Binding of two novel bisdaunorubicins to DNA studied by NMR spectroscopy

In the search for new generations of anthracycline drugs, lower cytotoxic side effects and higher activity against resistant cancer cells are two major goals. A new class of bis-intercalating anthracycline drugs has been designed, synthesized, and shown to have promising activity against multidrug-resistant cells. Two daunorubicins symmetrically linked together via a p-xylenyl group, either at their N3' (compound WP631) or N4' sites (compound WP652), exhibit extraordinary DNA binding affinities. We have used high-resolution NMR studies to understand the DNA binding mode of these two new bis-daunorubicin anticancer compounds. The structures of the WP631- d(ACGTACGT)₂ and the WP652-d(TGTACA)₂ complexes have been determined by NOE-restrained refinement. WP631 binds strongly to the 5'-CG(A/T)(A/T)CG hexanucleotide sequence, with the aglycons intercalated between the two CpG sites at both ends of the hexanucleotide sequence. The overall conformation of the WP631-d(CGTACG)₂ part is remarkably similar to the crystal structure of the 2:1 complex of daunorubicin and d(CGTACG)₂, as predicted previously [Gao, Y.-G., and Wang, A. H. J. (1996) J. Biomol. Struct. Dyn. 13, 103-117]. In contrast, the related bis-intercalator WP652 prefers the 5'-PyGTPu tetranucleotide sequence, with the aglycons intercalated between the PypG and TpPu sites. The binding of WP652 to DNA results in a severely distorted B- DNA duplex with the p-xylenyl tether moiety significantly protruded away from the bottom of the minor groove. While WP652 in some ways behaves similarly to other anticancer bis-intercalating antibiotics (e.g., triostine A and echinomycin), the detailed interactions between those two classes of bis- intercalators are quite different.