Role of quinone-iron(III) interaction in NADPH-dependent enzymatic generation of hydroxyl radicals

To study the effect of chelation of iron ions by quinones on the generation of OH radicals in biological redox systems, we have synthesized quinones that can form complexes with Fe(III) ions: 2-phenyl-4-(butylamino)naphtho[2,3-h]quinoline-7,12-dione (Qbc) and 2-phenyl-4-(octylamino)naphtho[2,3-h]quinoline-7,12-dione (Qoc). A quinone with a similar structure without chelating group was synthesized as a control sample: 2-phenyl-5-nitronaphtho[2,3-g]indole-6,11-dione (Qn). Using optical spectroscopy, we determined the stability constant of Qbc with Fe(III) [Ks = (7 +/- 1) x 10(18) M-3] and the stoichiometry of the complex Fe(Qbc)3 in chloroform solutions. One-electron reduction potentials of Qbc, Qn, and adriamycin in dimethyl sulfoxide were measured by cyclic voltammetry. In the presence of Fe(III) the one-electron reduction potentials shifted toward positive values by 0.16 and 0.1 V for Qbc and adriamycin, respectively. Using the spin trap 5,5'-dimethyl-1-pyroline N-oxide (DMPO) and EPR, it was found that Qbc in the Fe(III) complex stimulated the formation of OH radicals in the enzymatic system consisting of NADPH and NADPH-cytochrome P-450 reductase more efficiently than adriamycin and quinone Qn. This is indicated by the absence of a lag period in the spin adduct appearance for Qbc and by a significantly higher rate of the spin adduct production, as well as by a larger absolute concentration of the spin adduct obtained for Qbc in comparison with Qn in the presence of Fe(III).(ABSTRACT TRUNCATED AT 250 WORDS)

Trace transition metal-catalyzed reactions in the microsomal metabolism of alkyl hydrazines to carbon-centered free radicals

Radical production from alkyl hydrazines (i.e. phenelzine and benzylhydrazine) in rat liver microsomes has been proposed to occur via cytochrome P-450-catalyzed one-electron oxidation followed by beta-scission of an alkyl radical. In microsomes treated with phenelzine (2-phenylethylhydrazine), NADPH, and the spin trap alpha-(4-pyridyl 1-oxide)-N-tert-butylnitrone (4-POBN), the 4-POBN/2-phenylethyl radical adduct was detected by electron paramagnetic resonance spectroscopy. The addition of catalase and superoxide dismutase resulted in a 28.5 and 24% decrease in radical production, respectively. The concentration of the 4-POBN/2-phenylethyl radical adduct decreased significantly in the presence of metal chelators, i.e. EDTA, diethylenetriaminepentaacetic acid (DTPA), or deferoxamine mesylate. When phenelzine was incubated with deferoxamine mesylate-washed microsomes and NADPH in Chelex-treated incubation buffer, no significant radical adduct formation was detected. Addition of iron-chelator complexes (either Fe(3+)-DTPA or Fe(3+)-EDTA) greatly stimulated production of the 4-POBN/2-phenylethyl radical adduct in this system. These results show that the 2-phenylethyl radical produced from phenelzine in a microsomal system arises via a trace transition metal-catalyzed reaction. This reaction may occur through oxidation of phenelzine by the hydroxyl radical, which has also been spin-trapped with 4-POBN in this system.

Microsomal reduction of 3-amino-1,2,4-benzotriazine 1,4-dioxide to a free radical

The drug SR 4233 (3-amino-1,2,4-benzotriazine 1,4-dioxide) is under pharmacological study as the lead compound in a new series of hypoxia-activated drugs, the benzotriazine N-oxides. However, the stable two- and four-electron-reduced metabolites of SR 4233, formed by the successive loss of the two oxygen atoms, are not pharmacologically active. In order to evaluate the possibility of an initial one-electron intermediate as the active species, we have used microsomal reduction and EPR spectroscopy to identify the first free radical reduction product. The unpaired electron is primarily centered on the 1-nitrogen, and the radical is best described as a nitroxide. Results with spin-trapping experiments show that reduction of SR 4233 to a free radical is followed by its air oxidation, resulting in the formation of the superoxide radical. Experiments with specific inhibitors suggest that the drug is being reduced by microsomal NADPH-cytochrome P-450 reductase.

