DOX-induced DNA Damage Research Articles

Anticancer therapy induced cardiotoxicity: Involvement of EPAC1 in cardioprotection and anticancer therapy

Doxorubicin (Dox) is an anthracycline commonly used to treat many types of cancer; unfortunately this chemotherapeutic agent induces many side effects such as cardiotoxicity leading to dilated cardiomyopathy (DCM). The cardiotoxicity of Dox has been related to reactive oxygen species generation, DNA intercalation and topoisomerase II inhibition, bioenergetics alterations leading to cardiomyocyte death. Nowadays the challenge is to find new treatment options aiming at reducing Dox cardiotoxicity. Epac (exchange protein directly activated by cAMP) signaling could be worth investigating as Epac activates small G proteins which are known to be involved in Dox-induced cardiotoxicity. We investigated the time/dose-dependent Dox effect on Epac signaling in both in vivo mice model (C57Bl63/Knock-out Epac1 mice, iv injections, 12mg/kg cumulative dose) and in vitro (primary culture of neonatal rat cardiomyocytes (NRVM, 24h, Dox 1μM). In vivo, Dox-treated mice developed a DCM associated with Ca2 + homeostasis dysfunction (increase of Ca2 + waves and Ca2 + leaks). In vitro, as measured by flow cytometry and western blot, Dox (1μM) induced DNA damage and cell death in NRVM. This cell death is associated with apoptotic features including mitochondrial membrane permeabilization, caspase activation and cell size reduction. The inhibition of Epac1 (ESI09, CE3F4) decreased Dox-induced DNA damage, loss of mitochondrial membrane potential, apoptosis and finally cardiomyocyte death. Moreover, in vivo, Epac1 KO mice were protected against Dox-induced cardiotoxicity by unaltered cardiac function (no DCM) and calcium homeostasis at 15 weeks post-treatment. Inhibition of Epac1 could be a valuable therapeutic strategy to limit Dox-induced cardiomyopathy during cancer chemotherapy. Indeed, preliminary data show also that preventing Dox-induced cardiotoxicity, the inhibition of Epac1 can also potentiate cancerous cells death.

Prevention of doxorubicin (DOX)-induced genotoxicity and cardiotoxicity: Effect of plant derived small molecule indole-3-carbinol (I3C) on oxidative stress and inflammation

Doxorubicin (DOX) is an anthracycline group of antibiotic available for the treatment of broad spectrum of human cancers. However, patient receiving DOX-therapy, myelosuppression and genotoxicity which may lead to secondary malignancy and dose dependent cardiotoxicity is an imperative adverse effect. Mechanisms behind the DOX-induced toxicities are increased level of oxidative damage, inflammation and apoptosis. Therefore, in search of a potential chemoprotectant, naturally occurring glucosinolate breakdown product Indole-3-Carbinol (I3C) was evaluated against DOX-induced toxicities in Swiss albino mice. DOX was administered (5 mg/kg b.w., i.p.) and I3C was administered (20 mg/kg b.w., p.o.) in concomitant and 15 days pretreatment schedule. Results of the present study showed that I3C appreciably mitigated DOX-induced chromosomal aberrations, micronuclei formation, DNA damage and apoptosis in bone marrow niche. Histopathological observations revealed that DOX-intoxication resulted in massive structural and functional impairment of heart and bone marrow niche. However, oral administration of I3C significantly attenuated DOX-induced oxidative stress in the cardiac tissues as evident from decreased levels of ROS/RNS and lipid peroxidation, and by increased level of glutathione (reduced) and the activity of phase-II antioxidant enzymes. Additionally, administration of I3C significantly (P < 0.05) stimulated Nrf2-mediated activation of antioxidant response element (ARE) pathway and promoted expression of cytoprotective proteins heme oxygenase 1 (HO-1), NAD(P)H:quinine oxidoreductase 1 (NQO1) and GSTπ in bone marrow and cardiac tissues. In connection with that, I3C significantly attenuated DOX-induced inflammation by downregulation of pro-inflammatory mediators, viz., NF-kβ(p50), iNOS, COX-2 and IL-6 expression. Moreover, I3C attenuate DOX-induced apoptosis by up-regulation of Bcl2 and down-regulation of Bax and caspase-3 expression in bone marrow cells. Thus, this study suggests that I3C has promising chemoprotective efficacy against DOX-induced toxicities and indicates its future use as an adjuvant in chemotherapy.

