DNA cleavage by iron(III) complex of synthetic bleomycin model compound

Journal of Inorganic Biochemistry

M16 lJa_lfdlr.l~

N O N - H E M E IRON

327

DNA CLEAVAGE BY IRON(IH) COMPLEX OF SYNTHETIC BLEOMYCIN MODEL COMPOUND a Y. Ishikawa ,a M. Goto, a H. Matsuo, b M. Sugiyama, b and E. Kimura b

aFaculty of Pharmaceutical Sciences, Kumamoto University,5-1 Oe-honmachi, Kumamoto 862, Japan bDepartment of Medicinal Chemistry, Hiroshima University, School of Medicine, Kasumi, Minami-ku, Hiroshima, 734, Japan Bleomycins (BLMs) are antibiotic glycopeptides used clinically for squamous cell carcinoma, malignant lymphoma, and testistumor. Their therapeutic activities are closely related to the cleavage of cancer DNA. BLM, FeII, and molecular dioxygen form a ternary Fe-BLM-O2 complex and subsequently generate an activated oxygen species, so called activated BLM, and abstracts hydrogen from C4' of the deoxyribose moiety of DNA, which has been estimated by electrospray mass spectrometry as a ferric hydrogen peroxide. The activated oxygen species can be also formed by admixture of FelILBLM and hydrogen peroxide. The question as to whether a high-valent iron complex such as a ferryl (FeW=O) or a perferryl (FeV=O) in the oxidative pathway exists or not remains to be answered conclusively. In order to the structure of iron complex in solution and the mechanism of DNA scission, we synthesized Fe III complexes of the synthetic BLM model ligands, L1 and L2. We report the synthesis, spectral, and electrochemical properties, and DNA strand scission of Fe III complexes of L1 and L2. The reaction of the bleomycin model ligands, L 1 or L 2, with an equimolar amount of FeC13.6H20 in ethanol in the presence of N-methylimidazole afforded deep red microcrystals, [FelII(H. 1L1)] 2+ (1) or [FeIII(H_ 1L2)] 2+ (2), respectively. These Fe III complexes have been characterized by electronic and EPR spectroscopies and cyclic voltammetry. The electronic spectra of 1 and 2 in methanol are similar to that of authentic Felll-pepleomycin, which is a family of bleomycins. The EPR spectra of 1 and 2 in frozen methanol at 77 K exhibited rhombic low-spin Fe III signals (g 1 = 2.40, g2 = 2.32, and g3 = 1.86 for 1 and gl = 2.38, g2 = 2.31, g3 = 1.86 for 2). The cyclic voltammograms of 1 and 2 in DMF at I = 0.1 (tetra(n-butylammonium chloride)) displayed one-electron Fe III/II redox process at Ell 2 = - 0.05 V vs Ag/AgC1 for 1 and at + 0.03 V vs Ag/AgC1 for 2, respectively. The cleaving activities toward pUC19 DNA by 1 and 2 were examined in the presence of H202. Both Fe III complexes showed pUC19 DNA cleaving acitivity at 0.1 mM. R~R 2 ~

H

~/" "~H2 NH

3.. !

H L1; R ~ = R 2 = H

1.2;R1= H, R2= C O N H 2

[FelIIH.1Ld2*;1 [FelUH.1L~2+;2

2.1-