Pedro Sanchez-Cruz

Thiols oxidation and covalent binding of BSA by cyclolignanic quinones are enhanced by the magnesium cation

A novel cyclolignanic quinone, 7-acetyl-3′,4′-didemethoxy-3′,4′-dioxopodophyllotoxin (CLQ), inhibits topoisomerase II (TOPO II) activity. The extent of this inhibition was greater than that produced by the etoposide quinone (EQ) or etoposide. Glutathione (GSH) reduces EQ and CLQ to their corresponding semiquinones under anaerobic conditions. The latter were detected by EPR spectroscopy in the presence of MgCl2 but not in its absence. Semiquinone EPR spectra change with quinone/GSH mol ratio, suggesting covalent binding of GSH to the quinones. Quinone-GSH covalent adducts were isolated and identified by ESI-MS. These orthoquinones also react with nucleophilic groups from BSA to bind covalently under anaerobic conditions. BSA thiol consumption and covalent binding by these quinones are enhanced by MgCl2. Complex formation between the parent quinones and Mg+2 was also observed. Density functional calculations predict the observed blue-shifts in the absorption spectra peaks and large decreases in the partial negative charge of electrophilic carbons at the quinone ring when the quinones are complexed to Mg+2. These observations suggest a possible role of Mg+2 chelation by these quinones in increasing TOPO II thiol and/or amino/imino reactivity with these orthoquinones.

Metal-independent reduction of hydrogen peroxide by semiquinones.

The quinones 1,4-naphthoquinone (NQ), tetramethyl-1,4-benzoquinone (DQ), 2-methyl-1,4-naphthoquinone (MNQ), 2,3-dimethoxy-5-methyl-1,4-benzoquinone (UBQ-0), 2,6-dimethylbenzoquinone (DMBQ), 2,6-dimethoxybenzoquinone (DMOBQ), and 9,10-phenanthraquinone (PHQ) enhance the rate of H2O2 reduction by ascorbate, under anaerobic conditions, as detected from the amount of methane produced after hydroxyl radical reaction with dimethyl sulfoxide. The amount of methane produced increases with an increase in the quinone one-electron reduction potential. The most active quinone in this series, PHQ, is only 14% less active than the classic Fenton reagent cation, Fe2+, at the same concentration. Since PHQ is a common toxin present in diesel combustion smoke, the possibility that PHQ-mediated catalysis of hydroxyl radical formation is similar to that of Fe2+ adds another important pathway to the modes in which PHQ can execute its toxicity. Because quinones are known to enhance the antitumor activity of ascorbate and because ascorbate enhances the formation of H2O2 in tissues, the quinone-mediated reduction of H2O2 should be relevant to this type of antitumor activity, especially under hypoxic conditions.

Sonochemically Induced Covalent Binding of Calf Thymus DNA by Aziridinylquinones

Abstract Alegria, A. E., Sanchez-Cruz, P. and Lopez-Colon, D. Sonochemically Induced Covalent Binding of Calf Thymus DNA by Aziridinylquinones. Radiat. Res. 164, 446–452 (2005). Sonolysis of argon- or oxygen-containing samples in the presence of calf thymus DNA and the diaziridinylquinones 2,5-bis-aziridin-1-yl-3,6-dichloro-1,4-benzoquinone (AZClQ) and 2,5-bis(carboethoxyamino)-3,6-diaziridinyl-1,4-benzoquinone (AZQ) produced quinone-DNA covalent adducts at pH 5.5 and to a much lesser extent at pH 7.4. The corresponding semiquinone derivatives are detected using EPR spectroscopy after sonolysis of argon-saturated solutions at pH 7.4. The amount of covalent adducts decreases with addition of SOD, indicating a role of superoxide in this process. Addition of oxygen to the purging gas decreased but did not eliminate this covalent adduct. Thus this work suggests a possible synergism between bioreductive quinones and ultrasound in antitumor therapies based on alkylating quinone–DNA adduct formation with potential applications to both hypoxic and normally oxygenated conditions.

Quinone-enhanced sonochemical production of nitric oxide from s-nitrosoglutathione.