Attenuation of doxorubicin-induced cardiotoxicity and genotoxicity by an indole-based natural compound 3,3′-diindolylmethane (DIM) through activation of Nrf2/ARE signaling pathways and inhibiting apoptosis

The most crucial complication related to doxorubicin (DOX) therapy is nonspecific cytotoxic effect on healthy normal cells. The clinical use of this broad-spectrum chemotherapeutic agent is restricted due to development of severe form of cardiotoxicity, myelosuppression, and genotoxicity which interfere with therapeutic schedule, compromise treatment outcome and may lead to secondary malignancy. 3,3′-diindolylmethane (DIM) is a naturally occurring plant alkaloid formed by the hydrolysis of indolylmethyl glucosinolate (glucobrassicin). Therefore, the present study was undertaken to investigate the protective role of DIM against DOX-induced toxicity in mice. DOX was administered (5 mg/kg b.w., i.p.) and DIM was administered (25 mg/kg b.w., p.o.) in concomitant and 15 days pretreatment schedule. Results showed that DIM significantly attenuated DOX-induced oxidative stress in the cardiac tissues by reducing the levels of free radicals and lipid peroxidation, and by enhancing the level of glutathione (reduced) and the activity of antioxidant enzymes. The chemoprotective potential of DIM was confirmed by histopathological evaluation of heart and bone marrow niche. Moreover, DIM considerably mitigated DOX-induced clastogenicity, DNA damage, apoptosis, and myeloid hyperplasia in bone marrow niche. In addition, oral administration of DIM significantly (p < .05) stimulated the Nrf2-mediated activation of antioxidant response element (ARE) pathway and promoted expression of ARE-driven cytoprotective proteins, HO-1, NQO1, and glutathione-S-transferase (GST). In connection with that, DIM significantly attenuated DOX-induced apoptosis by upregulation of Bcl-2 expression and downregulation of Bax and caspase-3 expression. Thus, this study suggests that DIM has promising chemoprotective efficacy against DOX-induced toxicity and indicates its future use as an adjuvant in chemotherapy.

A multifunctional nanoparticle system combines sonodynamic therapy and chemotherapy to treat hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most common and deadly malignancies worldwide. To date, the survival of patients with HCC has not improved because of the insensitivity of HCC to conventional treatments. Sonodynamic therapy (SDT) is a promising new approach that shows remarkable potential in the treatment of HCC. Here, we designed a simple, biocompatible, and multifunctional nanosystem that combines SDT and chemotherapy to treat HCC. This nanosystem, called HPDF nanoparticles, had a core–shell structure in which hematoporphyrin (HP) was complexed with doxorubicin (DOX) to form the hydrophobic core and the surface was coated with Pluronic F68 to form the hydrophilic shell. In HCC cells, HPDF nanoparticles in combination with ultrasonic irradiation (1.0 MHz, 1.5 W/cm2, 30 s) exhibited potent cytotoxicity, resulting from the synergistic effects of a large amount of reactive oxygen species generated from HP and DOX-induced DNA damage. Notably, HPDF nanoparticles in combination with ultrasonic irradiation significantly reversed drug resistance in Nanog-positive cancer stem cells (CSCs) in HCC. In nude mice bearing HCC tumors, HPDF nanoparticles efficiently accumulated in the tumors and reached the maximum levels within 6‒8 h, post intravenous injection. HPDF nanoparticles, in combination with ultrasonic irradiation (1.0 MHz, 3 W/cm2, 5 min), suppressed tumor growth, angiogenesis, and collagen deposition, considerably. In summary, our results show that HPDF nanoparticles can effectively combine SDT and chemotherapy to inhibit HCC growth and progression through multiple mechanisms in both cellular and animal models.

Exercise during pregnancy decreases doxorubicin-induced cardiotoxic effects on neonatal hearts.

