Specific inhibition of ICAM-1 expression mediated by gene targeting with triplex-forming oligonucleotides

Selected sequences in the DNA double helix can be specifically recognized by oligonucleotides via hydrogen bonding interactions. The resulting triple helix can modulate DNA metabolism and especially interfere with transcription in a gene-specific manner. To explore the potential of triplex-forming oligonucleotides (TFOs) as gene repressors, a TFO was designed to target a 16-bp sequence within the third intron of the human intercellular-adhesion molecule-1 (ICAM-1) gene, which plays a key role in initiating inflammation. TFO binding to its ICAM-1 target sequence was characterized in vitro and also demonstrated in cell nuclei with the set-up of a novel magnetic capture assay, which represents a general experimental approach to the detection of specific TFO binding and to the determination of the accessibility of a given genomic DNA locus. In a human keratinocyte cell line (A431), we observed that: (i) the ICAM-1 target sequence in the chromatin context within the nuclei is still available for triplex formation and (ii) TFO inhibits sequence and gene-specific interferon-gamma-induced ICAM-1 surface expression. Collectively, the data demonstrate effective and specific inhibition of ICAM-1 expression by TFO treatment and support the view that triplex-mediated gene targeting might be a valuable technique for anti-inflammatory or anticancer strategies.