野黄芩苷对Caco-2细胞中P-gp蛋白表达及活性的影响

目的:研究野黄芩苷对Caco-2细胞中P-糖蛋白(P-gp)表达及活性的影响。方法:野黄芩苷(25,50及100μmol·L-1)与Caco-2细胞共孵育24 h,48 h及72 h后,通过western blot方法检测野黄芩苷对Caco-2细胞中P-gp蛋白表达的影响;通过罗丹明123转运试验,测定罗丹明123在Caco-2细胞内的累积量变化,以考察野黄芩苷对P-gp活性的影响。结果:野黄芩苷对Caco-2细胞中P-gp蛋白表达具有诱导作用,孵育24 h后,野黄芩苷(25,50及100μmol·L-1)对P-gp蛋白的上调倍数分别为2.34,2.65,2.00;孵育48 h后,野黄芩苷上调P-gp蛋白表达2.70,4.66,3.13倍;孵育72 h后,野黄芩苷(25,50及100μmol·L-1)对P-gp蛋白的上调倍数分别为2.82,2.62,1.84。野黄芩苷上调Caco-2细胞中P-gp蛋白表达的同时增加P-gp外排泵活性,孵育24 h后,野黄芩苷(25,50及100μmol·L-1)降低胞内罗丹明123累积量至70.6%,66.6%,76.6%;孵育48 h后,胞内罗丹明123累积量降低至55.6%,37.5%,65.2%;孵育72 h后,胞内罗丹明123累积量降低至45.5%,53.9%,60.3%。结论:野黄芩苷诱导Caco-2细胞中P-gp的蛋白表达,并能增加P-gp外排泵活性。     

盐酸度洛西汀对Caco-2细胞P-糖蛋白功能及表达的影响

目的 研究盐酸度洛西汀(DLX)对Caco-2细胞上P-糖蛋白(P-gp)功能和表达的影响.方法 将Caco-2细胞分为阴性对照组、维拉帕米10 μmol/L阳性对照组(VER组)和DLX 0.2、5、10 μmol/L不同浓度处理组.采用流式细胞术检测DLX干预后Caco-2细胞内罗丹明-123的荧光强度和细胞膜上P-gP的表达量.结果 与阴性对照组相比,DLX 0.2、5、10 μmol/L均显著抑制罗丹明-123从Caco-2细胞的外排(96.3±4.5 vs.129.5±14.5、131.2±7.0、135.6±17.1)(P＜0.05),而对P-gp阳性率无明显改变(90％ vs.94％、91％、89％)(P＞0.05).结论 DLX能抑制Caco-2细胞上P-gp的功能,降低罗丹明-123从Caco-2细胞中的外排,但并不影响P-gp的表达.     

熊果酸抑制P-糖蛋白外排功能

目的研究女贞子中的熊果酸对P-糖蛋白（P-gp）功能的影响。方法用环孢素A作为P-糖蛋白功能抑制的阳性对照,用流式细胞术分析熊果酸对P-糖蛋白底物——罗丹明123在Caco-2细胞中外排的影响。结果当熊果酸浓度在0.01μmol.L-1时,实验组细胞内荧光与阴性对照组间无显著性差异（P〉0.05）;当熊果酸浓度在0.1～1μmol.L-1时,实验组细胞内荧光强度显著强于阴性对照组（P〈0.05）,并随熊果酸浓度的增高而增强;当熊果酸浓度为10μmol.L-1时,实验组细胞内荧光强度却表现为减弱,并且显著弱于阴性对照组（P〈0.05）,其原因有待后续实验探讨。结论在低浓度时（0.01μmol.L-1）,熊果酸对P-gp的功能没有影响;当熊果酸浓度在0.1～1μmol.L-1时,熊果酸对P-gp的功能有抑制作用。     

