H-RAS 61ST CODON ACTIVATION IN ARCHIVAL PROLIFERATIVE HEPATIC-LESIONSISOLATED FROM FEMALE B6C3F1 MICE EXPOSED TO THE LEUKOTRIENE D-4-ANTAGONIST, LY171883

LY171883, a peroxisome proliferator and leukotriene D-4-antagonist, in duced a statistically significant increase in the number of hepatic le sions 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 th e 61st codon of H-ras was determined for 64 independent, archived lesi ons from the LY171883 2 year oncogenicity study using the polymerase c hain 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 hepato cellular atypia). These mutations consisted of 18 C-A transversions, 1 6 A-G transitions and seven A-T transversions. Compared to the mutatio n frequency for spontaneously occurring archival B6C3F1 hepatic lesion s (41%), the frequency of LY171883 lesions (64%) was significantly hig her (P < 0.01). The frequencies of H-ras 61st codon mutations among th e LY171883 lesion types (hepatocellular carcinomas 76%, hepatocellular adenomas 40%, focal hepatocellular hyperplasias 73% and hepatocellula r atypia 29%) were also significantly different (P = 0.035). In contra st, spontaneous lesions showed no statistical difference in the freque ncies of mutation among lesion types (P > 0.5). The mutation spectrum of the LY171883 lesions was not significantly different from the spont aneous spectra. It may be concluded that based on the similarity in mu tation spectrum and the increase in mutation frequency, LY171883 may s electively promote spontaneous hepatic lesions containing H-ras 61st c odon mutations. In addition, the difference in mutation frequency amon g lesion types does not support a linear progression of all LY171883 l esions through focal atypia, focal hepatocellular hyperplasias, hepato cellular adenomas and hepatocellular carcinomas.