Gibson N W, Zlotogorski C, Erickson L C
Carcinogenesis. 1985 Mar;6(3):445-50. doi: 10.1093/carcin/6.3.445.
In two recent reports we have shown that pretreatment of MER+ cells [cells proficient at: reactivating N-methyl-N'-nitro-N-nitrosoguanidine (MNNG)-treated adenovirus; removing O-6 methylguanine from their DNA; and preventing DNA interstrand crosslinks produced by the chloroethylnitrosoureas (CNUs)] with MNNG apparently inhibits the repair process that these cells utilize to prevent CNU-induced DNA interstrand crosslinking. The MNNG pretreatment, accompanied by a subsequent CNU treatment, resulted in a synergistic increase in cell kill of 2-3 logs. In the present study we have examined whether or not conditions which inhibit the ability of a cell to prevent CNU-induced DNA interstrand crosslinking can also prevent DNA interstrand crosslinking induced by four clinically used alkylating anti-tumor agents. The agents used in the present study include cis-diamminedichloroplatinum(II) (cis-Pt), L-phenylalanine mustard (L-PAM), nitrogen mustard (HN-2) and 4-S-(propionic acid)-sulfidocyclophosphamide (C-2), a derivative of cyclophosphamide. Alkaline elution analysis was used to measure DNA interstrand crosslinking, and colony formation assays to estimate cell survival. Unlike the CNUs, all four agents produced DNA interstrand crosslinks in a Mer+ cell line in the absence of MNNG pretreatment. MNNG pretreatment did not alter the levels of DNA interstrand crosslinks formed. Similar results were seen with a Mer- cell line. In cytotoxicity studies, in contrast to the CNUs, MNNG pretreatment did not appreciably increase the cell kill produced by the four agents. Since all four agents studied are thought to react primarily at the N-7 position in guanine, these data suggest that: the DNA repair system which prevents CNU-induced crosslinking is specific for methyl, ethyl, and chloroethyl monoadducts; this DNA repair system is specific for adducts only at the O-6 position of guanine and does not recognize and remove adducts at other positions in DNA; or a combination of the two explanations.
在最近的两份报告中，我们已经表明，用N-甲基-N'-硝基-N-亚硝基胍（MNNG）对MER +细胞[能够重新激活经MNNG处理的腺病毒的细胞；从其DNA中去除O-6-甲基鸟嘌呤；并防止氯乙基亚硝基脲（CNU）产生的DNA链间交联]进行预处理，显然会抑制这些细胞用于防止CNU诱导的DNA链间交联的修复过程。MNNG预处理，随后进行CNU处理，导致细胞杀伤协同增加2 - 3个对数。在本研究中，我们研究了抑制细胞防止CNU诱导的DNA链间交联能力的条件是否也能防止四种临床使用的烷基化抗肿瘤药物诱导的DNA链间交联。本研究中使用的药物包括顺式二氨二氯铂（II）（顺铂）、L-苯丙氨酸氮芥（L-PAM）、氮芥（HN-2）和4-S-（丙酸）-硫代环磷酰胺（C-2），一种环磷酰胺的衍生物。碱性洗脱分析用于测量DNA链间交联，集落形成试验用于估计细胞存活率。与CNU不同，在没有MNNG预处理的情况下，所有四种药物在Mer +细胞系中都产生了DNA链间交联。MNNG预处理并没有改变形成的DNA链间交联水平。在Mer -细胞系中也观察到了类似的结果。在细胞毒性研究中，与CNU相反，MNNG预处理并没有明显增加这四种药物产生的细胞杀伤。由于所研究的所有四种药物被认为主要在鸟嘌呤的N-7位置发生反应，这些数据表明：防止CNU诱导的交联的DNA修复系统对甲基、乙基和氯乙基单加合物具有特异性；这种DNA修复系统仅对鸟嘌呤O-6位置的加合物具有特异性，不识别和去除DNA其他位置的加合物；或者是这两种解释的结合。