川芎嗪对Caco-2细胞p-糖蛋白功能和表达的影响

目的研究川芎嗪对和Caco-2细胞p-糖蛋白功能和表达的影响。方法用p-糖蛋白底物罗丹明123在细胞外排和转运的改变指示细胞膜上p-糖蛋功能的改变,流式细胞仪分析Caco-2细胞膜上p-糖蛋白表达量的变化。结果中、高浓度(120、240μg.mL-1)的川芎嗪能够使罗丹明123从Caco-2细胞的外排量分别减少2.67倍和9.08倍,与细胞孵育72 h后能够使Caco-2细胞表面p-糖蛋白的表达水平下调46.4%和61.2%,在1.5 h使罗丹明123在Transwell的BL侧的累积排放量增加了1.3倍和1.8倍。结论川芎嗪可以显著减小罗丹明123在Caco-2细胞的外排,对罗丹明123跨细胞膜转运也有显著影响。将川芎嗪与Caco-2细胞共同培养72 h后,川芎嗪能够显著降低Caco-2细胞上p-糖蛋白的表达。川芎嗪与p-糖蛋白底物共同应用时要注意发生由p-糖蛋白介导的药物相互作用,川芎嗪可能是一种很有前途的多药耐药逆转剂。     

(E)-2-(4-二乙基胺甲基-苯亚甲基)-5,6-二甲氧基-2,3-二氢-1-茚酮与P-糖蛋白的相互作用

考察(E)-2-(4-二乙基胺甲基-苯亚甲基)-5,6-二甲氧基-2,3-二氢-1-茚酮(BYZX)在Bcap37和P-糖蛋白(P-gp)高表达的Bcap37/MDR1细胞中的积聚差异，以确证BYZX是否为P-gp的底物。同时，以罗丹明123为底物，比较在上述两种细胞中BYZX对罗丹明123积聚的影响，从而确证BYZX是否是P-gp的抑制剂。采用HPLC法测定BYZX在两种细胞中的累积量，酶标仪法测定细胞内罗丹明123的荧光强度。实验结果显示，BYZX在Bcap37及Bcap37/MDR1细胞内不同时间下的积聚量无明显差异(P>0.05)，且不同浓度的BYZX对罗丹明123的外排亦无明显的抑制作用(P>0.05)。这一结果表明BYZX与P-gp没有明显的相互作用，不会被P-gp外排到细胞外而影响其吸收，同时BYZX对P-gp也不存在抑制作用。     

灵芝多糖肽对Caco-2细胞上P糖蛋白功能、表达的影响

目的 研究灵芝多糖肽(ganoderma lucidum polysaccharides peptide,GLPP)对Caco-2细胞P糖蛋白(P-gp)功能和表达的影响.方法 用流式细胞仪测定Caco-2细胞中P-gp底物罗丹明123和抗体的荧光强度,分析药物对P-gp功能和表达的影响.双向跨膜转运实验考查GLPP对罗丹明123转运的影响.结果 10、20、50、100μg·mL-1的GLPP均抑制了Rh-123的外排,其外排分别降低了8％、16％、19％、33％,具有浓度依赖性.高、中浓度的GLPP(50、100 μg·mL-1)对Rh-123的双向转运有一定的抑制,外排率(ER)较阴性对照组降低了15％、18％.细胞与药物作用72 h后,细胞抗体荧光强度降低,P-gp的表达降低.结论 GLPP对P-gp的活性有一定的抑制作用,能在较短的时间内增加细胞内Rh-123的蓄积,抑制Rh-123的双向转运.长期使用GLPP可抑制P-gp的表达.     

高胰岛素对 MCF-7/ADR 细胞化疗敏感性的影响

摘要:目的 分析高胰岛素对 MCF-7/ADR 细胞 P-糖蛋白（P-gp）表达和功能的影响, 并初步探讨胰岛素对 MCF-7/ADR 细胞化疗敏感性的影响。方法 用不同胰岛素浓度（0.001、 0.005、 0.01、 0.05、 0.10 μmol/L）的全细胞培 养基干预 MCF-7/ADR 细胞, 分别采用 Real-time PCR 法检测细胞中 P-gp mRNA 表达, Western Blot 法检测细胞中 P-gp 蛋白表达水平, 罗丹明 123 荧光实验测定 P-gp 的外排功能变化, MTT 法检测 MCF-7/ADR 细胞活性及化疗敏 感性。结果 0.10 μmol/L 的胰岛素可促进 MCF-7/ADR 细胞增殖, 0.05 及 0.10 μmol/L 浓度的胰岛素可增加 MCF-7/ ADR 细胞 P-gp mRNA 及蛋白水平表达, 并能增加 P-gp 的外排功能, 降低 MCF-7/ADR 细胞对表阿霉素的化疗敏感 性。结论 高浓度胰岛素可能通过促进 MCF-7/ADR 细胞 P-gp 的表达和功能, 增加乳腺癌细胞化疗耐药性, 从而降 低 MCF-7/ADR 细胞的化疗敏感性。     

