Synergism of energy starvation and dextran-conjugated doxorubicin in the killing of multidrug-resistant KB carcinoma cells

Here we report that 2-deoxyglucose/Na azide treatment and free/conjugated d oxorubicin are synergistic in cell killing. As demonstrated by fluorescence confocal microscopy, KB-V1 cells retained more conjugated doxorubicin than free doxorubicin. Verapamil or 2-deoxyglucose/Na azide enhanced only the r etention of the free drug and the small (<70 kDa) conjugates, indicating th at P-glycoprotein (P-gp) is not effective against large conjugates, Conjuga ted doxorubicin was excluded from nuclei. Initially both free and conjugate d doxorubicin accumulated in cytoplasmic organelles. Upon 2-deoxyglucose/Na azide treatment, fluorescence labeling of organelles dissipated, Prolonged (24 h) incubation of conjugate-preloaded cells resulted in redistribution of some of the organelle-associated fluorescence to nuclei, suggesting deco upling, The appearance of free doxorubicin was confirmed by capillary elect rophoresis, 2-Deoxyglucose/Na azide treatment also retarded decoupling. Our results suggest that energy starvation, in addition to increasing cellular retention of P-gp substrates, may affect cellular fate of conjugated drugs with a possible enhancing effect in cancer cell killing. [(C) 1999 Lippinc ott Williams & Wilkins.].