The Dihydroorotase Inhibitor 5-Aminoorotic Acid Inhibits the Metabolism in the Rat of the Cardioprotective Drug Dexrazoxane and Its One-Ring Open Metabolites

Patel

2009

Cardiovasc Toxicol

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The use of the anticancer multikinase inhibitor sorafenib is associated with cardiac ischemia or infarction and an increase in hypertension. We investigated various mechanisms that might be responsible for its cardiotoxicity in a neonatal rat myocyte model. As measured by lactate dehydrogenase release, sorafenib treatment of myocytes caused dose-dependent damage at therapeutically relevant concentrations. It had been hypothesized that inhibition of RAF1 and BRAF kinases may be responsible for sorafenib induced cardiotoxicity. However, because sorafenib treatment did not inhibit phosphorylation of ERK (extracellular signal-regulated kinase), it was concluded that sorafenib did not exert its damaging effects through RAF inhibition of the RAF/MEK/ERK kinase cascade. The clinically approved doxorubicin cardioprotective agent dexrazoxane did not protect myocytes from damage. At lower sorafenib concentrations, at least, these results are consistent with sorafenib not being able to induce significant oxidative damage. In conclusion, given the extreme lack of kinase selectivity that sorafenib exhibits, it is likely that inhibition of kinases other than RAF, or combinations of kinases, contributes to the cardiotoxic effects of sorafenib.

Section: Drug Treatments and Ldh Determinationmentioning

confidence: 99%

Mechanisms of Myocyte Cytotoxicity Induced by the Multikinase Inhibitor Sorafenib

Patel

2009

Cardiovasc Toxicol

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“…Ventricular myocytes were isolated from 2-to 3-day-old Sprague-Dawley rats as described previously (Hasinoff et al, 2003Schroeder et al, 2008). In brief, minced ventricles were serially digested with collagenase and trypsin in Dulbecco's phosphate-buffered saline, pH 7.4/1% (w/v) glucose at 37°C in the presence of deoxyribonuclease and preplated in large Petri dishes to deplete fibroblasts.…”

Section: Methodsmentioning

confidence: 99%

“…The total cellular LDH activity, from which the percentage of LDH release was calculated, was determined from the activity of the lysate plus the activity of the three 80-l samples taken previously. The LDH activity was determined in quadruplicate in a spectrophotometric kinetic assay in 96-well plate in a Molecular Devices (Sunnyvale, CA) plate reader as described previously (Hasinoff et al, 2003Schroeder et al, 2008).…”

Section: Methodsmentioning

confidence: 99%

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Mechanisms of Myocyte Cytotoxicity Induced by the Multiple Receptor Tyrosine Kinase Inhibitor Sunitinib

Patel²,

O’Hara³

2008

Mol Pharmacol

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116

The anticancer tyrosine kinase inhibitor sunitinib has been shown recently to be cardiotoxic. Using a neonatal rat myocyte model, we investigated various mechanisms that might be responsible for its cardiotoxicity. Sunitinib potently inhibited the enzyme activity of both AMP-activated protein kinase (AMPK) and the ribosomal S6 kinase RSK1 at therapeutically relevant concentrations. Heart tissue with its high energy needs might be particularly sensitive to inhibition of AMPK because of its role as an energy sensor regulating ATP levels. As measured by lactate dehydrogenase release, sunitinib treatment of myocytes caused dose-dependent damage at therapeutic levels. Sunitinib treatment also caused a dose-dependent reduction in myocyte protein levels of the phosphorylated ␣ and ␤ isoforms of the AMPK phosphorylation target acetyl-Coenzyme A carboxylase.However, myocytes were not protected from sunitinib treatment by pretreating them with the AMPK-activating antidiabetic drug metformin. Sunitinib treatment of myocytes also did not affect cellular ATP levels. Together, these last two results do not suggest a major role for inhibition of AMPK in sunitinibinduced myocyte damage. Dexrazoxane, which is a clinically approved doxorubicin cardioprotective agent, also did not protect myocytes from damage, which suggests that sunitinib did not induce oxidative damage. In conclusion, even though sunitinib potently inhibits AMPK and RSK1, given the extreme lack of kinase selectivity that sunitinib exhibits, it is likely that inhibition of other kinases or combinations of kinases are responsible for the cardiotoxic effects of sunitinib. Sunitinib (Fig.

“…As previously described (Hasinoff and Patel, 2010;Hasinoff et al, 2013), we used percentage of LDH release to measure myocyte damage, which is a widely used measure of drug-induced damage to myocytes (Adderley and Fitzgerald, 1999;Schroeder et al, 2008). Using this LDH release assay, we compared the ability of continuous treatment with pixantrone or doxorubicin to damage myocytes starting 5 days after isolation (Fig.…”

Section: Mechanisms Of the Reduced Cardiotoxicity Of Pixantronementioning

confidence: 99%

Mechanisms of Action and Reduced Cardiotoxicity of Pixantrone; a Topoisomerase II Targeting Agent with Cellular Selectivity for the Topoisomerase II Isoform

Journal of Pharmacology and Experimental Therapeutics

Patel

et al. 2015

Pixantrone is a new noncardiotoxic aza-anthracenedione anticancer drug structurally related to anthracyclines and anthracenediones, such as doxorubicin and mitoxantrone. Pixantrone is approved in the European Union for the treatment of relapsed or refractory aggressive B cell non-Hodgkin lymphoma. This study was undertaken to investigate both the mechanism(s) of its anticancer activity and its relative lack of cardiotoxicity. Pixantrone targeted DNA topoisomerase IIa as evidenced by its ability to inhibit kinetoplast DNA decatenation; to produce linear double-strand DNA in a pBR322 DNA cleavage assay; to produce DNA double-strand breaks in a cellular phosphohistone gH2AX assay; to form covalent topoisomerase II-DNA complexes in a cellular immunodetection of complex of enzymeto-DNA assay; and to display cross-resistance in etoposideresistant K562 cells. Pixantrone produced semiquinone free radicals in an enzymatic reducing system, although not in a cellular system, most likely due to low cellular uptake. Pixantrone was 10-to 12-fold less damaging to neonatal rat myocytes than doxorubicin or mitoxantrone, as measured by lactate dehydrogenase release. Three factors potentially contribute to the reduced cardiotoxicity of pixantrone. First, its lack of binding to iron(III) makes it unable to induce iron-based oxidative stress. Second, its low cellular uptake may limit its ability to produce semiquinone free radicals and redox cycle. Finally, because the b isoform of topoisomerase II predominates in postmitotic cardiomyocytes, and pixantrone is demonstrated in this study to be selective for topoisomerase IIa in stabilizing enzyme-DNA covalent complexes, the attenuated cardiotoxicity of this agent may also be due to its selectivity for targeting topoisomerase IIa over topoisomerase IIb.