The study on the fluorescence of mithramycin -: DNA and chromomycin-A3 -: ADN systems

The interaction of two related anticancer drugs belonging to the aureolic family of antibiotics, mithramycin and chromomycin A(3), with calf thymus DNA was studied by fluorescence spectroscopy. The positive curvatures of the Stern-Volmer plots obtained for both drugs in the presence of DNA could be due to a static quenching by an association process. The results were rationalized in terms of the Schatchard, Schwarz and Watanabe models, in order to obtain the binding constants of drugs to DNA and the number of binding sites. For both drugs two processes were evidenced At little polymer-drug ratios (P/D) were found cooperative binding constants of 2,1(.)10(5)M(-1) for mithramycin and 1,9(.)10(5)M(-1) for chromomycin A(3). The binding constants of 3,1(.)10(5)M(-1) for mithramycin and 2,8(.)10(5)M(-1) for chromomycin A(3) and a low cooperativity characterize the process evidenced at higher ratios.