MOLECULAR RECOGNITION EFFECTS IN METAL-COMPLEX MEDIATED DOUBLE-STRANDCLEAVAGE OF DNA - REACTIVITY AND BINDING-STUDIES WITH MODEL SUBSTRATES

Double-strand breaks in duplex DNA are thought to be significant sourc es of cell lethality because they appear to be less readily repaired b y DNA repair mechanisms. We recently described the design and cleavage chemistry of dibenzyl-5-methyl-3,7-diazanonanedioato)copper(II) (1), which effects nonrandom double-strand cleavage of duplex DNA. After DN A nicking by generation of hydroxyl radicals, the key step in this pro cess appears to occur through recognition by the metal complex of the nicked-abasic site on duplex DNA, followed by delivery of OH. to cleav e at the opposing strand, forming a double-strand lesion. Tkrough the use of model nucleic acid substrates and comparison to DNA scission ch emistry, we have investigated the electrostatic and hydrophobic contri butions to DNA binding by complex 1. We have complemented these reacti vity studies with studies on the binding of 1 to a model nucleic acid substrate, using H-2 NMR spectroscopy with deuterated 1 and HDO T-1 re laxation enhancement methods to study the binding of 1 to nucleotide s ubstrates. With these methods, we have estimated that the association constant for the 1(+).5'-AMP(2-) complex is similar to 16 M-1 and that the binding interaction involves both electrostatic and aromatic stac king interactions between the nucleic acid base and the pendant aromat ic side chains of 1.