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The anthracycline (ANT) anticancer drugs such as doxorubicin or daunorubicin (DAU) can cause serious myocardial injury and chronic cardiac dysfunction in cancer survivors. A bisdioxopiperazine agent dexrazoxane (DEX) has been developed as a cardioprotective drug to prevent these adverse events, but it is uncertain whether it is the best representative of the class. The present study used a rabbit model of chronic ANT cardiotoxicity to examine another bisdioxopiperazine compound called GK-667 (meso-(butane-2,3-diylbis(2,6-dioxopiperazine-4,1-diyl))bis(methylene)-bis(2-aminoacetate) hydrochloride), a water-soluble prodrug of ICRF-193 (meso-4,4′-(butan-2,3-diyl)bis(piperazine-2,6-dione)), as a potential cardioprotectant. The cardiotoxicity was induced by DAU (3 mg/kg, intravenously, weekly, 10 weeks), and GK-667 (1 or 5 mg/kg, intravenously) was administered before each DAU dose. The treatment with GK-667 was well tolerated and provided full protection against DAU-induced mortality and left ventricular (LV) dysfunction (determined by echocardiography and LV catheterization). Markers of cardiac damage/dysfunction revealed minor cardiac damage in the group co-treated with GK-667 in the lower dose, whereas almost full protection was achieved with the higher dose. This was associated with similar prevention of DAU-induced dysregulation of redox and calcium homeostasis proteins. GK-667 dose-dependently prevented tumor suppressor p53 (p53)-mediated DNA damage response in the LV myocardium not only in the chronic experiment but also after single DAU administration. These effects appear essential for cardioprotection, presumably because of the topoisomerase IIβ (TOP2B) inhibition provided by its active metabolite ICRF-193. In addition, GK-667 administration did not alter the plasma pharmacokinetics of DAU and its main metabolite daunorubicinol (DAUol) in rabbits in vivo. Hence, GK-667 merits further investigation as a promising drug candidate for cardioprotection against chronic ANT cardiotoxicity.

Cardioprotective activity of dexrazoxane (ICRF-187), the only clinically approved drug against anthracycline-induced cardiotoxicity, has traditionally been attributed to its iron-chelating metabolite. However, recent experimental evidence suggested that the inhibition and/or depletion of topoisomerase IIβ (TOP2B) by dexrazoxane could be cardioprotective. Hence, we evaluated a series of dexrazoxane analogues and found that their cardioprotective activity strongly correlated with their interaction with TOP2B in cardiomyocytes, but was independent of their iron chelation ability. Very tight structure-activity relationships were demonstrated on stereoisomeric forms of 4,4'-(butane-2,3-diyl)bis(piperazine-2,6-dione). In contrast to its rac-form 12, meso-derivative 11 (ICRF-193) showed a favorable binding mode to topoisomerase II in silico, inhibited and depleted TOP2B in cardiomyocytes more efficiently than dexrazoxane, and showed the highest cardioprotective efficiency. Importantly, the observed ICRF-193 cardioprotection did not interfere with the antiproliferative activity of anthracycline. Hence, this study identifies ICRF-193 as the new lead compound in the development of efficient cardioprotective agents.

The bisdioxopiperazine topoisomerase IIβ inhibitor ICRF-193 has been previously identified as a more potent analog of dexrazoxane (ICRF-187), a drug used in clinical practice against anthracycline cardiotoxicity. However, the poor aqueous solubility of ICRF-193 has precluded its further in vivo development as a cardioprotective agent. To overcome this issue, water-soluble prodrugs of ICRF-193 were prepared, their abilities to release ICRF-193 were investigated using a novel UHPLC-MS/MS assay, and their cytoprotective effects against anthracycline cardiotoxicity were tested in vitro in neonatal ventricular cardiomyocytes (NVCMs). Based on the obtained results, the bis(2-aminoacetoxymethyl)-type prodrug GK-667 was selected for advanced investigations due to its straightforward synthesis, sufficient solubility, low cytotoxicity and favorable ICRF-193 release. Upon administration of GK-667 to NVCMs, the released ICRF-193 penetrated well into the cells, reached sufficient intracellular concentrations and provided effective cytoprotection against anthracycline toxicity. The pharmacokinetics of the prodrug, ICRF-193 and its rings-opened metabolite was estimated in vivo after administration of GK-667 to rabbits. The plasma concentrations of ICRF-193 reached were found to be adequate to achieve cardioprotective effects in vivo. Hence, GK-667 was demonstrated to be a pharmaceutically acceptable prodrug of ICRF-193 and a promising drug candidate for further evaluation as a potential cardioprotectant against chronic anthracycline toxicity.

