In vivo transcription of a progesterone-responsive gene is specifically inhibited by a triplex-forming oligonucleotide

Oligonucleotides provide novel reagents for Inhibition of gene expression because of their high affinity binding to specific nucleotide sequences. We describe a 38 base, single-stranded DNA that forms a triple helix or ‘triplex’ on progesterone response elements of a target gene. This triplex-forming oligonucleotide binds with a Kd= 100 nM at 37°C and physiological pH, and blocks binding of progesterone receptors to the target. Furthermore, It completely inhibited progesterone receptor-dependent transcription In vitro. To approach In vivo conditions, triplex-forming ollgonucleotides were tested In cell transfection studies. The derivation of the oligonucleotides with cholesterol enhanced their cellular uptake and nuclear concentration by at least four-fold. The cholesterol-derivatized triplex-forming oligonucleotide specifically inhibited transcription of the PRE-containing reporter gene in cells when applied to the medium at micromolar concentrations. This Is the first demonstration of steroid-responsive gene inhibition by triplex formation and joins the growing body of evidence Indicating that oligonucleotides have therapeutic potential.