| Cancer is a major reason of death throughout the world. The past decades have demonstrated that great improvements have been made in the treatment of cancer. Currently, chemotherapeutics has a great curative potential for numerous tumours. Among them, the clinical use of DNA cross-linking drugs, which inhibit both DNA replication and gene expression by preventing the melting of the two strands, is well established.Nitrogen mustards are the most powerful alkylating agents widely used in the chemotherapy by coordinating to N (7) of purine bases through aziridine cation in vivo. However, these drugs are not selective toward neoplastic cells and produce undesirable effects. Quinone methides are important intermediates in a large number of DNA cross-linking and alkylating processes and can be be generated by many methods, such as photo-irradiation, oxidation, and fluoride-induced activation. In order to obtain more selective and efficient drugs, we designed and synthesized novel nitrogen mustard derivatives and quinone methide precursors as selective DNA cross-linking agents:(1) Several novel series of sesquiterpene mustards bearing nitrogen mustard and glutathione (GSH)-reactive a-methylene-y-butyrolactone groups were successfully prepared for the first time and most of them showed excellent antiproliferative activities in vitro. Among them,3a-oxo-p-[N, N-bis(2-chloroethyl)amino]benzoyl-4(15),10(14), 11(13)-triene-5a,7a-dihydroxyl-6a,12-guaiano-lide (2e) and 15-oxo-p-[N, N-bis(2-chloroethyl)amino]benzoyl-14-oxo-cis, cis-germacranolide (2g) displayed the highest antiproliferative properties with ICso values ranging from 2.5 to 8.7 μM and had been proved to be selective agents. Hoechst 33258 staining and flow cytometry experiments demonstrated that 2e and 2g could induce cell apoptosis and cycle arrest. In addition, further investigation showed that compounds 2e and 2g could obviously inhibit the proliferation of HepG2 cells by inducing significant DNA cross-linking and depleting GSH in cell media. The good cytotoxicity and selectivity of compounds 2e and 2g pointed them as promising leads for anticancer drug design.(2) GSH is the most abundant free thiol in the cells and the level of GSH in cancer tissues is apparently higher than in normal tissues. Therefore, we designed thiols-triggered anticancer prodrug N, N-bis(2-chloroethyl)-N-methyl-N-[4-(O-2,4-dinitrobenzenesulfonyl)benzyl]methanam-inium bromide (6) for a more effective cancer therapy.’H NMR analysis and denaturing alkaline agarose gel electrophoresis demonstrated that 6 was efficiently triggered by GSH and released chemotherapeutic agent mechlorethamine. Moreover, compound 6 was proved to deplete thiols and induce significant DNA cross-linking in cell media by fluorescence imaging and comet assay. Yet again, cytotoxic test indicated that 6 showed strong antiproliferation on human cancer cells and was selective for normal and cancer renal cells. Such a model reveals a promising scaffold for further development of tumor-specific alkylating agents to improve the therapeutic effectiveness and selectivity of current antitumor agents.(3) 1,4-Di-(O-2,4-dinitrobenzenesulfonyl)-2,5-di-(trimethylammonium iodide-methyl)phen-yl (16), 1-(O-2,4-dinitrobenzenesulfonyl)-2,6-di-(trimethylammonium iodide-methyl)-4-methyl-phenyl (17) and 4,4’-di-(O-2,4-dinitrobenzenesulfonyl)-3,3’-di-(trimethylammonium iodide-methyl)biphenyl (18) were further synthesized.’H NMR analysis suggested that 16-18 could release the corresponding phenol derivatives 1,4-dihydroxy-2,5-di-(trimethylammonium iodide-methyl)phenyl (19), 1-hydroxy-2,6-di-(trimethylammonium iodide-methyl)-4-methylphen-yl (20) and 4,4’-dihydroxy-3,3’-di-(trimethylammonium iodide-methyl)biphenyl (21) in five minutes though the sulfonyl ester was hydrolyzed to some extent in phosphate buffer (pH 7.3). Moreover, HPLC further indicated that the inducible reaction was instantaneous. Interestingly, the reaction mixture immediately exhibited brilliant red color after the addition of compounds 16-18, and showed orange color several seconds later. Finally, denaturing alkaline agarose gel electrophoresis indicated that 16 could induce DNA cross-linking in the presence of GSH through the quinone methide intermediate. In conclusion,2,4-dinitrobenzenesulfonyl derivatives could be triggered by the thiols and are potential for inducible DNA cross-linking agents. |
