James A. Plambeck

Further studies on the generation of reactive oxygen species from activated anthracyclines and the relationship to cytotoxic action and cardiotoxic effects

The relative ease of generation of reactive oxygen species from a series of reductively activated aglycone and sugar modified anthracyclines was compared by the extents of single strand scission in supercoiled PM2-covalently closed circular (CCC)-DNA. The electrochemical properties of these agents were used as a quantitative measure of the ease of reduction and subsequent reoxidation of the reduced species. The relationship of these processes to various biological properties of the anthracyclines, in particular to the measured cardiotoxicity of the drugs, was examined. An attempt was made to identify those structural changes which ameliorate the cardiotoxic effects measured in other test systems while permitting the expression of antitumor properties.

Diminished superoxide anion generation by reduced 5-iminodaunorubicin relative to daunorubicin and the relationship to cardiotoxicity of the anthracycline antitumor agents

Abstract 5-Iminodaunorubicin, when reductively activated, produces single strand scission in PM2-CCC-DNA by a mechanism which proceeds via production of Superoxide anion and hydroxyl radicals. Under comparable conditions, 5-iminodaunorubicin produces much less nicking than daunorubicin. With the aid of N -cyclohexyl-5-iminoquinizarin, as a model, assignment of polarographic waves to the quinone moiety of 5-iminodaunorubicin was possible. The electrochemical results indicate that 5-iminodaunorubicin is more difficult to reduce than daunorubicin and that reoxidation of the reduced form, 5,11-dihydro-5-iminodaunorubicin, is much more difficult than reoxidation of reduced daunorubicin. The latter conclusion is supported by independent chemical studies. By comparison of 5-iminodaunorubicin with daunorubicin and N -cyclohexyl-5-iminoquinizarine, the unusual stability of the reduced 5-iminodaunorubicin, is tentatively attributed to strong hydrogen bonding. The results suggest a correlation between the diminished generation of Superoxide anion by 5-iminodaunorubicin and its observed suppressed cardiotoxicity relative to other anthracyclines.

Redox activities of antitumor anthracyclines determined by microsomal oxygen consumption and assays for superoxide anion and hydroxyl radical generation

To explore the structural characteristics of various derivatives of the anticancer drugs, doxorubicin and daunorubicin, for exhibiting redox activities believed to be associated with toxic radical production, we tested over fifty derivatives in a rapid screening procedure for augmenting oxygen consumption by rat liver microsomes. Measurement of parent drug disappearance and of metabolite appearance for fourteen anthracyclines with a broad range of activities for augmenting oxygen consumption indicated that a single reaction, conversion to the 7-deoxyaglycone, occurred. Multiple tests of selected compounds showed that the liver microsome system exhibited saturation kinetics, and calculated values of Vmax/Km gave the same relative order of activities as did the screening test. The liver microsome system was not found to be stereoselective. Measurements of the abilities of a number of the anthracycline derivatives after chemical activation by reduction with sodium borohydride to convert oxygen to superoxide anion, or to the hydroxyl radical, were also made. The reactivities of the anthracyclines in these latter two assays were positively related to the activities obtained in the rat liver microsome screening test, suggesting that all three tests were measuring various steps in the sequence from anthracycline semiquinone radical formation through oxygen activation and radical formation. Superoxide anion generation from chemically reduced anthracyclines was inhibited by the addition of calf thymus DNA, and the extent of inhibition was positively correlated with the measured DNA association constants of the anthracyclines. However, the DNA association constants were unrelated to superoxide anion generation in the absence of DNA or to the augmentation of oxygen consumption in liver microsomes. Half-wave potentials were negatively correlated with both the results of the microsomal oxygen consumption test and the production of superoxide anion in the chemical test system. No relationships were discerned among the DNA association constants, half-wave potentials, or reoxidizabilities of the anthracyclines tested. Comparisons of the relatively low activities of certain of the anthracyclines in the biochemical and chemical tests for oxygen activation with their known high activities against murine tumors in vivo, but low cardiotoxicities in animal model systems, suggest that the separation of the cytotoxic antitumor and cardiotoxic actions of these derivatives may have been achieved.

