Topoisomerase IIα-dependent and -independent apoptotic effects of dexrazoxane and doxorubicin

In vitro to clinical translation of combinatorial effects of doxorubicin and dexrazoxane in breast cancer: a mechanism-based pharmacokinetic/pharmacodynamic modeling approach

Dexrazoxane (DEX) is the only drug clinically approved to treat Doxorubicin-induced cardiotoxicity (DIC), however its impact on the anticancer efficacy of DOX is not extensively studied. In this manuscript, a proof-of-concept in vitro study is carried out to quantitatively characterize the anticancer effects of DOX and DEX and determine their nature of drug-drug interactions in cancer cells by combining experimental data with modeling approaches. First, we determined the static concentration-response of DOX and DEX in breast cancer cell lines, JIMT-1 and MDA-MB-468. With a three-dimensional (3D) response surface analysis using a competitive interaction model, we characterized their interaction to be modestly synergistic in MDA-MB-468 or modestly antagonistic in JIMT-1 cells. Second, a cellular-level, pharmacodynamic (PD) model was developed to capture the time-course effects of the two drugs which determined additive and antagonistic interactions for DOX and DEX in MDA-MB-468 and JIMT-1, respectively. Finally, we performed in vitro to in vivo translation by utilizing DOX and DEX clinical dosing regimen that was previously identified to be maximally cardioprotective, to drive tumor cell PD models. The resulting simulations showed that a 10:1 DEX:DOX dose ratio over three cycles of Q3W regimen of DOX results in comparable efficacy based on MDA-MB-468 (additive effect) estimates and lower efficacy based on JIMT-1 (antagonistic effect) estimates for DOX + DEX combination as compared to DOX alone. Thus, our developed cell-based PD models can be used to simulate different scenarios and better design preclinical in vivo studies to further optimize DOX and DEX combinations.

Deep learning-assisted high-content screening identifies isoliquiritigenin as an inhibitor of DNA double-strand breaks for preventing doxorubicin-induced cardiotoxicity

BACKGROUND

Anthracyclines including doxorubicin are essential components of many cancer chemotherapy regimens, but their cardiotoxicity severely limits their use. New strategies for treating anthracycline-induced cardiotoxicity (AIC) are still needed. Anthracycline-induced DNA double-strand break (DSB) is the major cause of its cardiotoxicity. However, DSB-based drug screening for AIC has not been performed possibly due to the limited throughput of common assays for detecting DSB. To discover new therapeutic candidates for AIC, here we established a method to rapidly visualize and accurately evaluate the intranuclear anthracycline-induced DSB, and performed a screening for DSB inhibitors.

RESULTS

First, we constructed a cardiomyocyte cell line stably expressing EGFP-53BP1, in which the formation of EGFP-53BP1 foci faithfully marked the doxorubicin-induced DSB, providing a faster and visible approach to detecting DSB. To quantify the DSB, we used a deep learning-based image analysis method, which showed the better ability to distinguish different cell populations undergoing different treatments of doxorubicin or reference compounds, compared with the traditional threshold-based method. Subsequently, we applied the deep learning-assisted high-content screening method to 315 compounds and found three compounds (kaempferol, kaempferide, and isoliquiritigenin) that exert cardioprotective effects in vitro. Among them, the protective effect of isoliquiritigenin is accompanied by the up-regulation of HO-1, down-regulation of peroxynitrite and topo II, and the alleviation of doxorubicin-induced DSB and apoptosis. The results of animal experiments also showed that isoliquiritigenin maintained the myocardial tissue structure and cardiac function in vivo. Moreover, isoliquiritigenin did not affect the killing of HeLa and MDA-MB-436 cancer cells by doxorubicin and thus has the potential to be a lead compound to exert cardioprotective effects without affecting the antitumor effect of doxorubicin.

CONCLUSIONS

Our findings provided a new method for the drug discovery for AIC, which combines phenotypic screening with artificial intelligence. The results suggested that isoliquiritigenin as an inhibitor of DSB may be a promising drug candidate for AIC.

Analysis of two-gene signatures and related drugs in small-cell lung cancer by bioinformatics

Small-cell lung cancer (SCLC) has a poor prognosis and can be diagnosed with systemic metastases. Nevertheless, the molecular mechanisms underlying the development of SCLC are unclear, requiring further investigation. The current research aims to identify relevant biomarkers and available drugs to treat SCLC. The bioinformatics analysis comprised three Gene Expression Omnibus datasets (including GSE2149507, GSE6044, and GSE30219). Using the limma R package, we discovered differentially expressed genes (DEGs) in the current work. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analyses were made by adopting the DAVID website. The DEG protein-protein interaction network was built based on the Search Tool for the Retrieval of Interacting Genes/Proteins website and visualized using the CytoHubba plugin in Cytoscape, aiming to screen the top ten hub genes. Quantitative real-time polymerase chain reaction was adopted for verifying the level of the top ten hub genes. Finally, the potential drugs were screened and identified using the QuartataWeb database. Totally 195 upregulated and 167 downregulated DEGs were determined. The ten hub genes were NCAPG, BUB1B, TOP2A, CCNA2, NUSAP1, UBE2C, AURKB, RRM2, CDK1, and KIF11. Ten FDA-approved drugs were screened. Finally, two genes and related drugs screened could be the prospective drug targets for SCLC treatment.

Hypoxia signaling and oxygen metabolism in cardio-oncology

Cardio-oncology is a rapidly growing field in cardiology that focuses on the management of cardiovascular toxicities associated with cancer-directed therapies. Tumor hypoxia is a central driver of pathologic tumor growth, metastasis, and chemo-resistance. In addition, conditions that mimic hypoxia (pseudo-hypoxia) play a causal role in the pathogenesis of numerous types of cancer, including renal cell carcinoma. Therefore, therapies targeted at hypoxia signaling pathways have emerged over the past several years. Though efficacious, these therapies are associated with significant cardiovascular toxicities, ranging from hypertension to cardiomyopathy. This review focuses on oxygen metabolism in tumorigenesis, the role of targeting hypoxia signaling in cancer therapy, and the relevance of oxygen metabolism in cardio-oncology. This review will specifically focus on hypoxia signaling mediated by hypoxia-inducible factors and the prolyl hydroxylase oxygen-sensing enzymes, the cardiovascular effects of specific cancer targeted therapies mediated on VEGF and HIF signaling, hypoxic signaling in cardiovascular disease, and the role of oxygen in anthracycline cardiotoxicity. The implications of these therapies on myocardial biology and cardiac function are discussed, underlining the fine balance of hypoxia signaling in cardiac homeostasis. Understanding these cardiovascular toxicities will be important to optimize treatment for cancer patients while mitigating potentially severe cardiovascular side effects.

