Mitochondria as subcellular targets for clinically useful anthracyclines

Mitochondrial formation of reactive oxygen species

The reduction of oxygen to water proceeds via one electron at a time. In the mitochondrial respiratory chain, Complex IV (cytochrome oxidase) retains all partially reduced intermediates until full reduction is achieved. Other redox centres in the electron transport chain, however, may leak electrons to oxygen, partially reducing this molecule to superoxide anion (O2-*). Even though O2-* is not a strong oxidant, it is a precursor of most other reactive oxygen species, and it also becomes involved in the propagation of oxidative chain reactions. Despite the presence of various antioxidant defences, the mitochondrion appears to be the main intracellular source of these oxidants. This review describes the main mitochondrial sources of reactive species and the antioxidant defences that evolved to prevent oxidative damage in all the mitochondrial compartments. We also discuss various physiological and pathological scenarios resulting from an increased steady state concentration of mitochondrial oxidants.

Electrochemical monitoring of the interaction of doxorubicin with nicotinamide and Fe(III) ions under aerobic and anaerobic conditions

The interaction of doxorubicin with Fe(III) ions and nicotinamide (NA) has been followed by square-wave voltammetry, cyclic voltammetry and UV-VIS. spectroscopy techniques at aerobic and anaerobic conditions. Fe(III)-doxorubicin complex gives a 1-electron reversible step at -0.494 V and a shoulder at 580 nm. Further, the Fe(III)-doxorubicin complex was found to be more stable at aerobic conditions. In the presence of NA, an intermediate (NA-Fe(III)-DQ) forms at -0.462 V under aerobic conditions. Because of the formation of this intermediate, nicotinamide may reduce the cardiotoxic effect of doxorubicin and cause to its detoxification.

Distinct mechanisms of site-specific oxidative DNA damage by doxorubicin in the presence of copper(II) and NADPH-cytochrome P450 reductase

The anticancer mechanism of doxorubicin (DOX), an anthracycline antibiotic, is believed to involve DNA damage through topoisomerase II inhibition and free radical generation. The free radical generation may also participate in genotoxicity, as well as cardiotoxicity, in normal human cells. The present study showed that DOX generates 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo-dG), an indicator of oxidative DNA damage, in HL-60 cells, but not in H(2)O(2)-resistant HP100 cells, suggesting the involvement of H(2)O(2) in cellular DNA damage. Since DOX has both p-quinone and p-hydroquinone residues, free radical generation can be initiated by either reduction or oxidation of DOX. To clarify whether the oxidized or reduced form is more important for DOX-induced H(2)O(2) generation, we investigated the site-specific DNA damage induced by DOX in the presence of Cu(II), in comparison with that in the presence of cytochrome P450 reductase, using (32)P-labeled DNA fragments. DOX caused DNA damage in the presence of Cu(II) or cytochrome P450 reductase. The degree of Cu(II)-mediated DNA damage, including 8-oxodG formation, was much greater than that of cytochrome P450 reductase-mediated DNA damage. DOX plus Cu(II) caused DNA damage specifically at guanine, thymine and cytosine residues, particularly at 5'-GG-3', 5'-GT-3' and 5'-TG-3' sequences. Scavenger experiments suggested the involvement of reactive species generated from H(2)O(2) and Cu(I). When cytochrome P450 reductase and NADPH were used instead of Cu(II), every nucleotide was uniformly damaged, suggesting the participation of.OH. We conclude that DOX may induce carcinostatic and genotoxic effects through oxidation of its p-hydroquinone moiety by metal ion rather than through p-quinone reduction by cytochrome P450 reductase.