Bisdioxopiperazine agent dexrazoxane (ICRF-187) has been the only effective and approved drug for prevention of chronic anthracycline cardiotoxicity. However, the structure-activity relationships (SARs) of its cardioprotective effects remain obscure owing to limited investigation of its derivatives/analogs and uncertainties about its mechanism of action. To fill these knowledge gaps, we tested the hypothesis that dexrazoxane derivatives exert cardioprotection via metal chelation and/or modulation of topoisomerase IIβ (Top2B) activity in chronic anthracycline cardiotoxicity. Dexrazoxane was alkylated in positions that should not interfere with the metal-chelating mechanism of cardioprotective action; that is, on dioxopiperazine imides or directly on the dioxopiperazine ring. The protective effects of these agents were assessed in vitro in neonatal cardiomyocytes. All studied modifications of dexrazoxane molecule, including simple methylation, were found to abolish the cardioprotective effects. Because this challenged the prevailing mechanistic concept and previously reported data, the two closest derivatives [(±)-4,4'-(propane-1,2-diyl)bis(1-methylpiperazine-2,6-dione) and 4-(2-(3,5-dioxopiperazin-1-yl)ethyl)-3-methylpiperazine-2,6-dione] were thoroughly scrutinized in vivo using a rabbit model of chronic anthracycline cardiotoxicity. In contrast to dexrazoxane, both compounds failed to protect the heart, as demonstrated by mortality, cardiac dysfunction, and myocardial damage parameters, although the pharmacokinetics and metal-chelating properties of their metabolites were comparable to those of dexrazoxane. The loss of cardiac protection was shown to correlate with their abated potential to inhibit and deplete Top2B both in vitro and in vivo. These findings suggest a very tight SAR between bisdioxopiperazine derivatives and their cardioprotective effects and support Top2B as a pivotal upstream druggable target for effective cardioprotection against anthracycline cardiotoxicity. SIGNIFICANCE STATEMENT: This study has revealed the previously unexpected tight structure-activity relationships of cardioprotective effects in derivatives of dexrazoxane, which is the only drug approved for the prevention of cardiomyopathy and heart failure induced by anthracycline anticancer drugs. The data presented in this study also strongly argue against the importance of metal-chelating mechanisms for the induction of this effect and support the viability of topoisomerase IIβ as an upstream druggable target for effective and clinically translatable cardioprotection.

Background: Anthracycline-induced heart failure has been traditionally attributed to direct iron-catalyzed oxidative damage. Dexrazoxane (DEX)—the only drug approved for its prevention—has been believed to protect the heart via its iron-chelating metabolite ADR-925. However, direct evidence is lacking, and recently proposed TOP2B (topoisomerase II beta) hypothesis challenged the original concept. Methods: Pharmacokinetically guided study of the cardioprotective effects of clinically used DEX and its chelating metabolite ADR-925 (administered exogenously) was performed together with mechanistic experiments. The cardiotoxicity was induced by daunorubicin in neonatal ventricular cardiomyocytes in vitro and in a chronic rabbit model in vivo (n=50). Results: Intracellular concentrations of ADR-925 in neonatal ventricular cardiomyocytes and rabbit hearts after treatment with exogenous ADR-925 were similar or exceeded those observed after treatment with the parent DEX. However, ADR-925 did not protect neonatal ventricular cardiomyocytes against anthracycline toxicity, whereas DEX exhibited significant protective effects (10–100 µmol/L; P P Conclusions: This study strongly supports a new mechanistic paradigm that attributes clinically effective cardioprotection against anthracycline cardiotoxicity to interactions with TOP2B but not metal chelation and protection against direct oxidative damage.

