INHIBITION OF THE ERB-2 TYROSINE KINASE RECEPTOR IN BREAST-CANCER CELLS BY PHOSPHOROMONOTHIOATE AND PHOSPHORODITHIOATE ANTISENSE OLIGONUCLEOTIDES

Antisense activity against erbB-2 of a variety of sulfur-modified olig onucleotides was examined in a breast cancer cell line which overexpre sses this oncogene, Using a 15 base anti-erbB-2 sequence previously sh own to be effective, various backbone configurations containing phosph oromonothioate or phosphorodithioate linkages were evaluated for anti- sense activity by a two-color flow cytometric assay. This sequence was effective in inhibiting the production of erbB-2 protein when it was configured as a monothioate at each linkage and as an alternating dith ioate/phosphodiester. Both of these compounds were also able to specif ically inhibit erbB-2 mRNA expression, indicative of RNase H-mediated activity. The same sequence protected by either three dithioate or thr ee monothioate linkages at each end was ineffective as an antisense re agent, suggesting that endonuclease activity is a significant determin ant of the stability of oligonucleotides. Finally, the erbB-2 sequence target was shifted in an effort to improve antisense activity. A new lead sequence was identified that was significantly more effective in inhibiting erbB-2 protein levees and retained activity at lower concen trations.