CYTOTOXICITY AND DNA-BINDING CHARACTERISTICS OF DEXTRAN-CONJUGATED DOXORUBICINS

The antitumor antibiotic doxorubicin was conjugated with polymeric dex trans of various molecular weights and the cytotoxicity of the conjuga tes against human carcinoma KB-3-1 cells and its multidrug-resistant s ubclone KB-V-1 cells was measured by tetrazolium salt MTT assay. The c onjugates were much less toxic to the KB-3-1 cells than the free doxor ubicin but exhibited similar toxicity to the KB-V cells. The conjugate -DNA interactions were monitered in real-time using an optical biosens or based on evanescent wave detection to obtain the association (k(a)) and dissociation (k(d)) rate constants as well as the equilibrium bin ding constants (K-A) of the bindings. Both k(a) and k(d) values fur th e conjugates are more than three magnitudes smaller than those for fre e doxorubicin, while the K-A values of the conjugate-DNA complexes are only about 10 times smaller than that of the free doxorubicin-DNA com plex. The results indicate that the cytotoxicity and the DNA-binding k inetics of doxorubicin may be modified with dextran conjugation. The K -A values obtained from the biosensor measurements were in close agree ment with those determined in solution by fluorescent titration method , verifying the utility of the label-free biosensing measurements as a n efficient method for studying ligand-DNA interactions. (C) 1998 Else vier Science B.V.