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Multidrug resistance (MDR) of tumour cells is related to the overexpression of ATP-dependent pumps responsible for the active efflux of antitumour agents out of resistant cells. Benzoperimidine and anthrapyridone compounds exhibit comparable cytotoxic activity against sensitive and MDR tumour cells. They diffuse extremely rapidly across the plasma membrane and render the ATP-dependent efflux inefficient. Such uptake could disturb an energy metabolism of normal cells possessing an elevated level of ATP-dependent proteins, especially erythrocytes having a high level of the MRP1, MRP4 and MRP5 proteins. In this study the effect of five antitumour agents: benzoperimidine (BP1), anthrapyridones (CO1, CO7) and reference drugs used in the clinic: doxorubicin (DOX) and pirarubicin (PIRA), on the energetic state in human erythrocytes has been examined. These compounds have various types of structure and kinetics of cellular uptake (slow - DOX, CO7, moderate - PIRA, fast - BP1, CO1) resulting in their different ability to saturate ATP-dependent transporters. The energetic state of erythrocytes was examined by determination of purine nucleotide contents (ATP, ADP, AMP), NAD+ and values of adenylate energy charge (AEC) using an HPLC method. It was found that the level of nucleotides as well as the AEC value of erythrocytes were not changed during 24 h of incubation with these agents independently of their structure and ability to saturate ATP-dependent pumps. This is a very promising result in view of their potential use in the clinic as antitumour drugs against multidrug resistant cancers.
Some sterically hindered N-substituted derivatives of daunorubicin are known to be poor substrates for NADH dehydrogenase, NADPH cytochrome P450 reductase and xanthine oxidase. In consequence, poor oxygen radical generation by these compounds is observed. In this study we examined a new family of sugar-N-substituted derivatives of daunorubicin bearing a bulky substituent introduced on the nitrogen atom through the amidine spacer. These compounds were found to be very active in radical formation catalyzed by all three studied enzymes. Thus, the introduction of a heterocyclic ring, even if it is bulky but flexible, on the nitrogen atom of daunosamine moiety through the one-atom spacer (amidine group), does not induce the steric hindrance effect on the interaction of daunorubicin derivatives with these flavoprotein enzymes.
Anthraquinone derivatives are important anti-cancer drugs possessing, however, undesirable peroxidating and, in consequence, cardiotoxic properties. This results from the mediation by these compounds of the one-electron reduction processes of the oxygen molecule, which produces the highly toxic superoxide anion radical and other active oxygen species. This article summarizes the results of our studies on the molecular aspects of the mechanism of anthraquinone-mediated peroxidation which were carried out using enzymatic-assay, electrochemical, and quantum-mechanical methods.
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