Smith Sonali M, Ludeman Susan M, Wilson Lynette R, Springer James B, Gandhi Mihir C, Dolan M Eileen
Department of Medicine, University of Chicago, Chicago, IL 60637, USA.
Cancer Chemother Pharmacol. 2003 Oct;52(4):291-302. doi: 10.1007/s00280-003-0672-2. Epub 2003 Jul 4.
O6-benzylguanine (BG) is a unique purine analog that has been shown to influence nitrogen mustard activity and increase cytotoxicity. Ifosfamide is a nitrogen mustard with growing clinical applications; effective modulation may lead to improved efficacy. We thus undertook a preliminary investigation of BG's effects on ifosfamide and ifosfamide derivatives in vitro.
BG's effect on ifosfamide toxicity was studied in CHO cells transfected with O6-alkylguanine-DNA alkyltransferase (AGT) (CHOwtAGT) or control plasmid pcDNA3 (CHOpcDNA) using five ifosfamide derivatives and two control compounds: 4-hydroperoxyifosfamide (4HI), isophosphoramide mustard (IPM), phenylketoifosfamide (PKIF), 4-hydroperoxydidechloroifosfamide (4HDI), chloroacetaldehyde (CAA), didechloroisophosphoramide mustard (d-IPM), didechlorophenylketoifosfamide (d-PKIF). To further explore the mechanism of interaction, BG's effect on apoptosis (annexin V-FITC) and cell cycle distribution in cells exposed to ifosfamide was also analyzed.
BG substantially enhanced cytotoxicity induced only by agents that produce IPM (4HI, IPM, PKIF) in both CHOwtAGT and CHOpcDNA cell lines. BG did not modulate 4HDI or CAA cytotoxicity. The addition of BG to IPM in CHO cells increased the percentage of apoptotic cells from 5.5% to 28.9% at 72 h after treatment. Cell cycle analysis showed that BG exposure was associated with G1 arrest. At 16 h following treatment with IPM, PKIF, or phosphoramide mustard (PM), BG increased the percentage of cells in G1 from 16-20% to 29-64%.
BG's ability to increase 4HI-, IPM-, and PKIF-mediated cytotoxicity in cells devoid of AGT activity suggests a novel AGT-independent mode of action that is associated with increased apoptosis and may involve G1 arrest. BG selectively enhanced IPM toxicity without enhancement of acrolein and CAA toxicity. The data strongly support further investigation into combinations of BG and nitrogen mustards.
O6-苄基鸟嘌呤（BG）是一种独特的嘌呤类似物，已被证明可影响氮芥活性并增加细胞毒性。异环磷酰胺是一种临床应用日益广泛的氮芥；有效的调节可能会提高疗效。因此，我们对BG在体外对异环磷酰胺及其衍生物的作用进行了初步研究。
使用五种异环磷酰胺衍生物和两种对照化合物：4-氢过氧异环磷酰胺（4HI）、异磷酰胺氮芥（IPM）、苯甲酰异环磷酰胺（PKIF）、4-氢过氧二氯异环磷酰胺（4HDI）、氯乙醛（CAA）、二氯异磷酰胺氮芥（d-IPM）、二氯苯甲酰异环磷酰胺（d-PKIF），研究BG对转染了O6-烷基鸟嘌呤-DNA烷基转移酶（AGT）的CHO细胞（CHOwtAGT）或对照质粒pcDNA3（CHOpcDNA）中异环磷酰胺毒性的影响。为进一步探讨相互作用机制，还分析了BG对暴露于异环磷酰胺的细胞中凋亡（膜联蛋白V-FITC）和细胞周期分布的影响。
BG仅显著增强了在CHOwtAGT和CHOpcDNA细胞系中由产生IPM的试剂（4HI、IPM、PKIF）诱导的细胞毒性。BG未调节4HDI或CAA的细胞毒性。在CHO细胞中，将BG添加到IPM中，处理72小时后，凋亡细胞百分比从5.5%增加到28.9%。细胞周期分析表明，暴露于BG与G1期阻滞有关。在用IPM、PKIF或磷酰胺氮芥（PM）处理16小时后，BG使G1期细胞百分比从16 - 20%增加到29 - 64%。
BG在缺乏AGT活性的细胞中增加4HI、IPM和PKIF介导的细胞毒性的能力表明存在一种新的不依赖AGT的作用模式，这与凋亡增加有关，可能涉及G1期阻滞。BG选择性增强IPM毒性，而不增强丙烯醛和CAA毒性。这些数据有力地支持了对BG与氮芥联合使用的进一步研究。
