Multidrug Resistance-associated Protein mRNA Research Articles

IFN‑γ induces apoptosis in gemcitabine‑resistant pancreatic cancer cells.

Pancreatic ductal adenocarcinoma (PDAC) is the most prevalent and aggressive form of pancreatic cancer. Gemcitabine (GEM), the first‑line treatment for PDAC, which alleviates symptoms and enhances the quality of life of patients. However, it is prone to lead to the development of drug resistance during treatment. Interferon (IFN)‑γ exhibits antitumor and immunomodulatory properties. The present study aimed to explore the impact of IFN‑γ on the viability, migration and apoptosis of GEM‑resistant pancreatic cancer cells. Firstly, a GEM‑resistant pancreatic cancer cell line, named PANC‑1/GEM, was constructed. Hematoxylin and eosin staining analyzed the cell morphology, whereas reverse transcription‑quantitative PCR (RT‑qPCR) assessed the expression levels of the drug‑resistance genes multidrug resistance‑associated protein (MRP) and breast cancer resistance protein (BCRP). The MTT assay and cell counting techniques were used to determine the appropriate concentration of IFN‑y and its effects on cell viability. The IFN‑γ‑induced apoptosis of PANC‑1/GEM cells was assessed using an Apoptosis Detection Kit, whereas the impact of IFN‑γ on the migration of these cells was evaluated using a wound‑healing assay. The MTT assay revealed a resistance index of 22.4 in the PANC‑1/GEM cell line. RT‑qPCR indicated that, compared with in wild‑type cells, the PANC‑1/GEM resistant strain exhibited lower MRP and higher BCRP mRNA expression levels. The optimal concentration of IFN‑γ for affecting PANC‑1/GEM cells was determined to be 0.3 µg/ml. At this concentration, IFN‑γ induced PANC‑1/GEM cell apoptosis, along with a notable reduction in migration. Following treatment of PANC‑1/GEM cells with IFN‑γ, MRP expression increased whereas BCRP mRNA expression decreased, indicating a reversal in their drug‑resistance gene expression. In conclusion, IFN‑γ exhibited antitumor immune properties by upregulating MRP and downregulating BCRP expression, reversing drug‑resistance gene expression, and reducing cell viability and migration, while promoting apoptosis in PANC‑1/GEM cells. IFN‑γ could potentially serve as a treatment option for patients with GEM‑resistant pancreatic cancer.

Development of multi-drug resistance to anticancer drugs in HepG2 cells due to MRP2 upregulation on exposure to menthol.

Menthol exerts relaxing, antibacterial, and anti-inflammatory activities, and is marketed as a functional food and therapeutic drug. In the present study, the effects of menthol on the expression of multidrug resistance associated protein 2 (MRP2) and its association with the cytotoxicity of epirubicin (EPI) and cisplatin (CIS) were examined using HepG2 cells. The expression levels of target genes were examined by real-time PCR. The intracellular concentration of incorporated EPI was measured by high-performance liquid chromatography. Cell viability was evaluated by MTT analysis. The expression of MRP2 mRNA was increased by exposing HepG2 cells to menthol for 24 hr. Consistent with a previous report suggesting an inverse correlation between MRP2 and Akt behavior, increased expression of MRP2 was also observed on suppression of the Akt function. Intracellular accumulation of EPI was significantly decreased by exposure of HepG2 cells to menthol, and a significant decrease in the intracellular concentration of EPI remaining was observed in HepG2 cells exposed to menthol. The decreased intracellular accumulation of EPI was significantly suppressed by treatment with MK-571, but not verapamil. Both EPI and CIS exerted cytocidal effects on HepG2 cells, but the decrease in cell viability was significantly attenuated by 24-hr menthol pre-exposure. These results demonstrate that menthol causes hepatocellular carcinoma to acquire resistance to anticancer drugs such as EPI and CIS by MRP2 induction.

Directional Drug Transport through Membrane-Supported Monolayers of Human Liver-Derived Cell Lines.

