INHIBITION OF TRANSCRIPTION OF THE HUMAN C-MYC PROTOONCOGENE BY INTERMOLECULAR TRIPLEX

Tripler-forming oligonucleotides (TFOs) have been shown to inhibit bot h transcription in vitro and the expression of target genes in cell cu lture by binding to polypurine/polypyrimidine sequences in several hum an gene promoters. The c-myc protooncogene Is overexpressed in a varie ty of human cancers and appears to play an important role in;he prolif eration of these cells. In an attempt to assay the ability of tripler- forming oligonucleotides to inhibit expression of-a target gene in viv o, we have developed a cellular system involving transfection of a c-m yc promoter-driven luciferase reporter plasmid with triplex forming ol igonucleotides targeted to the human c-myc protooncogene. To increase the stability of the TFO, we have used modified phosphorothioate oligo nucleotides. Tripler formation with a modified phosphorothioate oligon ucleotide occurs with approximately equal binding affinity as that see n using a phosphodiester oligonucleotide. Phosphorothioate-modified TF Os targeted to c-myc? inhibit transcription of the c-myc promoter in H eLa cells as demonstrated by a decrease in luciferase expression from a luciferase reporter gene construct, These results suggests that trip ler formation may represent a gene-specific means of inhibiting specif ic protooncogene expression.