5-羟基雷公藤内酯醇不是P-糖蛋白底物或抑制剂

目的:评价5-羟基雷公藤内酯醇(T8)是否是依赖P-糖蛋白(P-glycoprotein,P-gp)介导的底物或抑制剂,从而评价T8在临床上和其他药物(P-糖蛋白的底物或抑制剂)合用时发生药物-药物相互作用的可能性,为临床药物相互作用研究提供参考。方法:采用MDCK-MDR1细胞模型,测定T8(1μmol/L)的校正外排比(corrected efflux ratio,CER)和以罗丹明123(Rhodamine123,Rho123)和紫杉醇为底物时1μmol/L和5μmol/L的T8对P-gp的抑制率。结果:T8的校正外排比为1.07,T8对P-gp的抑制率均接近0。结论:T8不是P-gp的潜在底物和抑制剂,因此T8和P-gp的底物和抑制剂发生药物-药物相互作用的可能性很低。     

洛美利嗪对大鼠脑微血管内皮细胞上P-糖蛋白活力的影响与P-gp及mdr1基因mRNA表达无关

目的：研究洛美利嗪对原代培养的大鼠脑微血管内皮细胞（RBMECs）上P-糖蛋白（P-gP）功能和表达的影响。方法：使用流式细胞术分析洛美利嗪对P-gp底物-罗丹明123（rhodaminel23，Rh123）在RBMECs中外排的影响，使用流式细胞术分析了洛美利嗪对RBMECs上P-gp表达的影响，应用RT-PCR技术分析了洛美利嗪对RBMECs mdr1基因mRNA水平表达的影响，还使用Transwell模型研究了洛美利嗪对Rh123通透RBMECs单层细胞转运的影响。结果：洛美利嗪通过抑制了RBMECs胞内Rh123的外排；洛美利嗪对P—gP功能的影响与RBMECs上P-gp及mdr1基因mRNA表达无关；在Transwell模型中，洛美利嗪还能显著增加Rh123跨RBMECs单层细胞膜的、经上室至下室的转运，并抑制相反方向的Rh123的转运。结论：洛美利嗪能显著地抑制RBMECs上P-gp的活性，并对P-gp底物的跨细胞转运产生影响。     

流式细胞仪筛选P-糖蛋白的底物或抑制剂

目的以Caco-2细胞模型筛选妥舒沙星、斯帕沙星、辛伐他汀是否为P-糖蛋白(P-gp)的底物。方法以Caco-2细胞为模型,以酮康唑、兰索拉唑为对照,用流式细胞仪测定妥舒沙星、斯帕沙星、辛伐他汀对Caco-2细胞表面的P-gp转运罗丹明-123的影响,经筛选得到可能为P-gp底物的药物后,再用药物转运实验,验证其是否为P-gp的底物。结果妥舒沙星和斯帕沙星存在明显抑制P-gp向细胞外转运罗丹明-123的作用;在加入P-gp抑制剂(酮康唑)后,妥舒沙星的PappBL→AP/PappAP→BL由10.03±0.47降至0.93±0.19,斯帕沙星PappBL→AP/PappAP→BL由2.54±0.12降至1.02±0.04。结论流式细胞仪联用罗丹明-123可简单有效地从多种药物中筛选出可能是P-gp底物的药物(如妥舒沙星和斯帕沙星)及转运机制等。     

枸杞多糖对Caco-2细胞P-糖蛋白作用的影响

目的 研究枸杞多糖(LBP)对Caco-2细胞P-糖蛋白(P-gp)功能和表达的影响.方法 采用MTT法确定药物实验剂量;采用Rh-123摄取法评价P-gp的功能;利用流式细胞术与免疫荧光抗体检测P-gp的表达;采用经典的Caco-2细胞单层模型,研究P-gp外向转运这一动态过程受枸杞多糖作用后的变化.结果 由MTT法得到枸杞多糖＜100μg·mL-1时,细胞的存活率＞90％;枸杞多糖使细胞内Rh-123累积增加,对功能表现为抑制作用;高浓度组(100μg·mL-1)枸杞多糖对P-gp表达有诱导作用;高浓度组(100μg ·mL-1)枸杞多糖使Caco-2细胞单层模型外排率(ER)降低,对P-gp有抑制作用.结论 枸杞多糖对P-gp功能表现为抑制作用,而对P-gp表达表现为诱导作用.     