Cancer treatment with Doxorubicin (DOX) is limited due its dose-dependent cardiotoxicity, mainly related to the oxidative stress production. In experimental models of DOX treatment exercise can be used as a beneficial adjuvant therapy. This work aimed to investigate the effects of exercise during pregnancy on DOX-induced cardiotoxicity in cardiomyocytes of progeny, examining the possible intergenerational cardioprotective effects of maternal exercise. For this purpose pregnant rats were divided in control and exercise groups and pre-treated during gestational days. Hearts of newborns were used to obtain a culture of cardiomyocytes to be treated with DOX for analyses of cell viability, apoptosis and necrosis; ROS production; DNA damage; SOD and CAT activities; and Sirt6 protein expression. The results showed that exercise during pregnancy induced an increase in the viability of neonatal cardiomyocytes and a decrease in DOX-induced apoptotic and necrotic death which were correlated to the decrease in ROS production and an increase in antioxidant defenses. Exercise also protected neonatal cardiomyocytes from DOX-induced DNA damage, demonstrating a reduction in the oxidative DNA breaks. Likewise, exercise induced an increase in expression of Sirt6 in neonatal cardiomyocytes. Therefore, these results demonstrate for the first time that exercise performed by mothers protects the neonatal heart against DOX-induced toxicity. Our data demonstrate the intergenerational effect of exercise in cardiomyocytes of progeny, where the modulation of oxidative stress through antioxidant enzymes, and DNA integrity via Sirt6, were induced due to exercise in mothers, increasing the resistance of the neonatal heart against DOX toxicity.

Pim2 is important for regulating DNA damage response in multiple myeloma cells.

Pan proviral integrations of Moloney virus (PIM) inhibition in multiple myeloma (MM) results in reduced cell viability in tested human-derived MM cell lines and reduces tumor burden in xenograft mouse models, making PIMs important therapeutic targets for the disease. PIM kinase inhibitors are currently being tested clinically in MM. We sought to elucidate the role of the various PIMs in MM. Our data demonstrate that Pim2 has a significant role in MM cell cytotoxicity. Our data provide evidence for a novel role for Pim2 in the regulation of the DNA damage response (DDR). Knockdown of Pim2 upregulates several downstream DDR markers, mimicking the effects of doxorubicin (Dox) treatment of MM cells, and suggesting a role for the kinase as a negative regulator of this pathway. Dox-induced DNA damage results in a decrease in Pim2 levels, placing the kinase directly downstream of the site of Dox-DNA binding. Overexpression of Pim2 confers a slight survival advantage against Dox through antiapoptotic activity, further underscoring its relevance in the DDR pathway. These data provide insights into a novel mechanism of PIM kinase activity and provide the framework for designing therapeutic approaches in MM.

Doxorubicin-induced necrosis is mediated by poly-(ADP-ribose) polymerase 1 (PARP1) but is independent of p53.

Necrosis, unregulated cell death, is characterized by plasma membrane rupture as well as nuclear and cellular swelling. However, it has recently been reported that necrosis is a regulated form of cell death mediated by poly-(ADP-ribose) polymerase 1 (PARP1). PARP1 is thought to mediate necrosis by inducing DNA damage, although this remains unconfirmed. In this study, we examined the mechanisms of PARP1-mediated necrosis following doxorubicin (DOX)-induced DNA damage in human kidney proximal tubular (HK-2) cells. DOX initiated DNA damage response (DDR) and upregulated PARP1 and p53 expression, resulting in morphological changes similar to those observed during necrosis. Additionally, DOX induced mitochondrial hyper-activation, as evidenced by increased mitochondrial respiration and cytosolic ATP (cATP) production. However, DOX affected mitochondrial mass. DOX-induced DNA damage, cytosolic reactive oxygen species (cROS) generation, and mitochondrial hyper-activation decreased in cells with inhibited PARP1 expression, while generation of nitric oxide (NO) and mitochondrial ROS (mROS) remained unaffected. Moreover, DOX-induced DNA damage, cell cycle changes, and oxidative stress were not affected by p53 inhibition. These findings suggest that DNA damage induced necrosis through a PARP1-dependent and p53-independent pathway.

Early Administration of Carvedilol Protected against Doxorubicin-Induced Cardiomyopathy.