Deregulation of gene expression in fetal oocytes exposed to doxorubicin

Doxorubicin is an effective anticancer drug but its use is limited due to its adverse side effects such as infertility and cardiomyopathy. Some possible mechanisms of the action of doxorubicin have been postulated, but the initial gene deregulation response has not been investigated. Fetal life stages are critical periods in mammalian oogenesis. This study analyzes gene expression alterations in mouse fetal oocytes exposed in vitro to this anticancer agent. cDNA libraries were generated from isolated fetal oocytes and differential screenings performed with cDNAs from in vitro doxorubicin-treated and -untreated oocytes. Differentially expressed genes were assessed by real-time RT-PCR to quantify the extent of their transcriptional control in doxorubicin-exposed oocytes. The results show that doxorubicin alters the expression of genes involved in the mitochondrial respiratory chain, intracellular transport and cell differentiation. Finally, the up-regulation of a differentially expressed gene (metaxin) mediated by its promoter was evaluated in a functional assay. When treated with doxorubicin, somatic cells transfected with a genetic construct including the promoter of metaxin and a reporter gene showed increases in expression similar to those observed in fetal oocytes. This demonstrates the direct effect of agent on the regulation of a specific gene.

Mitochondria as a target for inducing death of malignant hematopoietic cells

Mitochondria plays a central role in apoptotic cell death. The intermembrane space of mitochondria contains a number of soluble molecules whose release from the organelle to the cytosol or the nucleus induces cell death. Thus, molecules that directly trigger mitochondria membrane permeabilisation are efficient cytotoxic drugs. Mitochondria is one of the cellular targets for commonly used epipodophyllotoxins, adenine deoxynucleoside analogs and taxanes as well as recently developped agents such as the pentacyclic triterpene betulinic acid and the lymphotoxic agent FTY720. Most informations on anthracyclines point to the mitochondrial membrane as the main target of cardiotoxicity. Mitochondria is also a target for arsenite trioxide, an old cytotoxic agent recently used for treating acute promyelocytic leukemia, lonidamine, a dichlorinated derivative of indazole-3-carboxylic acid developped as a chemosensitizer, the retinoic acid receptor gamma activator CD437 and nitric oxide (NO). Recently, cytotoxic drugs have been specifically designed to directly affect the mitochondrial function. These include the positively charged alpha-helical peptides, which are attracted to and disrupt the negatively charged mitochondrial membrane, thus inducing mammalian cell apoptosis when targeted intracellularly. Various strategies have been proposed also to directly inhibit Bcl-2 and related anti-apoptotic proteins, including antisense oligonucleotides (e.g. Genasense, currently tested in phase III trials), small molecules that mimic the BH3 dimerization domain of these proteins and kinase inhibitors. Ligands of the mitochondrial benzodiazepine receptor such as the isoquinolone carboxamide derivative PK11195 also overcome the membrane-stabilizing effect of Bcl-2, whereas the adenosine nucleotide translocator (ANT) and the mitochondrial DNA are two other potential cellular targets for cytotoxic agents. Potentially, new compounds directly targeting the mitochondria may be useful in treating hematological malignancies. The challenge is now to selectively target these mitochondria permeabilizing agents to malignant cells. This review briefly summarizes the role of the mitochondria in cell death and describes these various strategies for targeting the mitochondria to induce apoptosis.

Reductive activation of terpenylnaphthoquinones

Four terpenylnaphthoquinones were found to enhance the rate of superoxide production in the presence of ascorbate as detected from the superoxide dismutase (SOD)-inhibitable initial oxygen consumption rates. Initial rates of oxygen consumption in the presence of ascorbate plus quinone increase with an increase in the half-wave reduction potentials of the quinones. These quinones also enhance the rate of Cyt(III)c reduction by xanthine/xanthine oxidase (X/XO) in both air- and nitrogen-saturated aqueous solutions at pH 7.4. Maximum rates of Cyt(III)c reduction in nitrogen and oxygen-saturated solutions (V(max)), in the presence of X/XO, increase with an increase in the half-wave reduction potentials of the quinones. SOD inhibits Cyt(III)c reduction rates in the presence of these quinones and X/XO in a manner which is also dependent on the quinone half-wave redox potential. The relative antineoplastic activity of two of these quinones follows the order in rates of oxygen consumption or Cyt(III)c reduction. This is consistent with an antineoplastic action of these quinones through the mechanism of redox cycling or possible interference or inhibition of mitochondrial respiration.