Interim Analysis of the Phase II Study: Noninferiority Study of Doxorubicin with Upfront Dexrazoxane plus Olaratumab for Advanced or Metastatic Soft-Tissue Sarcoma

PURPOSE

To report the interim analysis of the phase II single-arm noninferiority trial, testing the upfront use of dexrazoxane with doxorubicin on progression-free survival (PFS) and cardiac function in soft-tissue sarcoma (STS).

PATIENTS AND METHODS

Patients with metastatic or unresectable STS who were candidates for first-line treatment with doxorubicin were deemed eligible. An interim analysis was initiated after 33 of 65 patients were enrolled. Using the historical control of 4.6 months PFS for doxorubicin in the front-line setting, we tested whether the addition of dexrazoxane affected the efficacy of doxorubicin in STS. The study was powered so that a decrease of PFS to 3.7 months would be considered noninferior. Secondary aims included cardiac-related mortality, incidence of heart failure/cardiomyopathy, and expansion of cardiac monitoring parameters including three-dimensional echocardiography. Patients were allowed to continue on doxorubicin beyond 600 mg/m2 if they were deriving benefit and were not demonstrating evidence of symptomatic cardiac dysfunction.

RESULTS

At interim analysis, upfront use of dexrazoxane with doxorubicin demonstrated a PFS of 8.4 months (95% confidence interval: 5.1-11.2 months). Only 3 patients were removed from study for cardiotoxicity, all on > 600 mg/m2 doxorubicin. No patients required cardiac hospitalization or had new, persistent cardiac dysfunction with left ventricular ejection fraction remaining below 50%. The median administered doxorubicin dose was 450 mg/m2 (interquartile range, 300-750 mg/m2).

CONCLUSIONS

At interim analysis, dexrazoxane did not reduce PFS in patients with STS treated with doxorubicin. Involvement of cardio-oncologists is beneficial for the monitoring and safe use of high-dose anthracyclines in STS.See related commentary by Benjamin and Minotti, p. 3809.

Anthracycline-induced cardiomyopathy: cellular and molecular mechanisms

Despite the known risk of cardiotoxicity, anthracyclines are widely prescribed chemotherapeutic agents. They are broadly characterized as being a robust effector of cellular apoptosis in rapidly proliferating cells through its actions in the nucleus and formation of reactive oxygen species (ROS). And, despite the early use of dexrazoxane, no effective treatment strategy has emerged to prevent the development of cardiomyopathy, despite decades of study, suggesting that much more insight into the underlying mechanism of the development of cardiomyopathy is needed. In this review, we detail the specific intracellular activities of anthracyclines, from the cell membrane to the sarcoplasmic reticulum, and highlight potential therapeutic windows that represent the forefront of research into the underlying causes of anthracycline-induced cardiomyopathy.

Evaluation of the Anticancer Activities of Novel Transition Metal Complexes with Berenil and Nitroimidazole

Novel transition metal complexes (Au, Pd, Pt) with berenil and 2-(1-methyl-5-nitroimidazol-2-yl)ethanol were obtained through two-step synthesis. The cytotoxicity assay against MCF-7 and MDA-MB-231 breast cancer cells revealed that novel platinum and palladium complexes cause a reduction on the viability of MCF-7 and MDA-MB-231 breast cancer cells to a greater extent than cisplatin. The complexes showed lower cytotoxicity on normal MCF-10A human breast epithelial cells than on tumor cells. Furthermore, we observed that these complexes selectively concentrate in tumor cell mitochondria due to the characteristic for these cells increased membrane potential that may explain their increased proapoptotic activity. The activity of the synthesized compounds against topoisomerase type IIα and their increased impact on DNA defragmentation also were documented. The novel complexes also induced autophagosome changes and inhibited tumor growth in xenograft models (established using breast cancer cells).

Gp130 degradation induced by epirubicin contributes to chemotherapy efficacy

Two anthracyclines, doxorubicin and epirubicin have been widely used alone or in combination with other antitumor reagents in the chemotherapeutic treatment of various malignancies. Although therapeutic efficacy of anthracyclines has been studied extensively, precise cytotoxic mechanism of these drugs is not been completely elucidated. Here we show that epirubicin-induced degradation of transmembrane protein gp130 contributes to antitumor effect of epirubicin. gp130 is degraded by epirubicin in a proteasome- and autophagy-dependent manner. Epirubicin induces activation of p38-MK2 signaling pathway to phosphorylate gp130 at Ser 782, which results in gp130 internalization and degradation by lysosome. Although mutation of Ser 782 to Ala or Cys in gp130 upregulates global epirubicin-induced autophagy, reduced degradation of gp130 accompanied with enhanced Stat3 phosphorylation at tyrosine 705 is observed. We also show that epirubicin-resistant tumor cells express higher level of gp130. Altogether, our results indicate that degradation of gp130 and subsequent reduction of gp130-Stat3 signaling contributes to epirubicin-induced tumor cell death.

Insights into Doxorubicin-induced Cardiotoxicity: Molecular Mechanisms, Preventive Strategies, and Early Monitoring

Doxorubicin (DOX) is one of the most effective anticancer drugs to treat various forms of cancers; however, its therapeutic utility is severely limited by its associated cardiotoxicity. Despite the enormous amount of research conducted in this area, the exact molecular mechanisms underlying DOX toxic effects on the heart are still an area that warrants further investigations. In this study, we reviewed literature to gather the best-known molecular pathways related to DOX-induced cardiotoxicity (DIC). They include mechanisms dependent on mitochondrial dysfunction such as DOX influence on the mitochondrial electron transport chain, redox cycling, oxidative stress, calcium dysregulation, and apoptosis pathways. Furthermore, we discuss the existing strategies to prevent and/or alleviate DIC along with various techniques available for therapeutic drug monitoring (TDM) in cancer patients treated with DOX. Finally, we propose a stepwise flowchart for TDM of DOX and present our perspective at curtailing this deleterious side effect of DOX.

