Fluorescence polarization studies of the binding of BMS 181176 to DNA.

The DNA binding of BMS 181176, an antitumor antibiotic derivative of rebeccamycin was characterized by DNA unwinding assays, as well as by fluorescence emission and polarization spectroscopic techniques. Unwinding and rewinding of supercoiled DNA was interpreted in terms of intercalation of BMS 181176 into DNA. BMS 181176 shows an enhanced fluorescence emission upon binding to the AT sequence and no enhancement upon binding to the GC sequence. BMS 181176 appears to be a weaker binder to poly(dAdT).poly(dAdT) compared to doxorubicin and ethidium bromide. When bound to DNA, the rotational motion of BMS 181176 is substantially decreased as evident from the increase in fluorescence polarization. BMS 181176 exhibits a range of binding strengths depending on the DNA. This is demonstrated by the Acridine Orange displacement assay using fluorescence polarization.