DOUBLE-STRAND CLEAVAGE OF DNA BY A MONOFUNCTIONAL TRANSITION-METAL CLEAVAGE AGENT

A copper-based transition metal complex has been designed which perfor ms double-stranded cleavage of DNA in a nonrandom fashion. The complex , ((2S, benzyl-5-methyl-3,7-diazanonanedioate)copper-(II), presents an ammonium group on one side of the metal equatorial coordination plane to the DNA backbone phosphate groups, while the aromatic phenylalanin e-derived side chains are constrained to the opposite side of the coor dination plane toward the DNA groove. This structure was designed to b ind at locations where phosphate groups are in proximity to accessible hydrophobic regions of the DNA. We have estimated single-strand break to double-strand break ratios for DNA strand scission by this complex under a variety of activation conditions, and they are substantially lower than that predicted by statistical models for a random DNA linea rization process. This means that more double-strand breaks are produc ed per single strand break than can be accounted for by random coincid ent single-strand breaks. We have also investigated the formation of a basic sites, and found that at least as many abasic sites can be cleav ed to linear DNA as are linearized in the initial cleavage reaction. W e interpret this to mean that the complex binds both at the intact DNA surface for strand scission, and binds at nicked sites on the DNA (wh ere the charged end groups of the nick are likely to be proximate to t he accessible hydrophobic interior) for reactivation and complementary strand scission. Insofar as double-strand cleavage may be more potent biologically than single-strand cleavage as a source of lethal DNA le sions, the recognition characteristics of this complex may aid in the design of chemotherapeutic agents.