IN-VIVO TRANSCRIPTION OF A PROGESTERONE-RESPONSIVE GENE IS SPECIFICALLY INHIBITED BY A TRIPLEX-FORMING OLIGONUCLEOTIDE

Oligonucleotides provide novel reagents for inhibition of gene express ion because of their high affinity binding to specific nucleotide sequ ences. 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 K(d) = 100 nM at 37 -degrees-C and physiological pH, and blocks binding of progesterone re ceptors to the target. Furthermore, it completely inhibited progestero ne receptor-dependent transcription in vitro. To approach in vivo cond itions, triplex-forming oligonucleotides were tested in cell transfect ion studies. The derivation of the oligonucleotides with cholesterol e nhanced their cellular uptake and nuclear concentration by at least fo ur-fold. The cholesterol-derivatized triplex-forming oligonucleotide s pecifically inhibited transcription of the PRE-containing reporter gen e in cells when applied to the medium at micromolar concentrations. Th is is the first demonstration of steroid-responsive gene inhibition by triplex formation and joins the growing body of evidence indicating t hat oligonucleotides have therapeutic potential.