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The role of P-glycoprotein (P-gp, ABCB1) on the absorption process was investigated by drug-drug interaction studies of TAK-427 with P-gp inhibitors (erythromycin, ketoconazole or quinidine) in rats and by transport studies using rat multidrug resistance (MDR1) stably expressing cells and rat small intestine mounted in a Ussing-type chamber. TAK-427 showed high efflux activity with low permeability in rat MDR1a and MDR1b stably expressing cells and was revealed to be a typical substrate for P-gps. Although TAK-427 was mainly absorbed from the small intestine in rats, a large part of the dosed compound remained in the gastrointestinal tract. Orally co-administered P-gp inhibitors (50 mg/kg) increased the AUC of TAK-427 after a 5 mg/kg oral dose 5.4- to 18.3-fold, whereas orally administered P-gp inhibitors had a minor effect on the increase in the AUC of TAK-427 (1.3- to 2.2-fold) after a 0.5 mg/kg intravenous dose. Thus, the bioavailability of TAK-427 after oral administration in rats (7.3%) markedly increased when co-administered with P-gp inhibitors (28.6-57.6%). Moreover, the transport of TAK-427 was predominantly secretory throughout the rat small intestine and was inhibited by P-gp inhibitors. In conclusion, P-gp can markedly reduce the absorption of a typical P-gp substrate by its efflux activity throughout the absorption site.

Previously, we clarified the species differences in P-glycoprotein (P-gp)-mediated drug transport activity using human MDR1, monkey MDR1, canine MDR1, rat MDR1a, rat MDR1b, mouse mdr1a, and mouse mdr1b transfected LLC-PK(1) cell lines. However, the species differences in the inhibitory effects on P-gp-mediated drug transport have not been clarified yet. The purpose of the present study was to evaluate the species differences in the inhibitory effects of typical P-gp inhibitors, quinidine and verapamil, on P-gp-mediated drug transport using MDR1 transfected cell lines. The transcellular transport of [(3)H]daunorubicin, [(3)H]digoxin, and [mebmt-beta-(3)H]cyclosporin A across monolayers of the MDR1 transfected cells were measured in the presence or absence of P-gp inhibitors. On daunorubicin transport, the relative IC(50) value (quinidine IC(50)/verapamil IC(50)) of human P-gp was 5.25 and those from other species ranged from 0.89 to 10.70. The transport of digoxin and cyclosporin A also showed different relative IC(50) values among human, monkey, canine, rat, and mouse P-gps. The present study revealed that species differences in the inhibitory effects on P-gp-mediated drug transport should not be disregarded among human, monkey, canine, rat, and mouse. This study will provide useful information for predicting drug interactions mediated by P-gp.

P-glycoprotein (P-gp) plays an important role in the pharmacokinetics of drugs. There is little information on the species differences in P-gp-mediated drug transport activity. The purpose of the present study was to clarify the differences in the kinetic parameters and the existence of species differences in the P-gp-mediated drug transport activity using seven multidrug resistence1 (MDR1) transfected cell lines, in which the cDNA was from human, monkey, canine, rat (MDR1a and MDR1b), and mouse (mdr1a and mdr1b). The transcellular transport of diltiazem, cyclosporin A, and dexamethasone across monolayers of MDR1 transfected cells. The apparent K(m) values of diltiazem exhibited approximately 16.5-fold differences among the seven cell lines. Concerning the diltiazem transport, the V(max)/K(m) value of human P-gp corrected by the P-gp expression level was similar to that of monkey P-gp, but was 5.6-fold higher than that of canine P-gp. On the other hand, the corrected V(max)/K(m) value of human P-gp for cyclosporin A transport was 3.8-fold higher than that of monkey P-gp. The present study would be valuable to evaluate the P-gp function of various animals in the same experimental condition. It was clarified that the species differences in P-gp-mediated drug transport activity evaluated by the corrected V(max)/K(m) value differed according to the substrate., ((c) 2006 Wiley-Liss, Inc. and the American Pharmacists Association)

Purpose: Stable transformants expressing human multidrug resistance 1 (MDR1), monkey MDR1, canine MDR1, rat MDR1a, rat MDR1b, mouse mdr1a, and mouse mdr1b in LLC-PK1 were established to investigate species differences in P-glycoprotein (P-gp, ABCB1) mediated efflux activity., Methods: The seven cDNAs of MDR1 from five animals were cloned, and their transformants stably expressing the series of MDR1 in LLC-PK1 were established. Transport studies of clarithromycin, daunorubicin, digoxin, erythromycin, etoposide, paclitaxel, propranolol, quinidine, ritonavir, saquinavir, verapamil, and vinblastine were performed by using these cells, and efflux activity was compared among the species., Results: Except for propranolol, all compounds showed efflux activity in all transformants, and were judged to be substrates of P-gp. There were slight interspecies and interisoforms differences in the substrate recognition. However, the efflux ratio among the series of the MDR1 stably expressing cells showed good correlation as represented between human and monkey MDR1, and poor correlation as represented between human MDR1 and mouse mdr1a, and human and canine MDR1., Conclusions: Results in the present study indicate that all MDR1 stably expressing cells have efflux activity for various P-gp substrates, and that interspecies differences and similarities of the P-gp substrate efflux activity may exist.

Numerous signaling pathways were reported to be involved in the resistance for conventional cytotoxic drugs, although one of the main reasons is the overexpression of P-glycoprotein (P-gp) in multidrug resistant cancer cells. The overexpression of P-gp has been associated with the resistance to a wide range of anticancer drugs. Doxorubicin and paclitaxel are substrates of this transporter system and have an important role for the various human malignancies. In the present study, drug-sensitive MCF7 and multidrug resistant MCF7/ADR (characterized by overexpression of P-gp) human breast cancer cell lines were used as an experimental model. We have found that PS341 and MG132, proteasome inhibitors, reduced the degree of the multidrug resistance (MDR) in MCF7/ADR cells. This phenomenon was accompanied by a decrease in the IC50 value of doxorubicin and paclitaxel from 55.9 +/- 3.46 to 0.60 +/- 0.08 microM, and from 17.61 +/- 1.77 to 0.59 +/- 0.12 microM, respectively. The IC50 values of sensitive cells for doxorubicin and paclitaxel were about 0.42 and 0.83 microM, respectively. The effect of PS341 and MG132 on MCF7/ADR cells was associated with a significant decrease in both protein and gene levels of P-gp expression. Moreover, with regard to the expression of possible signal transduction pathways of mitogen-activated protein kinase (MAPK) related to the activation of mdr1, proteasome inhibitors did significantly influence the activation of these proteins. Western blot analysis revealed that 24 hr exposure of multidrug resistant MCF7/ADR cells with proteasome inhibitors did change the levels of DNA binding activity of nuclear factor-kappaB (NF-kappaB), pERK1/2, c-Jun, and p-c-Jun. In conclusion, we could remark that proteasome inhibitors (especially PS341) attenuate the resistance of MCF7/ADR cells for P-gp substrate drugs of doxorubicin and paclitaxel. Several proteins are supposed to be associated with the resensitization of the cells to conventional cytotoxic drugs, although decreased activity of P-gp is at least involved in the proteasome inhibitor-related resensitization. And influence with MAPK pathways, which have been reported to be associated with the regulation of P-gp, might be contributed to the resensitization brought by proteasome inhibitors., (Copyright 2005 Wiley-Liss, Inc.)