The cardioprotective effect of dexrazoxane (Cardioxane) is consistent with sequestration of poly(ADP-ribose) by self-assembly and not depletion of topoisomerase 2B

Following systematic scrutiny of the evidence in support of the hypothesis that the cardioprotective mechanism of action of dexrazoxane is mediated by a 'depletion' or 'downregulation' of Top2β protein levels in heart tissue, the author concludes that this hypothesis is untenable. In seeking to understand how dexrazoxane protects the heart, the outcomes of a customised association rule learning algorithm incorporating the use of antecedent surrogate variables (CEME, 2017 McCormack Pharma) reveal a previously unknown relationship between dexrazoxane and poly(ADP-ribose) (PAR) polymer. The author shows how this previously unknown relationship explains both acute and long-term cardioprotection in patients receiving anthracyclines. In addition, as a direct inhibitor of PAR dexrazoxane has access to the epigenome and this offers a new insight into protection by dexrazoxane against doxorubicin-induced late-onset damage [McCormack K, manuscript in preparation]. Notably, through this review article, the author illustrates the practical application of probing natural language text using an association rule learning algorithm for the discovery of new and interesting associations that, otherwise, would remain lost. Historically, the use of CEME enabled the first report of the capacity of a small molecule to catalyse the hybrid self-assembly of a nucleic acid biopolymer via canonical and non-canonical, non-covalent interactions analogous to Watson Crick and Hoogsteen base pairing, respectively.

Optimizing Cardiovascular Care in Children With Acute Myeloid Leukemia to Improve Cancer-Related Outcomes

The Oncology Grand Rounds series is designed to place original reports published in the Journal into clinical context. A case presentation is followed by a description of diagnostic and management challenges, a review of the relevant literature, and a summary of the authors' suggested management approaches. The goal of this series is to help readers better understand how to apply the results of key studies, including those published in Journal of Clinical Oncology, to patients seen in their own clinical practice. A 14-year-old African American female presented with fatigue, easy bruising, and fever. On examination, she had scattered bruising, lymphadenopathy, and hepatosplenomegaly. Laboratory evaluation revealed pancytopenia with peripheral blasts, and acute myeloid leukemia (AML; French-American-British M2, t[8;21][q22;q22.1]) was diagnosed on bone marrow biopsy. A baseline echocardiogram revealed normal left ventricular (LV) systolic function (ejection fraction [EF], 60%; shortening fraction [SF], 32%), and conventional chemotherapy was initiated that consisted of two cycles of remission induction (cytarabine, etoposide, and daunorubicin [50 mg/m² × 3 days per cycle]) followed by intensification 1 (high-dose cytarabine and etoposide), intensification 2 (high-dose cytarabine and mitoxantrone [12 mg/m²/dose daily; four total doses]), and intensification 3 (high-dose cytarabine and l-asparaginase). Of note, an echocardiogram was not repeated before the start of intensification 1. During intensification 1, the patient developed Streptococcus viridans sepsis, which required 4 days in the intensive care unit with antimicrobial and inotropic support. Repeat echocardiogram after recovery from the sepsis episode demonstrated low-normal LV systolic function (EF, 53%; SF, 27%), and she subsequently began intensification 2. On day 3 of intensification 2, the patient developed afebrile tachypnea, tachycardia, and an increasing oxygen requirement. Chest x-ray revealed cardiomegaly and pulmonary vascular congestion. Cardiac troponins were normal, whereas N-terminal pro B-type natriuretic peptide was 10 times the upper limit of normal. Repeat echocardiogram showed an enlarged LV with moderate to severely depressed LV function (EF, 28%; SF, 14%). Day 4 mitoxantrone was omitted and a cardiology consult obtained.

Comprehensive review of cardiovascular toxicity of drugs and related agents

Cardiovascular diseases are a leading cause of morbidity and mortality in most developed countries of the world. Pharmaceuticals, illicit drugs, and toxins can significantly contribute to the overall cardiovascular burden and thus deserve attention. The present article is a systematic overview of drugs that may induce distinct cardiovascular toxicity. The compounds are classified into agents that have significant effects on the heart, blood vessels, or both. The mechanism(s) of toxic action are discussed and treatment modalities are briefly mentioned in relevant cases. Due to the large number of clinically relevant compounds discussed, this article could be of interest to a broad audience including pharmacologists and toxicologists, pharmacists, physicians, and medicinal chemists. Particular emphasis is given to clinically relevant topics including the cardiovascular toxicity of illicit sympathomimetic drugs (e.g., cocaine, amphetamines, cathinones), drugs that prolong the QT interval, antidysrhythmic drugs, digoxin and other cardioactive steroids, beta-blockers, calcium channel blockers, female hormones, nonsteroidal anti-inflammatory, and anticancer compounds encompassing anthracyclines and novel targeted therapy interfering with the HER2 or the vascular endothelial growth factor pathway.

Utility of Dexrazoxane for the Attenuation of Epirubicin-Induced Genetic Alterations in Mouse Germ Cells

Dexrazoxane has been approved to treat anthracycline-induced cardiomyopathy and extravasation. However, the effect of dexrazoxane on epirubicin-induced genetic alterations in germ cells has not yet been reported. Thus, the aim of this study was to determine whether dexrazoxane modulates epirubicin-induced genetic damage in the germ cells of male mice. Our results show that dexrazoxane was not genotoxic at the tested doses. Furthermore, it protected mouse germ cells against epirubicin-induced genetic alterations as detected by the reduction in disomic and diploid sperm, spermatogonial chromosomal aberrations, and abnormal sperm heads. The attenuating effect of dexrazoxane was greater at higher dose, indicating a dose-dependent effect. Moreover, sperm motility and count were ameliorated by dexrazoxane pretreatment. Epirubicin induced marked biochemical changes characteristic of oxidative DNA damage including elevated 8-hydroxy-2'-deoxyguanosine levels and reduction in reduced glutathione. Pretreatment of mice with dexrazoxane before epirubicin challenge restored these altered endpoints. We conclude that dexrazoxane may efficiently mitigate the epirubicin insult in male germ cells, and prevent the enhanced risk of abnormal reproductive outcomes and associated health risks. Thus, pretreating patients with dexrazoxane prior to epirubicin may efficiently preserve not only sperm quality but also prevent the transmission of genetic damage to future generations.

