Reductive activation of potential antitumor bis(aziridinyl)benzoquinones by xanthine oxidase: competition between oxygen reduction and quinone reduction

The reduction of a series of 2,5-bis(1-aziridinyl)-1,4-benzoquinone (BABQ) derivatives with various 3,6 substituents by the enzyme xanthine oxidase has been studied. The reduction rate has been assayed by measuring the rate of reduction of cytochrome c, which is very efficiently reduced by reduced BABQ species. Under nitrogen, the reduction rate correlated with the quinone reduction potential and steric parameters. Comparing reduction rates under nitrogen and air demonstrates that at BABQ concentrations greater than 25 microM the competition for electrons from xanthine oxidase between oxygen and the BABQ derivative is dominated by the latter. This is also confirmed by the effect of superoxide dismutase (SOD): in the presence of a BABQ derivative, cytochrome c reduction can be totally inhibited by SOD, although the required amount of SOD depends on the redox potential of the quinones. This indicates that SOD causes the equilibrium between semiquinone and superoxide to shift, resulting in a decrease of the semiquinone concentration. It is concluded that reduction by xanthine oxidase is a simple and effective method for reducing aziridinylbenzoquinones.     

Alkylated benzoquinones from Iris kumaonensis

Six novel alkylated p-Benzoquinones irisoquin (A-F) (1-2, 4-7) together with a known cytotoxic quinone, irisoquin (3) along with three known isoflavones, tectoregenin, iristectorin and irigenin were isolated from the rhizomes of Iris kumaonensis and characterized. The structures of compounds 1-2, 4-7 were confirmed by extensive spectroscopic analysis, IR, MS, HRMS, GC, GC-MS, 1D (1H, 13C, NOE) and 2D (HMQC and HMBC) NMR and comparison with literature data of known compounds.     

The anti-tumour efficacy of human recombinant interleukin 2

Summary Experiments were designed to test what percentage of experimental MC-induced murine sarcomas were sensitive to the local tumour inhibitory effect of IL-2 and whether any correlation existed between the sensitivity of these sarcomas to the immunotherapeutic effect of IL-2 and their susceptibility to the cytolytic effect of IL-2-activated killer cells. It was found that the sensitivity of MC-induced sarcomas to local IL-2 immunotherapy was a general phenomenon. Repeated peri-tumoural injections of RIL-2 inhibited the growth of five (MC11, MC13, MC14, MC15, MC16) out of six sarcomas in syngeneic mice. The sixth murine sarcoma (MC12) was found to be resistant to the tumour inhibitory effect of IL-2. Similarly, five (MC11, MC13, MC14, MC15, MC16) out of six murine sarcoma cell lines were sensitive to the cytolytic effect of IL-2-activated syngeneic killer spleen cells when examined in vitro, whereas the sixth (MC12) sarcoma cell line was resistant. These results suggest that LAK cells represent the effector cell mechanism responsible for the anti-tumour efficacy of local IL-2 immunotherapy and that in vitro testing of sensitivity to the LAK cell-mediated cytolysis may be used to detect tumours responding to IL-2 immunotherapy in vivo.Abbreviations IL-2 interleukin 2 - RIL-2 human recombinant interleukin 2 - LAK lymphokine-activated killer - MC 3-methylcholanthrene - B10 C57BL/10ScSnPh - MSV murine sarcoma virus (Harvey) - MEM minimal essential medium     

The anti-tumour effect of Klebsiella pneumoniae capsular polysaccharides

K24 capsular polysaccharide (K24-CPS), with a known structure of a repeating unit, was isolated from the capsule of Klebsiella pneumoniae serotype K24. The polysaccharide was found to suppress the proliferation of Ehrlich ascites tumour (EAT) cells in vitro, but did not alter the cell cycle distribution of cells. K24-CPS treatment reduced the tyrosine phosphorylation of some proteins in EAT cells. Furthermore, the treatment also decreased the expression of c-JUN, but had no effect on the levels of c-FOS and c-MYC. It is speculated that the growth suppression effect of K24-CPS may be related to its effect in down-regulating c-JUN expression.     

Reactions of glutathione and glutathione radicals with benzoquinones.