The aim of this work is to develop a new assay system for screening biliary excretion drugs. When monolayers of human liver-derived cell lines HepG2 and Huh-7 were grown on an insert membrane, the efflux ratio (ER: ratio of the apparent permeability coefficient in the basal-to-apical direction (Papp,B-to-A) to that in the apical to basal direction (Papp,A-to-B)) of sulfobromophthalein (BSP), a model substrate of multidrug resistance-associated protein 2 (MRP2), was greater than 1.0, indicating transport of BSP in the efflux direction. The efflux transport was significantly suppressed by MK-571, an inhibitor of MRPs, in both cell lines. Expression of MRP2 mRNA in HepG2 and Huh-7 was 3.5- and 1.4-fold higher, respectively, than in primary human hepatocytes, while expression of P-glycoprotein and breast cancer resistance protein mRNAs was markedly lower, supporting the idea that MRP2 is the main mediator of directional BSP transport in this assay system. The advantage of our system is the potential to quantitatively evaluate biliary excretion of MRP2 substrates in vitro.

Interaction of arsenic trioxide and etoposide in Ewing sarcoma cell lines.

Ewing sarcomas (ES) are highly malignant mesenchymal tumors, which most often occur in children and adolescents. The current treatment of choice comprises wide resection in combination with multimodal chemotherapy including etoposide (Eto). Due to the serious side effects associated with common chemotherapeutics and prevalent multidrug resistance in recurrent and metastatic ES, there is a growing demand for alternative strategies and add‑on drugs. Previous research has demonstrated efficient cell death induction by Eto in combination with arsenic trioxide (ATO) in ES cell lines. The aim of the present study was to investigate the effect of different temporal sequences of ATO and Eto administration on apoptosis induction and to explore the effect of both drugs on inhibitory glycogen synthase kinase‑3β (GSK3‑β) phosphorylation as well as multidrug transporter gene expression. The intensity of caspase activation was mainly determined by the Eto doses in A673 and TC‑71cells, whereas in RD‑ES cells ATO application actively suppressed Eto‑induced apoptosis. This coincided with an increase in inhibitory GSK‑3β phosphorylation in ATO‑treated RD‑ES cells. Inherent mRNA expression of multidrug resistance‑associated protein1 (MRP1) was low in the ES cell lines compared to that observed in the mesenchymal stem cells (MSC), whereas multidrug resistance protein1 (MDR1) gene expression was considerably increased in the ES cell lines. ATO treatment reduced MRP1 mRNA expression in the A673 and TC‑71cells, while expression was induced in the MSC and RD‑ES cells. In contrast, MDR1 mRNA expression was specifically induced by ATO in the A673 and TC‑71cells, reinforcing the expression differences between MSC and the ES cell lines. Although a reliable cell death induction by the combination of ATO and Eto has been previously shown in ES cell lines, the present study showed marked heterogeneity of the ES cell response to ATO and Eto treatment, illustrating the difficulty of prediction of individual treatment outcome in ES.

Expression levels of MRP1, GST-π, and GSK3β in ovarian cancer and the relationship with drug resistance and prognosis of patients.

Expression levels of multidrug resistance-associated protein 1 (MRP1), glutathione S-transferase π (GST-π) and glycogen synthase kinase-3β (GSK3β) were investigated in ovarian epithelial cancer and the relationship with the primary drug resistance of patients with ovarian cancer to chemotherapy. One hundred and twenty-one ovarian cancer tissue samples from patients who underwent ovarian cancer resection from January 2013 to June 2015 in Liaoning Cancer Hospital and Institute, Cancer Hospital of China Medical University were enrolled in the Experimental group, while 58 ovarian tissue samples from patients with fallopian tube obstruction but with no ovarian cancer who received surgical treatment for blocked fallopian tube were included in the Control group. After the detection of the expression levels of MRP1, GST-π, and GSK3β mRNA by RT-PCR and the analysis of related clinical pathological factors, patients in the Experimental group were divided into the Chemotherapy-sensitive and Chemotherapy-resistant groups according to the chemotherapy efficacy. Additionally, with the mean expression levels of MRP1, GST-π, and GSK3β in ovarian cancer tissues as the boundaries, the expression levels of the three genes in the Experimental group were classified into high expression and low expression. Ovarian cancer tissues had much higher expression levels of MRP1, GST-π, and GSK3β mRNA than normal ovarian tissues (P<0.05). The expression levels of MRP1, GST-π, and GSK3β mRNA in the Chemotherapy-sensitive group were significantly lower than those in the Chemotherapy-resistant group (P<0.05). Patients with high expression of MRP1, GST-π, and GSK3β mRNA had a much lower 3-year survival rate than patients with low expression of the genes (P<0.05). Highly expressed in patients with ovarian cancer, MRP1, GST-π, and GSK3β mRNA play an important role in the development and drug resistance of ovarian cancer, which ensures this study is of positive clinical guiding significance in developing proper treatment for ovarian cancer and evaluating the efficacy of chemotherapy.

