COMPARATIVE 2-STAGE CANCER TESTS OF ETHYLENE-OXIDE, N-(2-HYDROXYETHYL)-N-NITROSOUREA AND X-RAYS

Mutagenicity tests have shown that the potencies of ethylene oxide and other alkylating agents relative to that of low-LET ionising radiatio n are approximately the same in different biological systems. In the p resent study this relationship, the radiation-dose equivalence (''rad- equivalence'') of doses of genotoxic chemicals, was tested for the ind uction of tumours in skin and lung of mice using different initiation- promotion protocols. The initiators used were X-rays, ethylene oxide a nd N-(2-hydroxyethyl)-N-nitrosourea (HOENU). This short-term treatment was followed by treatment with the ''promoters'' 12-O-tetradecanoylph orbol 13-acetate (TPA) and carbon tetrachloride. Unexpectedly, the ani mals treated with carbon tetrachloride did not show treatment-related liver tumours, but exhibited precocious death, mostly with lung tumour s. According to estimates from in vitro tests the total in vivo dose f rom exposure to 400 ppm for 4 x 5 h corresponds to 700 rad-equivalents . Although still with great statistical uncertainty, this ratio is sup ported by the observed time-dependent frequencies of animals with papi llomas (in the TPA series) and lung tumours (in the carbon tetrachlori de series). Animals treated with HOENU exhibited high incidences of tu mours of both these types in approximate agreement with the higher rad -equivalence of the treatments with this compound.