Conformational analysis of site-specific DNA cross-links of cisplatin-distamycin conjugates

The requirement for novel platinum antitumor drugs led to the concept of sy nthesis of novel platinum drugs based on targeting cisplatin to various car rier molecules. We have shown [Loskotova, H., and Brabec, V. (1999) fur. J, Biochem, 266, 392-402] that attachment of DNA minor-groove-binder distamyc in to cisplatin changes several features of DNA-binding mode of the parent platinum drug. Major differences comprise different conformational changes in DNA and a considerably higher interstrand crosslinking efficiency. The s tudies of the present work have been directed to the analysis of oligodeoxy ribonucleotide duplexes containing single, site-specific adducts of platinu m-distamycin conjugates. These uniquely modified duplexes were analyzed by Maxam-Gilbert footprinting, phase-sensitive gel electrophoresis bending ass ay and chemical probes of DNA conformation. The results have indicated that the attachment of distamycin to cisplatin mainly affects the sites involve d in the interstrand cross-links so that these adducts are preferentially f ormed between complementary guanine and cytosine residues. This interstrand cross-link bends the helix axis by similar to 35 degrees toward minor groo ve, unwinds DNA by approximately 95 degrees and distorts DNA symmetrically around the adduct. In addition, CD spectra of restriction fragments modifie d by the cisplatin-distamycin conjugates have demonstrated that distamycin moiety in the interstrand cross-links of these compounds interacts with DNA . This interaction facilitates the formation of these adducts. Hence, the s tructural impact of the specific interstrand cross-link detected in this st udy deserves attention when biological behavior of cisplatin derivatives ta rgeted by oligopeptide DNA minor-groove-binders is evaluated.