A cell-permeable Streptomyces-derived antibiotic that contains two bicyclic peptide-linked quinoxalines and acts as a sequence-specific DNA bisintercalator. Echinomycin at 10 µM is shown to inhibit HIF-1 and Myc/Max DNA binding activities in U251 and MCF-7 nuclear extracts by >90%, while exhibiting little effect against the binding of AP-1 or NF-κB to their respective DNA targets that lack the 5'-ACGTG-3' core structure in cell-free EMSA assays. Reversibly inhibits hypoxia-induced HIF-1 transcription activity in an HRE promoter-based reporter assay in U215 cells (EC₅₀ = 1.2 nM) and is of no effect against SV40 promoter-driven transcription activity. Despite echinomycin's in vitro apoptosis-inducing activity and the initial report of its in vivo antitumor effect in mice, clinical trials have not yet resulted in promising data regarding its therapeutic efficacy in cancer treatment.