This study tested for the benefits of early administration of carvedilol as protection against doxorubicin (DOX)-induced cardiomyopathy. Thirty male, adult B6 mice were categorized into group 1 (untreated control), group 2 [DOX treatment (15 mg/every other day for 2 weeks, i.p.], and group 3 [carvedilol (15 mg/kg/d, from day 7 after DOX treatment for 28 days)], and euthanized by day 35 after DOX treatment. By day 35, the left ventricular ejection fraction (LVEF) was significantly lower in group 2 than in groups 1 and 3, and significantly lower in group 3 than in group 1, whereas the left ventricular (LV) end-diastolic and LV end-systolic dimensions showed an opposite pattern to the LVEF among the three groups. The protein expressions of fibrotic (Smad3, TGF-β), apoptotic (BAX, cleaved caspase 3, PARP), DNA damage (γ-H2AX), oxidative stress (oxidized protein), mitochondrial damage (cytosolic cytochrome-C), heart failure (brain natriuretic peptide), and hypertrophic (β-MHC) biomarkers of the LV myocardium showed an opposite pattern to the LVEF among the three groups. The protein expressions of antifibrotic (BMP-2, Smad1/5), α-MHC, and phosphorylated-Akt showed an identical pattern to the LVEF among the three groups. The microscopic findings of fibrotic and collagen-deposition areas and the numbers of γ-H2AX(+) and 53BP1(+) cells in the LV myocardium exhibited an opposite pattern, whereas the numbers of endothelial cell (CD31(+), vWF(+)) markers showed an identical pattern to the LVEF among the three groups. Cardiac stem cell markers (C-kit(+) and Sca-1(+) cells) were significantly and progressively increased from group 1 to group 3. Additionally, the in vitro study showed carvedilol treatment significantly inhibited DOX-induced cardiomyoblast DNA (CD90/XRCC1(+), CD90/53BP1(+), and r-H2AX(+) cells) damage. Early carvedilol therapy protected against DOX-induced DNA damage and cardiomyopathy.

Alteration in the Doxorubicin-Induced DNA Damage in Cultured V79 Cells by Aegle marmelos (L.) Correa (Bael): A Comet Assay Study

The clinical applicability of wide spectrum chemotherapeutic drug, doxorubicin is limited due to induction of severe cardiomyopathy resulting from DNA damage. The present study was aimed to evaluate the protective effect of bael (Aegle marmelos) extract (AME) on the doxorubicin-induced molecular DNA damage in V79 cells. V79 (Chinese hamster lung fibroblasts) cells were treated with 0 or 25 μg/ml AME before exposure to 0, 1, 2.5, 5, 10, 25 or 50 μg/ml doxorubicin DOX. The DNA damage was studied at different post-doxorubicin treatment times using single cell gel electrophoresis. Doxorubicin caused a maximum DNA damage at 1 h post-DOX treatment indicated by a highest Olive Tail Movement (OTM) and tail DNA, whereas treatment of V79 cells with 25 μg/ml AME enhanced DNA repair at all assessment times with a maximum repair up to 6 h which did not alter thereafter. In another experiment DOX caused a concentration dependent increase in the DNA damage and treatment of V79 cells with 25 μg/ml AME significantly inhibited DOX-induced DNA damage at all post-DOX treatment times. The rate of DNA repair was higher in AME pre-treated cells than DOX-treatment alone. Assessment of cell survival showed a concentration dependent decline in the clonogenicity after DOX-treatment, whereas AME pre-treatment arrested the DOX-induced reduction in the cell survival. The DNA damage and clonogenicity of cells showed a close but inverse relationship, i.e., with increasing DNA damage there was a corresponding reduction in the cell survival. This relationship between cell survival and DNA damage was linear quadratic. Our study demonstrates that AME pretreatment reduced the DOX-induced DNA damage and hastened the DNA repair in V79 cells, thus demonstrating the chemoprotective potential of AME.

Protective effects of deep sea water against doxorubicin‑induced cardiotoxicity in H9c2 cardiac muscle cells.

