In vitro inhibition of rat liver DNA polymerases α and β by β-blockers

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.

Inhibition of DNA and RNA synthesis in rat liver nuclei by oncogenic and non-oncogenic beta-blockers

The beta-blocker DL-1-(2-nitro-3-methylphenoxy)-3-tert-butylaminopropan-2-ol (ZAMI 1305), hepatocarcinogenic to the female rat, and the non-oncogenic beta-blockers DL-1-(2-nitro-5-methylphenoxy)-3-tert-butylaminopropan-2-ol (ZAMI 1327), DL-propranolol, and DL-atenolol were studied for their capacity to interfere with hepatic DNA and RNA synthesis. These moieties inhibit DNA and RNA synthesis, in a dose-dependent fashion, when added in vitro to nuclei isolated from the liver of male or female rats. The inhibition is due to a decrease of the initial rate of synthesis and of the total amount of labeled precursor incorporated into the growing chains. When administered in vivo both the oncogenic ZAMI 1305 and its non-oncogenic isomer ZAMI 1327 inhibit hepatic DNA and RNA synthesis in female rats, as evaluated by the determination of nucleic acids synthesis in liver nuclei isolated from female rats 5 and 15 min after the injection of the drug. No influence on hepatic DNA and RNA synthesis is observed when the molecules are administered to male rats. The in vivo administration of DL-propranolol causes an increase of hepatic DNA and RNA synthesis in male rats, while it is uneffective in female rats.

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

The influence on nucleic acids synthesis and DNA integrity of the D-isomer and of the DL-racemic form of the oncogenic beta-blocker 1-(2-nitro-3-methyl-phenoxy)-3-tert-butylamino-propan-2-ol (ZAMI 1305) and of the non-oncogenic beta-blocker propranolol was tested in vitro and in vivo. Both D- and DL-ZAMI 1305, when added in vitro to nuclei isolated from rat liver, cause inhibition of DNA and RNA synthesis and DNA fragmentation, as evaluated by alkaline sucrose gradient analysis, in a similar dose-dependent fashion. D- and DL-ZAMI 1305 also inhibit to a similar extent the activity of DNA polymerase alpha and beta from regenerating rat liver. When administered in vivo to female rats both D and DL-ZAMI 1305 cause a dose-dependent fragmentation of liver DNA. The D-isomer and DL-racemic form of the non-oncogenic beta-blocker propranolol inhibit DNA and RNA synthesis and cause DNA fragmentation when added in vitro to isolated liver nuclei, being instead without effect when administered in vivo.