H-ras 61st codon activation in archival proliferative hepatic lesions isolated from female B6C3F1 mice exposed to the leukotriene D4-antagonist, LY171883

Abstract

LY171883, a peroxisome proliferator and leukotriene D4-antagonist, induced a statistically significant increase in the number of hepatic lesions in B6C3F1 female mice in a 2 year oncogenicity study at dietary doses of 0.0225% and 0.075%. The mutation frequency and spectrum of the 61st codon of H-ras was determined for 64 independent, archived lesions from the LY171883 2 year oncogenicity study using the polymerase chain reaction (PCR), allele specific oligo hybridization (ASO) and DNA sequencing. Results showed 41 (64%) of these lesions had mutations at the 61st codon (16/21 hepatocellular carcinomas, 4/10 hepatocellular adenomas, 19/26 focal hepatocellular hyperplasias and 2/7 focal hepatocellular atypia). These mutations consisted of 18 C-A transversions, 16 A-G transitions and seven A-T transversions. Compared to the mutation frequency for spontaneously occurring archival B6C3F1 hepatic lesions (41%), the frequency of LY171883 lesions (64%) was significantly higher (P < 0.01). The frequencies of H-ras 61st codon mutations among the LY171883 lesion types (hepatocellular carcinomas 76%, hepatocellular adenomas 40%, focal hepatocellular hyperplasias 73% and hepatocellular atypia 29%) were also significantly different (P = 0.035). In contrast, spontaneous lesions showed no statistical difference in the frequencies of mutation among lesion types (P > 0.5). The mutation spectrum of the LY171883 lesions was not significantly different from the spontaneous spectra. It may be concluded that based on the similarity in mutation spectrum and the increase in mutation frequency, LY171883 may selectively promote spontaneous hepatic lesions containing H-ras 61st codon mutations. In addition, the difference in mutation frequency among lesion types does not support a linear progression of all LY171883 lesions through focal atypia, focal hepatocellular hyperplasias, hepatocellular adenomas and hepatocellular carcinomas.

Metabolic Activation Capacity of Neonatal Mice in Relation to the Neonatal Mouse Tumorigenicity Bioassay

“…The H-ras oncogene point mutation in codon 61, a CAA to AAA transversion (G to T in the nontranscribed strand), is the principal ras-oncogene mutation occurring in both spontaneous and carcinogen-induced B6C3F 1 mouse liver tumors [61][62][63][64][65][66][67][68]. Using enzymatic amplification and confirmation by direct sequencing [69], we have also shown that the liver tumors induced in the neonatal B6C3F 1 mouse by the human aromatic amine carcinogen, 4-aminobiphenyl (4-ABP), had a high proportion (16/16) of the same specific codon 61 mutation (CAA to AAA) in the H-ras oncogene (Table 3).…”

“…mutations were observed in the K-ras or N-ras oncogenes. During development of liver tumors, ras-oncogene activation occurs during focus formation, as well as at later stages (e.g., during adenoma and carcinoma formation) [67].…”

Neonatal Mouse Tumorigenicity Bioassay

“…These sequence alterations in the ras-protooncogenes frequently reflect the mutational specificity of the carcinogen (63,64). It has been found that rus-oncogene activation occurs both at an early stage (eg, during focus formation) as well as at later stages of liver tumor development (eg, during adenoma and carcinoma formation) (65).…”

“…A CAA to AAA transversion (G to T in the nontranscribed strand), in particular, is the principal H-rus point mutation in codon 61 occurring in both the spontaneous and the carcinogen-induced B6C3Fl mouse liver tumors (59,62,(65)(66)(67)(68)(69)(70)(71)(72)(73)(74)(75)(76)(77).…”

Effect of Nitro Orientation on Ras -Protooncogene Mutation in Liver Tumors from 7-Nitrodibenz[ a,h ]anthracene-Treated Mice

“…Most published tumor ras mutational profiles originate from tumors induced in the B6C3F 1 hybrid mouse. With only a few exceptions, it has been found that point mutation in codon 61 of H-ras is the principal ras-oncogene mutation in these tumors (10)(11)(12). The results from our studies on PAHs and their derivatives represent a major exception and may indicate a chemical-class specificity for these mutations.…”