Inhibition Of P-glycoprotein Function Research Articles

Cepharanthine synergistically promotes methylprednisolone pharmacodynamics against human peripheral blood mononuclear cells possibly via regulation of P-glycoprotein/glucocorticoid receptor translocation

BackgroundCepharanthin® alone or in combination with glucocorticoid (GC) has been used to treat chronic immune thrombocytopenia (ITP) since the 1990s. Cepharanthine (CEP) is one of the main active components of Cepharanthin®. The purpose of this study was to investigate the effects of CEP on GC pharmacodynamics on immune cells and analyse the possible action mechanism of their interactions.MethodsPeripheral blood mononuclear cells (PBMCs), T lymphocytic leukemia MOLT-4 cells and daunorubicin resistant MOLT-4 cells (MOLT-4/DNR) were used to evaluate the pharmacodynamics and molecular mechanisms. Drug pharmacodynamics was evaluated by WST-8 assay. P-glycoprotein function was examined by rhodamine 123 assay. CD4+CD25+Foxp3+ regulatory T cells and Th1/Th2/Th17 cytokines were detected by flow cytometry. P-glycoprotein expression and GC receptor translocation were examined by Western blot.ResultsCEP synergistically increased methylprednisolone (MP) efficacy with the suppressive effect on the cell viability of PBMCs. 0.3 and 1 μM of CEP significantly inhibited P-glycoprotein efflux function of CD4+ cells, CD8+ cells, and lymphocytes (P<0.05). 0.03~3 μM of CEP also inhibited the P-glycoprotein efflux function in MOLT-4/DNR cells in a concentration-dependent manner (P<0.001). However, 0.03~3 μM of CEP did not influence P-glycoprotein expression. 0.03~0.3 μM of CEP significantly increased the GC receptor distribution from the cytoplasm to the nucleus in a concentration-dependent manner in MOLT-4/DNR cells. The combination did not influence the frequency of CD4+, CD4+CD25+ and CD4+CD25+Foxp3+ T cells or the secretion of Th1/Th2/Th17 cytokines from PBMCs. In contrast, CEP alone at 1 μM decreased the percentage of CD4+ T cell significantly (P<0.01). It also inhibited the secretion of IL-6, IL-10, IL-17, TNF-α, and IFN-γ.ConclusionsCEP synergistically promoted MP pharmacodynamics to decrease the cell viability of the mitogen-activated PBMCs, possibly via inhibiting P-glycoprotein function and potentiating GC receptor translocation. The present study provides new evidence of the therapeutic effect of Cepharanthin® alone or in combination with GC for the management of chronic ITP.

Extract of Codiaeum luzonicum Merr. overcomes multidrug resistance in human colon cancer cells by modulating P-glycoprotein

Objective: To investigate anti-multidrug resistance (MDR) activity and safety of the bioactive fraction (CL11) from Codiaeum luzonicum crude leaf extract. Methods: Cytotoxic activity of CL11 against MDR and non- resistant colon cancer cells was assessed using MTT assay. Mode of cell death was investigated by annexin V-propidium iodide staining, TUNEL, and JC-1 assays. To examine mechanism of action, the effect on the expression and function of the MDR-implicated protein P-glycoprotein was tested using Western blotting and calcein assay, respectively. Results: CL11 had an EC50 of 0.18, 1.03 and 38.52 μg/mL against HCT-15, HCT-15/Dox and HCT116, respectively. Cytotoxicity was mediated by inhibition of P-glycoprotein function and expression. The mode of cell death involved mitochondrial membrane depolarization and was mostly non-apoptotic at EC50 concentrations against HCT-15 and HCT-15/Dox. Conclusions: Fraction CL11 of Codiaeum luzonicum induces non- apoptotic cell death in MDR cancer cells by overcoming MDR through inhibition of P-glycoprotein expression and function.

Compound 968 reverses adriamycin resistance in breast cancer MCF-7ADR cells via inhibiting P-glycoprotein function independently of glutaminase

Adriamycin (ADR) is a chemotherapeutic drug widely utilized to treat multiple types of cancers; however, the clinical efficacy of ADR is compromised due to the development of drug resistance in patients. The combination of drugs with ADR may provide a better therapeutic regimen to overcome this obstacle. Glutaminase (GLS) has been explored as a therapeutic cancer target, and its inhibition also results in increased sensitivity of tumor cells to chemotherapeutic agents. This study aimed to investigate whether GLS inhibition could reverse ADR resistance. We treated the ADR-resistant MCF-7 (MCF-7ADR) cells with a GLS inhibitor, compound 968 or CB-839, in combination with ADR. We found that compound 968, rather than CB-839, together with ADR synergistically inhibited the cell viability. These results indicated that compound 968 reversed ADR resistance in MCF-7ADR cells independently of GLS. Moreover, we modified the structure of compound 968 and finally obtained a compound 968 derivative, SY-1320, which was more potent than compound 968 in eliminating the drug resistance in MCF-7ADR cells. Furthermore, using drug affinity responsive target stability and streptavidin–biotin immunoprecipitation assays, we demonstrated that SY-1320 could specifically target P-glycoprotein (P-gp) and increase ADR accumulation through inhibition of P-gp, thereby resulting in cell death in MCF-7ADR cells. Together, our findings indicate that compound 968 or SY-1320 might be a promising drug for new combination chemotherapy in breast cancer to overcome the drug resistance.