Sonolysis at 75 kHz of argon- and air-saturated aqueous solutions at pH 7.4 containing s-nitrosogluthathione (GSNO) enhances the production rate of nitric oxide (NO). The quinones, anthraquinone-2-sulfonate (AQ2S) and anthraquinone-2,7-disulfonate (AQ27S) further enhance the NO production over that produced in quinone-depleted sonicated solutions. In contrast, the hydrophobic quinones juglone (JQ) and 1,4-naphthoquinone (NQ) inhibit ultrasound-induced NO detection as compared to quinone-depleted solutions. Larger sonolytical decomposition of the hydrophobic quinones NQ and JQ, as compared to AQ2S and AQ27S, is detected which correlates with a larger production of pyrolysis-derived carbon-centered radicals. Reaction of those radicals with NO could explain NQ and JQ inhibition. This work suggests that sulfonated quinones could be used to enhance NO release from GSNO in tissues undergoing ultrasound irradiation.

Synthesis and Evaluation of Folate-Conjugated Phenanthraquinones for Tumor-Targeted Oxidative Chemotherapy

Almost all cells are easily killed by exposure to potent oxidants. Indeed, major pathogen defense mechanisms in both animal and plant kingdoms involve production of an oxidative burst, where host defense cells show an invading pathogen with reactive oxygen species (ROS). Although cancer cells can be similarly killed by ROS, development of oxidant-producing chemotherapies has been limited by their inherent nonspecificity and potential toxicity to healthy cells. In this paper, we describe the targeting of an ROS-generating molecule selectively to tumor cells using folate as the tumor-targeting ligand. For this purpose, we exploit the ability of 9,10-phenanthraquinone (PHQ) to enhance the continuous generation of H2O2 in the presence of ascorbic acid to establish a constitutive source of ROS within the tumor mass. We report here that incubation of folate receptor-expressing KB cells in culture with folate-PHQ plus ascorbate results in the death of the cancer cells with an IC50 of ~10 nM (folate-PHQ). We also demonstrate that a cleavable spacer linking folate to PHQ is significantly inferior to a noncleavable spacer, in contrast to most other folate-targeted therapeutic agents. Unfortunately, no evidence for folate-PHQ mediated tumor regression in murine tumor models is obtained, suggesting that unanticipated impediments to generation of cytotoxic quantities of ROS in vivo are encountered. Possible mechanisms and potential solutions to these unanticipated results are offered.

Role of quinones in the ascorbate reduction rates of S-nitrosoglutathione.

Quinones are one of the largest classes of antitumor agents approved for clinical use, and several antitumor quinones are in various stages of clinical and preclinical development. Many of these are metabolites of, or are, environmental toxins. Because of their chemical structure they are known to enhance electron transfer processes such as ascorbate oxidation and NO reduction. The paraquinones 2,6-dimethyl-1,4-benzoquinone (DMBQ), 1,4-benzoquinone, methyl-1,4-benzoquinone, 2,6-dimethoxy-1,4-benzoquinone, 2-hydroxymethyl-6-methoxy-1,4-benzoquinone, trimethyl-1,4-benzoquinone, tetramethyl-1,4-benzoquinone, and 2,3-dimethoxy-5-methyl-1,4-benzoquinone; the paranaphthoquinones 1,4-naphthoquinone, menadione, 1,4-naphthoquinone-2-sulfonate, 2-ethylsulfanyl-3-methyl-1,4-naphthoquinone and juglone; and phenanthraquinone (PHQ) all enhance the anaerobic rate of ascorbate reduction of GSNO to produce NO and GSH. Rates of this reaction were much larger for p-benzoquinones and PHQ than for p-naphthoquinone derivatives with similar one-electron redox potentials. The quinone DMBQ also enhances the rate of NO production from S-nitrosylated bovine serum albumin upon ascorbate reduction. Density functional theory calculations suggest that stronger interactions between p-benzo- or phenanthrasemiquinones and GSNO than between p-naphthosemiquinones and GSNO are the major causes of these differences. Thus, quinones, and especially p-quinones and PHQ, could act as enhancers of NO release from GSNO in biomedical systems in the presence of ascorbate. Because quinones are exogenous toxins that could enter the human body via a chemotherapeutic application or as an environmental contaminant, they could boost the release of NO from S-nitrosothiol storages in the body in the presence of ascorbate and thus enhance the responses elicited by a sudden increase in NO levels.

