Turesky R J, Markovic J
Nestec Ltd., Research Centre, Lausanne, Switzerland.
Chem Res Toxicol. 1994 Nov-Dec;7(6):752-61. doi: 10.1021/tx00042a007.
DNA adduct formation of 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) has been investigated by 32P-postlabeling. Similar adduct profiles were observed from calf thymus DNA modified in vitro with the putative carcinogenic metabolite N2-acetoxyamino-3-methylimidazo[4,5-f]-quinoline (N-acetoxy-IQ) and from hepatic DNA of rats treated with IQ. N-(Deoxyguanosin-8-yl)-2-amino-3-methylimidazo[4,5-f]quinoline (dG-C8-IQ) accounted for approximately 90% of the total adducts observed in calf thymus DNA under postlabeling conditions where ATP was limiting; however, 5-(deoxyguanosin-N2-yl)-2-amino-3-methylimidazo[4,5- f]quinoline (dG-N2-IQ) was detected only when DNA was labeled with excess ATP. Under these labeling conditions, dG-C8-IQ and dG-N2-IQ accounted for approximately 75% and 7% of the total adducts, respectively. Five other spots accounted for the remaining radioactivity. Comparable results were obtained from rat liver DNA. Following DNA adduct enrichment by solid phase extraction, dG-C8-IQ and dG-N2-IQ accounted for 60-76% and 10-13%, respectively, of the total adducts in rat liver. The adduct profiles obtained from reaction of 2'-deoxyguanosine 3'-monophosphate (dG-3'-PO4-) with the photoactivated azide derivative of IQ, 2-azido-3-methylimidazo[4,5-f]quinoline (N3-IQ), were qualitatively similar to those obtained by reaction with N-acetoxy-IQ. The C-8 and N2 adducts were the only reaction products detected. The reactivity and sites of adduct substitution were dependent upon solvent conditions and pH, with increasing adduct formation under alkaline pH. The chemical reactivity of photoactivated N3-IQ with dG-3'-PO4- was significantly greater than that of N-acetoxy-IQ when reactions were conducted in water, in citrate buffer (pH 5.0), or in phosphate buffer (pH 7.4). Increased reactivity was attributed to increased levels of dG-C8-IQ adduct formation, except for reactions conducted in citrate buffer (pH 5.0), where there was a proportional increase in both C-8 and N2 guanine adducts. However, the chemical reactivity of these two IQ derivatives and their sites of dG substitution were identical when the reactions were conducted in phosphate buffer (pH 9.0). The ratio of the dG-N2-IQ adduct to the total adducts increased at alkaline pH in reactions involving N3-IQ, but the ratio was not affected by a change in the pH of the medium for reactions with N-acetoxy-IQ. The ratio of the dG-N2-IQ adduct to the total adducts also increased as a function of phosphate concentration for reactions involving both N-acetoxy-IQ and N3-IQ.(ABSTRACT TRUNCATED AT 400 WORDS)
通过³²P后标记法研究了2-氨基-3-甲基咪唑并[4,5-f]喹啉（IQ）的DNA加合物形成情况。在用假定的致癌代谢物N²-乙酰氧基氨基-3-甲基咪唑并[4,5-f]喹啉（N-乙酰氧基-IQ）体外修饰的小牛胸腺DNA以及用IQ处理的大鼠肝脏DNA中，观察到了相似的加合物谱。在ATP受限的后标记条件下，N-（脱氧鸟苷-8-基）-2-氨基-3-甲基咪唑并[4,5-f]喹啉（dG-C8-IQ）约占小牛胸腺DNA中观察到的总加合物的90%；然而，仅当DNA用过量ATP标记时才检测到5-（脱氧鸟苷-N²-基）-2-氨基-3-甲基咪唑并[4,5-f]喹啉（dG-N2-IQ）。在这些标记条件下，dG-C8-IQ和dG-N2-IQ分别约占总加合物的75%和7%。其他五个斑点占剩余的放射性。从大鼠肝脏DNA也获得了类似的结果。通过固相萃取富集DNA加合物后，dG-C8-IQ和dG-N2-IQ分别占大鼠肝脏总加合物的60 - 76%和10 - 13%。从2'-脱氧鸟苷3'-单磷酸（dG-3'-PO4-）与IQ的光活化叠氮衍生物2-叠氮基-3-甲基咪唑并[4,5-f]喹啉（N3-IQ）反应得到的加合物谱，在质量上与用N-乙酰氧基-IQ反应得到的相似。检测到的唯一反应产物是C-8和N2加合物。加合物取代的反应性和位点取决于溶剂条件和pH值，在碱性pH下加合物形成增加。当在水中、柠檬酸盐缓冲液（pH 5.0）或磷酸盐缓冲液（pH 7.4）中进行反应时，光活化的N3-IQ与dG-3'-PO4-的化学反应性明显大于N-乙酰氧基-IQ。反应性增加归因于dG-C8-IQ加合物形成水平的提高，除了在柠檬酸盐缓冲液（pH 5.0）中进行的反应，在该缓冲液中C-8和N2鸟嘌呤加合物都有相应增加。然而，当在磷酸盐缓冲液（pH 9.0）中进行反应时，这两种IQ衍生物的化学反应性及其dG取代位点是相同的。在涉及N3-IQ的反应中，碱性pH下dG-N2-IQ加合物与总加合物的比例增加，但在与N-乙酰氧基-IQ反应时，该比例不受介质pH变化的影响。在涉及N-乙酰氧基-IQ和N3-IQ的反应中，dG-N2-IQ加合物与总加合物的比例也随磷酸盐浓度的增加而增加。（摘要截断于400字）
