sdz-psc-833 and niguldipine

A convenient functional assay of the multidrug resistance (MDR) pump is useful for the diagnosis of MDR-1 cancers and the quantitative determination of the potency of inhibitors of the pump. Calcein-AM, a substrate of the MDR pump, was used to determine the concentration of SDZ PSC833 needed to completely inhibit the pump in CEM/VLB100 drug-resistant cells. The initial rates (in percent) for calcein retention by these MDR-1 cells were used to calculate values for the percent initial efflux of calcein-AM through the MDR pump in the presence of the inhibitors PSC833, cyclosporinA, and dexniguldipine. The percent efflux values at 250 and 60 nM calcein-AM were used to calculate the required concentration of each inhibitor to produce half-inhibition (I50) of initial efflux through the pump. These results are consistent with a noncompetitive inhibition of the MDR pump by each of the three inhibitors.

Topics: ATP Binding Cassette Transporter, Subfamily B, Member 1; Cyclosporine; Cyclosporins; Dihydropyridines; Drug Resistance, Neoplasm; Fluoresceins; Half-Life; Humans; Inhibitory Concentration 50; Kinetics; Leukemia; Lymphocytes; Molecular Weight; Tumor Cells, Cultured

The newly designed pyridine derivative B9309-068 and a series of structurally different compounds were tested for their ability to modulate rhodamine 123 (RHO) efflux from CD56+ hematopoietic cells in the presence of either 10% fetal calf serum or undiluted human AB serum. Furthermore, efflux modulation was investigated on CD34+ blast populations obtained from four patients with relapsed state AML. Target cells were specified throughout by labeling with peridinine chlorophyll protein (PerCP)-conjugated monoclonal antibodies, allowing clear differentiation from RHO emission spectrum by flow cytometry. In the presence of low serum each compound efficiently modulated RHO efflux without significant differences in the range of final concentrations (1.0-3.0 microM). At 0.1 microM, however, RHO efflux was differentially modulated following the series GF120918 approximately B9309-068 > PSC 833 > DNIG approximately DVER. With CD56+ cells in the presence of undiluted human AB serum at a final modulator concentration of 0.1 microM, all chemosensitizers tested were found to be inefficient. At final concentrations of 0.3 microM or higher, distinct RHO efflux modulation was found with the following efficacies: B9309-068 approximately GF120918 > PSC 833 >> DVER approximately DNIG. The efficacies seen in undiluted human AB serum at 3.0 microM were comparable to those seen on CD56+ cells at final modulator concentrations of 0.1 microM in low serum. Our results identify the pyridine derivative B9309-068 as a promising compound for modulating P-glycoprotein-mediated drug resistance under conditions resembling the clinical setting. Nonetheless, modulation potencies of a series of structurally very different chemosensitizers was revealed to be substantially diminished at high serum concentrations in vitro.

Topics: Acridines; Antigens, CD34; ATP Binding Cassette Transporter, Subfamily B, Member 1; ATP-Binding Cassette Transporters; Blood Proteins; Calcium Channel Blockers; CD56 Antigen; Cyclosporins; Dihydropyridines; Dose-Response Relationship, Drug; Flow Cytometry; Fluorescent Dyes; Gene Expression; Humans; Isoquinolines; Leukemia, Myeloid, Acute; Leukocytes, Mononuclear; Morpholines; Multidrug Resistance-Associated Proteins; Pyrimidines; Rhodamine 123; Rhodamines; Tetrahydroisoquinolines; Verapamil

P-glycoprotein(P-gp)- related resistance is one of the major obstacles in treating leukemia patients. Therefore, it is of clinical interest to find new potential modulators and compare their P-gp-modulating efficacy. The present analysis investigated the influence of P-gp modulators, such as verapamil, tamoxifen, droloxifene E, droloxifene Z, SDZ PSC 833 (PSC 833) and dexniguldipine in a leukemic T-cell line (CCRF-CEM) and its P-gp-resistant counterparts (CCRF-CEM/ACT400 and CCRF-CEM/VCR1000). P-gp expression was assessed with an immunocytological technique using the monoclonal antibody 4E3.16. It was characterized as the percentage of P-gp positive cells and also expressed as a D value by using the Kolmogorov Smirnov statistic. The efficacy of P-gp modulators was determined with the rhodamine-123 accumulation test and the MTT test. An in vitro modulator concentration between 0.1 microM and 3 microM was determined, where no genuine antiproliferative effect was apparent. The modulators PSC 833 and dexniguldipine were the significant (p

Topics: Antibodies, Monoclonal; ATP Binding Cassette Transporter, Subfamily B, Member 1; ATP-Binding Cassette Transporters; Cell Division; Cyclosporins; Dihydropyridines; Drug Resistance, Multiple; Drug Resistance, Neoplasm; Drug Screening Assays, Antitumor; Humans; Leukemia, T-Cell; Multidrug Resistance-Associated Proteins; Neoplasm Proteins; Tamoxifen; Tumor Cells, Cultured; Vault Ribonucleoprotein Particles; Verapamil

In the clinical therapy of cancer, resistance to many cytostatic drugs is a major cause of treatment failure. Among other mechanisms, the expression and pumping activity of P-glycoprotein (PGP) in the membrane of resistant cancer cells is responsible for the reduced uptake of cytostatics. The blockade or inhibition of PGP activity by chemosensitisers seems to be a tenable way to restore sensitivity to antineoplastic drugs and therapeutic efficacy. In the present work the influence of the new chemosensitiser dexniguldipine on rhodamine-123 accumulation in multidrug-resistant leukaemia cells was investigated. Dexniguldipine increases cellular rhodamine-123 accumulation dose-dependently.pEC50 values (-log concentration of drug showing a half maximal effect) in accumulation studies are dependent on pH of the test system and are in the range of 6.5 (pH 7.2) to 7.2 (pH 8.0) for dexniguldipine. In comparison with other chemosensitisers such as SDZ PSC 833, cyclosporin A, verapamil, dipyridamole, quinidine and amiodarone, dexniguldipine is the most potent drug in this test system. In addition to equilibrium measurements of rhodamine-123 accumulation, efflux of rhodamine-123 was analysed in the absence and presence of chemosensitisers. A clear dose-dependency was seen and, moreover, a dramatic decrease in efflux rates was achieved in the presence of chemosensitisers. The described system can be used to investigate PGP-mediated drug transport on a pharmacological and biochemical basis.

Topics: Antineoplastic Agents; Cyclosporins; Dihydropyridines; Dose-Response Relationship, Drug; Drug Resistance, Multiple; Humans; Hydrogen-Ion Concentration; Leukemia; Rhodamine 123; Rhodamines; Tumor Cells, Cultured