Optical isomers of the hepatocarcinogenic beta-blocker ZAMI 1305: influence on nucleic acids synthesis and DNA integrity

Further studies on the tumor-initiating activity of the beta-blocker DL-ZAMI 1305

The purpose of this study was to evaluate the initiating activity of the hepatocarcinogen beta-blocker DL-1-(2-nitro-3-methyl-phenoxy)-3-tert-butylamino-propan-2-ol (DL-ZAMI 1305) by the initiation-promotion protocol of Pereira. Female Wistar rats were given a single dose 150 mg/kg of body weight of DL-ZAMI 1305 by gavage 24 hours before or 24 hours after partial hepatectomy. One week later rats were given phenobarbital (0.05%) in the diet for a period of 7 weeks. DL-ZAMI 1305-treatment resulted in the appearance of gamma-glutamyltranspeptidase foci and of other preneoplastic lesions in all animals. Preneoplastic lesions were also present in a fraction of DL-ZAMI 1305-treated animals not subjected to partial hepatectomy, whether given or not phenobarbital. Results obtained in a separate experiment demonstrated that DL-ZAMI 1305-treatment inhibits cell proliferation and induces DNA damage in the regenerating rat liver. The results of this study clearly demonstrated that the beta-blocker DL-ZAMI 1305 is an initiating carcinogen for the liver of female Wistar rats.

Early liver alterations induced by the sex-dependent hepatocarcinogen beta-blocker ZAMI 1305

Liver alterations occurring after 1, 6 or 10 days of treatment with the hepatocarcinogen beta-blocker DL-1-(2-nitro-3-methyl-phenoxy)-3-tert-butyl-amino-propan-2-ol (ZAMI 1305) were studied in male and female Wistar rats. In agreement with its sex-dependent oncogenicity, ZAMI 1305 administration causes DNA damage in the liver of the female but not of the male rat, with the only exception of 2 out of 4 males treated for 6 days. In female rat, the amount of DNA damage increases from 1 to 6 days of treatment, being unchanged at 10 days; a small portion of DNA is however damaged. ZAMI 1305 administration to female rat induces also: (i) an increase of the relative liver weight, of the DNA and RNA synthesizing activity; (ii) a decrease of the number of hepatocytes in mitosis; (iii) a minimal oval cell hyperplasia. When the same parameters were studied in ZAMI 1305-treated male rats, they were unaffected or changed to a less extent in respect to female rats.