Studies of sequence-specific DNA binding, DNA cleavage, and topoisomerase inhibition by the dimeric chromomycin A3 complexed with FeII

Chromomycin A(3) (Chro) has been evidenced to exhibit much higher binding affinity toward Fell by forming a highly stable 2:1 drug/metal complex, compared to its structural analogue, mithramycin (Mith). Different properties of the [(ChrO)(2)-Fe-II] complex acting on DNA, such as sequence specificity, DNA cleavage, and topoisomerase I (TopI) inhibition were studied. Kinetic analyses of surface plasmon resonance showed that the affinity of the [(Chro)(2)-Fe-II] complex upon binding to hairpin DNA duplexes containing various tetranucleotide sequences follows the order: GGCC > CGCG > CCGG similar to GCGC > AGCT > ACGT > TGCA > TCGA. According to circular dichroism (CD) studies, most hairpin DNA duplexes appeared to retain their B-type conformations in the presence of the [(Chro)(2)-Fe-II] complex, except the duplex containing the GGCC sequence, which exhibited the features of both A- and B-type DNA. In DNA-cleavage assays, the [(ChrO)(2)-Fe-II] complex was shown to cause single-stranded cleavage of plasmid DNA because of a Fenton-type reaction. DNA cleavage activity of the [(Chro)(2)-Fe-II] complex was increased at low pH. Moreover, the complex was capable of inhibiting Top] activity. The [(Chro)(2)-Fe-II] complex exhibited higher cytotoxicity than the [(Mith)(2)-Fe-II] complex in several cancer cell lines, most likely owing to its more stable dimeric structure and higher DNA-binding affinity. Our results provide significant evidence that the [(Chro)(2)-Fe-II] complex could be promising in terms of its biological applications in the future.