Cytotoxicity and DNA binding characteristics of dextran-conjugated doxorubicins

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