Nitrogen analogues of 1,4-benzoquinones. Activities against the ascitic sarcoma 180 of mice

Redox and addition chemistry of quinoid compounds and its biological implications

The overall biological activity of quinones is a function of the physico-chemical properties of these compounds, which manifest themselves in a critical bimolecular reaction with bioconstituents. Attempts have been made to characterize this bimolecular reaction as a function of the redox properties of quinones in relation to hydrophobic or hydrophilic environments. The inborn physico-chemical properties of quinones are discussed on the basis of their reduction potential and dissociation constants, as well as the effect of environmental factors on these properties. Emphasis is given on the effect of methyl-, methoxy-, hydroxy-, and glutathionyl substituents on the reduction potential of quinones and the subsequent electron transfer processes. The redox chemistry of quinoid compounds is surveyed in terms of a) reactions involving only electron transfer, as those accomplished during the enzymic reduction of quinones and the non-enzymic interaction with redox couples generating semiquinones, and b) nucleophilic addition reactions. The addition of nucleophiles, entailing either oxidation or reduction of the quinone, are exemplified in reactions with oxygen- or sulfur nucleophiles, respectively. The former yields quinone epoxides, whereas the latter yields thioether-hydroquinone adducts as primary molecular products. The subsequent chemistry of these products is examined in terms of enzymic reduction, autoxidation, cross-oxidation, disproportionation, and free radical interactions. The detailed chemical mechanisms by which quinoid compounds exert cytotoxic, mutagenic and carcinogenic effects are considered individually in relation to redox cycling, alterations of thiol balance and Ca++ homeostasis, and covalent binding.

Quinoneimines as substrates for quinone reductase (NAD(P)H: (quinone-acceptor)oxidoreductase) and the effect of dicumarol on their cytotoxicity

Several quinoneimines have been shown to be substrates for partly purified rat liver cytosolic quinone reductase with either NADH or NADPH as cofactor. Km and Vmax values with NADH as cofactor for N-acetyl-p-benzoquinoneimine were 54.9 microM and 278 mumol/min/mg; for 2-amino-1,4-naphthoquinoneimine, 2.8 microM and 38 mumol/min/mg; for N,N-dimethylindoaniline, 1.7 microM and 22 mumol/min/mg; and 2-acetamido-N,N-dimethylindoaniline, 0.4 microM and 9 mumol/min/mg. All the quinoneimines showed substrate inhibition at high concentrations. At 30 microM dicumarol, an inhibitor of quinone reductase, potentiated the acute toxicity of quinoneimines to cultured phenobarbital-induced rat hepatocytes by 0.7- to 2.9-fold. Dicumarol was toxic to cultured non-induced rat hepatocytes and produced little or no increase in quinoneimine toxicity. Dicumarol potentiated the toxicity of 2-methyl-1,4-naphthoquinone (menadione) to cultured non-induced, as well as phenobarbital-induced, hepatocytes. Levels of quinone reductase in both types of hepatocytes were similar. Quinoneimines exhibited strong growth inhibitory properties with Chinese hamster ovary (CHO) cells and A204 human rhabdomyosarcoma cells. Dicumarol, 0.1 mM, potentiated growth inhibition by N,N-dimethylindoaniline and 2-acetamido-N,N-dimethylindoaniline in A204 but not in CHO cells. Growth inhibition by 2-amino-1,4-naphthoquinoneimine was inhibited by dicumarol in both cell lines. Dicumarol potentiated growth inhibition by 2-methyl-1,4-naphthoquinone in A204 and CHO cells. Quinone reductase activity in A204 cells was 48% and in CHO cells 1% of the activity in cultured hepatocytes. The lack of a correlation between the effects of dicumarol on quinoneimine and quinone growth inhibition and levels of cellular quinone reductase suggests that dicumarol has effects in cells in addition to, or other than, inhibition of quinone reductase. It is concluded that quinone reductase may protect cells against quinoneimine toxicity under certain conditions, as with phenobarbital-induced hepatocytes, but does not appear to play a major role in modifying quinoneimine toxicity in non-induced hepatocytes, or growth inhibition in CHO cells or A204 cells.

