title: Reversible inhibition of human thioredoxin reductase activity by cytotoxic alkyl 2-imidazolyl disulfide analogues.
abstract: The thioredoxin/thioredoxin reductase system is important for several aspects of the regulation of cellular proliferation by both intracellular and extracellular mechanisms. The effects of n-butyl 2-imidazolyl disulfide (III-2), 1-methylpropyl 2-imidazolyl disulfide (IV-2), and n-decyl 2-imidazolyl disulfide (VII-2) on purified human placental thioredoxin reductase activity were examined. The analogues were competitive inhibitors with DTNB for reduction by thioredoxin reductase, with Ki values for III-2, IV-2, and VII-2 being 3.3, 13.0, and 8.6 microM, respectively. The inhibition was noncompetitive with reduced nicotinamide adenine dinucleotide phosphate (NADPH). None of the analogues was a suicide substrate inhibitor of the flavoenzyme. III-2 and VII-2 were metabolized by thioredoxin reductase at about half the rate of DTNB, whereas IV-2 was not detectably metabolized. The second order rate constants for the reactions of III-2 and IV-2 with reduced GSH were 931 and 91 M-1 s-1, respectively. The lower reactivity of IV-2 with reduced GSH and the lack of the analogue's metabolism by thioredoxin reductase may be due to the more sterically hindered structure of this analogue. The 50% inhibitory concentrations (IC50 values) for the inhibition of serum-dependent cellular proliferation of Swiss 3T3 murine fibroblasts by III-2, IV-2, and VII-2 were 2.0, 3.5, and 4.0 microM, respectively. IV-2 was considerably more potent as an inhibitor of the thioredoxin-dependent cellular proliferation of Swiss 3T3 fibroblasts, showing an IC50 value of 60 nM. Thus, inhibition of cellular proliferation by alkyl 2-imidazolyl disulfide analogues may involve interaction with thioredoxin, thioredoxin reductase, or an alternative target that is redox-regulated by thioredoxin.
authors.affiliation: Arizona Cancer Center, Tucson 85715.
authors.forename: J E
authors.initials: JE
authors.lastname: Oblong
authors.forename: E L
authors.initials: EL
authors.lastname: Chantler
authors.forename: A
authors.initials: A
authors.lastname: Gallegos
authors.forename: D L
authors.initials: DL
authors.lastname: Kirkpatrick
authors.forename: T
authors.initials: T
authors.lastname: Chen
authors.forename: N
authors.initials: N
authors.lastname: Marshall
authors.forename: G
authors.initials: G
authors.lastname: Powis
mesh_terms: D000818:Animals; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D004220:Disulfides / Q000378:metabolism / Q000494:pharmacology*; D005260:Female; D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D007093:Imidazoles / Q000378:metabolism / Q000494:pharmacology*; D051379:Mice; D013329:Structure-Activity Relationship; D013880:Thioredoxin-Disulfide Reductase / Q000037:antagonists & inhibitors*; D013879:Thioredoxins / Q000037:antagonists & inhibitors* / Q000302:isolation & purification
chemical_list: D004220:Disulfides; D007093:Imidazoles; D013879:Thioredoxins; D013880:Thioredoxin-Disulfide Reductase