title: Effect of duration of exposure to S9788, cyclosporin A or verapamil on sensitivity of multidrug resistant cells to vincristine or doxorubicin.
abstract: In order to explain the high potency of S9788, a new multidrug resistance modifier currently in clinical development, we investigated its accumulation and retention in sensitive and resistant cells. Our results show that S9788 is 13-fold more accumulated and 23-fold more retained than VRP in the resistant S1/tMDR cell line. We also studied the effect of duration of incubation on the ability of S9788, verapamil and cyclosporin A to overcome the resistance of S1/tMDR and KB-A1 cells to a short exposure of doxorubicin or vincristine. Compared to a single co-incubation of 4 h, a 24 h post-incubation with 5 microM S9788 markedly increased the reversal of S1/tMDR resistance to VCR (fold reversal 4 h = 123; fold reversal 24 h = 4739), while it moderately increased S1/tMDR sensitivity to DOX (fold reversal 4 h = 1.9; fold reversal 24 h = 2.9). Similar results were obtained on KB-A1 resistance to VCR (fold reversal 4 h = 41, fold reversal 24 h = 21819) and KB-A1 resistance to DOX (fold reversal 4 h = 89; fold reversal 24 h = 160). This phenomenon also occurred with verapamil and cyclosporin A. These results clearly show that the effect of duration of exposure on the modulating activity of S9788 and of the 2 other modulators depends on the cytotoxic drug. Although the direct transposition of these results to a clinical situation is difficult, they suggest that a continuous infusion of S9788, starting simultaneously with the administration of the cytotoxic drug and ending 24 h later, might be a more effective schedule for clinical administration than a bolus administration.
authors.affiliation: Institut de Recherches Servier, Suresnes, France.
authors.forename: V
authors.initials: V
authors.lastname: Pérez
authors.forename: A
authors.initials: A
authors.lastname: Pierré
authors.forename: S
authors.initials: S
authors.lastname: Léonce
authors.forename: M
authors.initials: M
authors.lastname: Anstett
authors.forename: G
authors.initials: G
authors.lastname: Atassi
mesh_terms: D000970:Antineoplastic Agents / Q000378:metabolism / Q000494:pharmacology*; D001692:Biological Transport; D002294:Carcinoma, Squamous Cell; D016572:Cyclosporine / Q000378:metabolism / Q000494:pharmacology*; D004317:Doxorubicin / Q000633:toxicity*; D004351:Drug Resistance / Q000235:genetics; D006801:Humans; D007700:Kinetics; D008175:Lung Neoplasms; D009062:Mouth Neoplasms; D010880:Piperidines / Q000378:metabolism / Q000494:pharmacology*; D013997:Time Factors; D014162:Transfection; D014227:Triazines / Q000378:metabolism / Q000494:pharmacology*; D014407:Tumor Cells, Cultured; D014700:Verapamil / Q000378:metabolism / Q000494:pharmacology*; D014750:Vincristine / Q000633:toxicity*
chemical_list: D000970:Antineoplastic Agents; D010880:Piperidines; D014227:Triazines; C077022:S 9788; D014750:Vincristine; D004317:Doxorubicin; D016572:Cyclosporine; D014700:Verapamil