Evison Benny J, Chiu Francis, Pezzoni Gabriella, Phillips Don R, Cutts Suzanne M
Department of Biochemistry, La Trobe University, Victoria 3086, Australia.
Mol Pharmacol. 2008 Jul;74(1):184-94. doi: 10.1124/mol.108.045625. Epub 2008 Apr 15.
The topoisomerase II poison mitoxantrone is important in the clinical management of human malignancies. Pixantrone, a novel aza-anthracenedione developed to improve the therapeutic profile of mitoxantrone, can efficiently alkylate DNA after formaldehyde activation. In vitro transcriptional analysis has now established that formaldehyde-activated pixantrone generates covalent adducts selectively at discrete CpG or CpA dinucleotides, suggesting that the activated complex binds to guanine or cytosine (or both) bases. The stability of pixantrone adduct-induced transcriptional blockages varied considerably, reflecting a mixture of distinct pixantrone adduct types that may include relatively labile monoadducts and more stable interstrand cross-links. 6,9-Bis-[[2-(dimethylamino)ethyl]amino]benzo[g]isoquinoline-5,10-dione (BBR 2378), the dimethyl N-substituted analog of pixantrone, could not form adducts, suggesting that pixantrone alkylates DNA through the primary amino functions located in each side chain of the drug. Pixantrone generated DNA adducts only when guanine was present in substrates and exhibited a lack of adduct formation with inosine-containing polynucleotides, confirming that the N2 amino group of guanine is the site for covalent attachment of the drug. Mass spectrometric analysis of oligonucleotide-drug complexes confirmed that formation of covalent pixantrone-DNA adducts is mediated by a single methylene linkage provided by formaldehyde and that this occurs only with guanine-containing double stranded oligonucleotide substrates. CpG methylation, an epigenetic modification of the mammalian genome, significantly enhanced the generation of pixantrone-DNA adducts within a methylated DNA substrate, indicating that the methylated dinucleotide may be a favored target in a cellular environment.
拓扑异构酶II抑制剂米托蒽醌在人类恶性肿瘤的临床治疗中具有重要作用。匹杉琼是一种为改善米托蒽醌治疗效果而研发的新型氮杂蒽二酮，在甲醛激活后能有效使DNA烷基化。目前的体外转录分析表明，甲醛激活的匹杉琼在离散的CpG或CpA二核苷酸处选择性地产生共价加合物，这表明激活的复合物与鸟嘌呤或胞嘧啶（或两者）碱基结合。匹杉琼加合物诱导的转录阻断稳定性差异很大，反映出不同类型的匹杉琼加合物的混合，其中可能包括相对不稳定的单加合物和更稳定的链间交联。匹杉琼的二甲基N-取代类似物6,9-双[[2-(二甲氨基)乙基]氨基]苯并[g]异喹啉-5,10-二酮（BBR 2378）不能形成加合物，这表明匹杉琼通过药物每个侧链中的伯氨基功能使DNA烷基化。匹杉琼仅在底物中存在鸟嘌呤时才产生DNA加合物，并且与含肌苷的多核苷酸不形成加合物，这证实了鸟嘌呤的N2氨基是药物共价连接的位点。寡核苷酸-药物复合物的质谱分析证实，共价匹杉琼-DNA加合物的形成是由甲醛提供的单个亚甲基连接介导的，并且这仅发生在含鸟嘌呤的双链寡核苷酸底物上。CpG甲基化是哺乳动物基因组的一种表观遗传修饰，它显著增强了甲基化DNA底物中匹杉琼-DNA加合物的生成，表明甲基化的二核苷酸可能是细胞环境中的一个有利靶点。
