MUTAGENIC SPECIFICITY OF 2-AMINO-3-METHYLIMIDAZO[4,5-F]QUINOLINE AND 2-AMINO-1-METHYL-6-PHENYLIMIDAZO[4,5-B]PYRIDINE IN THE SUPF SHUTTLE VECTOR SYSTEM

2 Amino-3-methylimidazo [4,5-f]quinoline (IQ) and 2-amino-l-methyl-6-p henylimidazo[4,5-b]pyridine (PhIP) are heterocyclic amine mutagens/car cinogens formed from the cooking of meat. Here we used the pSP189 shut tle vector developed by Parris and Seidman (Gene, 117: 1-5, 1992) to s tudy and compare the mutation spectre induced by these compounds. pSP1 89 was adducted by reaction with the N-acetoxy derivatives of IQ or Ph IP. P-32-Postlabeling analysis was used to measure the C-g-guanine add uct level and the total adduct levels formed in the plasmid. Plasmids were replicated and mutagenized in repair-proficient [GM0637(SV40)] or repair-deficient XP12Be(SV40)1 human fibroblasts. Resulting inactivat ion mutations in the supF gene were determined by the formation of whi te or light blue colonies on indicator bacteria (carrying a lacZ amber mutation) and cycle sequencing. With both compounds in either cell li ne, 85-93 % of the mutations induced were base substitutions and the r emainder of the mutations were base deletions. The majority of the sub stitution mutations involved a single base, and nearly all base substi tution mutations (>97%) were at guanine. This latter finding is consis tent with the results from P-32-postlabeling showing that both compoun ds adduct to the guanine base with the major adduct being formed at th e C,-guanine position. The predominant mutation found with IQ and PhIP in either cell line was G:C to T:A transversion, followed by G:C to A :T transition, and then G:C to C:G transversion; these mutations accou nted for 59-72%, 19-27%, and 6-14% of total base substitution mutation s, respectively. There was a preference seen with both compounds to in duce mutations at a guanine base having a neighboring guanine or cytos ine (i.e., GG and GC sites). However, despite the striking similarity in the kinds of base substitution mutations induced by IQ and PhIP, th eir mutation spectra were distinct. For example, in repair-proficient cells, 26% of the mutations induced with PhIP, but not with IQ, also i nvolved a GA site, containing the Ei-base pair sequence 5 '-GCAGA3 '. Mutation spectra for IQ and PhIP were also different between repair-de ficient and repair-proficient cells. The findings shown here may serve to be predictive of the kinds of mutations induced by the adducts of IQ and PhIP in oncogenes and tumor suppressor genes altered during het erocyclic amine-induced carcinogenesis.