Substrate Specificity of Human O6-Methylguanine-DNA Methyltransferase for O6-Benzylguanine Derivatives in Oligodeoxynucleotides

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• 作者：Isamu Terashima ; Hisaya Kawate ; Kunihiko Sakumi ; Mutsuo Sekiguchi ; and Kohfuku Kohda
• 刊名：Chemical Research in Toxicology
• 出版年：1997
• 出版时间：November 1997
• 年：1997
• 卷：10
• 期：11
• 页码：1234 - 1239
• 全文大小：176K
• 年卷期：v.10,no.11(November 1997)
• ISSN：1520-5010

文摘

To investigate the substrate specificity of humanO⁶-methylguanine-DNAmethyltransferase(MGMT) for O⁶-benzylguanine (6BG) derivativesincorporated in oligodeoxynucleotides, weprepared 25-mer lengths of sequences containing various 6BG derivativesand their relatedcompounds and then measured the ability of these derivatives toinactivate MGMT in vitro.Oligodeoxynucleotides containing a 6BG,O⁶-(2-fluorobenzyl)guanine (2F-6BG),O⁶-(3-fluorobenzyl)guanine (3F-6BG),O⁶-(4-fluorobenzyl)guanine (4F-6BG),O⁶-benzylhypoxanthine(6BH), or O⁶-methylguanine (6MG) were all goodsubstrates for MGMT, and no obviousdifferences were observed among them. Oligodeoxynucleotidescontaining N²-isobutyrylated6BG and 6MG showed only a slightly reduced capacity for inactivatingMGMT compared toN²-nonmodified forms of these derivatives.No obvious differences were observed in thecorresponding double-stranded and single-strandedoligodeoxynucleotides. MGMT substratespecificity for the 6BG derivatives in the oligodeoxynucleotide wasfound to be quite differentfrom that seen in our previous study [Mineura, K., et al. (1994)Int. J. Cancer 58, 706-712;(1995) Int. J. Cancer 63, 148-151. Kohda,K., et al. (1995) Biol. Pharm. Bull.18, 424-430]and others [Moschel, R. C., et al. (1992) J. Med. Chem.35, 4486-4491. Chae, M.-Y., et al.(1994) J. Med. Chem. 37, 342-347] using thecorresponding free bases. In brief, (i) 6BG, 3F-6BG, and 4F-6BG greatly inhibited human MGMT, whereas 2F-6BG, 6BH, and6MG displayedmuch weaker activity; (ii) any modifications at the 2-amino group ofthe 6BG resulted in severereductions in the ability to inactivate MGMT. These resultsobtained by the experiments usingoligodeoxynucleotides and free bases suggest that human MGMT has lowsubstrate specificityfor 6BGs in oligodeoxynucleotides. Conformational changes in humanMGMT which favorbinding to oligodeoxynucleotides containing 6BG derivatives and thesubsequent transfer oftheir benzyl groups may account for the difference in substratespecificity between theincorporated 6BG derivatives and their free base form.