Experimental systemic toxicology of 4'-epidoxorubicin, a new, less cardiotoxic anthracycline antitumor agent.

The acute and chronic iv toxicity of 4'-epidoxorubicin, a new antitumor anthracycline antibiotic, was compared with doxorubicin. The LD50 of 4'-epidoxorubicin was 16.07 mg/kg in mice, 14.27 mg/kg in rats, and about 2 mg/kg in dogs; the LD50 of doxorubicin was 11.98 mg/kg in mice, 10.51 mg/kg in rats, and about 2.5 mg/kg in dogs. Rats and dogs were also dosed iv for 91 days (3 injections/week) with 4'-epidoxorubicin or doxorubicin at doses of 0.128, 0.32, and 0.8 mg/kg to rats and 0.064, 0.16, and 0.4 mg/kg to dogs. A comprehensive toxicological evaluation of the animals was carried out before, throughout, and at the end of the study. High-dose 4'-epidoxorubicin induced toxic clinical signs in dogs, and in both species caused loss of body weight, antiproliferative effects on blood-forming organs and testes, and degenerative lesions in kidneys and heart. The cardiac damage was moderate in rats and very mild in dogs; only three male rats died at this dose. The medium dose induced less pronounced changes and no heart lesions and the low dose was practically nontoxic. Doxorubicin showed similar antiproliferative activity, but more evident toxic effects, especially on the heart; many rats given the high dose died and some at the medium dose showed initial cardiac lesions. Thus 4'-epidoxorubicin appeared less toxic than doxorubicin; in particular cardiac damage was much less evident in animals chronically injected with the new drug.

Cardiomyopathy of doxorubicin in experimental animals, Factors affecting the severity, distribution and evolution of myocardial lesions.

Heart lesions induced in mice, rats, rabbits and dogs by Doxorubicin administered i.v. according to various schedules were studied by light and electron microscopy Vacuolization of myocardial cytoplasm due to distention of the sarcoplasmic reticulum, the T-tubule system and the Golgi vesicles was one of the most common findings. Myocytolysis, clumping and loss of fibrils, fragmentation of sarcomeres, swelling of mitochondria and an increase in lysosomes and residual bodies were also observed. The severity of the cardiomyopathy, quantitatively evaluated by a score system, proved to be dose-dependent. Cardiomyopathy was more severe when the treatment was given in a short period by administration of high doses than when the same cumulative dose was administered as low doses repeated for a long period. The left atrium was more severely affected than the ventricles when high doses were given, whereas it was less affected in animals given low doses. The cardiomyopathy was less severe in animals receiving the same dose in a high volume of solvent and during a long perfusion time. Threshold doses were needed both to induce the cardiomyopathy and to establish it as a progressive disease.