Inhibition of P-glycoprotein-mediated vinblastine transport across HCT-8 intestinal carcinoma monolayers by verapamil, cyclosporine A and SDZ PSC 833 in dependence on extracellular pH.

摘要: The ability of the multidrug resistance modifiers R- and R,S-verapamil (VPL), cyclosporine A (CsA) its non-immunosuppressive derivative SDZ PSC 833 (PSC 833) to inhibit P-glycoprotein (P-gp)-mediated transepithelial flux tritiated vinblastine was investigated using tight highly resistant (R>1,400 Ω cm2) monolayer cultures intestinal adenocarcinoma-derived HCT-8 cells grown on permeable tissue-culture inserts. Apical addition these chemosensitisers inhibited drug (137 pmol h−1 cm−2; range, 133–142 cm−2) in basal apical secretory direction at clinically relevant concentrations, with showing highest activity, exhibiting inhibition concentrations as low 10 ng/ml (9 nM). Acidification modulator-containing compartment an extracellular pH (pHo) 6.8 had no influence MDR reversal by CsA 1 μg/ml (0.9 μM; inhibition, 52%) or 100 (0.09 60%), contrast R,S- R-VPL, which showed decreased caused less accumulation under this condition (flux 35% 23%, respectively, pHo vs 50% 43%, 7.5). P-gp-mediated rhdamine 123 efflux from dye-loaded single-cell suspensions measured flow cytometry not impeded comparison 7.5 standard medium, but inhibitory activity r-VPL (29% 60% rhodamine inhibition) diminished significantly, again without a reduction effect (rhodamine 75%). In conclusion, extrusion across polarised monolayers, offer model for normal epithelia tumour border areas, is presence similar described suspensions, resulting increased (2.2- 3.7-fold) intracellular accumulation. Functional P-gp expression, absence paracellular leakage modulator-sensitive single indicate transcellular monolayers. high MDR-reversing capacity, affected acidic conditions, reduce VPL-induced retention significantly. As far contributes overall cellular solid tumours hypoxic microenvironments, holds greatest promise clinical unresponsiveness respective group chemotherapeutics.