Doxorubicin (DOX) is one of the most effective chemotherapeutic agents in the treatment of a variety of tumors. However, its clinical use has been compromised by the risk of cardiotoxicity. Thus, many efforts have been focused on exploring new strategies to prevent or reverse DOX-induced cardiotoxicity. Recently, deep sea water (DSW) has drawn much scientific interest for therapeutic intervention due to its enrichment in nutrients and minerals. In this study, we investigated whether DSW has protective effects against DOX-induced cardiotoxicity. Pre-treatment with DSW significantly increased the viability of DOX-treated rat H9c2 cardiac muscle cells. This protective effect of DSW appears to be mediated through the inhibition of DNA damage rather than suppression of reactive oxygen species (ROS) production in DOX‑treated H9c2 cardiac muscle cells. The inhibitory effect of DSW on DOX-induced DNA damage subsequently attenuated apoptotic signaling such as activation of cysteine-aspartic acid protease-3 (caspase-3) and fragmentation of poly(ADP-ribose) polymerase (PARP), whereas the expression of anti-apoptotic protein B-cell lymphoma-extra large (Bcl-xL) was increased. Moreover, DSW treatment rescued the activation of protein kinase B (Akt) to protect cells from DOX-triggered apoptosis. Taken together, our data showed that DSW has protective effects against DOX-induced cardiotoxicity, suggesting that DSW has some promise as a novel protective supplement for promoting the successful use of DOX in clinical regimen.

0018: Role of epac signalling in doxorubicin-induced cardiotoxicity

The canonical mechanisms underlying doxorubicin (Dox)-induced cardiotoxicity involve Reactive Oxygen Species production, DNA intercalation and topoisomerase II inhibition which trigger DNA damage, oxidative stress and alteration of calcium homeostasis leading to myocyte death and heart dysfunction. However, alternative mechanisms with prior or concomitant dox induced alteration of signalling pathways are emerging. β-adrenergic signalling and especially Epac (exchange protein directly activated by cAMP) could be worth investigating as Epac activate small G proteins Rac1 and Rho A known to be implicated in dox-induced cardiotoxicity. We investigated the time/dosedependent Dox effect in in vitro (neonatal rat cardiomyocytes) and in vivo on a mice models on 1/ the transcriptional activity of cardiac remodelling markers (ANF, SRE and SkM β-actin) 2/Epac's downstream effectors (small G proteins expression, MEF-2, NFAT) and 3/Epac's role in dox-induced DNA damage. In vitro, Dox treatment resulted in an alteration of Epac signalling through inhibition of stress and remodelling markers, a modulation of Epac's downstream effectors and a direct effect of Dox on Epac1 and Epac2 expression. Moreover, the protein level of DNA damage marker (H2AX pS139) was modulated by Epac1 and 2 inhibitors and by Epac2 inhibitor which suggest a new protective pathway through Epac1 specific inhibition. In vivo, echocardiography of Dox-treated mice (3 iv injections, 12 mg/kg total dose) showed a dilated cardiomyopathy from 15 weeks. At the molecular level, we observed a statistically significant Epac1, Epac2, Rho A and Rac1 expression modulation between 6 and 20 weeks suggesting a time-dependent regulation of Epac signalling in Dox-induced cardiotoxicity. Our results indicate for the first time an integrated time-course of Dox induced-alteration in Epac signalling, and a potential role of Epac in myocyte death induced by Dox.

Protective role of atorvastatin against doxorubicin-induced cardiotoxicity and testicular toxicity in mice

Doxorubicin (DOX), a potent chemotherapeutic agent, is widely used for the treatment of various malignancies. However, its clinical uses are limited due to its dose-dependent adverse effects particularly cardiac and testicular toxicities. DOX-induced toxicity is mainly due to the induction of oxidative stress. Atorvastatin (ATV), a 3-hydroxy 3-methyl glutaryl coenzyme A reductase inhibitor, with lipid-lowering activity, acts as an antioxidant at lower doses. It possesses pleiotropic effects independent of cholesterol-lowering property usually shown at lower doses, which include antioxidant and anti-inflammatory activities. The present study was aimed to investigate the possible protection exerted by atorvastatin against oxidative stress and DNA damage induced by DOX in the heart and testes of mice. The protective role of ATV in the heart and testes of DOX-treated mice was evident from the amelioration of oxidative stress, DNA and cellular damage. The present study clearly indicates that ATV offers a significant protection against DOX-induced oxidative stress and DNA damage in the heart and testes of mice.

