High Field¹H-NMR Analysis of the 1:1 Intercalation Complex of the Antitumor Agent Mitoxantrone and the DNA Duplex [d(CpGpCpG)]₂

Complete 1H-nmr assignment has been achieved of the stoichiometric 1:1 complex of the antitumor agent mitoxantrone with the duplex oligomer [d(CpGpCpG)]2. The techniques used included 2D-COSY, 1D-NOE and 2D-HH-INADEQUATE. Comparisons of 1H and 13C chemical shift changes upon addition of drug suggest symmetrical intercalative binding to the center of the tetramer. NOE difference measurements and 31P studies suggest binding of the terminal OH groups of the side chains to the central phosphate groups such that the methylene groups are proximate to C(3)6, C(3)6 and G(4)8 base protons all in the major groove. The data suggest that the side chains bind to the neighboring base pairs from the intercalation site. This is in accord with independent evidence of G,C base preference for binding from spectroscopic and electron microscopy studies.