Bisdioxopiperazine agent dexrazoxane (ICRF-187) has been the only effective and approved drug for prevention of chronic anthracycline cardiotoxicity. However, the structure-activity relationships (SARs) of its cardioprotective effects remain obscure owing to limited investigation of its derivatives/analogs and uncertainties about its mechanism of action. To fill these knowledge gaps, we tested the hypothesis that dexrazoxane derivatives exert cardioprotection via metal chelation and/or modulation of topoisomerase II

Introduction Anthracyclines (ANT; e.g. doxorubicin, epirubucin or daunorubicin) are still indispensable part of modern chemotherapy regiments, despite of their well-known risk to induce cardiotoxicity leading even to heart failure. Thus, there is a need for effective cardioprotective strategy. Dexrazoxane (DEX) is the only clinically approved drug clearly effective both in clinics and clinically relevant experimental models. However, mechanisms of ANT-cardiotoxicity induction as well as DEX protection are not elucidated yet. Traditionally, ANTs have been believed to induce iron-catalyzed oxidative damage to cardiomyocytes. DEX should prevent this via its metal-chelating metabolite ADR-925, but direct evidence is missing. This paradigm has been recently challenged by topoisomerase IIβ (TOP2B) hypothesis of ANT cardiotoxicity. Hence, the aims of this study were to examine if ADR-925 is really the protective agent in DEX-afforded cardioprotection against daunorubicin (DAU) cardiotoxicity, along with the involvement of TOP2B interaction in this process. Methods Firstly, a pharmacokinetic studies were employed to set up ADR-925 doses ensuring same or even higher exposition of isolated rat neonatal ventricular cardiomyocytes (NVCMs) and rabbits’ heart than after endogenously formed ADR-925 after DEX administration. Cardioprotective effectcs of DEX and ADR-925 (both in 10–100 uM) were compared using NVCMs treated with DAU (1.2 uM). In rabbits (n=50), cardiotoxicity was induced with DAU (3 mg/kg IV, once weekly/10 weeks). Prior to each DAU dose, ADR-925 was administered in two schedules (60 mg/kg 30-min-infusion alone or with additional the same s.c. bolus dose after 2 hrs). Cardiotoxicity markers, LV function and interaction with TOP2B were compared to effects of DEX pre-treatment (60 mg/kg IP). Results ADR-925 administration did not provide any meaningful cardioprotection against ANT cardiotoxicity in NVCMs. Regardless various administration schedule in rabbits, ADR-925 did not protect against DAU-induced mortality due to end-stage heart failure, decrease of LV function (dP/dtmax and LVFS), increase of cTnT levels, ANP or BNP mRNA as well as histopathological changes. This sharply contrasted with remarkable cardioprotective effects of DEX. Further experiments documented that the parent compound can inhibit and deplete TOP2B and prevent DAU-induced genotoxic damage in cardiomyocytes in contrast to ADR-925. Conclusion The present investigation strongly encourages the shift of mechanistic paradigm in clinically translatable cardioprotection against anthracycline cardiotoxicity - from metal chelation and protection from direct oxidative damage towards a TOP2B interaction. This study was supported by the Czech Science Foundation [Grant n. 18–08169S], the Charles University Research Program PROGRES [Grant n. Q40/5] and by the project EFSA-CDN (No. CZ.02.1.01/0.0/0.0/16_019/0000841) co-funded by ERDF. Conflict of Interest None declared

Dexrazoxane (DEX) is a clinically available cardioprotectant that reduces the toxicity induced by anthracycline (ANT) anticancer drugs; however, DEX is seldom used and its action is poorly understood. Inorganic nitrate/nitrite has shown promising results in myocardial ischemia-reperfusion injury and recently in acute high-dose ANT cardiotoxicity. However, the utility of this approach for overcoming clinically more relevant chronic forms of cardiotoxicity remains elusive. Hence, in this study, the protective potential of inorganic nitrate and nitrite against chronic ANT cardiotoxicity was investigated, and the results were compared to those using DEX. Chronic cardiotoxicity was induced in rabbits with daunorubicin (DAU). Sodium nitrate (1g/L) was administered daily in drinking water, while sodium nitrite (0.15 or 5mg/kg) or DEX (60mg/kg) was administered parenterally before each DAU dose. Although oral nitrate induced a marked increase in plasma NOx, it showed no improvement in DAU-induced mortality, myocardial damage or heart failure. Instead, the higher nitrite dose reduced the incidence of end-stage cardiotoxicity, prevented related premature deaths and significantly ameliorated several molecular and cellular perturbations induced by DAU, particularly those concerning mitochondria. The latter result was also confirmed in vitro. Nevertheless, inorganic nitrite failed to prevent DAU-induced cardiac dysfunction and molecular remodeling in vivo and failed to overcome the cytotoxicity of DAU to cardiomyocytes in vitro. In contrast, DEX completely prevented all of the investigated molecular, cellular and functional perturbations that were induced by DAU. Our data suggest that the difference in cardioprotective efficacy between DEX and inorganic nitrite may be related to their different abilities to address a recently proposed upstream target for ANT in the heart - topoisomerase IIβ.

