Effect of platinum-drug binding on the flexibility of DNA determined by time-dependent fluorescence depolarization

摘要

The interactions of calf thymus DNA with the chemotherapeutic drug cis-diamminedichloroplatinum (II), and with the clinically ineffective trans-isomer, have been studied by time-dependent fluorescence depolarization of intercalated ethidium. The effect of binding these compounds on the flexibility of DNA has been determined by monitoring the rapid internal torsional and bending motions of the DNA via depolarization of the ethidium fluorescence. The depolarization data are analyzed with an elastic model of DNA dynamics and yield an estimate of the torsional rigidity of DNA. Binding of the cis-isomer to DNA has a pronounced effect on the torsional rigidity, causing increased rigidity at low binding levels and decreased rigidity at high levels. These results are discussed in terms of intrastrand cross-link formation and local melting of DNA duplex-structure. The torsional rigidity of DNA is unaffected by binding of the trans-isomer. The possible relevance of these alterations of DNA flexibility to the selective drug action of the cis-isomer is considered.