Doxorubicin induced heart failure: Phenotype and molecular mechanisms

Long term survival of childhood cancers is now more than 70%. Anthracyclines, including doxorubicin, are some of the most efficacious anticancer drugs available. However, its use as a chemotherapeutic agent is severely hindered by its dose-limiting toxicities. Most notably observed is cardiotoxicity, but other organ systems are also degraded by doxorubicin use. Despite the years of its use and the amount of information written about this drug, an understanding of its cellular mechanisms is not fully appreciated. The mechanisms by which doxorubicin induces cytotoxicity in target cancer cells have given insight about how the drug damages cardiomyocytes. The major mechanisms of doxorubicin actions are thought to be as an oxidant generator and as an inhibitor of topoisomerase 2. However, other signaling pathways are also invoked with significant consequences for the cardiomyocyte. Further the interaction between oxidant generation and topoisomerase function has only recently been appreciated and the consequences of this interaction are still not fully understood. The unfortunate consequences of doxorubicin within cardiomyocytes have promoted the search for new drugs and methods that can prevent or reverse the damage caused to the heart after treatment in cancer patients. Alternative protocols have lessened the impact on newly diagnosed cancer patients. However the years of doxorubicin use have generated a need for monitoring the onset of cardiotoxicity as well as understanding its potential long-term consequences. Although a fairly clear understanding of the short-term pathologic mechanisms of doxorubicin actions has been achieved, the long-term mechanisms of doxorubicin induced heart failure remain to be carefully delineated.

The catalytic topoisomerase II inhibitor dexrazoxane induces DNA breaks, ATF3 and the DNA damage response in cancer cells

BACKGROUND AND PURPOSE

The catalytic topoisomerase II inhibitor dexrazoxane has been associated not only with improved cancer patient survival but also with secondary malignancies and reduced tumour response.

EXPERIMENTAL APPROACH

We investigated the DNA damage response and the role of the activating transcription factor 3 (ATF3) accumulation in tumour cells exposed to dexrazoxane.

KEY RESULTS

Dexrazoxane exposure induced topoisomerase IIα (TOP2A)-dependent cell death, γ-H2AX accumulation and increased tail moment in neutral comet assays. Dexrazoxane induced DNA damage responses, shown by enhanced levels of γ-H2AX/53BP1 foci, ATM (ataxia telangiectasia mutated), ATR (ATM and Rad3-related), Chk1 and Chk2 phosphorylation, and by p53 accumulation. Dexrazoxane-induced γ-H2AX accumulation was dependent on ATM. ATF3 protein was induced by dexrazoxane in a concentration- and time-dependent manner, which was abolished in TOP2A-depleted cells and in cells pre-incubated with ATM inhibitor. Knockdown of ATF3 gene expression by siRNA triggered apoptosis in control cells and diminished the p53 protein level in both control and dexrazoxane -treated cells. This was accompanied by increased γ-H2AX accumulation. ATF3 knockdown also delayed the repair of dexrazoxane -induced DNA double-strand breaks.

CONCLUSIONS AND IMPLICATIONS

As with other TOP2A poisons, dexrazoxane induced DNA double-strand breaks followed by activation of the DNA damage response. The DNA damage-triggered ATF3 controlled p53 accumulation and generation of double-strand breaks and is proposed to serve as a switch between DNA damage and cell death following dexrazoxane treatment. These findings suggest a mechanistic explanation for the diverse clinical observations associated with dexrazoxane.

Chronic heart damage following doxorubicin treatment is alleviated by lovastatin

The anticancer efficacy of anthracyclines is limited by cumulative dose-dependent early and delayed cardiotoxicity resulting in congestive heart failure. Mechanisms responsible for anthracycline-induced heart damage are controversially discussed and effective preventive measures are preferable. Here, we analyzed the influence of the lipid lowering drug lovastatin on anthracycline-induced late cardiotoxicity three month after treatment of C57BL/6 mice with five low doses of doxorubicin (5×3mg/kg BW; i.p.). Doxorubicin increased the cardiac mRNA levels of BNP, IL-6 and CTGF, while the expression of ANP remained unchanged. Lovastatin counteracted these persisting cardiac stress responses evoked by the anthracycline. Doxorubicin-induced fibrotic alterations were neither detected by histochemical collagen staining of heart sections nor by analysis of the mRNA expression of collagens. Extensive qRT-PCR-array based analyses revealed a large increase in the mRNA level of heat shock protein Hspa1b in doxorubicin-treated mice, which was mitigated by lovastatin co-treatment. Electron microscopy together with qPCR-based analysis of mitochondrial DNA content indicate that lovastatin attenuates doxorubicin-stimulated hyperproliferation of mitochondria. This was not paralleled by increased expression of oxidative stress responsive genes or senescence-associated proteins. Echocardiographic analyses disclosed that lovastatin protects from the doxorubicin-induced decrease in the left ventricular posterior wall diameter (LVPWD), while constrictions in fractional shortening (FS) and ejection fraction (EF) evoked by doxorubicin were not amended by the statin. Taken together, the data suggest beneficial effects of lovastatin against doxorubicin-induced delayed cardiotoxicity. Clinical studies are preferable to scrutinize the usefulness of statins for the prevention of anthracycline-induced late cardiotoxicity.

Dexrazoxane may prevent doxorubicin-induced DNA damage via depleting both topoisomerase II isoforms

BACKGROUND

The bisdioxopiperazine dexrazoxane (DRZ) prevents anthracycline-induced heart failure, but its clinical use is limited by uncertain cardioprotective mechanism and by concerns of interference with cancer response to anthracyclines and of long-term safety.

METHODS

We investigated the effects of DRZ on the stability of topoisomerases IIα (TOP2A) and IIβ (TOP2B) and on the DNA damage generated by poisoning these enzymes by the anthracycline doxorubicin (DOX).

RESULTS

DRZ given i.p. transiently depleted in mice the predominant cardiac isoform Top2b. The depletion was also seen in H9C2 cardiomyocytes and it was attenuated by mutating the bisdioxopiperazine binding site of TOP2B. Consistently, the accumulation of DOX-induced DNA double strand breaks (DSB) by wild-type, although not by mutant TOP2B, was reduced by DRZ. In contrast, the DRZ analogue ICRF-161, which is capable of iron chelation but not of TOP2B binding and cardiac protection, did not deplete TOP2B and did not prevent the accumulation of DOX-induced DSB. TOP2A, re-expressed in cultured cardiomyocytes by fresh serum, was depleted by DRZ along with TOP2B. DRZ depleted TOP2A also from fibrosarcoma-derived cells, but not from lung cancer-derived and human embryo-derived cells. DRZ-mediated TOP2A depletion reduced the accumulation of DOX-induced DSB.

