Definition of the intermediates and mechanism of the anticancer drug bleomycin using nuclear resonance vibrational spectroscopy and related methods

Bleomycin (BLM) is a glycopeptide anticancer drug capable of effecting single- and double-strand DNA cleavage. The last detectable intermediate prior to DNA cleavage is a low spin Fe-III peroxy level species, termed activated bleomycin (ABLM). DNA strand scission is initiated through the abstraction of the C-4' hydrogen atom of the deoxyribose sugar unit. Nuclear resonance vibrational spectroscopy (NRVS) aided by extended X-ray absorption fine structure spectroscopy and density functional theory (DFT) calculations are applied to define the natures of (FeBLM)-B-III and ABLM as (BLM)Fe-III-OH and (BLM)Fe-III-(eta(1)-OOH) species, respectively. The NRVS spectra of (FeBLM)-B-III and ABLM are strikingly different because in ABLM the delta Fe-O-O bending mode mixes with, and energetically splits, the doubly degenerate, intense O-Fe-N-ax transaxial bends. DFT calculations of the reaction of ABLM with DNA, based on the species defined by the NRVS data, show that the direct H-atom abstraction by ABLM is thermodynamically favored over other proposed reaction pathways.