Exacerbation of doxorubicin cardiotoxicity by digoxin administration in an experimental rabbit model

Doxorubicin-induced cardiotoxicity and risk factors

Doxorubicin (DOX) is an anthracycline antibiotic widely used as a chemotherapeutic agent to treat solid tumours and hematologic malignancies. Although useful in the treatment of cancers, the benefit of DOX is limited due to its cardiotoxic effect that is observed in a large number of patients. In the literature, there is evidence that the presence of various factors may increase the risk of developing DOX-induced cardiotoxicity. A better understanding of the role of these different factors in DOX-induced cardiotoxicity may facilitate the choice of the therapeutic approach in cancer patients suffering from various cardiovascular risk factors. In this review, we therefore discuss the latest findings in both preclinical and clinical research suggesting a link between DOX-induced cardiotoxicity and various risk factors including sex, age, ethnicity, diabetes, dyslipidaemia, obesity, hypertension, cardiovascular disease and co-medications.

Onco-cardiology: Drug-drug interactions of antineoplastic and cardiovascular drugs

Cardiovascular diseases (CVD) and cancer are still the leading causes of death. There are many common etiologic factors, especially smoking and obesity. Therefore, it is not uncommon for CVD and cancer to coexist. Drug-drug interactions (DDIs) inevitably occur in this group of patients, where polypharmacy is increasing due to older age and multiple comorbidities. However, multidisciplinary studies, especially close collaboration of medical oncologists and cardiologists, who deals with the diagnosis and treatment of these diseases, awareness and preventive approaches to DDIs may reduce serious morbidity and mortality. In this review, information about the common treatments used in cardiology and oncology and possible DDIs are discussed.

Cardiac side-effects of cancer chemotherapy

The spectrum of cardiac side-effects of cancer chemotherapy has expanded with the development of combination, adjuvant and targeted chemotherapies. Their administration in multiple regimens has increased greatly, including in older patients and in patients with cardiovascular and/or coronary artery disease (CAD). Cardiac toxicity of anthracyclines involves oxidative stress and apoptosis. Early detection combines 2D-echocardiography and/or radionuclide angiography and recent methods such as tissue Doppler imaging, strain rate echocardiography and sampling of serial troponin and/or NT-proBNP levels. Dexrazoxane has proven effective in the prevention of dose-related toxicity in children and adults. High doses of the alkylating drugs cyclophosphamide and ifosfamide may result in a reversible heart failure and in life-threatening arrhythmias. Myocardial ischemia induced by the antimetabolites 5-fluorouracil and capecitabine impacts prognosis of patients with prior CAD. Severe arrhythmias may complicate administration of microtubule inhibitors. Targeted therapies with the antibody-based tyrosine kinases (TK) inhibitors trastuzumab and, to a lesser extent, alemtuzumab induce heart failure or asymptomatic LV dysfunction in 1-4% and 10%, respectively. Cetuximab and rituximab induce hypotension, whereas bevacizumab may promote severe hypertension and venous thromboembolism. Small molecule TK inhibitors may also elicit LV dysfunction, in only few patients treated with imatinib mesylate, but in a substantially higher proportion of those receiving the multitargeted TK inhibitor sunitinib or the recently approved drugs erlotinib, lapatinib and dasatinib. Management of patients at increased cardiovascular risk associated with advancing age, previous CAD or targeted therapies may be optimized by referral to a cardiologist in a cross-specialty teamwork.

Digoxin and ouabain induce P-glycoprotein by activating calmodulin kinase II and hypoxia-inducible factor-1alpha in human colon cancer cells

Digoxin and ouabain are cardioactive glycosides, which inhibit the Na+/K+-ATPase pump and in this way they increase the intracellular concentration of cytosolic calcium ([Ca2+](i)). They are also strong inducers of the P-glycoprotein (Pgp), a transmembrane transporter which extrudes several drugs, including anticancer agents like doxorubicin. An increased amount of Pgp limits the absorption of drugs through epithelial cells, thus inducing resistance to chemotherapy. The mechanism by which cardioactive glycosides increase Pgp is not known and in this work we investigated whether digoxin and ouabain elicited the expression of Pgp with a calcium-driven mechanism. In human colon cancer HT29 cells both glycosides increased the [Ca2+](i) and this event was dependent on the calcium influx via the Na+/Ca2+ exchanger. The increased [Ca2+](i) enhanced the activity of the calmodulin kinase II enzyme, which in turn activated the transcription factor hypoxia-inducible factor-1alpha. This one was responsible for the increased expression of Pgp, which actively extruded doxorubicin from the cells and significantly reduced the pro-apoptotic effect of the drug. All the effects of glycosides were prevented by inhibiting the Na+/Ca2+ exchanger or the calmodulin kinase II. This work clarified the molecular mechanisms by which digoxin and oubain induce Pgp and pointed out that the administration of cardioactive glycosides may widely affect the absorption of drugs in colon epithelia. Moreover, our results suggest that the efficacy of chemotherapeutic agent substrates of Pgp may be strongly reduced in patients taking digoxin.

Comparative study of chronic toxic effects of daunorubicin and doxorubicin in rabbits

This study compares the chronic toxicity of two anthracyclines--daunorubicin and doxorubicin, commonly used for induction of anthracycline cardiomyopathy in the rabbit model. Such a comparative study has not been published until now. Both drugs were administered intravenously to male Chinchilla rabbits in doses at 3 mg/kg (50 mg/m2) once weekly for 10 weeks. Selected biochemical, haematological and cardiovascular parameters and body weights were regularly monitored; additionally, a histological evaluation of heart, kidney and liver was performed at the end of the experiment. In the daunorubicin group, there were marked signs of the progressive development of heart failure, like the significant increases of the pre-ejection period/left ventricular ejection time index values (up to 134%)--and histological changes within the myocardium were also observed. On the other hand, the 10-week doxorubicin administration did not cause these changes that are typical for heart injury. Haematotoxicity, manifested particularly by aplastic anaemia, was apparent in both the experimental groups. Significant body weight loss (by 45.2%) and high premature mortality (100% versus 36.4%) reflected a greater general toxicity, especially nephrotoxicity of doxorubicin in comparison with daunorubicin. Further studies are necessary to find a possible explanation for these findings.