DNA interactions of cisplatin tethered to the DNA minor groove binder distamycin

Modifications of natural DNA in a cell-free medium using cisplatin tethered to the AT-specific, minor groove binder distamycin, were studied using var ious methods of biochemical analysis or molecular biophysics. These methods include: binding studies using differential pulse polarography and flamele ss atomic absorption spectrophotometry, mapping DNA adducts using a transcr iption assay, use of ethidium bromide as a fluorescent probe for DNA adduct s of platinum, measurement of DNA unwinding by gel electrophoresis, measure ment of CD spectra, an interstrand cross-linking assay using gel electropho resis under denaturing conditions, measurement of melting curves with the a id of absorption spectrophotometry and the use of terbium ions as a fluores cent probe for distorted base pairs in DNA. The results indicate that attac hment of distamycin to cisplatin changes several features of the DNA-bindin g mode of the parent platinum drug. Major differences comprise different co nformational alterations in DNA and a considerably higher efficiency of the conjugated drug to form in DNA interstrand cross-links. Cisplatin tethered to distamycin, however, coordinates to DNA with similar base sequence pref erences as the untargeted platinum drug. The results point to a unique prof ile of DNA binding for cisplatin-distamycin conjugates, suggesting that tet hering cisplatin to minor groove oligopeptide binders may also lead to an a ltered biological activity profile.