Curcuma drugs and curcumin regulate the expression and function of P-gp in Caco-2 cells in completely opposite ways

Curcumin is a phenolic compound isolated from rhizomes of C. longa, C. aromatica and other Curcumas except C. zedoaria. Recently, both curcumin and Curcumas have become prevalent as supplement. P-gp has been reported as an important determinant for drug absorption in small intestine. In this study, Caco-2 cell monolayers were treated with methanol extracts of Curcumas (0.1 mg/ml) or curcumin (30 microM) for 72h to investigate the relationship between the potential affects of Curcumas and curcumin on P-gp. [(3)H]-digoxin and rhodamine 123 were used to evaluate P-gp activity. All Curcumas significantly increased the activity of P-gp by up-regulating the expressions of P-gp protein and MDR1 mRNA levels. Interestingly, contrary to Curcumas, curcumin treatment inhibited the activity of P-gp with a decrease in P-gp protein and MDR1 mRNA expression levels. Curcumas might alter the pharmacokinetics of co-administrated drugs by up-regulating the function and expression levels of intestinal P-gp. However, curcumin has no relationship with the inductive effect of Curcumas since curcumin showed an opposite effects. Caution should be exercised when Curcumas or curcumin are to be consumed with drugs that are P-gp substrates because Curcumas and curcumin might regulate the function of P-gp in completely opposite ways.     

Effects of benzo(e)pyrene and benzo(a)pyrene on P-glycoprotein-mediated transport in Caco-2 cell monolayer: a comparative approach.

The previous studies from our laboratory reported that benzo(a)pyrene (Bap) influenced efflux transport of rhodamine 123 (Rho-123) by induction of P-glycoprotein (P-gp) in Caco-2 cells. The present study investigated whether induction of P-gp and the enhanced efflux transport of Rho-123 were caused by benzo(e)pyrene (Bep), which has a structure similar to Bap, but is not a carcinogenic compound. In Caco-2 monolayer exposed to 50 microM Bep for 72 h, the ratio of the apparent permeability coefficient (P(app)) of Rho-123 efflux increased significantly compared to that of the control monolayer. Similarly, a significant increase in expression of MDR1 mRNA and of P-gp at the protein level were detected by RT-PCR and by Western blot analysis, respectively, in Caco-2 cells exposed to Bep, compared to that of the control. Caco-2 cells exposed to Bep showed oxidative stress that was detected by fluorescence microscopy using aminophenyl fluorescein. However, the oxidative stress was weaker compared with that of Bap. The cellular GSH content was decreased to 80% or 59% of control cells, respectively, in Caco-2 cells exposed to either Bep or Bap. Our results further show that Bep or Bap-induced P-gp in Caco-2 cells might have been the result of oxidative stress rather than DNA damage.     

Effect of hr-IL2 treatment on intestinal P-glycoprotein expression and activity in Caco-2 cells

Caco-2 cells were used to investigate the effect of human recombinant interleukin-2 (IL2) on intestinal P-glycoprotein (P-gp) transporter activity in-vitro. More specifically the efflux function of P-gp was studied by measuring the transepithelial transport of rhodamine-123, a fluorescent substrate of P-gp. Its transport was completely inhibited by two specific P-gp inhibitors, ciclosporin A and GG918, in our experiments. Conversely, these two specific P-gp inhibitors inhibited only 50% of transepithelial transport when [3H]vincristine was used as substrate. After Caco-2 cells were treated with 100 IU mL-1 (6.1 ng mL-1) IL2 for 24 h, a significant diminution (21%) of P-gp transporter function was observed with rhodamine-123 substrate. This effect was also confirmed after 48 and 72 h of exposure to IL2. However, for higher concentrations of IL2 (1000 and 5000 IU mL-1), diminution of P-gp function only occurred after a longer treatment period (48 h and more). The inhibitory effect of IL2 on P-gp activity was found to be independent of tight junction function as demonstrated by constant transepithelial electrical resistance (TEER) measurements for all experimental conditions encountered in this study (time and concentration of IL2 exposure). Furthermore, the MDR1 mRNA level was found to be strongly repressed in Caco-2 cells exposed with 1000 IU mL-1 IL2 for 72 h while the amount of MRP1 mRNA remained unchanged. In conclusion, acute incubation of Caco-2 cells with IL2 induced a decrease of P-gp transporter expression and activity.     

