Doxorubicin (DOX), a widely used chemotherapeutic agent, exhibits cardiotoxicity as an adverse side effect in cancer patients. DOX-mediated cardiomyopathy is linked to its ability to induce apoptosis in endothelial cells and cardiomyocytes by activation of p53 protein and reactive oxygen species. We evaluated the potential roles of H 2 O 2 and p53 in DOX-induced apoptosis in normal bovine aortic endothelial cells and adult rat cardiomyocytes and in tumor cell lines PA-1 (human ovarian teratocarcinoma) and MCF-7 (human breast adenocarcinoma). Time course measurements indicated that activation of caspase-3 preceded the stimulation of p53 transcriptional activity in endothelial cells. In contrast, DOX caused early activation of p53 in tumor cells that was followed by caspase-3 activation and DNA fragmentation. These findings suggest that the transcriptional activation of p53 in DOX-induced apoptosis in endothelial cells may not be as crucial as it is in tumor cells. Further evidence was obtained using a p53 inhibitor, pifithrin-␣. Pifithrin-␣ completely suppressed DOX-induced activation of p53 in both normal and tumor cell lines and prevented apoptosis in tumor cell lines but not in endothelial cells and cardiomyocytes. In contrast, detoxification of H 2 O 2 , either by redox-active metalloporphyrin or overexpression of glutathione peroxidase, decreased DOX-induced apoptosis in endothelial cells and cardiomyocytes but not in tumor cells. This newly discovered mechanistic difference in DOX-induced apoptotic cell death in normal versus tumor cells will be useful in developing drugs that selectively mitigate the toxic side effects of DOX without affecting its antitumor action.

Doxorubicin (DOX) is a broad spectrum anthracycline antibiotic used to treat a variety of cancers. Redox activation of DOX to form reactive oxygen species has been implicated in DOX-induced cardiotoxicity. In this work we investigated DOX-induced apoptosis in cultured bovine aortic endothelial cells and cardiomyocytes isolated from adult rat heart. Exposure of bovine aortic endothelial cells or myocytes to submicromolar levels of DOX induced significant apoptosis as measured by DNA fragmentation and terminal deoxynucleotidyltransferase-mediated nick-end labeling assays. Pretreatment of cells with 100 M nitrone spin traps, N-tert-butyl-␣-phenylnitrone (PBN) or ␣-(4-pyridyl-1-oxide)-N-tert-butylnitrone (POBN) dramatically inhibited DOX-induced apoptosis. Ebselen (20 -50 M), a glutathione peroxidase mimetic, also significantly inhibited apoptosis. DOX (0.5-1 M) inactivated mitochondrial complex I by a superoxide-dependent mechanism. PBN (100 M), POBN (100 M), and ebselen (50 M) restored complex I activity. These compounds also inhibited DOX-induced caspase-3 activation and cytochrome c release. PBN and ebselen also restored glutathione levels in DOX-treated cells. We conclude that nitrone spin traps and ebselen inhibit the DOX-induced apoptotic signaling mechanism and that this antiapoptotic mechanism may be linked in part to the inhibition in formation or scavenging of hydrogen peroxide. Therapeutic strategies to mitigate DOX cardiotoxicity should be reexamined in light of these emerging antiapoptotic mechanisms of antioxidants.

Doxorubicin (DOX) is a widely used anti-tumour drug. Cardiotoxicity is a major toxic side effect of DOX therapy. Although recent studies implicated an apoptotic pathway in DOX-induced cardiotoxicity, the mechanism of DOX-induced apoptosis remains unclear. In the present study, we investigated the role of reactive oxygen species and the nuclear transcription factor nuclear factor kappaB (NF-kappaB) during apoptosis induced by DOX in bovine aortic endothelial cells (BAECs) and adult rat cardiomyocytes. DOX-induced NF-kappaB activation is both dose- and time-dependent, as demonstrated using electrophoretic mobility-shift assay and luciferase and p65 (Rel A) nuclear-translocation assays. Addition of a cell-permeant iron metalloporphyrin significantly suppressed NF-kappaB activation and apoptosis induced by DOX. Overexpression of glutathione peroxidase, which detoxifies cellular H(2)O(2), significantly decreased DOX-induced NF-kappaB activation and apoptosis. Inhibition of DOX-induced NF-kappaB activation by a cell-permeant peptide SN50 that blocks translocation of the NF-kappaB complex into the nucleus greatly diminished DOX-induced apoptosis. Apoptosis was inhibited when IkappaB mutant vector, another NF-kappaB inhibitor, was added to DOX-treated BAECs. These results suggest that NF-kappaB activation in DOX-treated endothelial cells and myocytes is pro-apoptotic, in contrast with DOX-treated cancer cells, where NF-kappaB activation is anti-apoptotic. Removal of intracellular H(2)O(2) protects endothelial cells and myocytes from DOX-induced apoptosis, possibly by inhibiting NF-kappaB activation. These findings suggest a novel mechanism for enhancing the therapeutic efficacy of DOX.

In this review, we discuss the role of nitric oxide synthase in doxorubicin (DOX)-induced cardiomyopathy, a prominent side effect of DOX chemotherapy in cancer patients. It is becoming increasingly clear that apoptosis of myocardial cells plays a critical role in the onset ofcardiomyopathy. DOX exposure to endothelial cells and cardiomyocytes caused apoptotic cell death at sub-micromolar concentrations. DOX-induced generation ofHP2 has been shown to be responsible for this drug's toxicity and apoptosis. HzO z in tum enhanced endothelial nitric oxide synthase (eNOS) transcription in endothelial cells and myocytes.Antisense eNOS depressed DOX-induced oxidative stress and apoptosis. Redox-metal chelators inhibited DOX-induced apoptosis, clearly suggesting a role for reactive oxygen species in DOX-induced apoptosis. Here, we will focus on the role of eNOS expression, iron chelation, and iron signaling on DOX-mediated apoptosis. (Mol Cell Biochem 234/235: 119-124, 2002)

Doxorubicin (DOX), a widely used antitumour drug, causes dose-dependent cardiotoxicity. Cardiac mitochondria represent a critical target organelle of toxicity during DOX chemotherapy. Proposed mechanisms include generation of ROS (reactive oxygen species) and disturbances in mitochondrial calcium homoeostasis. In the present study, we probed the mechanistic link between mitochondrial ROS and calcium in the embryonic rat heart-derived H9c2 cell line and in adult rat cardiomyocytes. The results show that DOX stimulates calcium/calcineurin-dependent activation of the transcription factor NFAT (nuclear factor of activated T-lymphocytes). Pre-treatment of cells with an intracellular calcium chelator abrogated DOX-induced nuclear NFAT translocation, Fas L (Fas ligand) expression and caspase activation, as did pre-treatment of cells with a mitochondria-targeted antioxidant, Mito-Q (a mitochondria-targeted antioxidant consisting of a mixture of mitoquinol and mitoquinone), or with adenoviral-over-expressed antioxidant enzymes. Treatment with GPx-1 (glutathione peroxidase 1), MnSOD (manganese superoxide dismutase) or a peptide inhibitor of NFAT also inhibited DOX-induced nuclear NFAT translocation. Pre-treatment of cells with a Fas L neutralizing antibody abrogated DOX-induced caspase-8- and -3-like activities during the initial stages of apoptosis. We conclude that mitochondria-derived ROS and calcium play a key role in stimulating DOX-induced 'intrinsic and extrinsic forms' of apoptosis in cardiac cells with Fas L expression via the NFAT signalling mechanism. Implications of ROS- and calcium-dependent NFAT signalling in DOX-induced apoptosis are discussed.