Mutation Research 557 (2004) 29–40 Adenomatous polyposis coli truncation mutations in 2-amino- 1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP)-induced intestinal tumours of multiple intestinal neoplasia mice Linda Møllersen, Rose Vikse 1 , Åshild Andreassen 1 , Inger-Lise Steffensen, Arne Mikalsen, Jan Erik Paulsen, Jan Alexander ∗ Department of Food Toxicology, Division of Environmental Medicine, Norwegian Institute of Public Health, P.O. Box 4404 Nydalen, N-0403 Oslo, Norway Received 15 April 2003; received in revised form 25 August 2003; accepted 27 September 2003 Abstract The heterocyclic amine 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) induces intestinal tumours in C57BL/6J- multiple intestinal neoplasia (Min)/+ mice. The main mechanism for PhIP-induced tumour induction in Min/+ mice is loss of the wild-type adenomatous polyposis coli (Apc) allele, i.e. loss of heterozygosity (LOH). In this study, single injections of either 10, 17.5 or 25 mg/kg PhIP on days 3–6 after birth all increased the mean number of small intestinal tumours two to three-fold, from 37.7 in controls to 124.8 in the PhIP-treated Min/+ mice. In total, we analysed 292 small intestinal tumours and 253 of these had LOH. The frequency of LOH in the Apc gene was 88, 93, 83 and 84% in tumours of 0, 10, 17.5 and 25mg/kg PhIP-treated mice, respectively. Therefore, these lower doses of PhIP did not reduce the frequency of LOH, as found in our previous study with a single injection of 50 mg/kg PhIP (Mutat. Res. 1–2 (2002) 157). In the second part of this study, we wanted to characterise Apc truncation mutations from tumour samples apparently retaining the Apc wild-type allele from this and two previous experiments with PhIP-exposed Min/+ mice. In the first half of exon 15 in Apc, we verified 25 mutations from 804 tumour samples of PhIP-treated mice. Of these were 60% G → T transversions, and 16% G deletions, indicating that these are the predominant types of PhIP-induced truncation mutations in the Apc gene in Min/+ mice. Most of the mutations were located between codon 989 and 1156 corresponding to the first part of the -catenin binding region. We also identified two Apc truncation mutations from 606 spontaneously formed intestinal tumours from untreated Min/+ mice, one C → T transition and one T insertion, which were different from those induced by PhIP. © 2003 Elsevier B.V. All rights reserved. Keywords: Apc; Mutation; PhIP; Min mouse; Intestine Abbreviations: APC/Apc, adenomatous polyposis coli (hu- man/murine); FAP, familial adenomatous polyposis; IVSP, in vitro synthesised protein; LOH, loss of heterozygosity; Min, multi- ple intestinal neoplasia; MCR, mutation cluster region; PhIP, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine ∗ Corresponding author. Tel.: +47-22042253; fax: +47-22042243. E-mail address: jan.alexander@fhi.no (J. Alexander). 1 These authors have contributed equally to this work. 1. Introduction High consumption of well-done red meat is associ- ated with an increased risk of colorectal cancer [1,2]. Fried meat contains heterocyclic aromatic amines, which are carcinogenic in rodents [3]. 2-Amino-1-me- thyl-6-phenylimidazo[4,5-b]pyridine (PhIP), the most abundant heterocyclic amine in red meat [4], induces 1383-5718/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.mrgentox.2003.09.008