Del Bino G, Bruno S, Yi P N, Darzynkiewicz Z
Cancer Research Institute, New York Medical College, Valhalla 10523.
Cell Prolif. 1992 Nov;25(6):537-48. doi: 10.1111/j.1365-2184.1992.tb01458.x.
We have previously observed that the DNA topoisomerase I inhibitor camptothecin (CAM), or DNA topoisomerase II inhibitors teniposide (TEN) and amsacrine (m-AMSA) trigger endonucleolytic activity in myelogenous (HL-60 or KG1), but not lymphocytic (MOLT-4) leukaemic cell lines. DNA degradation and other signs of apoptotic death were seen as early as 2-4 h after cell exposure to these inhibitors. Cells replicating DNA (S phase) were selectively sensitive whereas cells in G1 were resistant; the sensitivity of G2 or M cells could not be assessed in these studies. The present studies were aimed at revealing whether DNA repair replication induced by ionizing radiation can sensitize the cells, and to probe the sensitivity of cells arrested in G2 or M, to these inhibitors. The data show that gamma-irradiation (0.5-15 Gy) of HL-60 cells does not alter their pattern of sensitivity, i.e. G1 cells, although engaged in DNA repair replication, still remain resistant to CAM compared with the S phase cells. Likewise, irradiation of MOLT-4 cells also does not render them sensitive to either CAM or TEN, regardless of their position in the cell cycle. Irradiation, however, by slowing the rate of cell progression through S, increased the proportion of S phase cells, and thus made the whole cell population more sensitive to CAM. HL-60 cells arrested in G2 either by irradiation or treatments with Hoechst 33342 or doxorubicin appear to be more resistant to CAM relative to S phase cells. Also resistant are cells arrested in M by vinblastine. The data suggest that some factor(s) exist exclusively in S phase cells, which precondition them to respond to the inhibitors of DNA topoisomerases by rapid activation of endogenous nuclease(s) and subsequent death by apoptosis. HL-60 cells in G1, G2 or M, or MOLT-4 cells, regardless of the phase of the cycle, appear to be protected from such a mechanism, and even induction of DNA repair replication cannot initiate DNA degradation in response to DNA topoisomerase inhibitors. These data, together with the evidence in the literature that topoisomerase I may be involved in DNA repair, suggest that a combination of these inhibitors with treatments that synchronize cells in the S phase and/or recruit quiescent cells to proliferation, including radiation, may be of value in the clinic.
我们之前观察到，DNA拓扑异构酶I抑制剂喜树碱（CAM）或DNA拓扑异构酶II抑制剂替尼泊苷（TEN）和安吖啶（m-AMSA）可在髓源性白血病细胞系（HL-60或KG1）中引发核酸内切酶活性，但在淋巴细胞白血病细胞系（MOLT-4）中则不会。早在细胞接触这些抑制剂后2-4小时，就可观察到DNA降解及其他凋亡死亡迹象。正在复制DNA的细胞（S期）具有选择性敏感性，而G1期细胞则具有抗性；在这些研究中无法评估G2期或M期细胞的敏感性。本研究旨在揭示电离辐射诱导的DNA修复复制是否会使细胞敏感，以及探究停滞在G2期或M期的细胞对这些抑制剂的敏感性。数据表明，对HL-60细胞进行γ射线照射（0.5-15 Gy）不会改变其敏感性模式，即G1期细胞尽管参与DNA修复复制，但与S期细胞相比，对CAM仍具有抗性。同样，对MOLT-4细胞进行照射也不会使其对CAM或TEN敏感，无论它们在细胞周期中的位置如何。然而，照射通过减缓细胞通过S期的进程，增加了S期细胞的比例，从而使整个细胞群体对CAM更敏感。通过照射或用Hoechst 33342或阿霉素处理而停滞在G2期的HL-60细胞相对于S期细胞似乎对CAM更具抗性。被长春碱阻滞在M期的细胞也具有抗性。数据表明，某些因素仅存在于S期细胞中，这些因素使它们通过快速激活内源性核酸酶并随后凋亡死亡来对DNA拓扑异构酶抑制剂作出反应。处于G1期、G2期或M期的HL-60细胞，或MOLT-4细胞，无论处于细胞周期的哪个阶段，似乎都受到这种机制的保护，即使诱导DNA修复复制也无法引发对DNA拓扑异构酶抑制剂的DNA降解反应。这些数据，连同文献中关于拓扑异构酶I可能参与DNA修复的证据，表明这些抑制剂与使细胞同步于S期和/或促使静止细胞增殖的处理方法（包括辐射）联合使用，可能在临床上具有价值。
