Ewesuedo R B, Wilson L R, Friedman H S, Moschel R C, Dolan M E
Department of Pediatrics, University of Chicago, IL 60637, USA.
Cancer Chemother Pharmacol. 2001;47(1):63-9. doi: 10.1007/s002800000202.
The purpose of this study was to determine the usefulness of various 8-substituted O6-benzylguanine (BG) analogs as modulators of the DNA repair protein. O6-alkylguanine-DNA alkyltransferase (AGT). More specifically, the degree of inactivation of AGT in mouse brain, liver, kidney and tumor by O6-benzyl-8-oxoguanine (8-oxoBG), 8-aza-O6-benzylguanine (8-azaBG), O6-benzyl-8-bromoguanine (8-bromoBG) and O6-benzyl-8-trifluoromethylguanine (8-tfmBG) was compared to inactivation by BG, a modulator in phase II clinical trials. BG is converted rapidly to 8-oxoBG in rodents, monkeys and humans. It was reasoned that 8-substituted analogs of BG would exhibit different pharmacological properties compared to BG which could influence tissue bioavailability and, thus, the extent of AGT inactivation in vivo. We compared the tissue distribution of these agents and AGT activity following administration of the 8-substituted analogs.
At various time points up to 24 h after i.p. administration of the BG analogs, tissues (i.e. brain, liver, kidney), A549 lung tumor xenografts (i.p.) or D456 brain tumor xenografts (i.c.) were harvested from athymic nude mice for AGT analysis. AGT activity was quantified in tissue extracts using a biochemical assay with [3H]methylated DNA as a substrate. In addition, concentrations of BG and 8-oxoBG were determined by HPLC with fluorescence detection in mouse tissues following administration of drug.
Each of the 8-substituted analogs of BG demonstrated variable AGT inactivation capabilities that were comparable to or better than those of BG especially in kidney and brain tissues. There was a more pronounced depletion of AGT inactivation in brain and D456 brain tumor xenografts following administration of BG compared to 8-oxoBG that could be explained by a much greater concentration of AGT-inactivating drug (BG plus the metabolite 8-oxoBG for mice treated with BG versus 8-oxoBG for mice treated with 8-oxoBG) present in these tissues. The AUCs for brain, kidney and liver were 3.2, 6.9 and 1 1.8 times greater for BG than for 8-oxoBG.
8-substituted analogs of BG possess unique AGT-inactivation profiles in vivo that are different from that of BG. The AGT-inhibitory activities of BG and its major metabolite, 8-oxoBG, are related to tissue disposition of both drugs.
本研究的目的是确定各种8-取代的O6-苄基鸟嘌呤（BG）类似物作为DNA修复蛋白O6-烷基鸟嘌呤-DNA烷基转移酶（AGT）调节剂的效用。更具体地说，比较了O6-苄基-8-氧代鸟嘌呤（8-氧代BG）、8-氮杂-O6-苄基鸟嘌呤（8-氮杂BG）、O6-苄基-8-溴鸟嘌呤（8-溴BG）和O6-苄基-8-三氟甲基鸟嘌呤（8-三氟甲基BG）对小鼠脑、肝、肾和肿瘤中AGT的失活程度与BG（II期临床试验中的一种调节剂）的失活程度。BG在啮齿动物、猴子和人类中会迅速转化为8-氧代BG。据推测，与BG相比，BG的8-取代类似物将表现出不同的药理特性，这可能会影响组织生物利用度，从而影响体内AGT失活的程度。我们比较了这些药物的组织分布以及给予8-取代类似物后AGT的活性。
在腹腔注射BG类似物后长达24小时的不同时间点，从无胸腺裸鼠中采集组织（即脑、肝、肾）、A549肺肿瘤异种移植物（腹腔内）或D456脑肿瘤异种移植物（脑内）用于AGT分析。使用以[3H]甲基化DNA为底物的生化测定法对组织提取物中的AGT活性进行定量。此外，在给药后通过高效液相色谱荧光检测法测定小鼠组织中BG和8-氧代BG的浓度。
BG的每种8-取代类似物都表现出可变的AGT失活能力，与BG相当或优于BG，尤其是在肾和脑组织中。与8-氧代BG相比，给予BG后脑和D456脑肿瘤异种移植物中AGT失活的消耗更为明显，这可以通过这些组织中存在的使AGT失活的药物浓度更高来解释（给予BG的小鼠中为BG加上代谢物8-氧代BG，而给予8-氧代BG的小鼠中为8-氧代BG）。BG在脑、肾和肝中的曲线下面积分别是8-氧代BG的3.2倍、6.9倍和11.8倍。
BG的8-取代类似物在体内具有独特的AGT失活谱，与BG不同。BG及其主要代谢物8-氧代BG的AGT抑制活性与两种药物的组织分布有关。
