Binding of transferrin-iron by adriamycin at acidic pH

APPLICATIONS OF NUCLEAR MICROPROBE ANALYSIS IN CANCER CELL BIOLOGY AND PHARMACOLOGY

Nuclear microprobe analysis studies in cancer cell pharmacology and biology carried out at Bordeaux-Gradignan are reported. The cellular pharmacology of two anticancer agents, cis-diammine-dichloroplatinum(II), and 4′-iodo-4′-deoxy-doxorubicin, were investigated, as well as the role of iron in neuroblastoma carcinogenesis, and chromium(III) in trans-generation carcinogenesis. Nuclear microprobe analysis, using PIXE and particle backscattering microanalysis, was able to reveal intracellular and tissue distributions of the elements under investigation. Moreover, the fully quantitative and multi-elemental character of nuclear microprobe analysis offered information on possible mechanisms of drug action, metal carcinogenesis, and interactions with endogenous trace elements in cancer cells.

Tumor acidity, ion trapping and chemotherapeutics. I. Acid pH affects the distribution of chemotherapeutic agents in vitro

Resistance to anti-cancer chemotherapies often leads to regional failure, and can be caused by biochemical and/or physiological mechanisms. Biochemical mechanisms include the overexpression of resistance-conferring proteins. In contrast, physiological resistance involves the tumor microenvironment, and can be caused by poor perfusion, hypoxia and/or acidity. This communication investigates the role of tumor acidity in resistance to a panel of chemotherapeutic agents commonly used against breast cancer, such as anthracyclines, taxanes, anti-metabolites and alkylating agents. The effects of pH on the cytotoxicity of these agents were determined, and ion trapping was confirmed by monitoring the effect of pH on the cellular uptake of radiolabeled anthracyclines. Furthermore, pH-dependent cytotoxicity and uptake were compared between parental drug sensitive MCF-7 cells and variants overexpressing p-glycoprotein (MDR-1) and Breast Cancer Resistance Protein. These data indicate that the magnitude of physiological resistance from pH-dependent ion trapping is comparable to biochemical resistance caused by overexpression of drug efflux pumps. Hence, microenvironment-based ion trapping is a significant barrier to anthracycline-based chemotherapy and can itself be a therapeutic target to enhance the efficacy of existing chemotherapies.

Formation of adriamycin--DNA adducts in vitro

Adriamycin is known to induce the formation of adducts with DNA when reacted under in vitro transcription conditions. The factors affecting the extent of adduct formation were examined in order to establish the critical components and optimal conditions required for the reaction, and to gain insight into the nature of the DNA-adduct complex. There was a strong dependence on reaction temperature (with a 40-fold increase of adducts at 40-50 degrees C compared to 10 degrees C), pH (maximum adducts at pH 7), but little dependence on the oxygen level. There was an absolute requirement for a reducing agent, with adducts detected with DTT, beta-mercaptoethanol and glutathione, maximal adducts were formed at high levels of DTT (5-10 mM). Adducts were also formed with a xanthine oxidase/NADH reducing system, with increasing amounts of adducts detected with increasing NADH; no adducts were detected in the absence of either the enzyme or NADH. Of fourteen derivatives studied, only four yielded a similar extent of adduct formation as adriamycin; there was no absolute requirement for a carbonyl at C13 or hydroxyl at C14. Adducts were also observed with ssDNA but required a longer reaction time compared to dsDNA. The sequence specificity of adduct formation with ssDNA was examined using a primer-extension assay; almost all adducts were associated with a guanine residue. Overall, the results are consistent with a two-step reaction mechanism involving reductive activation of adriamycin, with the activated species then reacting with the guanine residues of either dsDNA or ssDNA.

Interactions of iron-anthracycline complexes with living cells: a microspectrofluorometric study

The interaction of iron-anthracycline complexes with tumor cells has been studied using microspectrofluorometry. The anthracyclines used were adriamycin, 4'-O-tetrahydropyranyladriamycin and daunorubicin. In every case, a 1:3 Fe(III)-anthracycline complex is formed. The three daunorubicin molecules that bind to one Fe(III) are not chemically modified through complexation with iron. In the case of the Fe(III)-adriamycin and Fe(III)-4'-O-tetrahydropyranyladriamycin complexes, about one of the three anthracycline molecules is chemically modified, yielding a highly lipophilic derivative, the 7,8-dehydro-9,10-desacetyladriamycin. The others molecules remain unchanged, i.e., highly hydrophilic in the case of adriamycin. These two species have a different fluorescent spectrum and can be identified inside the cell, using microspectrofluorometry. In the case of the Fe(III)-adriamycin complex, the lipophilic derivative is more rapidly internalized in the cell than the hydrophilic one. Diffusion into the plasmic membrane is the limiting step for the uptake of anthracycline by cells; this means that the plasmic membrane speeds up the dissociation of the Fe(III)-anthracycline complex.

