DICHLOROACETIC ACID REDUCES HA-RAS CODON-61 MUTATIONS IN LIVER-TUMORSFROM FEMALE B6C3F1 MICE

Dichloroacetic acid (DCA), a disinfection by-product of chlorination f ound in drinking water, is a hepatocarcinogenic in the B6C3F1 mouse. P revious studies have shown that DCA does not significantly alter the i ncidence of Ha-ras codon 61 mutations in male mouse liver carcinomas f rom that observed in spontaneous tumors (similar to 50% have Ha-ras mu tations) but it alters the proportions of mutations that occur in Ha-r as codon 61, Twenty-two tumors were produced in female B6C3F1 mice aft er treatment with 3.5 g DCA per liter of drinking water over a period of 104 weeks. To detect potential Ha-ras mutations in the liver tumor tissue of female B6C3F1 mice, genomic DNA was isolated from tumors tha t had been frozen, The polymerase chain reaction (PCR) and single-stra nded conformational polymorphism (SSCP) was used to screen tumor DNA f or mutations in Ha-ras exon 2. In DNA from liver tumors in female B6C3 F1 mice induced by DCA-treatment we found only one mutation in exon 2 among the 22 tumors analyzed (4.5%). Direct-sequencing of exon 2 revea led a CAA. to CTA transversion in Ha-ras codon 61, The result of this study indicates that tumor formation in DCA-treated female B6C3F1 mice is, therefore, not associated with a mutationally activated Ha-ras co don 61. This result differs from previous results obtained in male B6C 3F1 mice.