Cardiotoxicity is a serious drawback of anthracycline anti-cancer drugs and dexrazoxane is the only cardioprotective agent with clinically established efficacy. Iron-mediated oxidative stress is traditionally believed to be the primary cause of anthracycline cardiotoxicity, and dexrazoxane-induced cardioprotection is attributed to iron chelating properties of its open ring metabolite, ADR-925, which may inhibit the oxidative injury. However, dexrazoxane is also a catalytic inhibitor of topoisomerase II (TOP2), and the role of oxidative stress in clinically relevant forms of cardiotoxicity has increasingly been questioned. In this study, novel analogues of dexrazoxane (MK-15, ES-5) and ADR-925 (KH-TA4, JR-159) were synthesized, and evaluated in vitro and in vivo. When examined in the leukemic cell line, HL-60, these novel analogues did not interfere with the anti-proliferative action of daunorubicin. In contrast to dexrazoxane, they had no anti-cancer effect on their own and the changes in the chemical structure resulted in a loss of TOP2 inhibitory activity. Although some of the novel compounds showed significant anti-oxidant and iron chelating properties in vitro, they did not protect isolated cardiomyocytes and rabbits from daunorubicin-induced cardiotoxicity and heart failure. Importantly, dexrazoxane has been found to be a relatively weak intracellular iron chelator and it failed to protect the isolated cardiomyocytes from model oxidative injury induced by hydrogen peroxide. However, in contrast to all novel analogues, dexrazoxane induced depletion of the TOP2 beta isoform. This isoform is typical for terminally differentiated cells and its genetic deletion has been reported to overcome anthracycline-induced cardiotoxicity. Hence, TOP2 beta, rather than (or along with) iron chelation, may be a promising target for effective cardioprotection induced by bisdioxopiperazine agents.

Dexrazoxane (DEX), the only cardioprotectant approved against anthracycline cardiotoxicity, has been traditionally deemed to be a prodrug of the iron-chelating metabolite ADR-925. However, pharmacokinetic profile of both agents, particularly with respect to the cells and tissues essential for its action (cardiomyocytes/myocardium), remains poorly understood. The aim of this study is to characterize the conversion and disposition of DEX to ADR-925 in vitro (primary cardiomyocytes) and in vivo (rabbits) under conditions where DEX is clearly cardioprotective against anthracycline cardiotoxicity. Our results show that DEX is hydrolyzed to ADR-925 in cell media independently of the presence of cardiomyocytes or their lysate. Furthermore, ADR-925 directly penetrates into the cells with contribution of active transport, and detectable concentrations occur earlier than after DEX incubation. In rabbits, ADR-925 was detected rapidly in plasma after DEX administration to form sustained concentrations thereafter. ADR-925 was not markedly retained in the myocardium, and its relative exposure was 5.7-fold lower than for DEX. Unlike liver tissue, myocardium homogenates did not accelerate the conversion of DEX to ADR-925 in vitro, suggesting that myocardial concentrations in vivo may originate from its distribution from the central compartment. The pharmacokinetic parameters for both DEX and ADR-925 were determined by both noncompartmental analyses and population pharmacokinetics (including joint parent-metabolite model). Importantly, all determined parameters were closer to human than to rodent data. The present results open venues for the direct assessment of the cardioprotective effects of ADR-925 in vitro and in vivo to establish whether DEX is a drug or prodrug.