The removal of metal ions from transferrin, ferritin and ceruloplasmin by the cardioprotective agent ICRF-187 [(+)-1,2-bis(3,5-dioxopiperazinyl-1-yl)propane] and its hydrolysis product ADR-925

The ability of the metal ion binding rings-opened hydrolysis product of the anthracycline cardioprotective agent ICRF-187 [dexrazoxane; (+)-1,2-bis(3,5-dioxopiperazinyl-1-yl)propane] to remove iron from transferrin and ferritin, and copper from ceruloplasmin was examined. ADR-925 completely removed Fe3+ from transferrin at below physiological pH but was unreactive at pH 7.4. ADR-925 slowly removed copper from ceruloplasmin at physiological pH (68% removal after 4.8 days). ADR-925 was capable of removing 18% of the iron from ferritin in 7.0 days. All of the metalloproteins displayed saturation behavior in their initial rates of metal ion removal by ADR-925. ICRF-187 may be, in part, preventing doxorubicin-induced cardiotoxicity by depleting iron and copper from these storage and transport proteins or by scavenging metal ions released from these proteins, thus inhibiting hydroxyl radical production by iron-doxorubicin complexes.

Inactivation of cytochrome c oxidase activity in mitochondrial membranes during redox cycling of doxorubicin

Interactions of doxorubicin (DX) with the cardiolipin-dependent cytochrome c oxidase have been examined by using pig heart submitochondrial particles (SMP). A progressive and irreversible loss of oxidase activity is demonstrated in 2 hr incubations of the SMP with 10-100 microM DX in air-equilibrated medium with excess NADH to support redox-cycling of the drug. This oxidative mechanism for oxidase inactivation occurs in connection with a peroxidation process in the bulk membrane lipid, and is independent on turnover of the enzyme. It is related in a complex manner to the electron flux in the respiratory chain with antioxidant properties, and is maximal at the high reduction level of respiratory chain Complex I obtained in the presence of rotenone. Reduction of DX per se plays a minor role, and trace concentrations of chelatable metal ions (iron) are required to catalyse the reaction. Iron in the iron storage protein ferritin is released by DX, and at physiological low O2 concentrations ([O2] less than 20 microM), this iron is a better promoter of oxidase inactivation than is endogenous iron in the SMP. Kinetic analysis of inactivation data indicates the interaction of DX with low affinity (Km 35-55 microM) binding sites in the SMP membranes. Overall, the results point to the possible role of ferritin-iron in the mechanism of DX mitochondrial toxicity and argue against site specific effects of the DX-reduction/oxidation cycle on the cytochrome c oxidase or on its essential phospholipid (cardiolipin) environment.

Time-dependent modifications of ferric-adriamycin

The biological and chemical properties of the ferric-Adriamycin complex changed with time after its preparation. Our experiments demonstrated that the toxicity of the iron-chelate in mice decreased as a function of its age. The reduced toxicity can be correlated with changes in the difference spectrum of ferric-Adriamycin vs Adriamycin (ADR), where a peak around 610 nm shifted to the 570 nm region. When ferric-Adriamycin "aged", the affinity of the drug for iron increased. Concurrently, the redox properties of the chelate changed, such that the bound iron was no longer reduced by glutathione or cysteine. The time-dependent changes observed did not involve the formation of polynuclear iron, as shown by electron spin resonance. Thin-layer chromatography showed that ADR undergoes accelerated degradation in the presence of iron. The iron-catalyzed degradation was oxygen independent. The changes evolving in the spectral and chemical properties of the chelate were shown to stem from transfer of the iron from ADR to one of the degradation products.