Preventive and protective effects of silymarin on doxorubicin-induced testicular damages correlate with changes in c-myc gene expression

This study aimed to investigate the preventive and protective effects of silymarin (SMN) on doxorubicin (DOX)-induced damages in the testis. Wistar rats were divided into six groups (n=8), including: control (C), DOX-treated (DOX, 15mg/kg, i.p.), DOX- and SMN-treated and SMN-treated animals (SMN, 50mg/kg, orally). Those groups, which received either compounds, were sub-grouped based on the preventive (PVT), protective (PTT) and/or therapeutic regimens (TPT) of SMN administration. The antioxidant status analyses, hormonal assay, and histopathological examinations in the testis were conducted. The expression of c-myc at mRNA level also was analyzed. SMN in preventive and protective forms significantly (p<0.05) improved the DOX-induced weight loss and lowered the alkaline phosphatase level. Pretreatment and co-treatment with SMN attenuated the DOX-induced carbonyl stress. The DOX-induced histopathological damages including negative TDI and IR were significantly (p<0.05) improved with SMN pretreatment and co-administration. SMN in preventive and protective forms prevented from DOX-induced DNA fragmentation in the testis. SMN ameliorated the DOX-reduced serum level of sexual hormones including testosterone, inhibin B, LH and FSH in PVT and PTT groups. The c-myc expression at mRNA level was completely and relatively down regulated in the testis of animals that received SMN as pretreatment and concurrent administration, respectively. Our data suggests that the DOX-induced biochemical and histopathological alterations could be prevented and/or protected by SMN. Moreover, the SMN protective and preventive effects attribute to its capacity in the reduction of DOX-induced carbonyl stress and DNA damage, which may be mediated by c-myc expression.

Both XPA and DNA polymerase eta are necessary for the repair of doxorubicin-induced DNA lesions

Doxorubicin (DOX) is an important tumor chemotherapeutic agent, acting mainly by genotoxic action. This work focus on cell processes that help cell survival, after DOX-induced DNA damage. In fact, cells deficient for XPA or DNA polymerase eta (pol eta, XPV) proteins (involved in distinct DNA repair pathways) are highly DOX-sensitive. Moreover, LY294002, an inhibitor of PIKK kinases, showed a synergistic killing effect in cells deficient in these proteins, with a strong induction of G2/M cell cycle arrest. Taken together, these results indicate that XPA and pol eta proteins participate in cell resistance to DOX-treatment, and kinase inhibitors can selectively enhance its killing effects, probably reducing the cell ability to recover from breaks induced in DNA.

Persimmon Leaf Extract Inhibits the ATM Activity during DNA Damage Response Induced by Doxorubicin in A549 Lung Adenocarcinoma Cells

Persimmon leaf (PL) has been commonly recognized for its wide variety of health benefits. A previous study has reported that persimmon leaf extract (PLE) contained flavonols with the 2″-galloly moiety (PLEg). Galloylated homologues generically show stronger activity in their biological function, so enhanced functions can be expected for PLEg. We investigated in this present study the effect of PLEg on the cellular DNA damage checkpoint signaling to sensitize cancer chemotherapy. Treatment with PLE and PLEg significantly increased the cytotoxicity of doxorubicin (DOX) in A549 adenocarcinoma cells. PLE and PLEg reduced the phosphorylation of checkpoint proteins such as structural maintenance of chromosomes 1 (SMC1), checkpoint kinase 1 (Chk1), and p53 in DOX-treated cells. Moreover, PLE decreased the phosphorylation of ATM (ataxia telangiectasia mutated) in a dose-dependent manner. PLE, and especially PLEg, abrogated the G2/M checkpoint during DOX-induced DNA damage. These results suggest that PLEg specifically inhibited ATM-dependent checkpoint activation by DOX, and that PLEg might be a useful sensitizer in cancer chemotherapy.

