THE DEOXYFUCOSE-ANTHRANILATE OF ESPERAMICIN A1 CONFERS INTERCALATIVE DNA-BINDING AND CAUSES A SWITCH IN THE CHEMISTRY OF BISTRANDED DNA LESIONS

We report three as yet undescribed, critical features of the interacti on of the enediyne antitumor antibiotic esperamicin A1 (ESP A1) with D NA. First, results from hydrodynamic and spectroscopic studies reveale d an intercalative binding mode conferred by the deoxyfucose-anthranil ate of ESP A1. An intercalative binding mode is consistent with earlie r observations of nucleosome linker-selective DNA damage by ESP A1 [Yu , L. et al. J. Biol. Chem. 1994, 269, 4144-4151]. While capable of ado pting a planar structure, the N-(2-methoxyacrylyl) anthranilate group would represent an unusual intercalator, which by itself has no appare nt affinity for DNA, yet contributes 1-2 kcal/mol to the binding energ etics of ESP A1. Second, bistranded DNA lesions, which consist of a di rect strand break opposite an abasic site, represent 20-25% of ESP A1- mediated DNA damage. Finally, sequencing gel analysis and tritium abst raction studies revealed that the deoxyfucose-anthranilate caused a sw itch in the chemistry of ESP A1-mediated DNA damage from 4'-hydrogen a bstraction to 1'. We propose that intercalation of the anthranilate of ESP A1 alters the minor groove position of the diradical form of the drug and causes a switch in the hydrogen abstraction in bistranded les ions; the predominance of single-strand lesions associated with ESP A1 may be the result of the altered positioning or intramolecular quench ing of one of the drug radicals.