Quercetin and kaempferol increase the intestinal absorption of isorhamnetin coexisting in Elaeagnus rhamnoides (L.) A. Nelson (Elaeagnaceae) extracts via regulating multidrug resistance-associated protein 2

BackgroundIsorhamnetin (IS) is a flavonoid component with many biological activities such as antioxidant, anti-inflammatory, and anticancer, which is also the main active component in total flavones of Elaeagnus rhamnoides (L.) A. Nelson (Elaeagnaceae) (TFH); however, the interaction between IS and other components in TFH is unclear. PurposeThe aim of the present study was to investigate the enhancement of quercetin (QU) or kaempferol (KA) on the intestinal absorption of IS coexisting in TFH, and then preliminarily illuminate the related mechanisms. MethodsFirstly, the intestinal absorption of IS in the presence or absence of QU or KA was conducted by in vivo pharmacokinetics model, in situ single-pass intestinal perfusion model (SPIP), and MDCK II-MRP2 monolayer cell model to confirm the enhancement of QU or KA on IS absorption. Secondly, the effects of multidrug resistance-associated protein 2 (MRP2) inhibitors on the IS intestinal absorption were investigated to ascertain the mediation of MRP2 on IS absorption. Finally, the effects of QU or KA on MRP2 activity, protein expression, and mRNA level were performed by SPIP, everted-gut sacs, western blotting, and real-time polymerase chain reaction experiments to elucidate the related mechanisms. ResultsQU or KA increased IS intestinal absorption according to the increased AUC0–96h, Cmax, and Peff of IS after co-administrated with QU or KA to rats; the oral absorption of IS was mediated by MRP2 based on the facts that the average plasma concentration, AUC0–96h, and Peff of IS were increased when co-administrated with PR or MK571 (MRP2 inhibitors) as well as the Pratio(BL/AP) of IS was decreased by MK571 in MDCK II-MRP2 cell monolayer; the activity, protein expression, and mRNA level of MRP2 were inhibited or down-regulated by QU or KA because of the increased Peff of MRP2 substrate calcein (CA) and the down-regulated relative protein and mRNA intensity after co-treated with QU or KA. ConclusionQU and KA increased the intestinal absorption of IS in TFH by regulating the activity and expression of MRP2, which provides useful information for the investigation of the transporter-mediated interaction of flavonoid components in herbal extracts.

Effect of YHHJ on the expression of the hepatocellular bile acid transporters multidrug resistance-associated protein 2 and bile salt export pump in ethinylestradiol-induced cholestasis.

The herbal medicine Yin Huang Mixture (YHHJ; patent no. 200910031240.7) is an aqueous extract composed from various herbs, including Artemisia capillaries Thunb, Hypericum japonicum Thunb, Eucommia ulmoides Oliver, Rheum officinale Baill, Gardenia jasminoides Ellis, Poria cocos Wolf and Dictamnus dasycarpus Turcz. Previous studies have indicated that YHHJ treatment has a beneficial effect on ameliorating itching and reducing serum bile acid levels in patients with intrahepatic cholestasis of pregnancy (ICP). However, the molecular mechanisms of action of YHHJ in ICP have not been fully elucidated. Therefore, the present study investigated an experimental hepatocellular cholestasis model to explore the regulatory role of YHHJ on the expression of the bile acid carriers, multidrug resistance-associated protein 2 (MRP2) and the bile salt export pump (BSEP). Initially, 5 mg/kg/day 17-α ethinylestradiol (EE) was used to induce cholestasis in rats and primary isolated rat hepatocytes. Subsequently, 9 or 36 g/kg/day YHHJ water extract was administrated. Blood samples were collected and serum biochemical parameters of total bile acids (TBA), total bilirubin (TBil), alanine transaminase and aspartate aminotransferase levels were determined. Rat livers and primary isolated rat hepatocytes were obtained and the protein and mRNA expression levels of MRP2 and BSEP were analyzed by western blot analysis and reverse transcription-quantitative polymerase chain reaction, respectively. Results revealed that EE-induced hepatocellular cholestasis was associated with a significant increase in serum TBA and TBil levels, whereas, YHHJ treatment significantly reversed this effect (P<0.01). Further experiments on the molecular mechanism revealed that EE significantly decreased the expression of MRP2 and BSEP compared with the control group, whereas YHHJ treatment significantly upregulated MRP2 and BSEP expression in vivo and in vitro compared with no YHHJ treatment (P<0.01). In addition, to establish whether upregulation of MRP2 and BSEP protein expression levels resulted from increased expression of their respective mRNA, the mRNA expression levels were determined. Results indicated that YHHJ treatment significantly increased MRP2 and BSEP mRNA expression levels in EE-induced hepatocellular cholestasis compared with no YHHJ treatment (P<0.01). In conclusion, the present findings suggest that YHHJ effects EE-induced cholestasis and this process may be mediated through regulating hepatobiliary transporters, MRP2 and BSEP.

