Enhancement of BALB/c 3T3 cells transformation by 1,2-dibromoethane promoting effect

Two of the most representative halogenated aliphatic hydrocarbons, 1,2-dibromoethane and 1,1,2,2-tetrachloroethane, were tested in the two-stage cell transformation model for analysing the promoting ability. Both of these compounds had previously been found to exert genotoxic effects, probably acting as moderate initiators. BALB/c 3T3 cells were initiated with subtransforming doses of N-methyl-N-nitro-N-nitrosoguanidine or 3-methylcholanthrene and then exposed to a chronic treatment with different non-transforming dosages of the two haloalkanes. 1,1,2,2-Tetrachloroethane did not exert any promoting activity in that system. By contrast, significant promoting effects by 1,2-dibromoethane were observed both in cells treated with N-methyl-N-nitro-N-nitrosoguanidine and in cells treated with 3-methylcholanthrene. Promotion of the transformation process initiated with 3-methylcholanthrene was detectable when confluent cells in the chemical-treated plates were replated in the level-II amplification test. This experimental procedure allowed cells to perform further rounds of replications and transformed foci to became detectable. Results gave evidence for a promoting role of 1,2-dibromoethane in multistep carcinogenesis, probably responsible for the higher oncogenic ability of this compound with respect to 1,1,2,2-tetrachloroethane.