PROBING THE INTERACTIONS OF THE ANTICANCER DRUG DOXORUBICIN WITH POLYMERIC NANOPARTICLES USING FLUORESCENCE SPECTROSCOPY

Doxorubicin-loaded nanospheres have been shown to provide interesting colloidal carriers, able to partially suppress in vitro tumor-cell resistance to Doxorubicin (Cuvier et al., Biochem. Pharmacol. 44, 509 (1992)). In order to better characterize these carriers, we have probed the interactions developed between Doxorubicin and polyisohexylcyanoacrylate nanoparticles loaded during their polymerization or after their formation. Using fluorescence spectroscopy and Doxorubicin-DNA-quenching experiments, we have seen and quantified two types of bound forms: one adsorbed onto the nanosphere surface and one embedded into the polymeric matrix. These two forms coexist when the drug is added during the nanosphere polymerization process but only the adsorbed one is present when Doxorubicin is added to already-formed nanospheres. The adsorbed species appeared to be in equilibrium with the free drug present in the medium. We determined apparent equilibrium constants for the adsorption of Doxorubicin onto preloaded (386-nm diameter) and unloaded (332-nm diameter) nanospheres, equal to 0.14 × 106 and 0.03 × 106 M-1, respectively. The embedded species was not displaced by the presence of competitive binding agents in the external medium and did not diffuse throughout the polymeric matrix at 25°C in the time scale of 4 h. Finally, the importance of this sequestered fraction for the biological activity of the Doxorubicin-loaded NS is discussed. © 1994 by Academic Press, Inc.