Study of peripheral blood multidrug resistance-associated protein 1 expression of children intractable epilepsy.

The aim of this study was to analyze multidrug resistance-associated protein 1 (MRP1) expression of peripheral blood of children intractable epilepsy. Sixty children with epilepsy admitted to outpatient and inpatient services of Xuzhou Children's Hospital between November 2010 and October 2011 were divided into a refractory epilepsy group and a drug-controlled epilepsy group, with 30 cases each. Thirty healthy children who went to the hospital in the same year for health examination were enrolled as a control group. Reverse transcriptase polymerase chain reaction and Western blot method were used to determine peripheral blood MRP1 level, mRNA, and protein content of the 3 groups. MRP1 expression in the refractory epilepsy group was significantly higher than those of the epilepsy group with good drug control and of the control group. All differences had statistical significance (P<0.05), except for the comparison between the drug-controlled epilepsy group and the control group (P>0.05). Peripheral blood MRP1 expression in patients with refractory epilepsy increases.

Reversal effect and mechanism of Ginkgo biloba exocarp extracts in multidrug resistance of mice S180 tumor cells.

The aim of the present study was to investigate the reversal effect and its related mechanism of Ginkgo biloba exocarp extracts (GBEEs) in obtained multidrug resistance (MDR) of mice S180 tumor cells in vitro and in vivo. In order to simulate the clinical PFC [cis-dichlorodiamineplatinum, cisplatin (DDP) + fluorouracil (FU), FU+cyclophosphamide and cyclophosphamide] scheme, a gradually increasing dose was administered in a phased induction in order to induce S180 cells in vivo and to make them obtain multidrug resistance. The results in vitro demonstrated that GBEE could significantly increase the IC50 of DDP on S180 MDR cells, increase the accumulation of Adriamycin (ADR) and rhodamine 123 (Rho 123), and reduce the efflux of Rho 123 of S180 MDR cells. The results from the in vivo treatment with a combination of GBEE and DDP to S180 MDR ascites tumor in mice demonstrated that each dose of GBEE could effectively reverse the drug-resistance of S180 MDR cells to DDP in order to extend the survival time of mice with ascite tumors and inhibit tumor growth in solid tumor mice. In addition, GBEE effectively inhibited the expression of MDR-1 mRNA and multidrug resistance-associated protein-1 mRNA in S180 MDR cells of ascites tumor in mice and improved the expression levels of cytokines, including interleukin (IL)-3, IL-18 and interferon-γ in the blood serum of S180 MDR tumor-bearing mice. The present study showed that the mechanism of GBEE reversal of MDR may be associated with the inhibition of the functional activity of P-glycoprotein, the downregulation of drug resistance related gene expression of S180 MDR cells and the improvement of the production of related serum cytokines of S180 MDR tumor mice.

The trypanocidal benznidazole promotes adaptive response to oxidative injury: Involvement of the nuclear factor-erythroid 2-related factor-2 (Nrf2) and multidrug resistance associated protein 2 (MRP2)

