Mutations in the K-ras oncogene induced by 1,2-dimethylhydrazine in preneoplasic and neoplastic rat colonic mucosa

These experiments were conducted to determine whether point mutations activating K-ras or H-ras oncogenes, induced by the procarcinogen 1,2-dimethylhydrazine (DMH), were detectable in preneoplastic or neoplastic rat colonic mucosa. Rats were injected weekly with diluent or DMH at 20 mg/kg body wt for 5, 10, 15, or 25 wk, killed, and their colons dissected. DNA was extracted from diluent-injected control animals, histologically normal colonic mucosa from carcinogen-treated animals, and from carcinomas. Ras mutations were characterized by differ-ential hybridization using allele-specific oligonucleotide probes to polymerase chain reaction-amplified DNA, and confirmed byDNA sequencing. While no H-ras mutations were detectable in any group, K-ras (G to A) mutations were found in 66 % of DMH-induced colon carcinomas. These mutations were at the second nucleotide of codons 12 or 13 or the first nucleotide of codon 59 of the K-ras gene. The same type of K-ras mutations were observed in premalignant colonic mucosa from 2 out of 11 rats as early as 15 wk after beginning carcinogen injections when no dysplasia, adenomas, or carcinomas were histologi-cally evident, suggesting that ras mutation may be an early event in colon carcinogenesis. (J. Clin. Invest. 1991. 87:624-630.) Key words: ras mutations * colon cancer * polymerase chain reaction (PCR) * DNA sequencing * oligonucleotide probe hybridizatio