The effects of anions on the kinetics of reductive elimination of iron from monoferrictransferrins by thiols

The kinetics of reductive elimination of iron from the human serum monoferric transferrins by thioglycollate (TG), 3-mercaptopropionate (MP), cysteine (Cys), cysteamine (Cym) and 2-mercaptoethanol (ME) have been studied at 37 degrees C using bathophenanthroline sulphonate (BPS) as the ferrous ion acceptor. Analysis of the entire course of the reaction was possible only with thioglycollate since the other thiols cause eventual protein precipitation; in these cases, initial rates were used. The rate of iron release is linearly dependent on thiol concentration at low concentrations of reductant (less than approx. 0.2 M) and increases more rapidly with higher concentrations (up to 0.5-0.75 M). The thiols fall into two distinct groups, with TG, MP and Cys reacting at approx. the same rate, which is an order of magnitude faster than the reaction with Cym and ME. The carboxylate functionality present in the first group may be responsible for the faster reaction rate, by competitively weakening the interaction between the protein and synergistic anion. The pH-dependence of the rate of reductive elimination appears to depend on ionizable functionalities on both the protein and reducing agent. The addition of NaCl, NaClO4, NaHCO3 and Na2HPO4 increases the rate of iron release from the monoferric transferrins. The last two have particularly large accelerating effects and, in the case of the N-terminal monoferrictransferrin, gave saturation kinetics, suggesting that the observed effect is due to conformational changes in the protein caused by binding of ions. The role of the Fe-synergistic anion complex in the transferrins as a 'trapped intermediate' is considered.

Inhibition and inactivation of NADH-cytochrome c reductase activity of bovine heart submitochondrial particles by the iron(III)-adriamycin complex

The NADH-cytochrome c reductase activity of bovine heart submitochondrial particles was found to be slowly (half-time of 16 min) and progressively lost upon incubation with the Fe2(+)-adriamycin complex. In addition to this slow progressive inactivation seen on incubation, a reversible fast phase of inhibition was also seen. However, if EDTA was added to the incubation mixture within 15 s, the slow progressive loss in activity was largely preventable. Separate experiments indicated that EDTA removed about one-half of the iron from the Fe2(+)-adriamycin complex in about 40 s. These results indicated the requirement for iron for the inactivation process. Since the Vmax. for the fast phase of inhibition was decreased by the inhibitor, the inhibition pattern was similar to that seen for uncompetitive or mixed-type inhibition. The direct binding of both Fe3(+)-adriamycin and adriamycin to submitochondrial particles was also demonstrated, with the Fe3(+)-adriamycin complex binding 8 times more strongly than adriamycin. Thus binding of Fe3(+)-adriamycin to the enzyme or to the inner mitochondrial membrane with subsequent generation of oxy radicals in situ is a possible mechanism for the Fe3(+)-adriamycin-induced inactivation of respiratory enzyme activity.

Evidence of the selective alteration of anthracycline activity due to modulation by ICRF-187 (ADR-529)

Anthracyclines are powerful anticancer drugs whose use is limited by the development of chronic cardiotoxicity. The bisdioxopiperazine compound ICRF-187 (ADR-529) specifically abrogates this toxicity both in preclinical animal models and in humans. It does this without effecting either the acute toxicities or the anticancer activity. Therefore, with a specific antagonist, the mechanism of activity of the anthracyclines can be explored. This review discusses recent clinical trials and animal models addressing this issue and concludes by hypothesizing a mechanism of action.

Free radicals in anticancer drug pharmacology

This review examines the formation of free radical intermediates from a number of clinically active antitumor agents including quinone-containing antibiotics and etoposide. An attempt is also made to relate the formation of these reactive intermediates to biochemical and pharmacological basis for tumor cell kill and resistance. The formation of these intermediates in some tumor cells has been detected by both direct ESR and spin-trapping technique. The detection of free radicals in biological systems, however, depends upon cellular bioenvironments, e.g. reducing conditions, and the presence and/or absence of activation and detoxification mechanisms. Evidence shows that certain antitumor drugs generate free radicals in vitro and in vivo and that these reactive species kill tumor cells by causing damage to DNA, membranes or enzymes.

