Nucleotide Binding Preference of the Monofunctional Platinum Anticancer Agent Phenanthriplatin

摘要

The monofunctional platinum anticancer agent phenanthriplatin generates covalent adducts with the purine bases guanine and adenine. Preferential nucleotide binding was investigated using a polymerase stop assay and linear DNA amplification with a 163-base pair DNA double helix. Like cisplatin, phenanthriplatin forms the majority of adducts at guanosine residues, but significant differences in both the number and position of platination sites emerge when comparing results for the two complexes. Notably, the monofunctional complex generates a greater number of polymerasehalting lesions at adenosine residues than does cisplatin. Studies with 9-methyladenine reveal that, under abiological conditions, phenanthriplatin binds to the N¹ or N⁷ position of 9-methyladenine in approximately equimolar amounts. By contrast, comparable reactions with 9-methylguanine afforded only the N⁷-bound species. Both of the 9-methyladenine linkage isomers (N¹ and N⁷) exist as two diastereomeric species arising from hindered rotation of the aromatic ligands about their respective platinum–nitrogen bonds. Eyring analysis of rate constants extracted from variable temperature NMR spectroscopic data revealed that the activation energies for ligand rotation in the N¹ bound platinum complex and the N⁷ linkage isomers are comparable. Finally, a kinetic analysis indicated that phenanthriplatin reacts more rapidly by a factor of eight with 9-methylguanine than with 9-methyladenine, suggesting that the distribution of lesions formed on double-stranded DNA is kinetically controlled. In addition, implications for the potent anticancer activity of phenanthriplatin are discussed herein.