Oxidative stress is a frequent cause underlying drug-induced hepatotoxicity. Benznidazole (BZL) is the only trypanocidal agent available for treatment of Chagas disease in endemic areas. Its use is associated with side effects, including increases in biomarkers of hepatotoxicity. However, BZL potential to cause oxidative stress has been poorly investigated. Here, we evaluated the effect of a pharmacologically relevant BZL concentration (200μM) at different time points on redox status and the counteracting mechanisms in the human hepatic cell line HepG2. BZL increased reactive oxygen species (ROS) after 1 and 3h of exposure, returning to normality at 24h. Additionally, BZL increased glutathione peroxidase activity at 12h and the oxidized glutathione/total glutathione (GSSG/GSSG+GSH) ratio that reached a peak at 24h. Thus, an enhanced detoxification of peroxide and GSSG formation could account for ROS normalization. GSSG/GSSG+GSH returned to control values at 48h. Expression of the multidrug resistance-associated protein 2 (MRP2) and GSSG efflux via MRP2 were induced by BZL at 24 and 48h, explaining normalization of GSSG/GSSG+GSH. BZL activated the nuclear erythroid 2-related factor 2 (Nrf2), already shown to modulate MRP2 expression in response to oxidative stress. Nrf2 participation was confirmed using Nrf2-knockout mice in which MRP2 mRNA expression was not affected by BZL. In summary, we demonstrated a ROS increase by BZL in HepG2 cells and a glutathione peroxidase- and MRP2 driven counteracting mechanism, being Nrf2 a key modulator of this response. Our results could explain hepatic alterations associated with BZL therapy.

Abstract 4420: Factors potentially contributing to sensitivities of CD22-targeting agents in B-cell malignancies

Abstract In order to understand factors which may contribute to in vitro sensitivity of B-cell malignancies to CD22-targeting agents, we evaluated the mRNA expression levels of genes involved with diphthamide biosynthesis, multi-drug resistance, and CD22 (including the splice variant 3 with exon12 deletion) in untreated and 72-hour CD22-targeting agent-treated DLBCL and CLL cell lines. Cell line sensitivity (EC50) to CD22-targeting agent treatment was evaluated by 72 hour exposureto moxetumomab pasudotox (MP).Cell lines were characterized as insensitive if the EC50's were greater than100 ng/mL. The sensitivity to CD22 -targeting agent treatment was found to be significantly associated with baseline CD22 mRNA expression level, as determined by regression analysis. The highly resistant DLBCL cell line RCK8 and the resistant CLL cell line Z138 demonstrated low CD22 expression, corresponding to their elevated EC50′s. However, baseline mRNA was not significantly lower in some other less sensitive cell lines, suggesting that total mRNA CD22 levels may not be the only factor contributing to reduced sensitivity to anti-CD22 exposure. Given the critical roles of dipthamides in CD22 targeting, we evaluated baseline DPH4 levels and their methylation status. There was no correlation between CD22-targeting agent sensitivity and baseline levels of DPH4 expression/promoter methylation. We further explored how CD22, DPH4, WDR85 and MRP1 mRNA expression changed following a 72 hour exposure to MP. Following MP exposure, both mRNA and methylation levels of DPH4 were not significantly changed. However, the mRNA levels of both the diphthamide biosynthesis protein WDR85 and multidrug resistance-associated protein 1 (MRP1) were up-regulated in half of the cell lines following MP exposure. As expression of truncated CD22 has been reported in ALL, we also evaluated CD22 variant expression before and following CD22-targeting agent exposure. All CD22 variants were co-expressed in most cell lines, with significantly increased V3 observed following treatment in some cell lines with lower EC50′s. In conclusion, our results show sensitivity to CD22-targeting agent in the majority of the cell lines tested, and suggest that multiple factors may contribute to sensitivity including CD22 expression. Additionally, our results suggest that factors which may affect continued response to CD22 targeting agents may change with treatment, including increases in CD22 variant 3, MRP1 and WDR85. Ongoing research will evaluate whether these changes are relevant to CD22-targeting agent sensitivity in vivo. Citation Format: Xin Yao, Patricia Burke, Joyce O. Obidi, Xiaoru Chen, Haifeng Bao, Yihong Yao, Jiaqi Huang. Factors potentially contributing to sensitivities of CD22-targeting agents in B-cell malignancies. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4420. doi:10.1158/1538-7445.AM2015-4420

Upregulation of Multidrug Resistance-Associated Protein 1 by Allyl Isothiocyanate in Human Bronchial Epithelial Cell: Involvement of c-Jun N-Terminal Kinase Signaling Pathway.

