| Abstract: | Aberrant crypt foci (ACF) are putative peneoplastic lesions that develop after treatment of animals with colon carcinogens, including cooked-meat heterocyclic amines such as 2-amino-3-methylimidazo4,5-f]quinoline (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 carcinogen dose had an average of 4.4 ACF/colon and an average of 3.2 crypts/focus. The DNA from these ACF was amplified by the polymerase chain reaction and analyzed by 3′-primer mismatch and direct sequencing methods for mutations in the Ki-ras proto-oncogene. Of the 37 IQ-induced ACF screened, three contained a GGT→GAT mutation in codon 12 and one contained a GGC→GCC mutation in codon 13. The approximately 11% frequency of mutation in IQ-induced ACF is within the range of previous ACF studies of azoxymethane, which reported a 7–37% incidence of Ki-ras mutaion. These findings suggest that for both compounds, ras mutations occur during early stages of colorectal tumorigenesis. However, while ras mutations can be detected with increasing frequency in azoxymethane-induced adenomas and carcinomas, they are reportedly absent in IQ-induced colon tumors. Thus, for IQ and related compounds additional factors (possibly increased cell proliferation) may be important in the later stages of colorectal tumorigenesis. © 1995 Wiley-Liss Inc. |