The Impact of Gold Smelter Emissions on Vegetation and Soils of a Sub-Arctic Forest-Tundra Transition Ecosystem

Gold smelters near Yellowknife in Canadas Northwest Territories have emitted large quantities of sulfur dioxide and arsenic since inception of roasting in 1941. Although particulate wastes are well contained by baghouse fitters in the one remaining operating smelter, significant gaseous emissions continue. Soil and vegetation were sampled at 52 sites over an area of about 40 km radius from the source. Plant ecology was studied at 43 of those sites. After preliminary multi-element screening that indicated only arsenic was a serious persistent contaminant, x-ray fluorescence was used to measure arsenic content in sampled materials. The plant ecology data were synthesized into an Index of Vitality with numerical ratings of pertinent factors. In the marginal forests and rocky outcrops of the area, indicator species of vegetation permitted a division into zones of severe, moderate, mild, or no impact in order of increasing distance from the current center of emissions. Severe impact, including killing of tree...

Reactions of the antitumor agent carminic acid and derivatives with DNA

Abstract The antitumor agent carminic acid 1a does not bind to DNA but nicks it slowly, more rapidly when reduced in situ , and still more rapidly when prereduced at the quinone moiety. The nicking process requires oxygen and is selectively inhibited by (i) superoxide dismutase, (ii) catalase, and (iii) free radical scavengers indicating the involvement of O 2 • , H 2 O 2 , and OH . , respectively. The intermediacy of OH . was supported by spin trapping with N -t-butyl-α-phenylnitrone and epr of the radical produced via the carminic acid semiquinone. The single strand scission of DNA by carminic acid requires two adjacent hydroquinone moieties in the chromophore since reduced methyl tetra- O -methylcarminate 1b is without effect although it binds weakly to DNA. Polarographic redox potentials for the reversible (2 e , 2H + ) reduction of 1a and 1b are −0.736 ± 0.003 V and −0.56 ± 0.010 V against SCE, respectively. The fact that daunorubicin and adriamycin produce more extensive DNA strand scission than carminic acid under comparable conditions of prereduction and on a molar basis is largely attributed to the assistance of intercalative binding afforded in the case of the anthracyclines.

Electrochemical studies of antitumor antibiotics. V: An electrochemical method of measurement of the binding of doxorubicin and daunorubicin derivatives to DNA

A procedure has been developed for the measurement in aqueous solution of the association constant with native DNA of an agent which is electrochemically reducible. A fresh mercury drop is extruded into a solution containing both the agent and DNA, surface adsorption is reproducibly conditioned (, 90s, followed by −0.4V, 90s), and the peak current is measured during a rapid voltage scan. A suitable plot of current as a function of DNA concentration yields the desired constant. Data are given for a significant series of substituted daunorubicin and doxorubicin compounds and for control compounds.

Mechanism of action of 2-haloethylnitrosoureas on deoxyribonucleic acid: Nature of the intermediates from nitrosourea decomposition☆

Abstract Direct current (DC) and differential pulse polarographic analyses were used to measure the rates of decomposition of a series of 2-haloethylnitrosoureas in aqueous solution. Measured by these methods, the rates of the first and rate-determining step which show a marked pH and solvent dependence agree with the overall rate of decomposition measured by gas evolution. In the 1,3-bis(haloethyl)-1-nitrosourea series, changing the nature of the halogen X has a small effect on the rate of decomposition. In the 3-cyclohexyl-1-(2-haloethyl)-1-nitrosourea series, changing X for OH or OCH 3 results in the rate of hydrolysis being reduced considerably. A free—NH 2 group in the nitrosourea structure as in CNU, MNU, ENU, CPNU, 4-CBNU and 5-CPNU accelerates considerably the rate of decomposition relative to the BCNU and CCNU series. Arrhenius parameters for the decomposition in aqueous pH 7.1 solution in the temperature range 28–47° were obtained for BFNU, BCNU and BBNU: log A, −20.1± 1.4,−21.6± 0.7 and −22.3±1.6; E a , 24.4 ± 2.0, 26.5± 1.0 and 27.2 m 2.3 kcal / mole . The corresponding values for BINU were estimated as log A,−23.3± 3.0; E a , 28.0± 3.0 kcal / mole . Examination of the decomposition products of 1,3-bis(2-chloropropyl)-1-nitrosourea (BCNU-β-Me) and 1,3-bisl 1-(chloromethyl)ethyl]-1-nitrosourea (BCNU-α-Me) favors decomposition pathway B via the diazohydroxide and cyclic chloronium ion for BCNU-β-Me and via the diazohydroxide and/or 2-chloro-1-methylethyl carbonium ion for BCNU-α-Me. While there is no evidence for the contribution of pathway A via a 2-imino- N -nitrosooxazolidinone for these compounds, consideration of product type and yields implicates a third decomposition pathway, via a 1,2,3-oxadiazoline intermediate. Additional evidence for an oxadiazoline intermediate is obtained by the isolation of 2-bromoethanol when BCNU is decomposed in the presence of a high concentration of sodium bromide.