Multidrug resistance-associated protein 1 (MRP1) plays a protective role in the etiology and progression of chronic obstructive pulmonary disease (COPD) which results from oxidative stress and inflammation of lung injury. The lower functional MRP1 activity is related to COPD development. Our previous study showed that Allyl isothiocyanate (AITC) induced the expression and activity of MRP1 in a dose-dependent manner. However, which signaling pathway contributes to the upregulation of MRP1 by AITC is unclear. In this study, signaling pathway specific inhibitors were used to examine the mechanism of AITC. We found that JNK inhibitor SP600125 treatment decreased MRP1 mRNA expression in 16HBE14o- cells. But the ERK inhibitor U0126 or PI3K/Akt inhibitor LY294002 produced no obvious effect. The AITC-induced increase of MRP1 mRNA expression was abolished by cotreatment of SP600125, while it was not obviously affected by U0126 or LY294002. Furthermore, AITC acivates the JNK signaling pathway in 16HBE14o- cells. Finally, we found that JNK pathway mediated the upregulation of AITC-induced expression and function of MRP1. Taken together, our results indicated that AITC increased the expression and the activity of MRP1 via a JNK-dependent pathway. ERK and PI3K signaling pathway were not involved in the expression of MRP1 mRNA.

Down-Regulation of MRP1 Expression in C6/VP16 Cells by Chitosan-MRP1-siRNA Nanoparticles.

High expression of multidrug resistance-associated protein 1 (MRP1) in tumor cells reduces effectiveness of chemotherapy drugs. In this study, we screened MRP1 interfering RNA (MRP1-siRNA) molecules that are able to reverse etoposide (VP16) resistance in multidrug resistance rat glioma cell line C6/VP16, and identified one siRNA molecule that is able to effectively deplete the expression of MRP1 gene and reverse tumor cells resistance to etoposide. Since siRNA instability limits its application in treatment of diseases, we next tested silencing effect of chitosan-MRP1-siRNA nanoparticles and found that the nanoparticles with N:P ratio 175 are able to effectively inhibit MRP1 mRNA and protein expression. Our data demonstrate that chitosan can be used as siRNA carrier for high efficient gene silencing in tumor cells.

Transcriptional regulation, stabilization, and subcellular redistribution of multidrug resistance-associated protein 1 (MRP1) by glycogen synthase kinase 3αβ: novel insights on modes of cadmium-induced cell death stimulated by MRP1.

Cadmium (Cd) resistance is associated with the suppression of autophagy in H460 lung cancer cells, which is regulated by phospho(p)serine-glycogen synthase kinase (GSK) 3αβ. However, the involvement of multidrug resistance (MDR) in this signaling pathway and its underlying mechanisms remain to be elucidated. In this study, we used Cd-resistant cells (RH460), developed from H460 lung cancer cells, to demonstrate that the induction of MDR-associated protein (MRP1) in response to Cd is enhanced in H460 cells compared to RH460. Treating RH460 cells with Cd induced large cytoplasmic vacuoles, which was inhibited by the autophagy inhibitor 3-methyladenine. MRP1 was detected in the nuclear-rich membrane fractions and redistributed from the perinuclear to the cytoplasmic compartment following exposure to Cd. Cd-induced MRP1, p-Ser/p-Tyr GSK3αβ, and LC3-II were all suppressed by the GSK3 inhibitor SB216763, but increased by lithium. Furthermore, MRP1 was upregulated by the Ser/Thr phosphatase inhibitor okadaic acid and downregulated by the tyrosine phosphatase inhibitor vanadate, suggesting that MRP1 protein was stabilized by p-Ser GSK3αβ. In addition, co-immunoprecipitation and co-localization analyzes revealed a physical interaction between MRP1 and p-Ser GSK3αβ. Genetic knockdown of GSK3β decreased Cd-induced MRP1 mRNA and protein levels, whereas its overexpression upregulated MRP1 protein expression. MRP1 also co-localized with lysosomal membrane protein-2, which may cause lysosomal membrane permeabilization and the subsequent release of cathepsins into the cytosol. In mice chronically injected with Cd, MRP1 localized to the perinuclear region of bronchial and alveolar epithelial cells. Collectively, these data suggest that Cd toxicity is regulated by the transcriptional regulation, stabilization, and subcellular redistribution of MRP1 via the posttranslational modification of GSK3αβ. Therefore, the serine phosphorylation of GSK3αβ plays a critical role in MRP1-induced cell death.