Modulation of doxorubicin-induced genotoxicity by squalene in Balb/c mice

The present study aims to evaluate the protective effect of squalene against the genotoxicity of the chemotherapeutic agent doxorubicin (Dox) using two genotoxicity assays, the micronucleus assay and the comet assay. Different groups of mice were fed squalene at the doses of 1 and 4 mmol g(-1) body weight (100 or 400 μl as squalene oil) either at 4 h before or 1 h after Dox (20 mg kg(-1)) treatment. 24 h after the Dox treatment, bone marrow erythrocytes were evaluated for the incidence of micronuclei, and the induced DNA strand breaks were examined in heart tissue by the alkaline comet assay. As expected, Dox significantly induced micronuclei in polychromatic (immature) erythrocytes, as well as in total erythrocytes. The frequency of Dox-induced micronucleated erythrocytes was significantly reduced in the mice treated with squalene both before and after Dox administration. Squalene itself obviously did not induce any micronuclei in bone marrow erythrocytes. The comet assay also demonstrated a significant increase in DNA damage, especially DNA single strand breaks in the Dox-treated group of mice as compared to the control. The Dox-induced DNA damage was also effectively reduced by squalene when it was administered either before or after the Dox treatment. Squalene did not induce any significant DNA damage by itself. Compared to the pre-treatment of squalene, post treatment gave rise to more effective prevention against Dox-induced DNA damage. The data suggest that the complimentary use of squalene with Dox will be beneficial to reduce the adverse effect of Dox in cancer chemotherapy, such as the increased incidence of undesirable mutagenic side effects.

Grape Seed Proanthocyanidins Ameliorate Doxorubicin-Induced Cardiotoxicity

Doxorubicin (Dox) is one of the most widely used and successful chemotherapeutic antitumor drugs. Its clinical application is highly limited due to its cumulative dose-related cardiotoxicity. Proposed mechanisms include the generation of reactive oxygen species (ROS)-mediated oxidative stress. Therefore, reducing oxidative stress should be protective against Dox-induced cardiotoxicity. To determine whether antioxidant, grape seed proanthocyanidin extract (GSPE) attenuates Dox-induced ROS generation and protects cardiomyocytes from Dox-induced oxidant injury, cultured primary cardiomyocytes were treated with doxorubicin (Dox, 10 microM) alone or GSPE (50 microg/ml) with Dox (10 microM) for 24 hours. Dox increased intracellular ROS production as measured by 6-carboxy-2',7'-dichlorodihydrofluorescein diacetate, induced significant cell death as assessed by propidium iodide, and declined the redox ratio of reduced glutathione (GSH)/oxidized glutathione (GSSG) and disrupted mitochondrial membrane potential as determined by 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethlbenzimidazole-carbocyanide iodine (JC-1). Analysis of agarose gel electrophoresis revealed Dox-induced nuclear DNA damage with the ladder like fragmentation. GSPE treatment suppressed those alterations. Electron Spin Resonance (ESR) spectroscopy data also showed that GSPE strongly scavenged hydroxyl radical, superoxide and DPPH radicals. Together, these findings indicate that GSPE in combination with Dox has protective effect against Dox-induced toxicity in cardiomyocytes, which may be in part attributed to its antioxidative activity. Importantly, flow cytometric analysis demonstrated that co-treatment of Dox and GSPE did not decrease the proliferation-inhibitory effect of Dox in MCF-7 human breast carcinoma cells. Thus, GSPE may be a promising adjuvant to prevent cardiotoxicity without interfering with antineoplastic activity during chemotherapeutic treatment with Dox.

Effect of the anti-neoplastic drug doxorubicin on XPD-mutated DNA repair-deficient human cells

Doxorubicin (DOX), a member of the anthracycline group, is a widely used drug in cancer therapy. The mechanisms of DOX action include topoisomerase II-poisoning, free radical release, DNA adducts and interstrand cross-link (ICL) formation. Nucleotide excision repair (NER) is involved in the removal of helix-distorting lesions and chemical adducts, however, little is known about the response of NER-deficient cell lines to anti-tumoral drugs like DOX. Wild type and XPD-mutated cells, harbouring mutations in different regions of this gene and leading to XP-D, XP/CS or TTD diseases, were treated with this drug and analyzed for cell cycle arrest and DNA damage by comet assay. The formation of DSBs was also investigated by determination of γH2AX foci. Our results indicate that all three NER-deficient cell lines tested are more sensitive to DOX treatment, when compared to wild type cells or XP cells complemented by the wild type XPD cDNA, suggesting that NER is involved in the removal of DOX-induced lesions. The cell cycle analysis showed the characteristic G2 arrest in repair-proficient MRC5 cell line after DOX treatment, whereas the repair-deficient cell lines presented significant increase in sub-G1 fraction. The NER-deficient cell lines do not show different patterns of DNA damage formation as assayed by comet assay and phosphorylated H2AX foci formation. Knock-down of topoisomerase IIα with siRNA leads to increased survival in both MRC5 and XP cells, however, XP cell line still remained significantly more sensitive to the treatment by DOX. Our study suggests that the enhanced sensitivity is due to DOX-induced DNA damage that is subject to NER, as we observed decreased unscheduled DNA synthesis in XP-deficient cells upon DOX treatment. Furthermore, the complementation of the XPD-function abolished the observed sensitivity at lower DOX concentrations, suggesting that the XPD helicase activity is involved in the repair of DOX-induced lesions.

