Targeting the ets binding site of the HER2/neu promoter with pyrrole-imidazole polyamides.

Three DNA binding polyamides () were synthesized that bind with high affinity (K(a) = 8.7. 10(9) m(-1) to 1.4. 10(10) m(-1)) to two 7-base pair sequences overlapping the Ets DNA binding site (EBS; GAGGAA) within the regulatory region of the HER2/neu proximal promoter. As measured by electrophoretic mobility shift assay, polyamides binding to flanking elements upstream () or downstream (2 and 3) of the EBS were one to two orders of magnitude more effective than the natural product distamycin at inhibiting formation of complexes between the purified EBS protein, epithelial restricted with serine box (ESX), and the HER2/neu promoter probe. One polyamide, 2, completely blocked Ets-DNA complex formation at 10 nm ligand concentration, whereas formation of activator protein-2-DNA complexes was unaffected at the activator protein-2 binding site immediately upstream of the HER2/neu EBS, even at 100 nm ligand concentration. At equilibrium, polyamide 1 was equally effective at inhibiting Ets/DNA binding when added before or after in vitro formation of protein-promoter complexes, demonstrating its utility to disrupt endogenous Ets-mediated HER2/neu preinitiation complexes. Polyamide 2, the most potent inhibitor of Ets-DNA complex formation by electrophoretic mobility shift assay, was also the most effective inhibitor of HER2/neu promoter-driven transcription measured in a cell-free system using nuclear extract from an ESX- and HER2/neu-overexpressing human breast cancer cell line, SKBR-3.

Sequence-specific DNA recognition by polyamides.

Sequence-specific DNA-binding small molecules that can permeate cells could potentially regulate transcription of specific genes. Simple pairing rules for the minor groove of the double helix have been developed that allow the design of ligands for predetermined DNA sequences. Some of these polyamides have been shown to inhibit specific gene expression in mammalian cell culture.