CONCLUSIONS

Taken together, our data support a model of anthracycline-induced heart failure caused by TOP2B-mediated DSB and of its prevention by DRZ via TOP2B degradation rather than via iron chelation. The depletion of TOP2B and TOP2A suggests an explanation for the reported DRZ interference with cancer response to anthracyclines and for DRZ side-effects.

Glutathione redox dynamics and expression of glutathione-related genes in the developing embryo

Embryonic development involves dramatic changes in cell proliferation and differentiation that must be highly coordinated and tightly regulated. Cellular redox balance is critical for cell fate decisions, but it is susceptible to disruption by endogenous and exogenous sources of oxidative stress. The most abundant endogenous nonprotein antioxidant defense molecule is the tripeptide glutathione (γ-glutamylcysteinylglycine, GSH), but the ontogeny of GSH concentration and redox state during early life stages is poorly understood. Here, we describe the GSH redox dynamics during embryonic and early larval development (0-5 days postfertilization) in the zebrafish (Danio rerio), a model vertebrate embryo. We measured reduced and oxidized glutathione using HPLC and calculated the whole embryo total glutathione (GSHT) concentrations and redox potentials (Eh) over 0-120 h of zebrafish development (including mature oocytes, fertilization, midblastula transition, gastrulation, somitogenesis, pharyngula, prehatch embryos, and hatched eleutheroembryos). GSHT concentration doubled between 12h postfertilization (hpf) and hatching. The GSH Eh increased, becoming more oxidizing during the first 12h, and then oscillated around -190 mV through organogenesis, followed by a rapid change, associated with hatching, to a more negative (more reducing) Eh (-220 mV). After hatching, Eh stabilized and remained steady through 120 hpf. The dynamic changes in GSH redox status and concentration defined discrete windows of development: primary organogenesis, organ differentiation, and larval growth. We identified the set of zebrafish genes involved in the synthesis, utilization, and recycling of GSH, including several novel paralogs, and measured how expression of these genes changes during development. Ontogenic changes in the expression of GSH-related genes support the hypothesis that GSH redox state is tightly regulated early in development. This study provides a foundation for understanding the redox regulation of developmental signaling and investigating the effects of oxidative stress during embryogenesis.

Higenamine Combined with [6]-Gingerol Suppresses Doxorubicin-Triggered Oxidative Stress and Apoptosis in Cardiomyocytes via Upregulation of PI3K/Akt Pathway

Sini decoction is a well-known formula of traditional Chinese medicine, which has been used to treat cardiovascular disease for many years. Previously, we demonstrated that Sini decoction prevented doxorubicin-induced heart failure in vivo. However, its active components are still unclear. Thus, we investigated the active components of Sini decoction and their cardioprotective mechanisms in the in vitro neonatal rat cardiomyocytes and H9c2 cell line models of doxorubicin-induced cytotoxicity. Our results demonstrated that treatment with higenamine or [6]-gingerol increased viability of doxorubicine-injured cardiomyocytes. Moreover, combined use of higenamine and [6]-gingerol exerted more profound protective effects than either drug as a single agent, with effects similar to those of dexrazoxane, a clinically approved cardiac protective agent. In addition, we found that treatment with doxorubicin reduced SOD activity, increased ROS generation, enhanced MDA formation, induced release of LDH, and triggered the intrinsic mitochondria-dependent apoptotic pathway in cardiomyocytes, which was inhibited by cotreatment of higenamine and [6]-gingerol. Most importantly, the cytoprotection of higenamine plus [6]-gingerol could be abrogated by LY294002, a PI3K inhibitor. In conclusion, combination of higenamine and [6]-gingerol exerts cardioprotective effect against doxorubicin-induced cardiotoxicity through activating the PI3K/Akt signaling pathway. Higenamine and [6]-gingerol may be the active components of Sini decoction.

Rac1 modulates acute and subacute genotoxin-induced hepatic stress responses, fibrosis and liver aging

To investigate the importance of the Ras-homologous GTPase Rac1 for the hepatic response to genotoxic insults and liver aging, rac1 was deleted in liver of mice by Mx1-Cre-based recombination. Knockout of rac1 caused complex changes in basal as well as doxorubicin and ionizing radiation-induced mRNA expression of various genotoxic stress response-related genes, including hspa1b, rad51, wrn and xpc. Rac1 deletion protected the liver from acute toxicity following doxorubicin treatment. Moreover, the level of S139 phosphorylated histone H2AX (γH2AX), which is indicative of DNA damage, and mRNA expression of pro-inflammatory (IL-6) and pro-fibrotic (CTGF, TGFβ, αSMA) factors were mitigated in rac1 knockout animals. By contrast, lack of rac1 promoted subacute hepatotoxicity, which was determined 3 weeks after injection of multiple low doses of doxorubicin by assaying the γH2AX level, mitotic index and pro-fibrotic gene expression. Regarding ionizing radiation, rac1 deficiency had no major effects on DNA damage induction or acute pro-inflammatory and pro-fibrotic stress responses. Mice lacking hepatic rac1 for extended period of time (15 months) revealed increased mRNA expression of fibrosis-related factors (CTGF, TGFβ, collagen, MMP1) and fibrotic tissue remodeling. In addition, protein expression of the senescence marker p16 was enhanced in the absence of rac1. Taken together, the data provide evidence that Rac1 is required for doxorubicin-induced DNA damage induction. It is also involved in both the acute and delayed inflammatory and fibrotic stress response in the liver following doxorubicin, but not ionizing radiation, treatment and, furthermore, protects against endogenous liver aging.

Iron chelators with topoisomerase-inhibitory activity and their anticancer applications

SIGNIFICANCE

Iron and topoisomerases are abundant and essential cellular components. Iron is required for several key processes such as DNA synthesis, mitochondrial electron transport, synthesis of heme, and as a co-factor for many redox enzymes. Topoisomerases serve as critical enzymes that resolve topological problems during DNA synthesis, transcription, and repair. Neoplastic cells have higher uptake and utilization of iron, as well as elevated levels of topoisomerase family members. Separately, the chelation of iron and the cytotoxic inhibition of topoisomerase have yielded potent anticancer agents.