Effect of benzo[a]pyrene on P-glycoprotein-mediated transport in Caco-2 cell monolayer

The main exposure pathway of benzo[a]pyrene (Bap) for humans is considered to be via the daily diet. The purpose of this study was to investigate the effect of BaP on the intestinal transport of chemicals mediated by P-glycoprotein (P-gp). The intestinal epithelial membrane transport of rhodamine-123 (Rho-123), a substrate of P-gp, was examined using a monolayer of the human Caco-2 cell line grown in transwells. In the monolayer exposed to Bap for 72 h before transport experiments, the ratio of the apparent permeability coefficients (P(app)) of Rho-123 efflux increased compared to that of the control. The permeability of rhodamine-B (Rho-B), not a substrate of P-gp, showed no difference between the monolayers. Treatment with quinidine or cyclosporine A, which are P-gp inhibitors, decreased the P(app) of Rho-123 to the same degree in both monolayers. The transport of Rho-123 was not influenced by the presence of Bap. Thus, Bap seemed not to act directly on the efflux activity of P-gp and be a binding site competitor of Rho-123. In the Caco-2 cells that enhanced the efflux of Rho-123 by the treatment with Bap, an increase in mRNA expression of MDR 1 (P-gp) was confirmed compared to that of control by RT-PCR. Furthermore, Western blot analysis using a monoclonal antibody, C219, demonstrated the increase of P-gp in Caco-2 cells exposed to Bap, compared with controls. It was inferred that Bap exposure induced the expression of P-gp, which led to the observed increase in efflux transport of Rho-123. The possibility was suggested that Bap might affect the disposition of medicines by increasing P-gp expression.     

Effect of cell differentiation and passage number on the expression of efflux proteins in wild type and vinblastine-induced Caco-2 cell lines.

The mRNA level expression of MDR1, MRP1-6, BCRP and CYP3A4 was determined by quantitative PCR in wild type (Caco-2WT) and vinblastine-treated (Caco-2VBL) Caco-2 cells at different passage levels (32-53). Differentiation increased the mRNA levels of MDR1, BCRP and all the MRPs except MRP4. Corresponding mRNA levels were observed in Caco-2WT and Caco-2VBL, except that the expression of MRD1 was higher in Caco-2VBL than in Caco-2WT cells. CYP3A4 was barely detected in either cell line. MDR1 functionality was studied using rhodamine123 and verapamil as a substrate-inhibitor pair. Corresponding to the observed differences in mRNA levels, MDR1 activity was higher in the Caco-2VBL cells. In Caco-2WT, MDR1 functionality was elevated at low passage numbers (32-35) compared to higher ones (49-53). Verapamil inhibited MDR1 efflux except at higher passage Caco-2WT cells, where no MDR1 activity could be observed. The results support the use of Caco-2VBL cells in MDR1 screening. The functional expression is higher than in Caco-2WT and remains consistent across the studied passages without major differences in mRNA levels of other efflux proteins. As both the passage number and the level of cell differentiation affect the expression profile of efflux proteins, short-term cell growth protocols should be evaluated accordingly.     

Effects of budesonide on P-glycoprotein expression in intestinal cell lines

BACKGROUND AND PURPOSE: P-glycoprotein (P-gp) is an important efflux transporter that supports the barrier function of the gut against invading antigens and against administered drugs. Since glucocorticoids, such as budesonide, are frequently used during inflammatory bowel disease we investigated how budesonide influences P-gp expression in different intestinal cell lines. EXPERIMENTAL APPROACH: LS180 and Caco-2 cells were incubated with budesonide and changes in P-gp expression were determined on mRNA, protein and functional level. The mRNA expression levels of glucocorticoid receptor (GR) and pregnane X receptor (PXR) were determined in these cell lines. PXR receptor was transiently transfected into Caco-2 cells. KEY RESULTS: Budesonide showed an induction of P-gp in LS180 cells and a down-regulation in Caco-2 cells. Expression levels of nuclear receptors revealed high expression of PXR only in LS180 cells and exclusive expression of GR in Caco-2 cells. Mifepristone, an anti-glucocorticoid, could not reverse the down-regulation of P-gp by budesonide in Caco-2 cells. In PXR-transfected Caco-2 cells the budesonide-mediated down-regulation of P-gp was abolished. Furthermore the expression of cytochrome P450 3A4 (CYP3A4), another PXR target gene, was induced in PXR-transfected Caco-2 cells after budesonide treatment. CONCLUSIONS AND IMPLICATIONS: Budesonide has the potential to influence MDR1 expression in vitro. In LS180 cells, the induction of MDR1 by budesonide probably is mediated via PXR. The mechanism of the down-regulation in Caco-2 cells still remains unclear, but GR does not seem to be involved. Further studies are required to evaluate how budesonide alters P-gp expression in vivo.     