Tomato-oleoresin supplement prevents doxorubicin-induced cardiac myocyte oxidative DNA damage in rats

Doxorubicin (DOX) is an efficient chemotherapeutic agent used against several types of tumors; however, its use is limited due to severe cardiotoxicity. Since it is accepted that reactive oxygen species are involved in DOX-induced cardiotoxicity, antioxidant agents have been used to attenuate its side effects. To determine tomato-oleoresin protection against cardiac oxidative DNA damage induced by DOX, we distributed Wistar male rats in control (C), lycopene (L), DOX (D) and DOX + lycopene (DL) groups. They received corn oil (C, D) or tomato-oleoresin (5 mg/kg body wt. day) (L, DL) by gavage for a 7-week period. They also received saline (C, L) or DOX (4 mg/kg body wt.) (D, DL) intraperitoneally at the 3rd, 4th, 5th, and at 6th week. Lycopene absorption was checked by HPLC. Cardiac oxidative DNA damage was evaluated by the alkaline Comet assay using formamidopyrimidine-DNA glycosylase (FPG) and endonuclease III (endo III). Cardiomyocyte levels of SBs, SBs FPG and SBs Endo III were higher in rats from D when compared to other groups. DNA damage levels in cardiomyocytes from DL were not different when compared to C and L groups. The viability of cardiomyocytes from D or DL was lower than C or L groups ( p < 0.01). Lycopene levels (mean ± S.D. nmol/kg) in saponified hearts were similar between L (47.43 ± 11.78) and DL (49.85 ± 16.24) groups. Our results showed: (1) lycopene absorption was confirmed by its cardiac levels; (2) DOX-induced oxidative DNA damage in cardiomyocyte; (3) tomato-oleoresin supplementation protected against cardiomyocyte oxidative DNA damage.

Anthracycline-induced DNA breaks and resealing in doxorubicin-resistant murine leukemic P388 cells

Energy-dependent drug efflux is believed to be a major factor in cellular resistance to doxorubicin (DOX). However, recent studies have shown that decreased retention alone cannot account for anthracycline resistance, and possibly other factors, such as drug metabolism, free radical scavengers, and altered DNA damage/repair, may be involved. We have measured DOX-induced DNA damage and its repair in P388 cells sensitive (P388/S) and resistant (P388/R) to DOX. Our studies show 2- to 5-fold less DNA damage, measured as protein-associated single-strand DNA breaks, in P388/R cells when compared to similarly treated P388/S cells. The repair of DNA in whole cells, expressed as percent DNA rejoined, was complete in 4 hr in P388/R, whereas no repair was seen in P388/S cells until 20 hr. No difference in repair of DNA lesions was observed when nuclei were used in repair experiments. The absence of repair in sensitive whole cells may be due to high retention or slow drug efflux. Increase of cellular DOX retention by exposure of cells to trifluoperazine (TFP) or verapamil (VPL) did not result in the increase of DNA damage in P388/R cells. DOX analogs, Af-trifluoroacetyladriamycin-14-valerate (AD 32), 4′- O-tetrahydropyranyladriamycin (THP-adriamycin), and N-benzyladriamycin-14-valerate (AD 198), induced 2- to 4-fold more DNA damage than DOX in resistant cells. There was no difference in the poly(ADP-ribose) synthesis of P388/S and P388/R cells exposed to DOX or AD 32. Since ADP-ribose polymer synthesis is associated with free radical-induced DNA damage and is indicative of DNA repair by an excision-repair mechanism, data from these studies suggest that DNA breaks in anthracycline-exposed cells may not be due to free radical production but rather to other mechanisms, such as inhibition of DNA topoisomerase II activity. The present studies, in addition to emphasizing the role of DNA damage in resistance, also underscore the relative importance of DNA topoisomerase II function in anthracycline cytotoxicity.