Metabolism of the antitumor drug N(2)-methyl-9-hydroxy ellipticinium: Identification by surface-enhanced Raman spectroscopy of adducts formed with amino acids and nucleic acids

Abstract

The bioxidative transformation of the antitumor drug N(2)-methyl-9-hydroxy ellipticinium (NMHE) by the peroxidase-H2O2 system leads to a highly electrophilic quinoneimine species. This species may react with biological macromolecules such as proteins or nucleic acids, that contain suitable nucleophilic groups, to give covalent adducts through a Michael addition at C(10). When this reaction takes place in the presence of aliphatic primary amines, recyclisation process occurs during coupling leading to adducts of which the oxazolopyridocarbazole (OPC) structure has been established. Surface-enhanced Raman scattering (SERS) spectra of these OPC were recorded and analyzed to serve as references. On the basis of these spectral data, the SERS investigation of adducts obtained with aliphatic amino acids indicated that these species present the same chromophoric OPC-type structure as those obtained with aliphatic amines. On the other hand, we have studied the covalent binding of the drug to calf thymus DNA obtained under the same oxidative enzymatic procedure. Since previous studies have shown that adenosine was the preferential binding target within DNA, to determine the precise structure of DNA adducts we have synthesized a model adduct from this nucleoside to be used as a reference. Characterization by Fourier Transform infrared spectroscopy (FTIR), Near-IR FT Raman, and SERS of this adenosine-NMHE adduct suggests that the covalent binding occurs between the C(10) of the ellipticinium chromophore and the N(6) primary amine of the adenine. Finally, from hydrolysis of DNA adducts, their isolation by high-performance liquid chromatography, and the analysis of the SERS spectrum of the main adduct formed, it appears that the structure is probably the same as that proposed for the adenosine-NMHE adduct. © 1996 John Wiley & Sons, Inc.