RECENT ADVANCES

The chemotherapeutic drugs doxorubicin and dexrazoxane both chelate iron and target topoisomerase 2 alpha (top2α). Newer chelators such as di-2-pyridylketone-4,4,-dimethyl-3-thiosemicarbazone and thiosemicarbazone -24 have recently been identified as top2α inhibitors. The growing list of agents that appear to chelate iron and inhibit topoisomerases prompts the question of whether and how these two distinct mechanisms might interplay for a cytotoxic chemotherapeutic outcome.

CRITICAL ISSUES

While iron chelation and topoisomerase inhibition each represent mechanistically advantageous anticancer therapeutic strategies, dual targeting agents present an attractive multi-modal opportunity for enhanced anticancer tumor killing and overcoming drug resistance. The commonalities and caveats of dual inhibition are presented in this review.

FUTURE DIRECTIONS

Gaps in knowledge, relevant biomarkers, and strategies for future in vivo studies with dual inhibitors are discussed.

Topoisomerase IIα promotes activation of RNA polymerase I transcription by facilitating pre-initiation complex formation

Type II DNA topoisomerases catalyse DNA double-strand cleavage, passage and re-ligation to effect topological changes. There is considerable interest in elucidating topoisomerase II roles, particularly as these proteins are targets for anti-cancer drugs. Here we uncover a role for topoisomerase IIα in RNA polymerase I-directed ribosomal RNA gene transcription, which drives cell growth and proliferation and is upregulated in cancer cells. Our data suggest that topoisomerase IIα is a component of the initiation-competent RNA polymerase Iβ complex and interacts directly with RNA polymerase I-associated transcription factor RRN3, which targets the polymerase to promoter-bound SL1 in pre-initiation complex formation. In cells, activation of rDNA transcription is reduced by inhibition or depletion of topoisomerase II, and this is accompanied by reduced transient double-strand DNA cleavage in the rDNA-promoter region and reduced pre-initiation complex formation. We propose that topoisomerase IIα functions in RNA polymerase I transcription to produce topological changes at the rDNA promoter that facilitate efficient de novo pre-initiation complex formation.

Rac1 protein signaling is required for DNA damage response stimulated by topoisomerase II poisons

To investigate the potency of the topoisomerase II (topo II) poisons doxorubicin and etoposide to stimulate the DNA damage response (DDR), S139 phosphorylation of histone H2AX (γH2AX) was analyzed using rat cardiomyoblast cells (H9c2). Etoposide caused a dose-dependent increase in the γH2AX level as shown by Western blotting. By contrast, the doxorubicin response was bell-shaped with high doses failing to increase H2AX phosphorylation. Identical results were obtained by immunohistochemical analysis of γH2AX focus formation, comet assay-based DNA strand break analysis, and measuring the formation of the topo II-DNA cleavable complex. At low dose, doxorubicin activated ataxia telangiectasia mutated (ATM) but not ATM and Rad3-related (ATR). Both the lipid-lowering drug lovastatin and the Rac1-specific inhibitor NSC23766 attenuated doxorubicin- and etoposide-stimulated H2AX phosphorylation, induction of DNA strand breaks, and topo II-DNA complex formation. Lovastatin and NSC23766 acted in an additive manner. They did not attenuate doxorubicin-induced increase in p-ATM and p-Chk2 levels. DDR stimulated by topo II poisons was partially blocked by inhibition of type I p21-associated kinases. DDR evoked by the topoisomerase I poison topotecan remained unaffected by lovastatin. The data show that the mechanisms involved in DDR stimulated by topo II poisons are agent-specific with anthracyclines lacking DDR-stimulating activity at high doses. Pharmacological inhibition of Rac1 signaling counteracts doxorubicin- and etoposide-stimulated DDR by disabling the formation of the topo II-DNA cleavable complex. Based on the data we suggest that Rac1-regulated mechanisms are required for DNA damage induction and subsequent activation of the DDR following treatment with topo II but not topo I poisons.

Effects of MnDPDP and ICRF-187 on Doxorubicin-Induced Cardiotoxicity and Anticancer Activity

Oxidative stress participates in doxorubicin (Dx)-induced cardiotoxicity. The metal complex MnDPDP and its metabolite MnPLED possess SOD-mimetic activity, DPDP and PLED have, in addition, high affinity for iron. Mice were injected intravenously with MnDPDP, DPDP, or dexrazoxane (ICRF-187). Thirty minutes later, mice were killed, the left atria were hung in organ baths and electrically stimulated, saline or Dx was added, and the contractility was measured for 60 minutes. In parallel experiments, 10 µM MnDPDP or MnPLED was added directly into the organ bath. The effect of MnDPDP on antitumor activity of Dx against two human tumor xenografts (MX-1 and A2780) was investigated. The in vitro cytotoxic activity was studied by co-incubating A2780 cells with MnDPDP, DPDP, and/or Dx. Dx caused a marked reduction in contractile force. In vivo treatment with MnDPDP and ICRF-187 attenuated the negative effect of Dx. When added directly into the bath, MnDPDP did not protect, whereas MnPLED attenuated the Dx effect by approximately 50%. MnDPDP or ICRF-187 did not interfere negatively with the anti-tumor activity of Dx, either in vivo or in vitro. Micromolar concentrations of DPDP but not MnDPDP displayed an in vitro cytotoxic activity against A2780 cells. The present results show that MnDPDP, after being metabolized to MnPLED, protects against acute Dx cardiotoxicity. Both in vivo and in vitro experiments show that cardioprotection takes place without interfering negatively with the anticancer activity of Dx. Furthermore, the results suggest that the previously described cytotoxic in vivo activity of MnDPDP is an inherent property of DPDP.