Terpenylnaphthoquinones are reductively activated by NADH/NADH dehydrogenase

Novel terpenylnaphthoquinones were found to enhance the rate of oxygen consumption in the presence of NADH/NADH dehydrogenase in 1 : 1 v/v mixtures of 40 mM phosphate buffer (pH 7.4) and DMSO. Initial rates of oxygen consumption increase with an increase in the half-wave reduction potentials of the quinones. The amounts of spin trapped methyl radicals in the presence of DMSO, produced through the Haber–Weiss reaction of the oxygen consumption process, and of the corresponding semiquinones, generated under anaerobic conditions, also correlate with the quinone redox potential. Since this enzymatic system is found in mitochondria, a possible pathway in the cytotoxic activity of these terpenylnaphthoquinones could be the interference or inhibition of mitochondrial respiration by NADH depletion or by mitochondrial degradation due to reactive oxygen species generation.

Role of membrane charge and semiquinone structure on oxygen consumption rates

Rates of oxygen consumption of air-saturated aqueous solutions containing either 2,3-dimethoxy-5-methylbenzoquinone (UQ-0), 1,4-naphthoquinone (NQ) or phenanthroquinone (PHQ) and ascorbate were measured in the presence or absence of large unilamellar vesicles (LUVs) composed of either dimyristoylphosphatidylcholine (DMPC) or equimolar mixtures of DMPC with dimyristoylphospahtidic acid (DMPA) or hexadecyltrimethylammonium bromide (CTAB), at physiological pH. Semiquinone hydrophobicities follow the same order as that of the corresponding quinones. Rates increase with positively charged LUV concentration and decrease with either neutral or negatively charged LUV concentration in samples containing the hydrophobic quinones NQ and PHQ. Rates remain essentially unchanged in the presence of the most hydrophilic quinone, UQ-0. An increase in the ionic strength of the solution partially inhibits the observed changes in the rate of oxygen consumption, Rox, caused by the presence of positively charged membranes, thus implying that such changes are of electrostatic nature. Similar trends with membrane charge are observed for the rates of oxygen consumption in the presence of PHQ and dithiothreitol. The observed increase in the ascorbate oxidation rate in the presence of positively charged lipids occurs in systems where a decrease in semiquinone disproportionation is also detected, thus, implying that an increase in the quinone one-electron redox potential, caused by semiquinone–positively-charged-membrane interaction, could contribute to the observed effects.

Ortho -quinone-enhanced ascorbate oxidation. Combined roles of lipid charge and the magnesium cation

Quinones are widely distributed compounds in nature. Of these, ortho-quinones are found to be involved in the pathogenic mechanism of Parkinsons disease, in oxidative deaminations to free-radical redox reactions, and as intermediates in the pathways implicated in the carcinogenicity of 2,3- and 3,4-catechol estrogens. Addition of MgCl2 to solutions of the hydrophobic ortho-quinones, 1,10-phenanthroquinone (PHQ) and beta-lapachone (LQ) enhances ascorbate oxidation in the absence or presence of large unilamellar vesicles (LUVs) of the neutral lipid dimyristoylphosphatidylcholine (DMPC), although initial rates of ascorbate oxidation are smaller in the presence of lipid as compared to its absence. Addition of this salt to solutions of the para-quinone 1,4-naphthoquinone (NQ) did not affect the ascorbate rate of oxidation in the absence or presence of DMPC. Addition of MgCl2 to semiquinone solutions of PHQ or LQ in the presence or absence of DMPC increases semiquinone stability, as detected from the semiquinone disproportionation equilibrium displacement to semiquinone formation. Furthermore, MgCl2 increases the partition of the ortho-semiquinones into the aqueous phase, although no such effect is observed for the semiquinone of NQ. For all the quinones under study, smaller rates of ascorbate oxidation and of semiquinone equilibrium concentration occur in the presence of negatively charged LUVs composed of an equimolar mixture of DMPC and dimyristoylphosphatidic acid DMPA. Ascorbate oxidation rate enhancements correlate with an increase in semiquinone concentration with addition of MgCl2, in the absence or presence of neutral lipid. This observation favors the proposition that ascorbate oxidation rate increases are caused by semiquinone thermodynamic stabilization. Thus, the ascorbate oxidation rate enhancement by MgCl2 in solutions containing hydrophobic ortho-quinones is still possible in systems with hydrophobic environments analogous to that of DMPC.