INHIBITION OF AROMATASE EXPRESSION BY A PSORALEN-LINKED TRIPLEX-FORMING OLIGONUCLEOTIDE TARGETED TO A CODING SEQUENCE

The cytochrome P450 enzyme aromatase (P450arom) is an important target in breast cancer treatment. We have designed a 20-base pyrimidine oli godeoxynucleotide (ODN) which forms a sequence-specific triple helix ( tripler) with a purine-rich tract in the P450arom coding sequence. The psoralen-linked ODN (Pso20T) formed photo-induced cross-linked produc ts with target double-stranded DNA. Cross-linked adducts formed in vit ro between ODNs and P450arom expression constructs were used to transf ect COS and human MCF-7 breast cancer cells. Levels of aromatase trans cripts and enzyme activity were significantly lower in cultures transf ected with Pso20T-treated cDNA relative to controls. Pso20T had a less er inhibitory effect on aromatase expression from a mutant P450arom co nstruct, consistent with predicted effects of the mutations on tripler formation. These results are compatible with tripler-mediated interru ption of transcription within intact cells.