Direct evaluation of intracellular accumulation of free and polymer-bound anthracyclines.

Nanoparticulate carriers of anthracyclines are being developed with the aim of improving the pharmacokinetic or pharmacodynamic behavior of these drugs. To understand how the drug reaches its nuclear targets, we have developed two methods that allow the quantification of the interaction between an anthracycline and cellular DNA: (1) by direct evaluation of the quenching of anthracycline fluorescence due to the intercalation of the drug into DNA and (2) by the measurement of Hoechst 33258 fluorescence associated with its displacement from DNA-binding sites for which it competes with the anthracycline. We show that the intracellular accumulation and DNA binding of doxorubicin encapsulated in polyisohexylcyanoacrylate nanospheres (dox-NS) and of daunorubicin bound to polyglutamic acid are reduced by 30%-40% in comparison with those obtained for free doxorubicin (dox) and daunorubicin, respectively. The results obtained with dox or NS-dox are not modified by prior incubation with either of these compounds. The two methods yielded similar results, and we conclude that either technique is applicable to the evaluation of the interaction of carrier-bound anthracyclines with cellular DNA.