CYCLOPENTA[CD]PYRENE-INDUCED TUMORIGENICITY, KI-RAS CODON-12 MUTATIONS AND DNA-ADDUCTS IN STRAIN A J MOUSE LUNG/

Cyclopenta[cd]pyrene (CPP) is a ubiquitous cyclopenta-fused polycyclic aromatic hydrocarbon. CPP is highly genotoxic in bacterial and mammal ian systems inducing gene mutations, sister chromatid exchanges and mo rphological transformation. CPP is a mouse skin carcinogen, a mouse sk in tumor initiator and induces pulmonary tumors in newborn mice. We ha ve examined the tumorigenic activity of CPP in strain A/J mice, have d etermined the formation and persistence of CPP-induced DNA adducts in lung tissue, and analyzed the mutational spectrum in the Ki-ras oncoge ne from CPP-induced tumors. CPP dissolved in tricaprylin was administe red by i.p. injection to male A/J mice (20 mice/dose) at 0, 10, 50, 10 0 and 200 mg/kg. Animals were killed 8 months later and the lungs remo ved, fixed, and surface adenomas enumerated. CPP proved to be highly t umorigenic in A/J mice in terms of inducing lung adenomas. The observe d tumor multiplicities (Lung adenomas/mouse) were: 97.7 +/- 28.7 at 20 0 mg/kg, 32.8 +/- 15.4 at 100 mg/kg, 4.63 +/- 2.11 at 50 mg/kg and 0.5 8 +/- 0.82 at 10 mg/kg. Tricaprylin-treated controls produced 0.60 +/- 0.58 lung adenomas/mouse. Groups of mice treated under the same dosin g conditions as those in the tumor studies were killed 1, 3, 7, 14 and 21 days after treatment. The lungs were removed, and the DNA was subj ected to DNA adduct analysis by the P-32-postlabeling method. Total CP P- DNA adducts in mouse lung peaked at day 3 with 5870 amol CPP adduct s/mu g DNA after a single dose of 200 mg/kg. DNA adduct levels decreas ed to 1800 amol CPP adducts/mu g DNA at day 21. Qualitative DNA adduct analysis revealed four major adducts and one minor adduct. Co-chromat ography of the lung DNA from CPP-treated mice with calf thymus DNA tre ated,vith CPP-3,4-oxide indicated that all DNA adducts were oxide deri ved and comparison with CPP-3,4-oxide-treated polydeoxyguanylic acid s uggests that almost all of these adducts are CPP-3,4-oxide-2'-deoxygua nosine adducts. Ki-ras codon 12 mutation analysis of the DNA from tumo rs taken from the 100 and 200 mg/kg CPP dose groups demonstrated the f ollowing patterns: GGT-->CGT (50%); GGT-->GTT (15%); GGT-->TGT (25%); GGT-->GAT (10%). We conclude that CPP is highly tumorigenic in the A/J mouse lung adenoma model, being five times more active than benzo[a]p yrene. This is unlike the result of CPP as a mouse skin tumorigen or t umor initiator in which CPP is considerably less potent than benzo[a]p yrene. The increased activity of CPP may be related to the unique indu ction of the GGT-->CGT, Ki-ras codon 12 mutation. This conclusion is s upported by related results observed with another aromatic hydrocarbon , benz[j]-aceanthrylene.