Balch Curtis, Yan Pearlly, Craft Teresa, Young Suzanne, Skalnik David G, Huang Tim H-M, Nephew Kenneth P
Medical Sciences Program, Indiana University, 302 Jordan Hall, 1001 East Third Street, Bloomington, IN 47405, USA.
Mol Cancer Ther. 2005 Oct;4(10):1505-14. doi: 10.1158/1535-7163.MCT-05-0216.
Deoxycytosine methylation within CpG islands of tumor suppressor genes plays a prominent role in the development and progression of drug-resistant ovarian cancer. Consequently, epigenetic therapies directed toward tumor suppressor demethylation/reexpression could potentially reverse malignant phenotypes and chemosensitize recalcitrant tumors. In this report, we examined the demethylating agent zebularine [1-(beta-D-ribofuranosyl)-1,2-dihydropyrimidin-2-one], in comparison with the well-known methylation inhibitor 5-aza-2'-deoxycytidine (5-aza-dC), for its ability to inhibit ovarian cancer cell proliferation and to demethylate and induce tumor suppressor genes. Zebularine exerted significant (>5-aza-dC) antiproliferative effects against the ovarian cancer cell lines Hey, A2780, and the cisplatin-resistant A2780/CP in a dose-dependent manner (65% versus 35% inhibition at 48 hours, zebularine versus 5-aza-dC). Moreover, 48-hour treatment with 0.2 mmol/L zebularine significantly induced demethylation of the tumor suppressors ras-associated domain family 1A and human MutL homologue-1. RASSF1A gene reexpression was also observed, as was reexpression of two other tumor suppressors, ARHI and BLU, although levels differed from those induced by 5-aza-dC. Global analyses of DNA methylation revealed similar overall demethylation (2.5- to 3-fold) by 5-aza-dC and zebularine as determined by methyl acceptance assay. However, differences in demethylation of individual loci were observed as determined by differential methylation hybridization. Finally, we found that zebularine could resensitize the drug-resistant cell line A2780/CP to cisplatin, with a 16-fold reduction in the IC50 of that conventional agent. In summary, zebularine seems to be a promising clinical candidate, singly or combined with conventional regimens, for the therapy of drug-resistant ovarian cancer.
肿瘤抑制基因的CpG岛内的脱氧胞嘧啶甲基化在耐药性卵巢癌的发生和发展中起重要作用。因此，针对肿瘤抑制因子去甲基化/重新表达的表观遗传疗法可能逆转恶性表型并使顽固性肿瘤对化疗敏感。在本报告中，我们研究了去甲基化剂zebularine [1-(β-D-呋喃核糖基)-1,2-二氢嘧啶-2-酮]，并与著名的甲基化抑制剂5-氮杂-2'-脱氧胞苷（5-aza-dC）相比较，观察其抑制卵巢癌细胞增殖以及使肿瘤抑制基因去甲基化和诱导其表达的能力。Zebularine对卵巢癌细胞系Hey、A2780和顺铂耐药的A2780/CP具有显著（>5-aza-dC）的抗增殖作用，且呈剂量依赖性（48小时时抑制率为65%对35%，zebularine对5-aza-dC）。此外，用0.2 mmol/L zebularine处理48小时可显著诱导肿瘤抑制因子ras相关结构域家族1A和人MutL同源物-1的去甲基化。还观察到RASSF1A基因重新表达，另外两个肿瘤抑制因子ARHI和BLU也重新表达，尽管其水平与5-aza-dC诱导的不同。通过甲基接受试验确定，5-aza-dC和zebularine对DNA甲基化的整体分析显示出相似的总体去甲基化（2.5至3倍）。然而，通过差异甲基化杂交确定，观察到各个位点去甲基化存在差异。最后，我们发现zebularine可使耐药细胞系A2780/CP对顺铂重新敏感，使该传统药物的IC50降低16倍。总之，zebularine单独或与传统方案联合应用，似乎是治疗耐药性卵巢癌的有前景的临床候选药物。