Dexrazoxane ameliorates doxorubicin-induced injury in mouse ovarian cells

Doxorubicin (DXR) is a frontline chemotherapy agent implicated in unintended ovarian failure in female cancer survivors. The fertility preservation techniques currently available for cancer patients are often time and cost prohibitive and do not necessarily preserve endocrine function. There are no drug-based ovary protection therapies clinically available. This study provides the first investigation using dexrazoxane (Dexra) to limit DXR insult in ovarian tissue. In KK-15 granulosa cells, a 3-h DXR treatment increased double-strand (ds) DNA breaks 40%-50%, as quantified by the neutral comet assay, and dose-dependent cytotoxicity. Dexra exhibited low toxicity in KK-15 cells, inducing no DNA damage and less than 20% cell loss. Cotreating KK-15 cells with Dexra prevented acute DXR-induced dsDNA damage. Similarly, Dexra attenuated the DXR-induced 40%-65% increase in dsDNA breaks in primary murine granulosa cells and cells from in vitro cultured murine ovaries. DXR can cause DNA damage either through a topoisomerase II-mediated pathway, based on DXR intercalation into DNA, or through oxidative stress. Cotreating KK-15 cells with 2 μM Dexra was sufficient to prevent DXR-induced, but not H(2)O(2)-induced, DNA damage. These data indicated the protective effects are likely due to Dexra's inhibition of topoisomerase II catalytic activity. This putative protective agent attenuated downstream cellular responses to DXR, preventing H2AFX activation in KK-15 cells and increasing viability as demonstrated by increasing the DXR lethal dose in KK-15 cells 5- to 8-fold (LD(20)) and primary murine granulosa cells 1.5- to 2-fold (LD(50)). These data demonstrate Dexra protects ovarian cells from DXR insult and suggest that it is a promising tool to limit DXR ovarian toxicity in vivo.

Comparative analysis of stress responses of H9c2 rat cardiomyoblasts following treatment with doxorubicin and tBOOH

Cardiotoxicity is the major dose-limiting adverse effect of anthracyclines and is hypothesized to result from damage induced by reactive oxygen species (ROS) or inhibition of topoisomerase II. Here, we comparatively analyzed the effect of doxorubicin and the organic peroxide tertiary-butylhydroperoxide (tBOOH) on stress responses of rat cardiomyblast cells (H9c2). Moreover, we investigated the impact of serum factors and the novel prototypical protein kinase CK2 inhibitor resorufin on the sensentivity of H9c2 cells exposed to doxorubicin or tBOOH. Measuring cell viability by use of the WST assay as well as cell cycle progression and apoptotic death by FACS-based methods, we found that the sensitivity of H9c2 cells to doxorubicin and tBOOH was differently affected by both serum factors and resorufin. Formation of reactive oxygen species was observed after exposure of H9c2 cells to high doses (i.e. ≥5 μM) of doxorubicin only. Moreover, the antioxidant N-acetylcysteine protected H9c2 cells from cytotoxicity provoked by tBOOH but not doxorubicin. Analyzing the phosphorylation level of genotoxic stress responsive protein kinases and histone H2AX, which is indicative of an activated DNA damage response (DDR), we found that resorufin modulates doxorubicin- and tBOOH-induced responses in an agent specific manner. Taken together, the data indicate that (i) oxidative injury is not the most relevant type of damage triggering cell death of H9c2 cells following doxorubicin treatment, (ii) serum factors differently influence the sensitivity of cardiomyoblasts to doxorubicin and tBOOH and (iii) inhibition of CK2 unequally affects doxorubicin- and tBOOH-induced DDR of rat cardiomyoblasts.

Inhibition of Rac1 signaling by lovastatin protects against anthracycline-induced cardiac toxicity

Normal tissue damage limits the efficacy of anticancer therapy. For anthracyclines, the clinically most relevant adverse effect is cardiotoxicity. The mechanisms involved are poorly understood and putative cardioprotectants are controversially discussed. Here, we show that the lipid-lowering drug lovastatin protects rat H9c2 cardiomyoblasts from doxorubicin in vitro. Protection by lovastatin is related to inhibition of the Ras-homologous GTPase Rac1. It rests on a reduced formation of DNA double-strand breaks, resulting from the inhibition of topoisomerase II by doxorubicin. Doxorubicin transport and reactive oxygen species are not involved. Protection by lovastatin was confirmed in vivo. In mice, lovastatin mitigated acute doxorubicin-induced heart and liver damage as indicated by reduced mRNA levels of the pro-fibrotic cytokine connective tissue growth factor (CTGF) and pro-inflammatory cytokines, respectively. Lovastatin also protected from doxorubicin-provoked subacute cardiac damage as shown by lowered mRNA levels of CTGF and atrial natriuretic peptide. Increase in the serum concentration of troponin I and cardiac fibrosis following doxorubicin treatment were also reduced by lovastatin. Whereas protecting the heart from harmful doxorubicin effects, lovastatin augmented its anticancer efficacy in a mouse xenograft model with human sarcoma cells. These data show that statins lower the incidence of cardiac tissue injury after anthracycline treatment in a Rac1-dependent manner, without impairing the therapeutic efficacy.

An integrated Drosophila model system reveals unique properties for F14512, a novel polyamine-containing anticancer drug that targets topoisomerase II

F14512 is a novel anti-tumor molecule based on an epipodophyllotoxin core coupled to a cancer-cell vectoring spermine moiety. This polyamine linkage is assumed to ensure the preferential uptake of F14512 by cancer cells, strong interaction with DNA and potent inhibition of topoisomerase II (Topo II). The antitumor activity of F14512 in human tumor models is significantly higher than that of other epipodophyllotoxins in spite of a lower induction of DNA breakage. Hence, the demonstrated superiority of F14512 over other Topo II poisons might not result solely from its preferential uptake by cancer cells, but could also be due to unique effects on Topo II interactions with DNA. To further dissect the mechanism of action of F14512, we used Drosophila melanogaster mutants whose genetic background leads to an easily scored phenotype that is sensitive to changes in Topo II activity and/or localization. F14512 has antiproliferative properties in Drosophila cells and stabilizes ternary Topo II/DNA cleavable complexes at unique sites located in moderately repeated sequences, suggesting that the drug specifically targets a select and limited subset of genomic sequences. Feeding F14512 to developing mutant Drosophila larvae led to the recovery of flies expressing a striking phenotype, "Eye wide shut," where one eye is replaced by a first thoracic segment. Other recovered F14512-induced gain- and loss-of-function phenotypes similarly correspond to precise genetic dysfunctions. These complex in vivo results obtained in a whole developing organism can be reconciled with known genetic anomalies and constitute a remarkable instance of specific alterations of gene expression by ingestion of a drug. "Drosophila-based anticancer pharmacology" hence reveals unique properties for F14512, demonstrating the usefulness of an assay system that provides a low-cost, rapid and effective complement to mammalian models and permits the elucidation of fundamental mechanisms of action of candidate drugs of therapeutic interest in humans.

