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 develop after treatment of animals with colon carcinogens, including cooked-meat heterocyclic amines such as 2-amino-3-methylimidazo[4,5-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 mutation. 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.
Tachino
N
N
Department of Environmental Biochemistry, University of Hawaii, Honolulu.
Hayashi
R
R
Liew
C
C
Bailey
G
G
Dashwood
R
R
D000818:Animals; D001483:Base Sequence; D002273:Carcinogens / Q000633:toxicity*; D002471:Cell Transformation, Neoplastic; D003106:Colon / Q000187:drug effects / Q000378:metabolism / Q000473:pathology*; D017931:DNA Primers; D011905:Genes, ras; D008297:Male; D008969:Molecular Sequence Data; D016296:Mutagenesis; D017354:Point Mutation; D016133:Polymerase Chain Reaction; D011804:Quinolines / Q000633:toxicity*; D051381:Rats; D011916:Rats, Inbred F344
D002273:Carcinogens; D017931:DNA Primers; D011804:Quinolines; C029216:2-amino-3-methylimidazo(4,5-f)quinoline