Increased vinblastine binding to membrane vesicles from multidrug-resistant KB cells.

Human KB carcinoma cells resistant to high levels of colchicine, vinblastine, vincristine, adriamycin, and actinomycin D exhibit reduced accumulation of these structurally unrelated chemotherapeutic agents (Akiyama, S.-I., Fojo, A., Hanover, J. A., Pastan, I., and Gottesman, M. M. (1985) Somatic Cell Mol. Genet. 11, 117-126; Fojo, A., Akiyama, S.-I., Gottesman, M. M., and Pastan, I. (1985) Cancer Res. 45, 3002-3007). To examine the mechanism of reduced drug accumulation in these cells, we measured [3H]vinblastine ([3H]VBL) binding to membrane vesicles made from drug-sensitive (KB-3-1), drug-resistant (KB-C4), and revertant (KB-R1) cells. Membrane vesicles from KB-C4 cells bound up to 8-fold more [3H]VBL than vesicles from the parental KB-3-1 or revertant KB-R1 cell lines. No difference in binding of [3H]dexamethasone, to which the cells are equally sensitive, was observed. The difference in [3H]VBL binding by vesicles from resistant and sensitive cells was eliminated by the addition of 10 micrograms/ml verapamil, which is known to reverse the multidrug-resistance phenotype. Drug binding by KB-C4 vesicles was osmotically insensitive, temperature-dependent, and trypsin-sensitive. Binding of [3H]VBL by KB-C4 vesicles was inhibited by vinblastine, vincristine, and daunomycin (in decreasing order). Dexamethasone at 100 microM, colchicine at 100 microM, and actinomycin D at 100 microM did not significantly inhibit [3H]VBL accumulation. No significant differences in tubulin content were detected among vesicles from sensitive and resistant cells. These data demonstrate that membrane vesicles from multiply drug-resistant cells bind increased amounts of vinblastine.