Interaction between antitumor drugs and a double-stranded oligonucleotide studied by electrospray ionization mass spectrometry

Electrospray ionization mass spectrometry was used to investigate the compl ex formation between a double-stranded oligonucleotide and various antitumo r drugs belonging to two categories: intercalators (ethidium bromide, amsac rine and ascididemin) and minor groove binders (Hoechst 33258, netropsin, d istamycin A, berenil and DAPI), The goal of this study was to determine whe ther the relative intensities in the mass spectra reflect the relative abun dances of the species in the solution phase. The full-scan mass spectra sug gest non-specific binding for the intercalators and specific binding for th e minor groove binders, The preferential stoichiometries adopted by each mi nor groove binder were determined by studying the influence of the drug con centration on the spectra, We obtained 2:1> 1:1 for distamycin, 1:1 > 2:1 f or Hoechst 33258 and DAPI and only the 1:1 complex for netropsin and bereni l, These features reflect their known behavior in solution. The compared ta ndem mass spectra of the I:1 complexes with Hoechst 33258 and netropsin, wh en correlated with published crystallographic data, suggest the possibility of inferring some structural information, The relative binding affinities of the drug for the considered duplex mere deduced with two by two competit ion experiments, assuming that the relative intensities reflect the composi tion of the solution phase, The obtained affinity scale is netropsin > dist amycin A > DAPI > Hoechst 33258 > berenil, These examples show some of the potential uses of mass spectrometry as a useful tool for the characterizati on of specific drug binding to DNA, and possibly a rapid drug screening met hod requiring small amounts of materials, Copyright (C) 1999 John Wiley gr Sons, Ltd.