Pharmacology Unit bBiochemistry and Molecular Biology Unit, Tumour Biology Department, National Cancer Institute, Cairo University, Cairo, Egypt.
Anticancer Drugs. 2010 Mar;21(3):277-87. doi: 10.1097/CAD.0b013e328334b0ae.
Inhibition of the repair of 5-fluorouracil (FU)-induced DNA lesions may improve the response of many tumors to this anticancer agent. Despite the identified associations between DNA strand breaks and the lethality of thymidylate synthase inhibitors, the role of DNA double-strand break (DSB) repair pathways in a cellular response to 5-FU treatment has not been studied yet. Isogenic cell lines defective (irs1SF), wild type (AA8), or reconstituted (1SFK8) in the DSB repair protein XRCC3 were used to investigate the effect of defective DSB repair on the overall sensitivity of cells to 5-FU and to see how targeting DSB repair may affect other cellular responses to 5-FU. Treatment with 5-FU resulted in (i) similar induction of DSB in both cell lines as indicated by the formation of gamma-H2AX (a marker for DSB). The repair of these breaks was complete in AA8 but not in irs1SF cells. (ii) Concentration-dependent reduction in the survival of both cell lines. The AA8 cells were six times more sensitive to 5-FU than the irs1SF cells. (iii) An earlier and more prolonged G(1)/S phase arrest in AA8 compared with the irs1SF cells. (iv) Induction of apoptosis as indicated by sub-G(1) cells and caspase-3 activity in AA8 but not in irs1SF cells. XRCC3 complementation of irs1SF cells restored the wild-type phenotype. This result shows that targeting DSB repair is not always associated with increased sensitivity to DNA damaging agents such as 5-FU because it may affect other cellular responses such as cell cycle regulation and induction of apoptosis.
抑制 5-氟尿嘧啶（FU）引起的 DNA 损伤修复可能会提高许多肿瘤对这种抗癌药物的反应。尽管已经确定了 DNA 链断裂与胸苷酸合成酶抑制剂的致死性之间存在关联，但 DNA 双链断裂（DSB）修复途径在细胞对 5-FU 治疗的反应中的作用尚未得到研究。使用在 DSB 修复蛋白 XRCC3 中缺陷（irs1SF）、野生型（AA8）或重建（1SFK8）的同源细胞系来研究 DSB 修复缺陷对细胞对 5-FU 的整体敏感性的影响，并观察靶向 DSB 修复如何影响细胞对 5-FU 的其他反应。用 5-FU 处理导致：（i）在两种细胞系中形成 γ-H2AX（DSB 的标志物）表明 DSB 的类似诱导。这些断裂的修复在 AA8 中是完全的，但在 irs1SF 细胞中不是。（ii）两种细胞系的存活均呈浓度依赖性降低。AA8 细胞对 5-FU 的敏感性是 irs1SF 细胞的六倍。（iii）与 irs1SF 细胞相比，AA8 细胞中更早和更持久的 G1/S 期阻滞。（iv）AA8 细胞中诱导凋亡，如亚 G1 细胞和 caspase-3 活性所示，但 irs1SF 细胞中没有。irs1SF 细胞中 XRCC3 的互补恢复了野生型表型。该结果表明，靶向 DSB 修复并不总是与对 5-FU 等 DNA 损伤剂的敏感性增加相关，因为它可能影响其他细胞反应，如细胞周期调节和凋亡诱导。
