EVIDENCE FOR RAS GENE MUTATION IN 2-AMINO-3-METHYLIMIDAZO[4,5-F]QUINOLINE-INDUCED COLONIC ABERRANT CRYPTS IN THE RAT

Aberrant crypt foci (ACF) are putative preneoplastic lesions that deve lop after treatment of animals with colon carcinogens, including cooke d-meat heterocyclic amines such as 2-amino-3-methylimidazo[4,5-f]quino line (IQ). Male F344 rats given IQ by gavage on alternating days for 2 wk (130 mg/kg body weight) and killed 12 wk after the final carcinoge n dose had an average of 4.4 ACF/colon and an average of 3.2 crypts/fo cus. The DNA from these ACF was amplified by the polymerase chain reac tion and analyzed by 3'-primer mismatch and direct sequencing methods for mutations in the Ki-ras proto-oncogene. Of the 37 IQ-induced ACF s creened, three contained a GGT-->GAT mutation in codon 12 and one cont ained a GGC-->GCC mutation in codon 13. The approximately 11% frequenc y of mutation in IQ-induced ACF is within the range of previous ACF st udies of azoxymethane, which reported a 7-37% incidence of Ki-ras muta tion. These findings suggest that for both compounds, ras mutations oc cur during early stages of colorectal tumorigenesis. However, while ra s mutations can be detected with increasing frequency in azoxymethane- induced adenomas and carcinomas, they are reportedly absent in IQ-indu ced colon tumors. Thus, for IQ and related compounds additional factor s (possibly increased cell proliferation) may be important in the late r stages of colorectal tumorigenesis. (C) 1995 Wiley-Liss, Inc.