time course of gammaH2AX expression in irradiated cells. Whereas there was no significant difference in radiation-induced gammaH2AX foci at 6 h, the number of cells expressing gammaH2AX foci was significantly greater in the MS-275-treated cells at 24 h after irradiation. These results indicate that MS-275 can enhance radiosensitivity and suggest that this effect may involve an inhibition of DNA repair.
组蛋白去乙酰化酶（HDAC）抑制剂正处于癌症治疗的临床评估阶段。由于HDAC调节染色质结构和基因表达，而这些参数被认为会影响放射反应，我们研究了HDAC抑制剂MS-275对两种人类肿瘤细胞系（DU145前列腺癌和U251胶质瘤）放射敏感性的影响。在向培养基中添加和去除MS-275后，测定组蛋白H3和H4的乙酰化状态随时间的变化。添加MS-275后6小时，组蛋白乙酰化增加，在暴露24至48小时之间达到最大值；然后提供不含药物的新鲜培养基会导致组蛋白乙酰化减少，这种减少在6小时开始，到16小时接近未处理水平。用MS-275处理细胞48小时后再进行照射，对辐射诱导的细胞死亡几乎没有影响。然而，在照射前后暴露于MS-275会导致放射敏感性增加，DU145和U251细胞的剂量增强因子分别为1.9和1.3。这种MS-275处理方案并未导致细胞重新分布到细胞周期中更具放射敏感性的阶段，也未导致细胞凋亡增加。然而，MS-275确实改变了受照射细胞中γH2AX表达的时间进程。虽然在6小时时辐射诱导的γH2AX焦点没有显著差异，但在照射后24小时，MS-275处理的细胞中表达γH2AX焦点的细胞数量显著增加。这些结果表明MS-275可以增强放射敏感性，并表明这种效应可能涉及对DNA修复的抑制。
