ABSENCE OF KI-RAS MUTATIONS IN EXOCRINE PANCREATIC TUMORS FROM MALE-RATS CHRONICALLY EXPOSED TO GABAPENTIN

Human pancreatic malignancies originating from duct cells most frequen tly demonstrate activation of Ki-ras gene by G-to-A transition at codo ns 12 and 13. Rat pancreatic exocrine tumors more frequently and almos t exclusively derive from acinar cells and thus differ morphologically from human pancreatic neoplasms. Male Wistar rats fed with 2% gabapen tin (1-(aminomethyl)cyclohexane acetic acid) in diet for 2 years devel oped pancreatic exocrine adenomas and adenocarcinomas. To study the mu tations in Ki-ras gene, rat pancreatic proliferative lesions induced b y gabapentin were retrospectively analyzed by PCR amplification of DNA isolated from paraffin sections of formalin-fixed rat pancreatic aden omas and adenocarcinomas, using specific primers for regions encoding exon 1 (codon 12/13) and exon 2 (codon 61). The amplified 110-bp fragm ents of exon 1 and exon 2 were analyzed for mutations at codon 12/13 a nd 61. The results showed Ki-ras mutations at codon 12 in human pancre atic carcinomas. Novel mutations GGT-to-TGT and GGT-to-CGT were detect ed at codon 12 in 1/5 and 2/5 human pancreatic tumors. Rat adenomas or carcinomas induced by gabapentin expressed wild type sequences at cod ons 12, 13 and 61. These findings were confirmed by allele-specific ol igonucleotide hybridization, single-strand confirmation polymorphism o f exon 1 and direct sequencing of exon 1 and exon 2. The absence of mu tations in these rat pancreatic tumors suggests that these tumors do n ot correspond to the human tumors, and that the pathogenesis of this r odent tumor formation may follow different molecular mechanisms.