Rapid bioassay methods for carcinogens and modifiers of hepatocarcinogenesis.

It is very important to detect environmental carcinogens in a short period. For this purpose, a rapid bioassay system based on two-step hepatocarcinogenesis has been developed in our laboratory. Rats were initially given a single dose (200 mg/kg) of diethylnitrosamine (DEN) i.p. and, starting 2 weeks later, were treated with test compounds for 6 weeks and then sacrificed, all rats being subjected to a two thirds partial hepatectomy at week 3. Carcinogenic potential was scored by comparing the glutathione S-transferase placental form-positive foci in the liver with those of the corresponding control. More than 90% of hepatocarcinogens showed positivity, and none of the compounds reported as noncarcinogenic demonstrated positivity. Furthermore, this system also detected inhibitory effects. In order to detect nonhepatocarcinogens, other appropriate systems also have been developed, for example, using methylnitrosourea or other multispectrum carcinogens. These rapid bioassay systems are particularly useful for the screening of environmental carcinogens.