DNA-Binding Activity of Bis-Netropsin Containing a cis -Diaminoplatinum Group between Two Netropsin Fragments

The binding of Pt-bis-Nt and its modified analog Pt*-bis-Nt, which has two additional glycine residues in the linker between two netropsin fragments, to DNA has been studied. The elongation of the linker in the bis-netropsin molecule increases the cytotoxicity and leads to an almost complete loss of the antiherpetic activity of bis-netropsin. The study of the binding of two bis-netropsins to an oligonucleotide duplex containing an AT cluster, which is present at the origin of replication of herpes virus (OriS), revealed significant structural differences between the complexes of bis-netropsins with this DNA oligomer. It was shown by CD spectroscopy that the binding of Pt-bis-Nt in the extended conformation and in hairpin form with the parallel orientation of two bis-netropsin fragments makes a greater contribution to the interaction with the duplex than in the case of Pt*-bis-Nt. At high binding levels, Pt*-bis-Nt binds to the AT cluster in OriS predominantly in the form of associates based on the antiparallel, double-stranded, pyrrolcarboxyamide motif. The interaction of Pt-bis-Nt and Pt*-bis-Nt with a single-stranded oligonuclotide (64 nt) corresponding to the upper strand at the origin of replication of herpes virus (OriS*) was also studied. Substantial differences in the binding of bis-netropsins to OriS* and the thermostability of the resulting complexes were found by CD spectroscopy and UV melting studies.