The reactions of glutathione (GSH) and glutathione radicals with a series of methyl-substituted 1,4-benzoquinones and 1,4-benzoquinone have been studied. It was found that by mixing excess benzoquinone with glutathione at pH above 6.5, the products formed were complex and unstable. All of the other experiments were carried out at pH 6.0, where the main product was stable for several hours. Stopped-flow analysis allowed the measurement of the rates of the rapid reactions between GSH and the quinones, and the products were monitored by High Performance Liquid Chromatography (HPLC). The rates of the reactions vary by five orders of magnitude and must be influenced by steric factors as well as changes in the redox states. It was observed that simple hydroquinones were not formed when the different benzoquinones were mixed with excess GSH and suggests that the initial reaction is addition/reduction rather than electron transfer. In the presence of excess quinone, the hydroquinone of the glutathione conjugate is oxidized back to its quinone. The rates of the reaction were measured. By using the technique of pulse radiolysis, it was possible to measure the reduction of the quinones by GSSG.- and the oxidation of hydroquinones by GS(.). It is proposed that the appearance of GSSG in reactions of quinones with glutathione could be due to oxidation of the hydroquinone by oxygen and the subsequent superoxide or H2O2 promoting the oxidation of GSH to GSSG.     

The interaction of an anti-tumour platinum complex with DNA.

The interaction of the anti-tumour active cis platinum (II) complexes with DNA has been investigated using dichloro(ethylenediamine)platinum(II) and E. coli DNA. Equilibrium dialysis studies indicate that Pt(en)Cl2 binds reversibly to DNA to a saturation value of 0.57 Pt: P, which is consistent with the platinum being bound both monofunctionally and bifunctionally. Pt(en)Cl2 inhibits the intercalation of 9-aminoacridine (9AA) by cross-linking the bases of the double helix, but at no stage does all the bound platinum cross-link. It is suggested that this inhibition of intercalation is due to intrastrand cross-linking.     

Interaction of benzoquinones with mitochondria interferes with oxidative phosphorylation characteristics

Studies with four benzoquinones, viz. juglone, embelin, maesaquinone and maesanin, on rat liver mitochondria oxidative phosphorylation have been carried out. Three of the benzoquinones are uncouplers in the order juglone greater than maesoquinone greater than embelin, while maesanin is an inhibitor of electron transport and oxidative phosphorylation.     

Clostridium spores as anti-tumour agents

The successful treatment of cancer remains a huge challenge. Consequently, efforts are being made to develop alternative methods of tumour therapy. One of these is the use of live Clostridium species, based on the observation that obligatory anaerobic bacteria specifically colonize the hypoxic and necrotic regions that are present in solid tumours but normally absent in other parts of the body. Although past results have fuelled scepticism about its clinical use, recent promising findings emphasize the potential of Clostridium-directed tumour therapy. These recent developments are reviewed and the reintroduction of this tumour-targeting protein delivery system into clinical settings is discussed.     

Enhancement of anti-tumour effect by cooling

Protamine sulphate B.P. and Armeen DM16D acetate both inhibit a specific coagulative factor produced by malignant tumours. This factor aids the invasiveness of tumours, and its inhibition is known to retard tumour growth.Protamine and Armeen both had a greater effect on an implanted subcutaneous mouse tumour, Sarcoma 180, at 9° to 10°C than at 24° to 25°C.

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Zusammenfassung Sowohl Protaminsulfat als auch Armeen DM16D Acetat hemmen einen spezifischen gerinnung verursachenden Faktor, der von malignen Tumoren gebildet wird. Dieser Faktor erleichtert das infiltierende Wachstum der Tumoren und seine Hemmung verzögert es. Die Wachstumshemmung von subkutan implantierten Sarcoma 180 Tumoren durch Protamin und Armeen war grösser in Mäusen in der Kälte bei 9° bis 10°C als bei 24° bis 25°C.

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Resume Le sulfate de protamine et l'acétate d'armeen DM16D sont les inhibiteurs d'un principe coagulant spécifique produit par les tumeurs malignes. Ce principe facilite le développement et l'infiltration de la tumeur dans les tissus et son inhibition les ralentit. L'action inhibitive de la protamine et de l'armeen sur des tumeurs (Sarcoma 180) implantées sous la peau de souris fut plus efficace au froid (9° à 10°C) que par 24° à 25°C.