Hydroxyl radical generation by oligonucleotide derivatives of anthracycline antibiotic and synthetic quinone

For the first time the covalent binding of anticancer anthracycline drugs and their potential synthetic analogs to oligonucleotides of different sequences is proposed for obtaining site-specific DNA scission in systems in vitro and in vivo. New compounds such as daunomycin (Dm) and synthetic naphthoquinone (NQ), covalently bound to the heptadeoxynucleotide of pCCAAACA (Dm-pN7) and decadeoxythymidilate (pT10p-NQ), have been obtained. These oligonucleotide derivatives can form specific complexes with complementary oligonucleotide sequences; these compounds and their complementary complexes can be reduced by purified NADPH-cytochrome P-450 reductase. Using the spin trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO), it has been shown that in aerobic conditions Dm-pN7 and pT10p-NQ are capable of generating OH radicals with and without complementary oligonucleotides. The chemical stability of the compounds in redox reactions has been studied. Oligonucleotide derivatives of natural and synthetic quinones capable of generating OH radicals seem to be a promising tool for site-specific scission of DNA in solution and in cells.

Hydroxyl radical generation and DNA strand scission mediated by natural anticancer and synthetic quinones

Using ESR and spin-trapping techniques, it was found that synthetic 2-dimethylamino-3-chloro-1,4-naphthoquinone and the natural anticancer quinone daunomycin, when added to a system containing purified NADPH-cytochrome P-450 reductase, NADPH, ferric ions, and oxygen, (i) generated hydroxyl radicals and (ii) caused single-strand scission of supercoiled DNA of the plasmic pBR322. Since these two effects of the quinones were correlated to each other, we propose that potential anticancer quinones can be effectively screened by measuring their ability to form hydroxyl radicals in the above system.

Redox transformations of quinone antitumor drugs in liver microsomes

The hydroxyl radical has been spin trapped in microsomal and purified NADPH-cytochrome P-450 reductase systems in the presence of adriamycin, daunomycin and mitomycin C. The presence of a lag period in quinone-stimulated spin-adduct formation is associated with oxygen removal upon its reduction to H2O2. The hydroxy radical generation has been stimulated by the Fe-EDTA complex and completely inhibited by catalase. The mechanism of redox transformations of anthracyclines in a microsomal system has been proposed The single electron reduced quinone-containing anticancer antibiotics play the following roles: (i) they reduce oxygen to H2O2 and (ii) they reduce the ferric ions necessary for H2O2 decomposition with hydroxyl radical formation.

Microsomal oxidation of 2-dimethylamino-3-chloro-1,4-naphthoquinone. The possibility of substrate activation by cytochrome P-450

2-Dimethylamino-3-chloro-1,4-naphthoquinone (DCNQ) is bound to microsomal cytochrome P-450 as a type I substrate (lambda max = 391 nm, lambda min = 420 nm). The Ks is 40.5 microM. In a rat-liver microsomal system, the N-demethylation of DCNQ produces formaldehyde (rate 225 pmol/min per mg of protein). Induction by phenobarbital increases the rate of formation, while addition of metyrapone and SKF-525A into the system decreases the rate by 52% and 35%, respectively. The microsomal N-demethylation of DCNQ is not inhibited by CO. Under full anaerobiosis, the microsomal oxidation of DCNQ again gives formaldehyde (rate 416 pmol/min per mg of protein). The anaerobic oxidation of DCNQ is inhibited by metyrapone and SKF-525A. The microsomal, chemical and electrochemical reduction of DCNQ to the corresponding semiquinones and hydroquinones have been studied. Non-enzymic DCNQ reduction is insufficient for the formation of formaldehyde. Under anaerobic conditions the microsomal DCNQ oxidation is assumed to occur via the intramolecular oxazole bond which is then hydrolysed, yielding formaldehyde. This may be a new example of substrate activation by cytochrome P-450.