Cyclopenta[cd]pyrene-induced tumorigenicity, Ki-ras codon 12 mutations and DNA adducts in strain A/J mouse lung.

Abstract

Cyclopenta[cd]pyrene (CPP) is a ubiquitous cyclopenta-fused polycyclic aromatic hydrocarbon. CPP is highly genotoxic in bacterial and mammalian systems inducing gene mutations, sister chromatid exchanges and morphological transformation. CPP is a mouse skin carcinogen, a mouse skin tumor initiator and induces pulmonary tumors in newborn mice. We have examined the tumorigenic activity of CPP in strain A/J mice, have determined the formation and persistence of CPP-induced DNA adducts in lung tissue, and analyzed the mutational spectrum in the Ki-ras oncogene from CPP-induced tumors. CPP dissolved in tricaprylin was administered by i.p. injection to male A/J mice (20 mice/dose) at 0, 10, 50, 100 and 200 mg/kg. Animals were killed 8 months later and the lungs removed, fixed, and surface adenomas enumerated. CPP proved to be highly tumorigenic in A/J mice in terms of inducing lung adenomas. The observed tumor multiplicities (lung adenomas/mouse) were: 97.7 +/- 28.7 at 200 mg/kg, 32.8 +/- 15.4 at 100 mg/kg, 4.63 +/- 2.11 at 50 mg/kg and 0.58 +/- 0.82 at 10 mg/kg. Tricaprylin-treated controls produced 0.60 +/- 0.58 lung adenomas/mouse. Groups of mice treated under the same dosing 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 subjected to DNA adduct analysis by the 32P-postlabeling method. Total CPP-DNA adducts in mouse lung peaked at day 3 with 5870 amol CPP adducts/micrograms DNA after a single dose of 200 mg/kg. DNA adduct levels decreased to 1800 amol CPP adducts/micrograms DNA at day 21. Qualitative DNA adduct analysis revealed four major adducts and one minor adduct. Co-chromatography of the lung DNA from CPP-treated mice with calf thymus DNA treated with CPP-3,4-oxide indicated that all DNA adducts were oxide derived and comparison with CPP-3,4-oxide-treated polydeoxyguanylic acid suggests that almost all of these adducts are CPP-3,4-oxide-2'-deoxyguanosine adducts. Ki-ras codon 12 mutation analysis of the DNA from tumors taken from the 100 and 200 mg/kg CPP dose groups demonstrated the following 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]pyrene. This is unlike the result of CPP as a mouse skin tumorigen or tumor initiator in which CPP is considerably less potent than benzo[a]pyrene.(ABSTRACT TRUNCATED AT 400 WORDS)