title: Competition between glutathione and guanine for a ruthenium(II) arene anticancer complex: detection of a sulfenato intermediate.
abstract: The organometallic anticancer complex [(eta6-bip)Ru(en)Cl]+ (1; bip = biphenyl, en = ethylenediamine) selectively binds to guanine (N7) bases of DNA (Novakova, O.; Chen, H.; Vrana, O.; Rodger, A.; Sadler, P. J.; Brabec, V. Biochemistry 2003, 42, 11544-11554). In this work, competition between the tripeptide glutathione (gamma-L-Glu-L-Cys-Gly; GSH) and guanine (as guanosine 3',5'-cyclic monophosphate, cGMP) for complex 1 was investigated using HPLC, LC-MS and 1H,15N NMR spectroscopy. In unbuffered solution (pH ca. 3), the reaction of 1 with GSH gave rise to three intermediates: an S-bound thiolato adduct [(eta6-bip)Ru(en)(GS-S)] (4) and two carboxylate-bound glutathione products [(eta6-bip)Ru(en)(GSH-O)]+ (5, 6) during the early stages (<6 h), followed by en displacement and formation of a tri-GS-bridged dinuclear Ru(II) complex [((eta6-bip)Ru)2(GS-mu-S)3]2- (7). Under physiologically relevant conditions (micromolar Ru concentrations, pH 7, 22 mM NaCl, 310 K), the thiolato complex 4 was unexpectedly readily oxidized by dioxygen to the sulfenato complex [(eta6-bip)Ru(en)(GS(O)-S)] (8) instead of forming the dinuclear complex 7. Under these conditions, competitive reaction of complex 1 with GSH and cGMP gave rise to the cGMP adduct [(eta6-bip)Ru(en)(cGMP-N7)]+ (10) as the major product, accounting for ca. 62% of total Ru after 72 h, even in the presence of a 250-fold molar excess of GSH. The oxidation of coordinated glutathione in the thiolato complex 4 to the sulfenate in 8 appears to provide a facile route for displacement of S-bound glutathione by G N7. Redox reactions of cysteinyl adducts of these Ru(II) arene anticancer complexes could therefore play a significant role in their biological activity.
authors.affiliation: School of Chemistry, University of Edinburgh, West Mains Road, Edinburgh EH9 3JJ, United Kingdom.
authors.forename: Fuyi
authors.initials: F
authors.lastname: Wang
authors.forename: Jingjing
authors.initials: J
authors.lastname: Xu
authors.forename: Abraha
authors.initials: A
authors.lastname: Habtemariam
authors.forename: Juraj
authors.initials: J
authors.lastname: Bella
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Sadler
mesh_terms: D000970:Antineoplastic Agents / Q000737:chemistry* / Q000378:metabolism; D001667:Binding, Competitive; D006152:Cyclic GMP / Q000737:chemistry / Q000378:metabolism; D005978:Glutathione / Q000737:chemistry* / Q000378:metabolism; D006147:Guanine / Q000737:chemistry* / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D019906:Nuclear Magnetic Resonance, Biomolecular; D009942:Organometallic Compounds / Q000737:chemistry* / Q000378:metabolism; D012428:Ruthenium / Q000737:chemistry* / Q000378:metabolism; D014867:Water / Q000737:chemistry
chemical_list: D000970:Antineoplastic Agents; D009942:Organometallic Compounds; D014867:Water; D006147:Guanine; D012428:Ruthenium; D005978:Glutathione; D006152:Cyclic GMP