Antisense treatment directed against mutated Ki-ras in human colorectal adenocarcinoma

Background-Kirsten ras (Ki-ras) mutations are common in gastrointestinal ca ncer and one codon 12 mutation, glycine to valine, is particularly aggressi ve in colorectal cancer. Aims-To investigate if this valine point mutation could be targeted with an tisense oligonucleotides and to determine the efficacy of any antisense/mRN A interaction. Methods-Twenty nine antisense oligonucleotides were screened against target and control Ki-ras RNA in a cell free system and against target and contro l cell lines in culture. Results-The activity and specificity of the oligonucleotides varied. Result s for the individual oligonucleotides were consistent in a cell free model and in cell culture using two different uptake promoters. Only one oligonuc leotide was specific in its cleavage of target Ki-ras mRNA in the cell free system and appeared specific in cell culture, although changes in Ki-ras m RNA and protein expression following a single treatment could not be detect ed. Experiments in the cell free system showed that the point mutation is r elatively inaccessible to oligonucleotides. Other sites on the Ki-ras RNA m olecule, away from the point mutation, can be targeted more effectively. Conclusions-Successful targeting of the clinically relevant Ki-ras point mu tation with antisense oligonucleotides is difficult because of RNA structur e at the mutated site and is inefficient compared with other sites on the K i-ras mRNA.