Separation and determination of liposomal and non-liposomal daunorubicin from the plasma of patients treated with Daunoxome.

Several liposomal formulations of anthracyclines have been developed recently and are currently used in the clinical setting. We describe a technique of separation and quantification of the liposomal and non-liposomal forms of daunorubicin in the plasma of patients treated with DaunoXome, a liposomal formulation of daunorubicin. The method we propose is based upon the property of liposomes to cross reversed-phase C18 silicagel cartridges without being retained, while non-liposomal drug is retained on the stationary phase and is eluted with methanol. Extraction of liposomal and non-liposomal daunorubicin from plasma, therefore, is performed in two steps. This technique is rapid, can be automated in order to handle large series of samples, and the plasma can be frozen after sampling by addition of glycerol. The recovery of liposomal daunorubicin as well as the precision, linearity and accuracy of the technique appear satisfactory for pharmacokinetic purposes.

Preclinical evaluation of the cardiotoxicity of taxane-anthracycline combinations using the model of isolated perfused rat heart.

Paclitaxel strongly potentiates the cardiotoxicity of doxorubicin in the clinical setting. In this study, we aimed (1) to determine whether this potentiation could be reproduced in an ex vivo model and, if so, (2) to select drugs and protocols that did not cause this potentiation. The effect of paclitaxel and docetaxel on the cardiotoxicity induced by doxorubicin and epirubicin was studied using the model of isolated perfused rat heart. Cardiac performances were evaluated after several combination protocols administered every 2 days over a period of 12 days, and anthracycline concentrations in the heart and liver were determined on Day 12. When administered simultaneously, paclitaxel strongly potentiated the cardiotoxicity of doxorubicin ex vivo, and this effect was not due to Cremophor EL, the solvent used in the formulation of paclitaxel. The potentiation of anthracycline cardiotoxicity could be avoided by the replacement of doxorubicin by epirubicin, and/or of paclitaxel by docetaxel. Cardiotoxic potentiation was also avoided by the introduction of a 24-h lag time between the repetitive injections of doxorubicin and docetaxel. The concentration of doxorubicin and its cardiotoxic metabolite, doxorubicinol, in the heart and liver was not significantly altered by the taxanes, but that of epirubicin was increased twofold both in the heart and the liver. These results show that the potentiation of doxorubicin-induced cardiotoxicity by paclitaxel can be reproduced with an ex vivo model, and that it is not related to an increase in tissue concentration of the drug or active metabolite. Our model, therefore, may be useful for the selection of anthracycline-containing protocols with no increased risk of cardiotoxicity for the patients.

Comparative cardiotoxicity of idarubicin and doxorubicin using the isolated perfused rat heart model.

Attempts to reduce the incidence of congestive heart failure following anthracycline therapy include the replacement of the parent compounds (especially doxorubicin) by less cardiotoxic analogs. Among these analogs, idarubicin (4-demethoxy-daunorubicin) was shown to be less cardiotoxic than doxorubicin in phase II clinical trials, but its actual cardiotoxicity has never been evaluated in large series and has never been compared to that of doxorubicin in relevant experimental models. Using the isolated perfused rat heart model, we compared the cardiac effects (developed pressure, contractility and relaxation of the left ventricle) induced by idarubicin to those induced by doxorubicin. Drugs were administered i.v. every other day for 11 days at doses of 1, 2, 2.5 and 3 mg/kg per injection for doxorubicin and 0.5, 0.75 and 1 mg/kg per injection for idarubicin. We confirmed that similar general toxicity symptoms were obtained for a dose ratio of 1:4 (idarubicin:doxorubicin). However, at the maximum tolerated doses of both drugs (3 mg/kg per injection for doxorubicin and 0.75 mg/kg per injection for idarubicin), the cardiac toxicity of idarubicin remained significantly lower than that of doxorubicin. Anthracycline cardiac accumulation was evaluated in parallel and revealed a lower cardiac accumulation of idarubicin, which could explain the reduced cardiac toxicity of this analog. Direct perfusion of the drugs in the isolated hearts of untreated animals revealed that idarubicin was taken up more readily than doxorubicin in the cardiac tissue, despite the fact that it had less deleterious effects on cardiac function. This indicates that idarubicin also had less intrinsic cardiotoxicity than doxorubicin in this model.

Development of the model of rat isolated perfused heart for the evaluation of anthracycline cardiotoxicity and its circumvention.

1. In order to develop a predictive model for the preclinical evaluation of anthracycline cardiotoxicity and the means of preventing it, we have studied the functional parameters of perfused hearts isolated from rats receiving repeated doses of several anthracyclines. 2. The anthracyclines studied were doxorubicin, epirubicin, pirarubicin and daunorubicin, and we also studied a liposomal formulation of daunorubicin (DaunoXome) and the co-administration of dexrazoxane (ICRF-187) and doxorubicin. 3. Anthracyclines were administered i.p. at equimolar doses corresponding to 3 mg kg-1 per injection of doxorubicin, every other day for a total of six doses. Dexrazoxane was used at the dose of 30 mg kg-1 per injection and was administered either 30 min before or 30 min after doxorubicin. We evaluated any general toxicity towards the animals as well as alterations of left ventricular contractility and relaxation ex vivo. 4. Epirubicin and daunorubicin were significantly less cardiotoxic than doxorubicin, and neither pirarubicin nor DaunoXome caused significant alterations in cardiac function. There was a direct relationship between the decrease in cardiac contractility or relaxation and anthracycline accumulation in the heart, evaluated after the same treatment schedule. 5. Dexrazoxane induced a significant protection against doxorubicin-induced cardiac toxicity when administered 30 min before doxorubicin, whereas this protection was ineffective when administered 30 min after doxorubicin. Direct perfusion of DaunoXome in isolated hearts of untreated animals resulted in a 12-fold reduction of the accumulation of daunorubicin in heart tissue as compared to the perfusion of free daunorubicin, and did not cause alterations in cardiac function at a dosage for which free daunorubicin induced major alterations. 6. The isolated perfused rat heart appears to be a valuable model for screening of new anthracyclines and of strategies for circumventing anthracycline cardiotoxicity.

Evaluation of anthracycline cardiotoxicity with the model of isolated, perfused rat heart: comparison of new analogues versus doxorubicin.

We have compared the cardiotoxicity of 3 anthracyclines in a model of isolated perfused rat heart using the Langendorff technique. The contractile state and ventricular compliance were studied. Doxorubicin, epirubicin and pirarubicin were perfused at concentrations of 10(-6) and 10(-5) M during 70 min. The cardiac accumulation of the drugs was studied by HPLC. No significant alteration of cardiac functional parameters was observed at 10(-6) M. At 10(-5) M, epirubicin produced a significantly greater alteration of cardiac contractility than doxorubicin, whereas pirarubicin exerted first an inotropic effect followed by a recovery to initial values at the 60th min. Anthracycline accumulation in the heart was dose-dependent; epirubicin accumulated to a 30% greater extent than doxorubicin and pirarubicin heart concentrations were 4-5 times higher than those of doxorubicin at the end of the perfusion. These results suggest that doxorubicin and epirubicin have the same intrinsic cardiac toxicity, and that their distinct clinical cardiotoxicity must be explained by pharmacokinetic differences, whereas pirarubicin is much less cardiotoxic than the other anthracyclines because of different pharmacodynamic properties.