CONTRIBUTION OF SEQUENCE AND PHOSPHOROTHIOATE CONTENT TO INHIBITION OF CELL-GROWTH AND ADHESION CAUSED BY C-MYC ANTISENSE OLIGOMERS

c-myc is overexpressed in glioblastoma multiforme, the most common for m of brain tumor. To find a suitable target for in vivo antisense ther apy of gliomas, we investigated the biological effects on the human gl ioma cell line, U87MG, of antisense oligonucleotides targeted against the translation start site of c-myc mRNA. Parameters examined included c-myc protein level, cell proliferation, and cell adhesion to substra tum. Oligonucleotides were administered by electroporation as capped p hosphorothioates. Antisense oligomers caused a reduction in c-myc prot ein expression, loss of cell adhesion to plastic, and complete growth inhibition. Various control sequences, including sense, scrambled, and three-base mismatched oligomers, were also tested. Some of the contro ls retained a dG quartet found in the antisense sequence. Reduction in c-myc protein and cell growth and loss of cell adhesion were specific to the antisense sequence. Surprisingly, fully thioated antisense and scrambled sequences, either containing or lacking a dG quartet, were equally inhibitory to both cell growth and adhesion. Loss of cell adhe sion was observed with only phosphorothioate-containing oligomers, not with either their phosphodiester or nuclease-resistant PA congeners, and was completely reversed when cells were plated onto fibronectin. T hese results demonstrate that a commonly used c-myc antisense oligomer also displays dramatic, sequence- but not antisense-specific effects on cell proliferation and cellular adhesion, depending on the backbone .