A multifunctional nano-delivery system enhances the chemo-co-phototherapy of tumor multidrug resistance via mitochondrial-targeting and inhibiting P-glycoprotein-mediated efflux.

Despite the excellent progress of chemotherapy and phototherapy in tumor treatment, their effectiveness on multidrug-resistant (MDR) tumors is still unsatisfactory. One of the main obstacles is drug efflux caused by P-glycoprotein in MDR cells. Herein, we developed a nano-delivery system that combines a P-glycoprotein inhibitor with chemotherapy and phototherapy to overcome MDR. Briefly, the system is prepared by the self-assembly of a ROS-triggered doxorubicin prodrug (PTD) and mitochondrial-targeted D-α-tocopherol polyethyleneglycol succinate (TPP-TPGS), in which a photoactive drug, IR780, is encapsulated (PTD/TT/IR780). PTD/TT/IR780 can target the release of TPP-TPGS, doxorubicin and IR780 at the mitochondrial site of MDR cells through ROS trigger. D-α-Tocopherol polyethyleneglycol succinate (TPGS) is a P-glycoprotein inhibitor, which will reduce the efflux of doxorubicin and IR780 from MDR cells. Under irradiation of an 808 nm near-infrared laser, IR780 generates heat and ROS, causing mitochondrial damage and prompting MDR cell apoptosis. At the same time, ROS can reduce the ATP content, which inhibits the P-glycoprotein function. In addition, an increase in the ROS generates positive feedback, allowing more nanoparticles to be cleaved and further promoting payload release in MDR cells, thereby enhancing the synergistic efficacy of chemotherapy and phototherapy. The in vitro cellular assay showed that PTD/TT/IR780 significantly inhibited MDR cell proliferation at a very low drug concentration (IC50 = 0.27 μg mL-1 doxorubicin-equivalent concentration). In vivo animal experiments based on BALB/c nude mice bearing MCF-7/ADR tumors confirmed a superior antitumor efficacy and an excellent biosafety profile. These findings demonstrate that this multifunctional nanoplatform provides a new approach for the treatment of MDR tumors.

Plant extracts and betulin from Ligaria cuneifolia inhibit P-glycoprotein function in leukemia cells

Overexpression of P-glycoprotein (P-gp), which is linked to multidrug resistance (MDR), is one of the underlying obstacles to the success of chemotherapy as it reduces the efficacy of anticancer drugs and the side effects of these increase as a result of any increased dose to achieve the therapeutic effect. To identify agents with P-gp inhibitory properties, ethanol extracts from 80 plants were screened for their ability to increase intracellular doxorubicin-associated fluorescence, and the extract of Ligaria cuneifolia was found to be the most effective. Its bioassay-guided isolation yielded the pentacyclic triterpene betulin as active agent. This efficiently inhibited P-gp mediated efflux, as demonstrated by the enhancement of the intracellular accumulation of doxorubicin and rhodamine 123 from 1.56 μM in the P-gp overexpressing MDR leukemia cell, Lucena 1. Betulin was also able to render Lucena 1 sensitive to Dox from 0.39 μM. The docking studies revealed that betulin tightly binds to a key region of the TMDs, with a binding mode overlapping one main site of doxorubicin and, more interestingly, emulating the same contacts as tariquidar, as revealed by the per-residue energetic analysis from molecular dynamics simulations. MTT assay using peripheral blood mononuclear cells and hemolysis assay showed that betulin is devoid of toxicity.These findings provide important evidence that betulin may be a safe and promising entity to be further investigated to develop agents able to overcome P-gp-mediated MDR, resulting in a more effective and less toxic chemotherapy.

