Studies of Sequence-Specific DNA Binding, DNA Cleavage, and Topoisomerase I Inhibition by the Dimeric Chromomycin A₃ Complexed with Fe^II

Abstract

Chromomycin A3 (Chro) has been evidenced to exhibit much higher binding affinity toward Fe(II) 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 approximately 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 TopI 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.

Modification of the antibiotic olivomycin I at the 2′-keto group of the side chain. Novel derivatives, antitumor and topoisomerase I-poisoning activity

“…Some undesirable problems (that is, rapid diffusion of the drug from the Topo-I-DNA complex and tumor resistance to these drugs) justify the importance of a search for other types of drugs that act on Topo-I by a different mode of action. 11 The discovery in this study that olivomycin I and its analogs are effective Topo-I poisons and are endowed with antitumor activity and lesser side effects in mice than the parent drug extends the potential of this class of antibiotics as novel drug candidates for further (pre)clinical investigations.…”

The impact of spermine competition on the efficacy of DNA-binding Fe(II), Co(II), and Cu(II) complexes of dimeric chromomycin A3

“…In stark contract to the formation of Mg(II)-, Co(II)-, or Fe(II)-containing dimeric Chro complexes that showed an inversion of the band at about 275 nm during their formation, the formation of Cu(II)-containing dimeric Chro complex caused the negative peak to be redshifted to 290 nm (Supplementary data, Fig. 1SB) [4,34]. Square planar and tetragonal are the preferred geometries for Cu(II) coordination in several Cu(II)-coordinated complexes when Cu(II) is ligated by ligands via carboxylate oxygen or imidazole nitrogen [36][37][38][39].…”

“…The ionic radius of an octahedrally coordinated high-spin Fe(II) would be 92 pm, exceeding the maximum requirement of the ionic radii (85 pm). The spin state of Fe(II) in Fe II (Chro) 2 was therefore believed to be in a diamagnetically low-spin state [4,25,35] and the geometry around Fe(II) was proposed as an octahedral [4] (Fig. 6A).…”

“…This drug contains di-and trisaccharide moieties connected to a b-ketophenol chromophore via O-glycosidic bonds disposed in a 2, 6 relationship about the anthracene ring, with the disaccharide at the two position and the trisaccharide attached at the 6 position ( Fig. 1) [4]. Chro has been used to treat several malignant diseases, such as metastatic testicular tumors, and is of limited use in the treatment of hypercalcemia [2,5].…”

“…The antitumor properties of Chro can be attributed to its inhibitory effects on replication and transcription during cell proliferation [6]. Chro has also demonstrated the ability to downregulate the expression of many cancer-related genes by blocking binding of Sp1 to P1 promoter region to regulate cell proliferation [4,7]. Chro is also a potent inhibitor of neuronal apoptosis induced by oxidative stress, indicating that Chro could potentially serve as a neurological therapy [8].…”