ANTILEUKEMIA EFFECT OF C-MYC N3'-]P5' PHOSPHORAMIDATE ANTISENSE OLIGONUCLEOTIDES IN-VIVO

In vitro, uniformly modified oligonucleotide N3'-->P5' phosphoramidate s are apparently more potent antisense agents than phosphorothioate de rivatives. To determine whether such compounds are also effective in v ivo, severe combined immunodeficiency mice injected with HL-60 myeloid leukemia cells were treated systemically with equal doses of either p hosphoramidate or phosphorothioate c-myc antisense or mismatched oligo nucleotides. Compared with mice treated with mismatched oligodeoxynucl eotides, the peripheral blood leukemic load of mice treated with the a ntisense sequences was markedly reduced, and such effects were associa ted with significantly prolonged survival of the antisense-treated mic e. Moreover, with each of three different treatment schedules (100, 30 0, or 900 mu g/day for 6 consecutive days), survival of the phosphoram idate-treated mice was significantly longer than that of the phosphoro thioate-treated mice. Both phosphoramidate and phosphorothioate oligon ucleotides mere efficiently taken up by leukemic cells in vivo and wer e capable of specifically down-regulating c-Myc expression. Moreover, tissue distribution of the phosphoramidate derivatives was undistingui shable from that of the phosphorothioate derivatives. Collectively, th ese studies suggest that phosphoramidate oligonucleotides can serve as potent and specific antisense agents in the treatment of human leukem ia and probably of other malignancies.