Comparative inhibition of chloramphenicol acetyltransferase gene expression by antisense oligonucleotide analogues having alkyl phosphotriester, methylphosphonate and phosphorothioate linkages.

Several classes of oligonucleotide antisense compounds of sequence complementary to the start of the mRNA coding sequence for chloramphenicol acetyl transferase (CAT), including methylphosphonate, alkyltriester, and phosphorothioate analogues of DNA, have been compared to "normal" phosphodiester oligonucleotides for their ability to inhibit expression of plasmid-directed CAT gene activity in CV-1 cells. CAT gene expression was inhibited when transfection with plasmid DNA containing the gene for CAT coupled to simian virus 40 regulatory sequences (pSV2CAT) or the human immunodeficiency virus enhancer (pHIVCAT) was carried out in the presence of 30 microM concentrations of analogue. For the oligo-methylphosphonate analogue, inhibition was dependent on both oligomer concentration and chain length. Analogues with phosphodiester linkages that alternated with either methylphosphonate, ethyl phosphotriester, or isopropyl phosphotriester linkages were less effective inhibitors, in that order. The phosphorothioate analogue was about two-times more potent than the oligo-methylphosphonate, which was in turn approximately twice as potent as the normal oligonucleotide.