Carcinogenicity of cyproterone acetate in the mouse.

The synthetic progestin cyproterone acetate (CPA) has been shown to be a hepatocarcinogen in the rat, but little is known of its effects in mice. A 52 week CPA study in the mouse strain C57Bl/10J has been reported not to produce liver tumours, although CPA induced significant liver enlargement and induction of the mixed function oxidase CYP3A. The present study is a further investigation of the effects of CPA in mice of the C57Bl/10J strain dosed for 104 weeks. A group of 40 mice/sex were fed 800 p.p.m. CPA in the diet for 104 weeks with a control group of eight/sex. Mortality was high in females after 40 weeks due to hormonal effects in the uterus; no female and only four CPA-dosed males survived to 104 weeks. Liver cell hypertrophy with increased fat and glycogen and single cell or small multifocal areas of hepatocellular necrosis were universal. Proliferating cell nuclear antigen demonstrated an increase in proliferating cells within tumours and within the non-tumour bearing liver of CPA-dosed mice compared with normal livers of control mice. Hepatocellular tumours developed in 44% of males and 22% of females dosed with CPA, compared with none in the controls (the strain has a low, <10%, incidence of spontaneous liver tumours compared with other mouse strains). In addition, over 85% of both sexes dosed with CPA developed adenomatous polyps of the pyloric antrum and pancreatic islet cell hyperplasia, shown by immunostaining to be chiefly of insulin-secreting cells. Adrenocortical atrophy was also observed with other widespread effects in the endocrine system. The results suggest that the liver tumours, as in the rat, are likely to be related to effects on liver growth and mitogenesis. It is suggested that the tumours of the stomach and the pancreatic islet cell hyperplasia are manifestations of the effects of CPA in the endocrine system.

Expression of growth factors and growth factor receptors in the liver of C57BL/10J mice following administration of phenobarbitone.

Liver enlargement is a common feature of non-genotoxic rodent hepatocarcinogens administered at high doses. In the present study, the expression of growth factors and growth factor receptors was investigated in the C57BL/1OJ mouse during liver enlargement induced by the non-genotoxic rodent hepatocarcinogen, sodium phenobarbitone (PB). Male mice were dosed 0-2500 p.p.m. PB in the diet for 1, 4 and 13 weeks. There was a dose and time dependent increase in liver weight. Hepatocyte replication, assessed by incorporation of bromodeoxyuridine, was increased in a dose-dependent manner at week 1 only (18-fold increase at 2000 p.p.m.) and was predominantly localized in the centrilobular region. At week 1, PB (2500 p.p.m.) caused transient increases in transforming growth factor alpha (TGFalpha) and epidermal growth factor receptor (EGFR) and decreases in transforming growth factor beta1 (TGF-beta1) and mannose-6-phosphate receptor (M6PR) in centrilobular hepatocytes which correlated with the replication in this region. At week 1, there was an increase in both hepatocyte growth factor (HGF) and hepatocyte growth factor receptor (HGFR) which colocalized in centrilobular hepatocytes; in some mice or periportal hepatocytes in other mice. After 13 weeks, HGF and HGFR were localized in the cytoplasm of centrilobular hepatocytes of all mice but exhibited a differential intracellular distribution across the lobule. At 2500 p.p.m. PB, EGFR and HGFR mRNA were essentially unchanged over the 13 week dosing period whilst M6PR mRNA was increased 2- to 4-fold. At 2500 p.p.m. PB, EGFR protein levels from immunoblots showed a consistent decrease over the 13 weeks whilst M6PR and HGFR protein levels were essentially unchanged. The protein level and mRNA data for EGFR suggest post-transcriptional modification. Thus, phenobarbitone caused transient replication of hepatocytes and modulation of growth stimulatory and inhibitory factors and their associated receptors in terms of overall levels and regional distribution in the liver.

Lifetime carcinogenicity study of 1- and 2-naphthylamine in dogs.

Groups of male and female beagle dogs were given daily doses of 400 mg of various mixtures of naphthylamines for up to 109 months. Survivors were killed at 128 months. A variety of pathological conditions was diagnosed, but the only effect related to treatment was the induction of bladder neoplasms. All dogs which received pure 2-naphthylamine developed transitional-cell carcinomas of the bladder within 34 months. Two of 8 dogs receiving 6% 2-naphthylamine in 1-naphthylamine developed early carcinoma and 2/8 dogs receiving 0.5% 2-naphthylamine in 1-naphthylamine developed haemangioma of the bladder. Some of the dogs receiving 1-naphthylamine (total dose 950 g) and the controls had focal cystitis or hyperplasia, but no neoplasia of the bladder. These results confirm the carcinogenicity of 2-naphthylamine to dogs. No carcinogenic effect of 1-naphthylamine was observed, indicating that it is at least 200 times less potent as a carcinogen than 2-naphthylamine. The incidence of bladder cancer in dogs fed mixtures of both naphthylamines explains why previous experimental and epidemiological studies of impure 1-naphthylamine have revealed carcinogenicity.