Significance of multidrug resistance associated protein 1 and protein 2 expressions in peripheral blood mononuclear cells in children with intractable epilepsy

Objective To study the expression of multidrug resistance associated protein 1 (MRP1) and MRP2 in the peripheral blood mononuclear cells of children with intractable epilepsy (IE). Methods During Nov.2010 to Oct.2013, 50 children with IE were collected as the experimental group, simultaneously 50 children with epilepsy controlled by the anti-epileptic drugs (AEDs) and 50 healthy children without epilepsy were collected as the control group from the outpatient or inpatient of Xuzhou Children's Hospital. The expressions of MRP1 and MRP2 in the peripheral blood mononuclear cells of children were detected by reverse transcriptase polymerase chain reaction and Wes-tern blot. Results 1.The mean relative expression of MRP1 and MRP2 mRNA in the peripheral blood mononuclear cells of children with IE (0.795±0.042, 0.804±0.023) were higher than those in epilepsy controlled by AEDs (0.682±0.030, 0.675±0.021)and healthy children without epilepsy (0.665±0.031, 0.654±0.029) (all P 0.05). Conclusions MRP1 and MRP2 over-expression in the peripheral blood mononuclear cells of children with IE may be associated with drug-resistance mechanism for medically intractable epilepsy. Key words: Intractable epilepsy; Multidrug resistant associated protein; Peripheral blood mononuclear cell; Child

Flavonostilbenes from Sophora alopecuroides L. as multidrug resistance associated protein 1 (MRP1) inhibitors

Flavonoids have always attracted much attention due to their reversal activity on multidrug resistance (MDR). Eight flavonoids isolated from traditional Chinese medicine Sophora alopecuroides L. were applied to test their effect on MDR associated protein 1 (MRP1) through the established predicting assay. Three flavonostilbenes (alopecurone A, B and D) were first found exhibiting potent inhibitory activity on MRP1. All of them dramatically increased 6-carboxyfluorescein diacetate and doxorubicin accumulation in MRP1-transfected U-2 OS cells. The compounds significantly increased the cytotoxicity and decreased the IC50 value of doxorubicin on the MDR cells (12-, 5- and 8-fold, respectively) at a non-toxic concentration (20 μM). Besides, Q-PCR analysis reveals that the MRP1 mRNA level in U-2 OS/MRP1 was also markedly decreased by the three compounds. These findings indicate a new therapeutic role of the herb. The three flavonostilbenes may have the possibility for further development as novel therapeutic reversal agents against MDR.

Reversal effect of BM-cyclin 1 on multidrug resistance by down-regulating MRP2 in BALB/C nude mice bearing C-A120 cells

Our previous study demonstrated that BM-cyclin 1, a traditional anti-mycoplasma drug, could effectively reverse the multidrug resistance (MDR) of C-A120 cells. The present study aims to explore the reversal effect of BM-cyclin 1 on MDR and its mechanisms in BALB/C nude mice bearing C-A120 cells. Immunoblotting analysis and reverse transcription-polymerase chain reaction (RT-PCR) were used to study the change in multidrug resistance-associated protein 2 (MRP2) induced by BM-cyclin 1. We found that the expression levels of MRP2 protein and mRNA in C-A120 cells treated with BM-cyclin 1 were reduced significantly. Chemical colorimetry revealed no significant change in the level of glutathione (GSH). In the xenograft model, the inhibitory rate of C-A120 cells growth in BM-cyclin 1 plus adriamycin (ADM) group was 52%, which was significantly higher than in control group (P<0.01). The immunoblotting and RT-PCR results conclusively demonstrated that BM-cycin 1 could significantly reduce the expression of MRP2 in transplanted tumor. In conclusion, BM-cyclin 1 could effectively reverse the MDR of C-A120 cells in vivo by suppressing the expression of MRP2.