The EC-catalytic mechanism at the rotating disk electrode: Part II. Comparison of approximate theories for the second-order case and application to the reaction of bipyridinium cation radicals with dioxygen in non-aqueous solutions

Abstract Orthogonal collocation was used to obtain an efficient iterative solution to the problem of the second-order EC-catalytic mechanism at the rotating disk electrode (RDE). Application of the spline collocation technique provided accurate results for large values of the kinetic parameter or the substrate/catalyst concentration ratio. The numerical solution was in good agreement with approximate analytical solutions available for certain limiting cases. The second-order EC-catalytic mechanism at the RDE was used to measure the rate of reaction between bipyridinium cation radicals and dioxygen in non-aqueous solutions. Sixteen diquaternized derivatives of 2,2′- and 4,4′-bipyridine were studied including the commercially available herbicides diquot and paraquat (methyl viologen). Values obtained for the rate constant k1 in acetonitrile ranged from 5 × 103 M−1 s−1 to 2 × 108 M−1 s−1. The dependence of log k1 on the standard potentials of the reactants conformed to the Marcus equation for an activation-controlled reaction. The result obtained for the Gibbs energy of activation, 13.1 kJ/mol, was in good agreement with that calculated using the standard rate constant for the heterogeneous reduction of dioxygen. The rate constants in acetonitrile also showed a strong correlation with published data on the herbicidal activity of selected bipyridinium compounds in mustard and tomato.

The EC-catalytic mechanism at the rotating disk electrode: Part I. Approximate theories for the pseudo-first-order case and applications to the Fenton reaction

Abstract The polynomial approximation technique of orthogonal collocation applied to the boundary value problem posed by the pseudo-first-order EC-catalytic mechanism at the RDE gave results in good agreement with those calculated from solutions based on various analytical approximations. The numerical solution could accommodate differences in the diffusivities of oxidized and reduced catalyst species. The application of electrochemical techniques to the determination of the rate constant of the Fenton reaction in acidic chloride media was shown to yield consistently low results. Rate constants were found to be on the order of 38 to 42 M−1 s−1 provided that the stoichiometric factor was properly taken into account. Accounting for the difference in the diffusion coefficients of Fe(II) and Fe(III) species increased the estimates of the rate constant to between 50 and 55 M−1 s−1. The remaining error could be explained in terms of a hydroxyl-radical-induced decomposition of hydrogen peroxide in the reaction layer. The interference due to this reaction was aggravated by the pseudo-first-order conditions required in order to study the Fenton reaction on the time scale of the RDE experiment.

Electroreduction of uranyl ion in calcium nitrate tetrahydrate melt

Abstract The electrochemical reduction of uranyl ions in calcium nitrate tetrahydrate has been studied by polarography, cyclic voltammetry, chronopotentiometry and the potential-step techniques. The UO 2+ 2 /UO + 2 couple, reversible in the aqueous system, is complicated by disproportionation of UO + 2 and by formation of insoluble UO 2 ( s ), both as a monolayer and in bulk, on the electrode surface.