Early detection of 2-amino-1-methyl-6-phenylimidazo (4,5-b)pyridine(PhIP)-induced mutations within the Apc gene of rat colon

Abstract

A large proportion of human cancers result from exposure of individuals to environmental or occupational carcinogens. The early detection of carcinogen-induced mutations is a prerequisite for the identification of individuals at risk for developing cancer. Short G-rich repetitive sequences have been previously identified as hot-spots for frameshift mutagenesis induced by a large variety of carcinogens belonging to several families of widespread environmental pollutants. In order to test if these sequences, when mutated, might serve as biomarkers for carcinogen exposure, we designed a sensitive PCR-based strategy that allows the detection of rare mutational events within a whole genome. 2-Amino-1-methyl-6-phenylimidazo(4,5-b)pyridine (PhIP), the most abundant carcinogenic heterocyclic amine generated in cooked meat, induces mammary and colon carcinoma in F344 rats. About 25% of male rats exposed to 400 p.p.m. PhIP in the diet for >43 weeks present colon tumors with specific -1G mutations within 5'-GGGA-3' sequences of the APC: gene. Using our PCR assay we have assessed the occurrence of such specific events in rats exposed to PhIP for only 1, 2, 4 and 6 weeks. A specific amplification signal was already observed in the 1 week-treated population and increases in a treatment time-dependent manner. These data validate this approach for the early detection of mutations and demonstrate its usefulness for molecular epidemiology and early diagnosis.

Genetic analysis of colon tumors induced by a dietary carcinogen PhIP in CYP1A humanized mice: Identification of mutation of β‐catenin/Ctnnb1 as the driver gene for the carcinogenesis

“…Previous studies using different models established several potential mechanism of PhIP‐induced carcinogenesis. Using cultured cells and rats, it was found that PhIP metabolite attacks DNA, forms dG‐C8‐PhIP adduct, and subsequently induces G to C mutation or G deletion, which was suggested to result in the expression of truncated APC protein or dominant active mutant Ctnnb1 and lead to the activation of Wnt signaling . Notably, a ‐1G deletion in a G stretch such as 5'‐GGGA‐3' in Apc gene was found in 4 out of 8 PhIP‐induced F344 rat colon tumors causing reading frame shift and truncation .…”

A gene marker panel covering the Wnt and the Ras-Raf-MEK-MAPK signalling pathways allows to detect gene mutations in 80% of early (UICC I) colon cancer stages in humans

“…heterocyclic aromatic amines, HCA) may remain quite a long time in direct contact with the epithelial cells in the distal colon and rectum mucosa prior to evacuation, thus facilitating the uptake of these compounds in this particular part of the gastrointestinal tract. Furthermore, it has been shown that male rats fed 2-amino-1-methyl-6-phenylimidazo [4,5-b]pyridine (PhIP), the most abundant HCA in cooked meat, develop colon tumours, in which specific-1G mutations within 5 0 -GGGA-3 0 sequences of the APC gene were detected [39,40]. Moreover, the same authors suggested that these specific mutations could be useful for mutational fingerprinting of human cancers.…”

Genomic analysis of alachlor-induced oncogenesis in rat olfactory mucosa

“…BHP is, in addition, associated with mutations of ␤-catenin phosphorylation sites in the same model system (70). In contrast, the carcinogenic amine 2-amino-1-methyl-6-phenylimidazo(4,5-b)pyridine, associated with cooked meats, caused Apc mutations with as little as 1 wk of exposure in rats (10). In our experiments, nuclear localization of ␤-catenin appeared to be associated with the progression, rather than the initiation, of alachlor-induced olfactory neoplasms, as nuclear localization of ␤-catenin was not found in early lesions.…”