Regulation of Hepatic Drug Transporter Activity and Expression by Organochlorine Pesticides

Organochlorine (OC) pesticides constitute a major class of persistent and toxic organic pollutants, known to modulate drug-detoxifying enzymes. In the present study, OCs were demonstrated to also alter the activity and expression of human hepatic drug transporters. Activity of the sinusoidal influx transporter OCT1 (organic cation transporter 1) was thus inhibited by endosulfan, chlordane, heptachlor, lindane, and dieldrine, but not by dichlorodiphenyltrichloroethane isomers, whereas those of the canalicular efflux pumps MRP2 (multidrug resistance-associated protein 2) and BCRP (breast cancer resistance protein) were blocked by endosulfan, chlordane, heptachlor, and chlordecone; this latter OC additionally inhibited the multidrug resistance gene 1 (MDR1)/P-glycoprotein (P-gp) activity. OCs, except endosulfan, were next found to induce MDR1/P-gp and MRP2 mRNA expressions in hepatoma HepaRG cells; some of them also upregulated BCRP. By contrast, expression of sinusoidal transporters was not impaired (organic anion-transporting polypeptide (OATP) 1B1 and OATP2B1) or was downregulated (sodium taurocholate co-transporting polypeptide (NTCP) and OCT1). Such regulations of drug transporter activity and expression, depending on the respective nature of OCs and transporters, may contribute to the toxicity of OC pesticides.

Multidrug resistance-associated protein 1 decreases the concentrations of antiepileptic drugs in cortical extracellular fluid in amygdale kindling rats

To investigate whether multidrug resistance-associated protein 1 (MRP1) was responsible for drug resistence in refractory epilepsy in amygdale kindling rats. Rat amygdale kindling was used as a model of refractory epilepsy. The expression of MRP1 mRNA and protein in the brains was examined using RT-PCR and Western blot. MRP1-positive cells in the cortex and hippocampus were studied with immunohistochemical staining. The rats were intraperitoneally injected with phenytoin (50 mg/kg) or carbamazepine (20 mg/kg), and their concentrations in the cortical extracellular fluid were measured using microdialysis and HPLC. Probenecid, a MRP1 inhibitor (40 mmol/L, 50 μL) was administered through an inflow tube into the cortex 30 min before injection of the antiepileptic drugs. The expression of MRP1 mRNA and protein was significantly up-regulated in the cortex and hippocampus in amygdale kindling rats compared with the control group. Furthermore, the number of MRP1-positive cells in the cortex and hippocampus was also significantly increased in amygdale kindling rats. Microdialysis studies showed that the concentrations of phenytoin and carbamazepine in the cortical extracellular fluid were significantly decreased in amygdale kindling rats. Pre-administration of probenecid could restore the concentrations back to their control levels. Up-regulation of MRP1 is responsible for the resistance of brain cells to antiepileptic drugs in the amygdale kindling rats.

The effects of clobazam treatment in rats on the expression of genes and proteins encoding glucronosyltransferase 1A/2B (UGT1A/2B) and multidrug resistance‐associated protein-2 (MRP2), and development of thyroid follicular cell hypertrophy

Clobazam (CLB) is known to increase hepatobiliary thyroxine (T4) clearance in Sprague–Dawley (SD) rats, which results in hypothyroidism followed by thyroid follicular cell hypertrophy. However, the mechanism of the acceleration of T4-clearance has not been fully investigated.In the present study, we tried to clarify the roles of hepatic UDP-glucronosyltransferase (UGT) isoenzymes (UGT1A and UGT2B) and efflux transporter (multidrug resistance–associated protein-2; MRP2) in the CLB-induced acceleration of T4-clearance using two mutant rat strains, UGT1A-deficient mutant (Gunn) and MRP2-deficient mutant (EHBR) rats, especially focusing on thyroid morphology, levels of circulating hormones (T4 and triiodothyronine (T3)) and thyroid-stimulating hormone (TSH), and mRNA or protein expressions of UGTs (Ugt1a1, Ugt1a6, and Ugt2b1/2) and MRP2 (Mrp).CLB induced thyroid morphological changes with increases in TSH in SD and Gunn rats, but not in EHBR rats. T4 was slightly decreased in SD and Gunn rats, and T3 was decreased in Gunn rats, whereas these hormones were maintained in EHBR rats. Hepatic Ugt1a1, Ugt1a6, Ugt2b1/2, and Mrp2 mRNAs were upregulated in SD rats. In Gunn rats, UGT1A mRNAs (Ugt1a1/6) and protein levels were quite low, but UGT2B mRNAs (Ugt2b1/2) and protein were prominently upregulated. In SD and Gunn rats, MRP2 mRNA and protein were upregulated to the same degree. These results suggest that MRP2 is an important contributor in development of the thyroid cellular hypertrophy in CLB-treated rats, and that UGT1A and UGT2B work in concert with MRP2 in the presence of MRP2 function to enable the effective elimination of thyroid hormones.