H-ras mutations at codon 61 or 13 in tumors initiated with a NO donor in mouse skin

The tumor-initiating activity of nitric oxide (NO) in carcinogenesis was assessed using (±)-(E)-4-methyl-2-[(E)-hydroxyimino]-5-nitro-6-methoxy-3-hexenamide (NOR1), a synthetic NO donor. Topical application of NOR1 followed by 12-O-tetradecanoylphorbol 13-acetate (TPA) treatment twice a week for 20 weeks resulted in the development of papillomas in mice. All of the papillomas examined contained H-ras mutations at codons 61 or 13. At codon 61, CAA-CTA and CAA-TTA mutations were seen in 42/46 and 1/46 of the papillomas, respectively. Three papillomas without a mutation at codon 61 were mutated at codon 13. A GGC-CGC mutation was found in two of these samples while the third possessed a GGC-GTC mutation. These results suggest that NO possesses tumor-initiating activity through a process that induces mutation in H-ras.