RNASE H-INDEPENDENT ANTISENSE ACTIVITY OF OLIGONUCLEOTIDE N3'-]P5' PHOSPHORAMIDATES

Oligonucleotide N3'-->P5' phosphoramidates are a new and promising cla ss of antisense agents. Here we report biological properties of phosph oramidate oligonucleotides targeted against the human T cell leukemia virus type-1 Tax protein, the major transcriptional transactivator of this human retrovirus. Isosequential phosphorothioate oligodeoxynucleo tides and uniformly modified and chimeric phosphoramidate oligodeoxynu cleotides containing six central phosphodiester linkages are all quite stable in cell nuclei, The uniformly modified anti-tax phosphoramidat e oligodeoxynucleotide does not activate nuclear RNase H, as was shown by RNase protection assay, In contrast, the chimeric phosphoramidate- phosphodiester oligodeoxynucleotide is an efficient activator of RNase H, The presence of one or two mismatched nucleotides in the phosphodi ester portion of oligonucleotides affected this activation only neglig ibly, When introduced into tax-transformed fibroblasts ex vivo, only t he uniformly modified anti-tax phosphoramidate oligodeoxynucleotide ca used a sequence-dependent reduction in the Tax protein level, Neither the chimeric phosphoramidate nor the phosphorothioate oligodeoxynucleo tides significantly reduced tax expression under similar experimental conditions.