Self-reduction of the iron(III)-doxorubicin complex

The Fe3(+)-doxorubicin complex undergoes reactions that suggest that the complex self-reduces to a ferrous oxidized-doxorubicin free radical species. The Fe3(+)-doxorubicin system is observed to reduce ferricytochrome c, consume O2 and react with 2,2'-bipyridine. Bipyridine acts as a "ferrous ion scavenger" as it reacts with the ferrous ion produced by Fe3(+)-doxorubicin self-reduction. In the absence of O2, a ferrous doxorubicin complex accumulates. In the presence of oxygen, Fe2+ recycles back to Fe3+. The rates of these reactions were measured and the Fe3(+)-doxorubicin self-reduction was determined to be the rate-determining step. The Fe3(+)-doxorubicin induced inactivation of cytochrome c oxidase and NADH cytochrome c reductase on beef heart submitochondrial particles occurs at a rate similar to Fe3(+)-doxorubicin self-reduction. Thus the rate at which damage to these mitochondrial enzymes occurs may be controlled by a nonenzymatic Fe3(+)-doxorubicin self-reduction.

Adriamycin and its iron(III) and copper(II) complexes. Glutathione-induced dissociation; cytochrome c oxidase inactivation and protection; binding to cardiolipin

Some reactions of adriamycin (doxorubicin) and its Fe3+ and Cu2+ complexes were investigated with a view to understanding the mechanisms by which metal ion-adriamycin complexes damage cellular components. The ability of adriamycin in the presence of Cu2+ to inactivate the mitochondrial enzyme cytochrome c oxidase was effectively prevented by physiologic levels of glutathione. This result is explained by the observation that glutathione reacts with the Cu2+-adriamycin complex to produce free adriamycin. As sulfhydryl compounds are, in contrast, known to promote Fe3+-adriamycin-induced damage to cellular components, these results suggest that the response of a metal ion-adriamycin system to the presence of sulfhydryl compounds may be indicative of whether or not Cu2+-adriamycin is the damaging species. The partition of adriamycin into the octanol phase of an octanol-water two-phase system was greatly enhanced by the presence of cardiolipin. This result can be explained by the formation of a strong adriamycin-cardiolipin complex in the octanol phase which is one-half formed at an adriamycin concentration of 6 microM.

The iron(III)-adriamycin complex inhibits cytochrome c oxidase before its inactivation

Cytochrome c oxidase was found to be competitively inhibited by a complex formed between Fe3+ and the cardiotoxic antitumour drug adriamycin (doxorubicin) with an inhibition constant, Ki, of 12 microM. This competitive inhibition precedes the slower Fe3+-adriamycin induced inactivation of cytochrome c oxidase. In strong contrast with this result, free adriamycin was not observed to either inhibit or inactivate cytochrome c oxidase (Ki greater than 3 mM). Since, typically, polycations are known to inhibit cytochrome c oxidase, the competitive inhibition displayed by the Fe3+-adriamycin complex may also result from its polycationic character. Cytochrome c oxidase was also inhibited by pentan-1-ol (Ki 13 mM), and kinetic studies carried out in the presence of both inhibitors demonstrated that the Fe3+-adriamycin complex and pentan-1-ol are mutually exclusive inhibitors of cytochrome c oxidase. The inhibitor pentan-1-ol was also effective in preventing the slow inactivation of cytochrome c oxidase induced by Fe3+-adriamycin, presumably by blocking its binding to the enzyme. It is postulated that the slow inactivation of cytochrome c oxidase occurs when reactive radical species are produced while the Fe3+-adriamycin is complexed to cytochrome c oxidase in an enzyme-inhibitor complex. The Fe3+-adriamycin-induced inactivation of cytochrome c oxidase may be, in part, responsible for the cardiotoxicity of adriamycin.

A survey of chemicals inducing lipid peroxidation in biological systems

A great number of drugs and chemicals are reviewed which have been shown to stimulate lipid peroxidation in any biological system. The underlying mechanisms, as far as known, are also dealt with. Lipid peroxidation induced by iron ions, organic hydroperoxides, halogenated hydrocarbons, redox cycling drugs, glutathione depleting chemicals, ethanol, heavy metals, ozone, nitrogen dioxide and a number of miscellaneous compounds, e.g. hydrazines, pesticides, antibiotics, are mentioned. It is shown that lipid peroxidation is stimulated by many of these compounds. However, quantitative estimates cannot be given yet and it is still impossible to judge the biological relevance of chemical-induced lipid peroxidation.