Abstract
The carcinogenic potential of long term exposure to 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) was investigated in severe combined immunodeficiency (SCID) mice. A total of 130 female SCID mice, 7 weeks old, were administered 0 (45 mice) or 300 ppm IQ (85 mice) in the diet for 78 weeks. IQ-treatment and control groups were sacrificed at weeks 32, 52, and 78, and examined for tumorigenicity in the colon and other organs. The survival rate was 46% (control group) and 50% (IQ-treatment group) at the termination of the experiment 78 weeks. Tumors in the liver were significantly increased in the 300 ppm-IQ treated mice. Concerning colon cancer development, aberrant crypt foci (ACF), putative pre-cancerous lesions of the colon, were found in all IQ-treated mice at 32, 52, and 78 weeks. The number of ACF was increased in relation to the duration of exposure. The major induction site of ACF was the proximal colon, however, no colon tumors were observed except for an inflammatory polyp. One of the intestinal microflora, Lactobacillus, which was reported to detoxify IQ, was detected in IQ-treated and non-treated mice. Thus IQ showed hepatocarcinogenicity in SCID mice of the present study, but not colon carcinogenicity.