Novel dexrazoxane derivative JR-311 was prepared to investigate structure-activity relationships and mechanism(s) of protection against anthracycline cardiotoxicity. Its cardioprotective, antiproliferative, iron (Fe) chelation and inhibitory and/or depletory activities on topoisomerase IIbeta (TOP2B) were examined and compared with dexrazoxane. While in standard assay, JR-311 failed in both cardioprotection and depletion of TOP2B, its repeated administration to cell culture media led to depletion of TOP2B and significant protection of isolated rat neonatal ventricular cardiomyocytes from daunorubicin-induced damage. This effect was explained by a focused analytical investigation that revealed rapid JR-311 decomposition, resulting in negligible intracellular concentrations of the parent compound but high exposure of cells to the decomposition products, including Fe-chelating JR-H2. Although chemical instability is an obstacle for the development of JR-311, this study identified a novel dexrazoxane analogue with preserved pharmacodynamic properties, contributed to the investigation of structure-activity relationships and suggested that the cardioprotection of bis-dioxopiperazines is likely attributed to TOP2B activity of the parent compound rather than Fe chelation of their hydrolytic metabolites/degradation products. Moreover, this study highlights the importance of early stability testing during future development of novel dexrazoxane analogues.

So far dexrazoxane (DEX) is the only drug approved for prevention of chronic anthracycline (ANT) cardiotoxicity. However, molecular mechanisms responsible for its cardioprotective effects remain unclear. This report addresses traditional as well as alternative mechanisms of its cardioprotective action against chronic ANT cardiotoxicity. Daunorubicin (DAU, 3 mg/kg/week for 10 weeks) was used to induced cardiotoxicity in rabbits and DEX (60 mg/kg) was administered prior each DAU dose. LV myocardium was analyzed for oxidative stress, mitochondrial damage, changes in mtDNA and mtDNA/nDNA ratio, and perturbations in mitochondrial proteins expression. DEX ability to interact with iron was addressed in H9c2 cardiomyoblasts. In addition, topoisomerase-2β (TOP2b) expression was studied after DEX exposure in vitro and in vivo. DEX completely prevented DAU-induced heart damage as well as mitochondrial damage. This protection was not directly based on protection from oxidative damage of myocardium or common deletion in mtDNA. Instead, DEX was able to prevent DAU-induced significant decrease in expression of mitochondrial biogenesis regulators (e.g. TFAM) and OXPHOS subunits encoded by both nDNA and mtDNA. Noteworthy, in vitro experiments showed inability of DEX to mobilize iron from cells. Finally, DEX exposure decreased TOP2b protein levels which can correspond with recent data showing that ANT cardiotoxicity may beTOP2b-mediated. The present data suggest that DEX cardioprotective effects need not be based on iron chelation and prevention of oxidative stress or mtDNA deletions. Instead, DEX-induced depletion of TOP2b may be important for cardioprotection and merit further study. Supported by GACR 13–15008S and PRVOUK P37/05.

The toxic effects of anthracycline antineoplastic drugs to cardiomyocytes is a a serious drawback of their high antineoplastic efficiency. Dexrazoxane remains the only clinically approved protective substance against the cardiotoxicitity of anthracycline antineoplastic drugs. Although the mechanisms of the cardioprotection are elusive so far, widely accepted hypothesis represents dexrazoxane as a pro-drug yielding an EDTA-like metabolite ADR-925. By chelating iron, ADR-925 could prevent oxidative damage induced by anthracyclines. However, the relationship of dexrazoxane hydrolysis and its cardioprotective activity is only poorly characterised. We found that the rate of dexrazoxane decay (100 µM) to ADR-925 in the culture medium does not change in the presence of the cardiomyocytes. We also observed that ADR-925 passes through the plasma membrane into the cells, although more slowly than dexrazoxane. In cells ADR-925 chelates free intracellular iron. Also ADR-925 is able to displace iron from its complex with anthracyclines in solution. Interestingly, both dexrazoxane and ADR-925 were found to interact with topoisomerase II in cells, although in a different manner. The plasma and tissue concentrations of dexrazoxane and ADR-925 were measured also using validated analytic methods in plasma, myocardium, soleus muscle, liver and urine samples after a one dose of dexrazoxane and ADR-925 to rabbits (60 mg/kg, i.p.) and fundamental pharmacokinetic parameters were calculated. We documented that ADR-925 crosses the plasma membrane and also interacts with the topoiosomerase II beta in cardiomyocytes. These findings together with the in vivo data provide a valuable insight into the pharmacokinetic/pharmacodnamic relationship of the dexrazoxane cardioprotection of anthracycline cardiotoxicity.