Preclinical evaluation of the cardiac toxicity of HMR-1826, a novel prodrug of doxorubicin.

Cardiotoxicity represents the major side-effect limiting the clinical use of anthracyclines, especially doxorubicin, in cancer chemotherapy. The use of non-toxic prodrugs, or of liposome-encapsulated drugs, allows a better targeting of the tumours and may, therefore, improve the tolerance to the treatment. Using the model of isolated perfused rat heart, we have evaluated the cardiotoxicity of a novel prodrug of doxorubicin, HMR-1826, which consists of the association of doxorubicin to glucuronic acid. We have compared the cardiac effects (developed pressure, contractility and relaxation of the left ventricle) induced by HMR-1826 to those induced by doxorubicin and Doxil, a liposomal form of doxorubicin. HMR-1826 was administered intravenously every other day for 11 days at doses of 50-200 mg kg(-1) per injection while doxorubicin was administered according to the same protocol at doses of 1-3 mg kg(-1) per injection. Doxorubicin strongly decreased the cardiac functional parameters at the doses of 2.5 and 3 mg kg(-1) per injection. Doxil (3 mg kg(-1) and HMR-1826 (50-150 mg kg(-1)) were largely devoid of cardiotoxicity. HMR-1826 only induced significant alterations of the cardiac function at the highest dose used (200 mg kg(-1) per injection). These alterations were much lower than those of doxorubicin at 2.5 mg kg(-1) per injection, despite similar general toxicity symptoms (weight loss, nose bleeding and diarrhoea) at these respective doses. Thus, HMR-1826 appeared about 100-fold less cardiotoxic than doxorubicin.

Reduced basal NO-mediated dilation and decreased endothelial NO-synthase expression in coronary vessels of spontaneously hypertensive rats.

Basal vasomotor tone in coronary vessels is, in part, maintained by nitric oxide (NO) production by endothelial constitutive NO synthase (ecNOS). Alteration of coronary circulation observed in left ventricular hypertrophy secondary to hypertension could be associated with a decrease in NO production. The aim of this study was to measure: (1) coronary flow in the Langendorff-perfused heart model at baseline, after maximum vasodilation in response to adenosine (10(-5) M), after endothelium-dependent vasodilation in response to bradykinin (10(-8) M) and after ecNOS inhibition by nitro-L-arginine methyl ester (L-NAME) (10(-4) M); (2) medial thickening of coronary microvessels and perivascular collagen on histological heart sections; and (3) ecNOS expression by immunohistochemical staining in these vessels using 20-week-old spontaneously hypertensive (SHR) and Wistar-Kyoto control rats (WKY). These measurements were determined by computer-directed color analysis. When SHR were compared with WKY rats, we found: (1) a decrease in basal flow (10.1+/-0.6 v 15.3+/-1.2 ml/min/g, n=10, P<0.0001), in maximum flow (15.4+/-0.7 v 24.3+/-1.3 ml/min/g, n=10, P<0.001), in bradykinin-induced flow increment (1.5+/-0.3 v 2.6+/-0.3 ml/min/g, n=5, P<0.05) and in L-NAME-sensitive flow (3.3+/-0.6 v 6.3+/-0.9 ml/min/g, n=7, P<0.05); (2) an increase in medial thickness (9.4+/-0.6 v 5.4+/-0.3 microm, n=8, P<0.001) and in perivascular collagen area (1509+/-311 v 462+/-120 microm2, n=8, P<0.01) of coronary arterioles; and (3) a decrease in ecNOS expression in the endothelium (ecNOS-stained cross-sectional area in arterioles: 40.0+/-9.1 v 84.6+/-9.0 microm2, n=7, P

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.

Diltiazem and left ventricular hypertrophy in renovascular hypertensive rats.

The effects of diltiazem treatment (40-50 mg/kg/day orally for 8 weeks) of left ventricular hypertrophy on systemic and coronary hemodynamics and mechanical cardiac performance were investigated in renovascular hypertensive rats (Goldblatt, two-kidney, one clip). Systemic and coronary hemodynamics were determined by using radioactive microspheres in conscious, unrestrained rats. Mechanical performance was measured on isolated papillary muscle from the same animal. Nine treated hypertensive rats were compared with control groups: 12 untreated hypertensive and nine sham-operated rats. Diltiazem treatment led to an effective but incomplete control of blood pressure (from 208 +/- 5 mm Hg in the untreated hypertensive group to 155 +/- 3 mm Hg in the treated hypertensive group; p less than 0.01) associated with a significant but incomplete decrease of the left ventricular mass (from 3.10 +/- 0.19 mg/g in untreated hypertensive rats to 2.35 +/- 0.04 mg/g in treated hypertensive rats; p less than 0.01). A close correlation was found between left ventricular mass and systolic blood pressure in untreated, treated, and pooled groups (r = 0.84, p less than 0.001, n = 30). The left ventricular weight to systolic blood pressure ratio was equivalent in all three groups, so that the reduction of left ventricular mass in diltiazem-treated rats was commensurate with the reduction of blood pressure.(ABSTRACT TRUNCATED AT 250 WORDS)