FIGURE 9.

Lysosomotropic weak bases have no effect on the cytotoxicity of drugs that are not Pgp substrates. Incubation of KB31 (−Pgp) or KBV1 (+Pgp) cells with lysosomotropic weak bases has no effect on the cytotoxicity of cisplatin (A and B) or carboplatin (C and D), both of which are not Pgp substrates (32). Cells were incubated for 72 h at 37 °C with cisplatin or carboplatin in the presence or absence of the lysosomotropic weak bases ammonium chloride (NH₄Cl, 3 mm), CLQ (1 μm), or MA (100 μm). Proliferation was then assessed using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Results shown are mean ± S.D. (three experiments).