The iron chelator Dp44mT inhibits the proliferation of cancer cells but fails to protect from doxorubicin-induced cardiotoxicity in spontaneously hypertensive rats

PURPOSE

The iron chelator Dp44mT is a potent topoisomerase IIα inhibitor with novel anticancer activity. Doxorubicin (Dox), the current front-line therapy for breast cancer, induces a dose-limiting cardiotoxicity, in part through an iron-mediated pathway. We tested the hypothesis that Dp44mT can improve clinical outcomes of treatment with Dox by alleviating cardiotoxicity.

METHODS

The general cardiac and renal toxicities induced by Dox were investigated in the presence and absence of Dp44mT. The iron chelating cardioprotectant Dexrazoxane (Drz), which is approved for this indication, was used as a positive control. In vitro studies were carried out with H9c2 rat cardiomyocytes and in vivo studies were performed using spontaneously hypertensive rats.

RESULTS

Testing of the GI(50) profile of Dp44mT in the NCI-60 panel confirmed activity against breast cancer cells. An acute, toxic dose of Dox caused the predicted cellular and cardiac toxicities, such as cell death and DNA damage in vitro and elevated cardiac troponin T levels, tissue damage, and apoptosis in vivo. Dp44mT alone caused insignificant changes in hematological and biochemical indices in rats, indicating that Dp44mT is not significantly cardiotoxic as a single agent. In contrast to Drz, Dp44mT failed to mitigate Dox-induced cardiotoxicity in vivo.

CONCLUSIONS

We conclude that although Dp44mT is a potent iron chelator, it is unlikely to be an appropriate cardioprotectant against Dox-induced toxicity. However, it should continue to be evaluated as a potential anticancer agent as it has a novel mechanism for inhibiting the growth of a broad range of malignant cell types while exhibiting very low intrinsic toxicity to healthy tissues.

A murine experimental anthracycline extravasation model: pathology and study of the involvement of topoisomerase II alpha and iron in the mechanism of tissue damage

The bisdioxopiperazine topoisomerase II catalytic inhibitor dexrazoxane has successfully been introduced into the clinic as an antidote to accidental anthracycline extravasation based on our preclinical mouse studies. The histology of this mouse extravasation model was investigated and found to be similar to findings in humans: massive necrosis in the subcutis, dermis and epidermis followed by sequestration and healing with granulation tissue, and a graft-versus-host-like reaction with hyperkeratotic and acanthotic keratinocytes, occasional apoptoses, epidermal invasion by lymphocytes and healing with dense dermal connective tissue. The extension of this fibrosis was quantified, and dexrazoxane intervention resulted in a statistically significant decrease in fibrosis extension, as also observed in the clinic. Several mechanisms have been proposed in anthracycline extravasation cytotoxicity, and we tested two major hypotheses: (1) interaction with topoisomerase II alpha and (2) the formation of tissue damaging reactive oxygen species following redox cycling of an anthracycline Fe(2+) complex. Dexrazoxane could minimise skin damage via both mechanisms, as it stops the catalytic activity of topoisomerase II alpha and thereby prevents access of anthracycline to the enzyme and thus cytotoxicity, and also acts as a strong iron chelator following opening of its two bisdioxopiperazine rings. Using the model of extravasation in a dexrazoxane-resistant transgenic mouse with a heterozygous mutation in the topoisomerase II alpha gene (Top2a(Y165S/+)), we found that dexrazoxane provided a protection against anthracycline-induced skin wounds that was indistinguishable from that found in wildtype mice. Thus, interaction with topoisomerase II alpha is not central in the pathogenesis of anthracycline-induced skin damage. In contrast to dexrazoxane, the iron-chelating bisdioxopiperazine ICRF-161 do not inhibit the catalytic cycle of topoisomerase II alpha. This compound was used to isolate and test the importance of iron in the wound pathogenesis. ICRF-161 was found ineffective in the treatment of anthracycline-induced skin damage, suggesting that iron does not play a dominant role in the genesis of wounds.

Drugs and pharmaceuticals: management of intoxication and antidotes

The treatment of patients poisoned with drugs and pharmaceuticals can be quite challenging. Diverse exposure circumstances, varied clinical presentations, unique patient-specific factors, and inconsistent diagnostic and therapeutic infrastructure support, coupled with relatively few definitive antidotes, may complicate evaluation and management. The historical approach to poisoned patients (patient arousal, toxin elimination, and toxin identification) has given way to rigorous attention to the fundamental aspects of basic life support--airway management, oxygenation and ventilation, circulatory competence, thermoregulation, and substrate availability. Selected patients may benefit from methods to alter toxin pharmacokinetics to minimize systemic, target organ, or tissue compartment exposure (either by decreasing absorption or increasing elimination). These may include syrup of ipecac, orogastric lavage, activated single- or multi-dose charcoal, whole bowel irrigation, endoscopy and surgery, urinary alkalinization, saline diuresis, or extracorporeal methods (hemodialysis, charcoal hemoperfusion, continuous venovenous hemofiltration, and exchange transfusion). Pharmaceutical adjuncts and antidotes may be useful in toxicant-induced hyperthermias. In the context of analgesic, anti-inflammatory, anticholinergic, anticonvulsant, antihyperglycemic, antimicrobial, antineoplastic, cardiovascular, opioid, or sedative-hypnotic agents overdose, N-acetylcysteine, physostigmine, L-carnitine, dextrose, octreotide, pyridoxine, dexrazoxane, leucovorin, glucarpidase, atropine, calcium, digoxin-specific antibody fragments, glucagon, high-dose insulin euglycemia therapy, lipid emulsion, magnesium, sodium bicarbonate, naloxone, and flumazenil are specifically reviewed. In summary, patients generally benefit from aggressive support of vital functions, careful history and physical examination, specific laboratory analyses, a thoughtful consideration of the risks and benefits of decontamination and enhanced elimination, and the use of specific antidotes where warranted. Data supporting antidotes effectiveness vary considerably. Clinicians are encouraged to utilize consultation with regional poison centers or those with toxicology training to assist with diagnosis, management, and administration of antidotes, particularly in unfamiliar cases.