Specific inhibition of formation of transcription complexes by a calicheamicin oligosaccharide: a paradigm for the development of transcriptional antagonists.

Sequence-specific DNA ligands that antagonize DNA-protein interactions represent a potentially powerful means of modulating gene expression. Calicheamicin gamma 1I, a member of the DNA-cleaving enediyne class of anticancer antibiotics, binds to specific DNA sequences through an aryltetrasaccharide domain. To take advantage of this unique sequence-specific recognition capability, the methyl glycoside of the aryltetrasaccharide of calicheamicin gamma 1I (CLM-MG) was used to investigate the ability of glycoconjugate DNA ligands to inhibit DNA-protein interactions. CLM-MG inhibits the formation of DNA-protein complexes at micromolar concentrations in a sequence-specific manner and rapidly dissociates preformed complexes. CLM-MG also inhibits transcription in vivo with similar sequence specificity. These results suggest a strategy for the development of a class of novel biological probes and therapeutic agents.