Effect of curcumin on multidrug resistance in resistant human gastric carcinoma cell line SGC7901/VCR

AIM: To investigate the reversal effects of curcumin on multidrug resistance (MDR) in a resistant human gastric carcinoma cell line. METHODS: The cytotoxic effect of vincristine (VCR) was evaluated by MTT assay. The cell apoptosis induced by VCR was determined by propidium iodide (PI)-stained flow cytometry (FCM) and a morphological assay using acridine orange (AO)/ethidium bromide (EB) dual staining. P-glycoprotein (P-gp) function was demonstrated by the accumulation and efflux of rhodamine123 (Rh123) using FCM. The expression of P-gp and the activation of caspase-3 were measured by FCM using fluorescein isothiocyanate (FITC)-conjugated anti-P-gp and anti-cleaved caspase-3 antibodies, respectively. RESULTS: Curcumin, at concentrations of 5 micromol/L, 10 micromol/L, or 20 micromol/L, had no cytotoxic effect on a parent human gastric carcinoma cell line (SGC7901) or its VCR-resistant variant cell line (SGC7901/VCR). The VCR-IC50 value of the SGC7901/VCR cells was 45 times more than that of the SGC7901cells and the SGC7901/VCR cells showed apoptotic resistance to VCR. SGC7901/VCR cells treated with 5 micromol/L, 10 micromol/L, or 20 micromol/L curcumin decreased the IC50 value of VCR and promoted VCR-mediated apoptosis in a dose-dependent manner. Curcumin (10 micromol/L) increased Rh123 accumulation and inhibited the efflux of Rh123 in SGC7901/VCR cells, but did not change the accumulation and efflux of Rh123 in SGC7901 cells. P-gp was overexpressed in SGC7901/VCR cells, whereas it was downregulated after a 24-h treatment with curcumin (10 micromol/L). Resistant cells treated with 1 mumol/L VCR alone showed 77% lower levels of caspase-3 activation relative to SGC7901 cells, but the activation of caspase-3 in the resistant cell line increased by 44% when cells were treated with VCR in combination with curcumin. CONCLUSION: Curcumin can reverse the MDR of the human gastric carcinoma SGC7901/VCR cell line. This might be associated with decreased P-gp function and expression, and the promotion of caspase-3 activation in MDR cells.     

Induction of human P-glycoprotein in Caco-2 cells: development of a highly sensitive assay system for P-glycoprotein-mediated drug transport

The aim of this work is to develop a highly sensitive assay system for P-gp-mediated transport by using two methods, induction of P-gp and short-term culture of Caco-2 cells. To induce P-gp in Caco-2 cells, cells were cultured in vinblastine-containing medium. The mRNA level of P-gp was approximately 7-fold higher in Caco-2 cells cultured with vinblastine (P-gp-induced Caco-2 cells) than in control cells. Western blot analysis showed a significant increase in P-gp expression. After cell differentiation, the mRNA level of P-gp was downregulated, however, P-gp-induced Caco-2 cells still possessed a 5.6-fold higher mRNA level of P-gp compared to control cells. Polarized transport of substrate drugs was greater in the monolayer of P-gp-induced cells than in that of control cells. Moreover, we found that P-gp expression in Caco-2 cells could be further enhanced by applying the higher concentration of vinblastine. Transport activity of P-gp in Caco-2 cells cultured with higher concentration of vinblastine was markedly higher than that in P-gp-induced Caco-2 cells and was comparable with that in MDR1-MDCKII cells. In conclusion, this study provided a stable and highly sensitive in vitro assay system that can identify compounds that are subject to P-gp-mediated efflux.