Transforming activity of human c-Ha-ras-1 proto-oncogene generated by the binding of 2-amino-6-methyl-dipyrido[1,2-a:3',2'-d]imidazole and 4-nitroquinoline N-oxide: direct evidence of cellular transformation by chemically modified DNA.

An activity that transforms NIH 3T3 cells was generated by the in vitro modification of plasmids containing the human c-Ha-ras-1 proto-oncogene with the synthesized ultimate carcinogen, 2-acetoxyamino-6-methyldipyrido[1,2-a:3',2'-d]-imidazole (N-OAc-Glu-P-1). DNAs isolated from the transformed cells were analyzed by restriction fragment length polymorphism (RFLP) assay using the restriction enzyme Msp I. Of fourteen transformants studied, six contained a mutation in the region of the CCGG sequence of the eleventh and the twelfth codons, in which GG corresponds to the first two nucleotides of the twelfth codon. Transforming activity was also generated by the chemical modification of the plasmids with 4-acetoxyaminoquinoline N-oxide (N-OAc-4AQO). The results clearly indicate that formation of DNA adducts with N-OAc-Glu-P-1 or N-OAc-4AQO causes the induction of transformation of mammalian cells.