Murakami T, Li X, Gong J, Bhatia U, Traganos F, Darzynkiewicz Z
Cancer Research Institute, New York Medical College, Valhalla 10595, USA.
Cancer Res. 1995 Jul 15;55(14):3093-8.
There are conflicting data in the literature as to whether cytotoxicity of the cytidine antimetabolite 5'-azacytidine (AZC) is a consequence of its incorporation into RNA, DNA, or both. Because apoptosis appears to be the predominant mode of tumor cell death after treatment with most antitumor drugs, and in the case of some drugs, the proclivity of the cell to undergo apoptosis varies depending on the cell cycle position, this study was aimed toward elucidating whether induction of apoptosis by AZC is cell cycle phase specific. Human promyelocytic leukemic HL-60 cells were treated with varying concentrations of AZC, and flow cytometric methods that identify apoptotic cels and provide information about the cell cycle distribution of the apoptotic and nonapoptotic cell populations were used. At 2-6 microM concentrations of AZC, the cells in the G1 phase preferentially underwent apoptosis, whereas the cells in G2-M were particularly resistant. Although incorporation of bromouridine into RNA was suppressed at that low AZC concentration, the rate of 5'-bromo-2-deoxyuridine incorporation into DNA was not significantly affected. At an AZC concentration of 8-40 microM, no cell cycle phase specificity in induction of apoptosis was apparent, but both the rate of 5'-bromo-2-deoxyuridine incorporation into DNA and bromouridine into RNA were reduced in proportion to drug concentration. The data suggest that the mechanism of cell killing by AZC may be different, depending on its concentration. Namely, whereas incorporation of AZC into RNA may play a predominant role in the induction of cytotoxicity of G1 cells at low drug concentrations, the perturbation of both RNA and DNA metabolism may be responsible for triggering cell death in the G1 and S phases, as is seen at higher concentrations of this antimetabolite.
关于胞苷抗代谢物5'-氮杂胞苷（AZC）的细胞毒性是其掺入RNA、DNA还是两者兼而有之的结果，文献中的数据存在冲突。由于凋亡似乎是大多数抗肿瘤药物治疗后肿瘤细胞死亡的主要方式，并且对于某些药物而言，细胞发生凋亡的倾向因细胞周期位置而异，因此本研究旨在阐明AZC诱导的凋亡是否具有细胞周期阶段特异性。用不同浓度的AZC处理人早幼粒细胞白血病HL-60细胞，并使用能够识别凋亡细胞并提供有关凋亡和非凋亡细胞群体细胞周期分布信息的流式细胞术方法。在2-6 microM浓度的AZC下，G1期的细胞优先发生凋亡，而G2-M期的细胞则特别耐药。尽管在低AZC浓度下溴尿苷掺入RNA的过程受到抑制，但5'-溴-2'-脱氧尿苷掺入DNA的速率并未受到显著影响。在8-40 microM的AZC浓度下，诱导凋亡时未表现出细胞周期阶段特异性，但5'-溴-2'-脱氧尿苷掺入DNA的速率和溴尿苷掺入RNA的速率均与药物浓度成比例降低。数据表明，AZC杀死细胞的机制可能因其浓度而异。也就是说，在低药物浓度下，AZC掺入RNA可能在诱导G1期细胞的细胞毒性中起主要作用，而在较高浓度的这种抗代谢物作用下，RNA和DNA代谢的紊乱可能是触发G1期和S期细胞死亡的原因。
