ELECTROSPRAY-IONIZATION MASS-SPECTROMETRY OF COVALENT LIGAND-OLIGONUCLEOTIDE ADDUCTS - EVIDENCE FOR SPECIFIC DUPLEX ION FORMATION

Electrospray ionization mass spectrometry (ESI-MS) has been used to ex amine the covalent binding of the antitumour agents cisplatin and heda mycin with self-complementary oligonucleotides 5'-TACGTA-3', 5'-CACGTG -3', 5'-AGGCCT-3' or 5'-CGTACG-3' as models for binding to cellular DN A. The observation of duplex forms of oligonucleotide adducts of these compounds in the gas phase has been found to correlate with the stabi lity of the adducts in solution. Hedamycin, which both intercalates in to and alkylates DNA, enhances the stability of duplex ions in ESI mas s spectre. In contrast, the binding of cisplatin is known to destabili se duplexes in solution and only weak double-stranded peaks are observ ed in the ESI spectra of cisplatin-oligonucleotide adducts. Results of titration experiments with the hedamycin-5'-CACGTG-3' adduct and comp lementary and non-complementary oligonucleotides provide strong eviden ce that tbe observed duplex ions are the result of specific base-paire d associations in the gas phase, rather than non-specific interactions . Finally, estimates of the extent of cisplatin binding to different s equences based on ESI mass spectra of crude reaction mixtures are foun d to correlate web with data obtained by reversed-phase high-performan ce liquid chromatography. This work demonstrates the considerable pote ntial of ESI-MS as a tool for characterization of the interactions of antitumour agents with DNA.