title: 1,2-benzisoxazole phosphorodiamidates as novel anticancer prodrugs requiring bioreductive activation.
abstract: Several 1,2-benzisoxazole phosphorodiamidates have been designed as prodrugs of phosphoramide mustard requiring bioreductive activation. Enzymatic reduction of 1,2-benziosoxazole moiety is expected to result in the formation of imine intermediate due to the cleavage of the N-O bond. The imine should then be spontaneously hydrolyzed to a ketone metabolite, thereby facilitating base-catalyzed beta-elimination of cytotoxic phosphoramide mustard. As expected, the proposed prodrugs 4, 9, and 12 were at least 3-5-fold more potent cytotoxins than control compounds 5 and 15, which lack in the phosphoramide mustard group. Upon incubation with phenobarb-induced rat liver S-9 fraction, compounds 4, 9, and 12 underwent extensive NADPH-dependent metabolism with concomitant generation of alkylating activity under both hypoxic and oxic conditions. Corresponding ketone metabolites were detected for 9 and 15. NADPH-dependent bioreduction of 15 to its ketone metabolite 16 was located in the microsomal fraction and inhibited by SKF-525A and pCMBA. Compared with phenobarb-induced rat liver microsomal fraction, incubation of 15 with rat or human p450 reductase microsomes showed moderate generation of 16. Microsomal cytochrome p450 and/or p450 reductase appear to be involved in the reductive metabolism of 1,2-benzisoxazole moiety under hypoxic as well as oxic conditions.
authors.affiliation: Department of Pharmaceutical Sciences, College of Pharmacy and Allied Health Professions, St John's University, Jamaica, New York 11439, USA.
authors.forename: Monish
authors.initials: M
authors.lastname: Jain
authors.forename: Chul-Hoon
authors.initials: CH
authors.lastname: Kwon
mesh_terms: D000818:Animals; D018906:Antineoplastic Agents, Alkylating / Q000138:chemical synthesis* / Q000378:metabolism / Q000494:pharmacology; D002460:Cell Line; D006224:Cricetinae; D003412:Cricetulus; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D007555:Isoxazoles / Q000138:chemical synthesis* / Q000378:metabolism / Q000494:pharmacology; D008862:Microsomes, Liver / Q000201:enzymology / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D009251:NADPH-Ferrihemoprotein Reductase / Q000378:metabolism; D010084:Oxidation-Reduction; D010752:Phosphoramide Mustards / Q000008:administration & dosage / Q000378:metabolism*; D011355:Prodrugs / Q000138:chemical synthesis* / Q000378:metabolism / Q000494:pharmacology; D051381:Rats; D013329:Structure-Activity Relationship
chemical_list: D018906:Antineoplastic Agents, Alkylating; D007555:Isoxazoles; D010752:Phosphoramide Mustards; D011355:Prodrugs; D009249:NADP; D003577:Cytochrome P-450 Enzyme System; D009251:NADPH-Ferrihemoprotein Reductase