Charge transfer-oxy radical mechanism for anticancer agents: mAMSA derivatives, rhodamine 123, and nickel salicylaldoximate

The proposal is advanced that many anticancer agents may function via redox reactions resulting in generation of toxic oxy radicals which destroy neoplastic cells. Cyclic voltammetry was performed with some of the main types: iminium ions (protonated mAMSA derivatives), quinone derivatives (rhodamine 123) and metal complexes (nickel(II) salicylaldoximate). In addition, relevant literature data are provided. A rationale is offered that relates electrochemical data to physiological activity.

An integrated concept of amebicidal action: electron transfer and oxy radicals

Cyclic voltammetry data were obtained for most of the main categories of antiamebic agents, specifically, quinones, heterocyclic nitro compounds, metal derivatives and chelators, and iminium-type ions. The reductions (our data and literature values) were for the most part reversible, with potentials usually in the favorable range of +0.10 to -0.56 V. The drug effect is believed to result generally from the catalytic production of oxidative stress usually arising from the formation of superoxide via electron transfer. In addition, relevant literature data are provided.

Conjugated and cross-conjugated mesomeric betaines. Correlation of electroreduction with structure and physiological activity

Electroreduction studies were performed on several cross-conjugated mesomeric betaines containing the fused pyrazolium (2) and fused imidazolium (3) ring systems. Studies at acidic pH were of principal interest. Substituent effects for 2 were in line with prior findings, and reduction potentials were comparatively negative (-0.96 to -1.34 V). Reduction potentials fit the modified Hammett equation. Compound 3 was more readily reduced (-0.88 V). The related psi-oxatriazoles (6) gave values in the range of -0.85 to -1.22 V. The electrochemical characteristics are compared with those of the mesoionic sydnones (4) and sydnoneimines (5). These mesoionic compounds were generally reduced at more positive potentials than 2 and 3. A relationship between electroreduction and physiological activity is proposed. The overall results are in keeping with the hypothesis of widespread participation of iminium-type species in biological systems.

The in vitro trypanocidal activity of N-substituted p-benzoquinone imines: assessment of biochemical structure-activity relationships using the Hansch approach

It has previously been found that naphthoquinones can potentiate the rate of hydrogen peroxide production by mitochondrial preparations of Trypanosoma brucei brucei and that organisms treated with naphthoquinones are more susceptible to lysis, especially in the presence of compounds such as heme, which promote the homolytic cleavage of hydrogen peroxide. We have evaluated the lytic effect of various N-substituted p-benzoquinone imines both in vitro and in vivo and have attempted to correlate their structure with trypanocidal activity using the Hansch approach. While none of the compounds tested proved to be active in vivo, all caused the lysis of trypanosomes in vitro. The parameters that correlated best with trypanocidal activity were the conditional redox potential, the lipophilicity of the substituent attached to the nitrogen atom and the number of active hydrogens on the quinonoid ring. These findings suggest two possible modes of action, which may in fact be related. Conjugate nucleophilic addition and/or oxidative damage could be responsible for lysis of the parasites. These same compounds were previously found to be active against the ascitic sarcoma 180 in mice. The strong correlation between antineoplastic activity in vivo and trypanocidal activity in vitro suggests a similar mode of action in both cases. Further studies aimed at developing a quinonelike compound that will be active against trypanosomes in vivo are now in progress.

Inhibition of cell division and growth by a redox series of cyanine dyes

A series of cyanine dyes used in photography, with reduction potentials from -1.35 to -0.20 volts, were tested for their ability to inhibit mitosis and cell growth in fertilized sea urchin eggs. Low concentrations of dyes with reduction potentials more negative than -1.0 volt generally inhibited mitosis and growth, whereas those with more positive reduction potentials did not. The active dyes penetrated the cell, entered all subcellular compartments, were bound to numerous macromolecules, and inhibited synthesis of macromolecules. Thus mitosis and growth may be retarded with substances that can alter electrochemical activity in cells.