Carmen Teijeiro

Cyclic voltammetry of mitomycin C and DNA

Abstract Cyclic voltammetry (CV) in connection with the hanging mercury drop electrode was used to study mitomycin C (MC) and its mixtures with DNA. CV of the MC solution (without DNA) revealed that (a) at low MC concentrations (around 10 μM) the voltammetric cathodic peaks increase with consecutive cycles in the repeated cycle mode, (b) the CV responses of MC (both in the single-sweep and repeated cycle modes) depend strongly on the potential E A co which MC adsorbed at the electrode, (c) if the adsorption is performed at E A corresponding to the potentials of MC reduction, MC is so strongly bound to the electrode that the MC layer can be transferred to the electrolyte (not containing any dissolved MC) where it produces a response not substantially different from that obtained with the electrode immersed in the MC solution. These results have been tentatively explained by the reduction-initiated polymerization and/or insolubilization of MC at the electrode. Easy preparation of the MC-modified electrode demonstrated in this paper may find practical applications, namely in MC analysis. Preliminary results are reported on the behaviour of MC + DNA mixtures. The addition of double-stranded or single-stranded (denatured) DNAs into the MC solution results in suppression of the MC CV peaks in the first cycle. In the second cycle a new reversible couple appears which increases with the number of cycles. The anodic peak G of DNA (due to guanine) decreases simultaneously. These preliminary results suggest that some potential-controlled interactions of MC with DNA might occur at the electrode.

INTERACTIONS OF SURFACE-CONFINED DNA WITH ACID-ACTIVATED MITOMYCIN C

The anti-cancer drug mitomycin C (MC) was acid-activated and its interaction with single-stranded calf thymus DNA, immobilized at the surface of the hanging mercury drop electrode (DNA-modified HMDE) was studied by cyclic voltammetry. It was found that immersion of the DNA-modified electrode in a solution of acid-activated MC (at pH 3.9) for a short time (usually 1 min) at open current circuit, followed by transfer of the electrode in a neutral blank background electrolyte, resulted in a decrease of the anodic peak G (due to guanine residues in DNA) and in the formation of a reversible couple at approx. -0.44 V. The potential of the cathodic peak was approx. 50 mV more negative than the cathodic peak of the acid-activated MC obtained under the same conditions in the absence of DNA. No changes of peak G occurred and only a very small cathodic peak appeared if the DNA-modified electrode was immersed in an MC solution not exposed to acid pH. On the basis of these results and additional experiments, including dependence on concentration, time and pH during the interaction of MC with DNA at the electrode surface, we concluded that acid-activated MC is covalently bound to guanine residues in DNA immobilized at the electrode surface and that the quinone group in the DNA-MC adduct is reversibly reduced at the electrode.

Electrochemical Analysis of Anthramycin: Hydrolysis, DNA‐Interactions and Quantitative Determination

In aqueous solution, anthramycin methyl ether (AME), anhydroanthramycin (an imino form) and anthramycin are in equilibrium. It is found that anhydroanthramycin is electrochemically active. The AME hydrolysis reaction is studied by cyclic voltammetry. The kinetics of the DNA-drug reaction is followed by AdTSV and it is found that the slowness of the interaction is due to anthramycin changes which take place in solution independently of the DNA presence. DPP is used as a sensitive method for the quantitative determination of the drug and a detection limit of 70 nM is obtained.

Interactions of surface-confined DNA with electroreduced mitomycin C comparison with acid-activated mitomycin C.

The anticancer activity of the antineoplastic drug mitomycin C (MC) was investigated using transfer stripping cyclic voltammetry (TSCV) with single-stranded DNA-modified hanging mercury drop electrode (HMDE). Reductive activation of MC is necessary for drug covalent binding to DNA, and we have found that some potential-controlled interactions of MC with DNA occur at the electrode, i.e. MC can be activated by electroreduction. Acid and electroreductive MC activations were compared and different adducts were subsequently generated, suggesting that the drug can bind to DNA in more than one way. Under conditions of acid activated MC, a monofunctional adduct between C-1 of MC and N-7 of guanine was formed on the electrode surface, reduced at - 0.44 V (vs. SCE). However, when the DNA-modified electrode was immersed in a MC solution and potentials corresponding to the quinone moiety reduction (- 0.3 V or more negative vs. SCE) were applied, an intrastrand bifunctional adduct between C-1 and C-10 of MC and two N-7 of a pair of adjacent guanines in ssDNA were formed at the electrode, reduced at - 0.49 V, i.e. 50 mV more negative than the monoadduct. The results presented in this paper show for the first time electrochemical detection of DNA-MC adducts at the hanging mercury drop electrode.

