Lack of promoting activity of 7-methoxy-2-nitro-naphtho-[2,1-b]furan (R7000) in a medium-term rat liver bioassay.

Among the nitro-naphthofurans, 7-methoxy-2-nitro-naphtho[2,1-b]furan (R7000) has proved to be a very potent mutagen that causes sarcomas at the subcutaneous injection site and carcinomas in the forestomach after p.o. administration. In the present study, possible promoting activity for diethylnitrosamine (200 mg/kg, i.p.)-initiated liver carcinogenesis was assessed in rats. R7000 dissolved in 5% ethanol solution at doses of 10 or 50 mg/l given as the drinking water for 6 weeks did not enhance development of pre-neoplastic glutathione S-transferase placental form positive foci. Thus, it was concluded that R7000 may not be carcinogenic for the rat liver under the present experimental conditions.