     

Mutagenicity of natural naphthoquinones and benzoquinones in the Salmonella/microsome test

The mutagenicities of naturally occurring naphthoquinones and benzoquinones were tested by the pre-incubation method with Salmonella typhimurium strains TA98, TA100 and TA2637, which all contain plasmid pKM101. 6 of the 16 naphthoquinones tested, i.e., plumbagin, naphthazarin, 2-hydroxy-naphthoquinone, vitamin K3 (menadione), juglone and 7-methyljuglone, were mutagenic to strain TA2637 with metabolic activation. Except for juglone and 7-methyl-juglone, these compounds also had slight mutagenic effects on strain TA98 with S9 mix. All the mutagenic naphthoquinones contain one or two hydroxyl and/or methyl substituents. The naphthoquinone mompain, which has four hydroxyl groups, was not mutagenic. Unsubstituted beta-naphthoquinone, naphthoquinones with a prenyl side chain and all bi-naphthoquinone derivatives tested were non-mutagenic. None of the 13 benzoquinones examined was mutagenic to any of the strains used with or without metabolic activation. These results show that natural naphthoquinones are mutagenic when they have only one or two hydroxyl and/or methyl substituents.     

Biosynthesis of lipid resorcinols and benzoquinones in isolated secretory plant root hairs

The primary functions of root hairs are to increase the root surface area and to aid plants in water and nutrient uptake. However, some root hairs also have secretory functions and exude bioactive secondary metabolites. Sorghum (Sorghum bicolor) root hairs release a substantial amount of phenolic lipids including sorgoleone, a 3-pentadecatriene benzoquinone. The activity of the key enzymes involved in the biosynthesis of lipid resorcinols and benzoquinones was measured directly in isolated root hair preparations obtained from 6-d-old roots. The purified root hair preparation readily converted long-chain acyl-CoA starter units to their corresponding lipid resorcinols and decanoyl-CoA was the best substrate, yielding a 5-n-nonyl-resorcinol. The isolated root hair preparation also had high S-adenosyl-L-methionine-dependent O-methyltransferase activity, which catalyses the methylation of several 5-n-alkyl-resorcinols. Optimum activity was with 5-n-pentyl-resorcinol. Isolated root hairs also exhibited hydroxylase activity (putatively a P450 mono-oxygenase) that reacted with the lipophilic 5-pentadecyl-resorcinol substrate. The in situ hydroxylase activity was low relative to the other enzymes studied, but was still detectable in isolated root hairs. Thus, sorghum root hairs possess the entire metabolic machinery necessary for the biosynthesis of lipid resorcinols and benzoquinones. This will have implications for the genetic engineering of bioactive lipid resorcinols and benzoquinones in sorghum and in other plant species. It also demonstrates that some root hairs can function as specialized cells for the production of bioactive secondary metabolites.     

Multivariate analysis of Photosystem II fluorescence quenching by substituted benzoquinones and naphthoquinones

The present investigation examines the action of substituted benzoquinones and naphthoquinones as inhibitors of chlorophyll fluorescence in barley chloroplasts. Stern-Volmer analyses have been used to determine the fractions of chlorophyll fluorescence accessible to quinone as a measure of quinone-membrane solubility and the Stern-Volmer quenching constant as a measure of quinone intrinsic activity. Correlations between quinone structural properties and experimentally measured chlorophyll fluorescence parameters have been made to determine the contribution of lipophilic and electronic factors to quinone solubility and intrinsic activity. In particular, 1,4-benzoquinones must have hydrophobic substituents or hydrogen atoms at positions 2, 3, 5 and 6 for fluorescence quenching activity. The magnitude of the Stern-Volmer quenching constant is affected by the electronic character of hydrophobic substituents, with a maximum value observed in the presence of both electron-releasing and electron-withdrawing moieties. Similarly, the lipophilic character of 2,3-substituents of 1,4-naphthoquinones determines the fraction of chlorophyll fluorescence accessible to quinone, with a maximum accessibility observed for hydrophobic substituents. Naphthoquinone intrinsic activity is also correlated with the electronic character of the substituents and is observed to be at a maximum value with only electron-withdrawing substituents.