Electrochemical study of antineoplastic drug thiotepa hydrolysis to thiol form and thiotepa—DNA interactions

Abstract Thiotepa (TT) is an alkylating antineoplastic drug used in the chemotherapy of bladder carcinoma among other uses. In acetate buffer pH 4.2 and 37°C, TT is hydrolyzed to a thiol compound (TT-SH) and we have found that the conversion percentage of TT into TT-SH depends on TT concentration. In DC polarography the TT is inactive and the TT-SH produces a diffusion controlled anodic wave. In stripping voltammetry the TT presents a poorly reproducible adsorption peak and the TT-SH two cathodic peaks. In this paper, the interactions between TT and DNA have been studied using voltammetric techniques and agarose gel electrophoresis. The results show that aziridine moiety is liberated from the TT molecule and binds covalently to nitrogens in the DNA bases, introducing strand breaks into DNA.

Mass transport techniques as a tool for a better understanding of the structure of L-Dopa in aqueous solutions.

Mutual diffusion coefficients, D, densities, ρ, and viscosities, η, are reported for aqueous solutions of L-3,4-dihydroxyphenylalanine (L-Dopa) at 298.15K and 310.15K at concentrations from (0.00025 to 0.0075) moldm(-3). The aim of this study is to contribute to a better understanding of the structure of these systems and the thermodynamic behaviour of L-Dopa in solution. Thus, from these experimental data it was possible to estimate some parameters, such as the hydrodynamic radius, Rh, apparent molar volumes, ϕV, and diffusion coefficients at infinitesimal concentration, D(0), essential for a better understanding of disperse systems. From the measured diffusion coefficients, activity coefficients, γ, for aqueous L-Dopa solutions were also estimated by using Nernst-Hartley equation. The effect of the viscosity on the estimated hydrodynamic radius was also studied.

Methods for direct determination of mitomycin C in aqueous solutions and in urine

Stripping voltammetry (SV) is used to quantitatively determine concentrations of the anti-neoplastic drug mitomycin C (MMC) alone and in mixtures with 5-fluorouracil and cisplatin, both of which are used in combined chemotherapy withMMC. If the accumulation is performed at the potentials of MMC reduction (−0.35Vvs. SCE), reduced MMC is strongly adsorbed at the electrode. It is possible to prepare a MMCmodified electrode, which, after a washing step, is transferred to the background electrolyte to determine MMC by voltammetry. This procedure, which is termed transfer stripping voltammetry (TSV), helps to eliminate interferences and can be applied for a direct determination ofMMCalone or in mixtures with other drugs in urine.

Electrochemical behaviour and micromolar determination of the antineoplastic agent azaribine and its mixtures with cytidine

Abstract Azaribine, an antineoplastic drug of the pyrimidinic antimetabolites group, has been studied by means of polarography, cyclic voltammetry, coulometry and spectrophotometry in buffered aqueous Britton-Robinson medium at pH ranged between 2.5 and 12.0, at room temperature (25°C) and ionic strength 0.1 M. An acid-base equilibrium involving several proton donors present in the medium precedes the electrodic process, which is an overall two-electron process where the electroactive species is the azaribine acid form (neutral molecule) and the reducible group is the C(5)=N(6) double bond. The quantitative analysis of azaribine has been carried out using DPP at the optimum basal conditions. A detection limit of 0.2 μM corresponding to azaribine has been estimated. Quantitative determination of cytidine + azaribine mixtures is undertaken as well, since both compounds can appear together in biological samples. The investigation is carried out at a micromolar level and a mean error of about 2% has been detected.