Experimental Chemotherapy Laboratory, Regina Elena Cancer Institute, Tor Vergata University, Rome, Italy.
Clin Cancer Res. 2011 Apr 15;17(8):2227-36. doi: 10.1158/1078-0432.CCR-10-3033. Epub 2011 Feb 25.
We previously reported that the G-quadruplex (G4) ligand RHPS4 potentiates the antitumor activity of camptothecins both in vitro and in tumor xenografts. The present study aims at investigating the mechanisms involved in this specific drug interaction.
Combination index test was used to evaluate the interaction between G4 ligands and standard or novel Topo I inhibitors. Chromatin immunoprecipitation was performed to study the presence at telomeres of various types of topisomerase, while immunolabeling experiments were performed to measure the activation of DNA damage both in vitro and in tumor xenografts.
We report that integration of the Topo I inhibitor SN-38, but not the Topo II poison doxorubicin with telomere-based therapy is strongly effective and the sequence of drug administration is critical in determining the synergistic interaction, impairing the cell ability to recover from drug-induced cytotoxicity. The synergistic effect of this combination was also observed by using novel camptothecins and, more interestingly, mice treated with ST1481/RHPS4 combination showed an inhibition and delay of tumor growth as well as an increased survival. The study of the mechanism(s) revealed that treatment with G4 ligands increased Topo I at the telomeres and the functional relevance of this observation was directly assessed by showing that standard and novel camptothecins stabilized DNA damage both in vitro and in xenografts.
Our results demonstrate an outstanding efficacy of Topo I inhibitors/G4 ligands combination, which likely reflects an enhanced and persistent activation of DNA damage response as a critical determinant of the therapeutic improvement.
我们之前报道过 G-四链体（G4）配体 RHPS4 可增强喜树碱类药物在体外和肿瘤异种移植中的抗肿瘤活性。本研究旨在探讨这种特定药物相互作用的机制。
采用组合指数试验评估 G4 配体与标准或新型拓扑异构酶 I 抑制剂的相互作用。采用染色质免疫沉淀法研究各种拓扑异构酶在端粒上的存在情况，同时进行免疫标记实验测量体外和肿瘤异种移植中 DNA 损伤的激活情况。
我们报告称，拓扑异构酶 I 抑制剂 SN-38 的整合，而不是拓扑异构酶 II 毒剂阿霉素与基于端粒的治疗相结合，具有很强的有效性，且药物给药顺序对于确定协同作用至关重要，这会损害细胞从药物诱导的细胞毒性中恢复的能力。这种组合的协同作用也可以通过使用新型喜树碱类药物观察到，更有趣的是，用 ST1481/RHPS4 联合治疗的小鼠显示出肿瘤生长的抑制和延迟以及生存时间的延长。对机制的研究表明，G4 配体处理增加了端粒上的拓扑异构酶 I，并且通过显示标准和新型喜树碱类药物在体外和异种移植中稳定 DNA 损伤，直接评估了这一观察结果的功能相关性。
我们的结果表明，拓扑异构酶 I 抑制剂/G4 配体的联合具有出色的疗效，这可能反映了 DNA 损伤反应的增强和持续激活，是治疗效果改善的关键决定因素。
