Ki‐ras mutations in 4‐(methylnitrosamino)‐1‐(3‐pyridyl)‐1‐butanone—initiated and butylated hydroxytoluene—promoted lung tumors in A/J mice

The promotional effects of butylated hydroxytoluene (BHT) on lung tumorigenesis induced by 4‐(methylnitrosamino)‐1‐(3‐pyridyl)‐1‐butanone (NNK) was evaluated in a two‐stage model of lung tumorigenesis in the A/J mouse. Mice were treated in two separate experiments with 1.54 mmol/kg (9.1 mg/mouse) NNK, which induced an average of 8.4 and 9.1 tumors/mouse in the experiments. Animals fed a diet that contained 1 g/kg BHT after administration of the carcinogen in these two experiments demonstrated an increase of the tumor multiplicity by 63% and 43%. Multiplicity of forestomach tumors was not effected by BHT in the diet. No differences in lung tumor morphology were seen as a result of the promoting effect of BHT. Mutations in the Ki‐ras oncogene from lung tumors induced by NNK (19 tumors) or by NNK plus a diet containing BHT (34 tumors) were characterized by polymerase chain reaction, single‐strand conformational polymorphism, and direct sequencing. All 19 NNK‐induced tumors not promoted with BHT contained activated Ki‐ras genes with GC→AT transitions at the second base of codon 12. Only 11 of 34 NNK‐induced and BHT‐promoted tumors (32%) had this characteristic Ki‐ras alteration. These data suggest that the NNK‐initiated mouse lung tumorigenesis pathway, which involves the specific mutation of the Ki‐ras oncogene, is altered to a predominantly non‐ras mechanism when these tumors are promoted by BHT in the diet. ©1994 Wiley‐Liss, Inc.