Frequency of Ha-ras-1 gene mutations inversely correlated with furan dose in mouse liver tumors.

Liver tumors were induced in infant male B6C3F1 mice by preweaning administration of furan, either as a single dose of 400 mg/kg body weight or six doses of 200 mg/kg body weight. Six doses of 200 mg/kg furan resulted in an increased incidence and multiplicity of liver tumors relative to the multiple-dose vehicle control group and the single-dose furan group. In the single-dose group, there was an increase in overall tumor multiplicity but not prevalence of liver tumors. After polymerase chain reaction amplification of isolated DNA, slot-blot oligonucleotide hybridization was used to screen for mutations at known mutational hot-spots in the first three exons of Ha-ras-1 (Hras1). The relative frequency of Hras1 activation was 82% in the 28 tumors analyzed from the single-dose group and 32% in the 28 tumors analyzed from the multiple-dose group. The lack of histomorphologic evidence of chronic cytotoxicity in the livers and the pattern of Hras1 activation suggest that a genotoxic mode of action is responsible for at least part of the hepatocarcinogenicity of furan in B6C3F1 mice. These findings confirm previously documented hepatocarcinogenicity of furan in B6C3F1 mice and provide evidence that carcinogen dose may influence the frequency of Hras1 activation in mouse liver tumors.