Tetrandrine enhances glucocorticoid receptor translocation possibly via inhibition of P-glycoprotein in daunorubicin-resistant human T lymphoblastoid leukemia cells

Glucocorticoids are used as anticancer and immunosuppressive agents, whereas glucocorticoid resistance has been observed in a significant fraction of patients due to overexpression of P-glycoprotein encoded by multi-drug resistance-1 gene. Tetrandrine is a bisbenzylisoquinoline alkaloid isolated from traditional herb Fangji. According to our previous report, tetrandrine potentiated glucocorticoid pharmacodynamics partially via inhibiting P-glycoprotein function. In the present study, we investigated whether glucocorticoid receptor translocation was influenced indirectly by tetrandrine via P-glycoprotein inhibition, using human T lymphoblastoid leukemia MOLT-4 cell line with little P-glycoprotein expression and its multidrug resistant sub-line MOLT-4/DNR exhibiting a large amount of P-glycoprotein. Molecular mechanism investigation suggested that overexpressed P-glycoprotein weakened the glucocorticoid receptor translocation in MOLT-4/DNR cells comparing with the parent MOLT-4 cells. Our data also suggested that tetrandrine enhanced nuclear glucocorticoid receptor translocation in MOLT-4/DNR cells indirectly by dual influences on P-glycoprotein, inhibiting the efflux function and downregulating the protein expression. Therefore, tetrandrine potentiated the cytotoxic effect of methylprednisolone against MOLT-4/DNR cells with less effects on MOLT-4 cells. These effects of tetrandrine were suggested to be beneficial for the treatment of glucocorticoid resistant diseases induced by the overexpression of P-glycoprotein.

Tenulin and isotenulin inhibit P-glycoprotein function and overcome multidrug resistance in cancer cells

BackgroundMultidrug resistance (MDR) in cancer is one of the main obstacles in treatment with chemotherapy. Drug efflux through P-glycoprotein is the major mechanism involved in MDR. A potential strategy to provide the best possible clinical outcomes is to develop P-glycoprotein (P-gp) inhibitors from natural products. PurposeThe present study investigated the effects of the natural sesquiterpene lactone tenulin and its derivative isotenulin on human P-gp; the mechanisms of kinetic interactions were also explored. MethodsThe human P-gp (ABCB1/Flp-In™-293) stable expression cells were established by using the Flp-In™ system. The effects of tenulin and isotenulin on cell viability were evaluated by SRB assays in established cell lines, sensitive cancer cell line (HeLaS3), and resistant cancer cell line (KB-vin). The transporter inhibition ability was evaluated by calcein-AM uptake assays. The P-gp inhibition kinetics of tenulin and isotenulin were evaluated by rhodamine123 and doxorubicin efflux assays. The ATPase activity was evaluated with the Pgp-Glo™ Assay System. ResultsTenulin and isotenulin significantly inhibited the P-gp efflux function by stimulating P-gp ATPase activity. Tenulin and isotenulin interacted with the effluxes of rhodamine 123 and doxorubicin through a competitive and noncompetitive mechanism, respectively. The combinations of tenulin and isotenulin with chemotherapeutic drugs significantly resensitized MDR cancer cells. ConclusionThese results suggested that tenulin and isotenulin are potential candidates to be developed for synergistic treatment of MDR cancers.

常用厨房调味品与P-糖蛋白的相互作用

综述常用厨房调味品与P-糖蛋白的相互作用。以“P-糖蛋白、姜黄、生姜、大蒜、胡椒、辣椒”为中文检索词，以“P-Glycoprotein, Curcuma, Curcumine, Fresh Ginger, Garlic, Pepper, Piperine, Capsicum Chilli, Capsicine, Red Pigment”为英文检索词，由第一作者检索Pub Med数据库、Elsevier ScienceDirect、中国知网等数据库中关于常用厨房调味品与P-糖蛋白的相互作用的文章。许多常用厨房调味品存在诱导或抑制P-糖蛋白的作用，所以应该防止日常饮食与药物相互作用时可能发生的风险。 To review the interaction between commonly used flavouring in kitchen and P-Glycoprotein. A computer-based retrieval of Pub Med, Elsevier ScienceDirect and CNKI databases was performed for articles concerning the interaction between commonly used flavouring in kitchen and P-Glycoprotein published from 1978 to 2017. The keywords were “P-糖蛋白, 姜黄, 生姜, 大蒜, 胡椒, 辣椒” and “P-Glycoprotein, Curcuma, Curcumine, Fresh Ginger, Garlic, Pepper, Piperine, Capsicum Chilli, Capsicine, Red Pigment” in Chinese and English, respectively. Many commonly used flavouring in kitchen induce or inhibit P-Glycoprotein function. Thus, the possibility of risk between daily diet and drug should be prevented.

Refractory Extranodal Nasal NK/T-Cell Lymphoma with CNS Involvement Treated with Radiotherapy and Pralatrexate: Case Report

IntroductionPeripheral T-Cell Lymphoma represents a clinically and biologically heterogeneous group of Non-Hodgkin's lymphomas. One uncommon subtype is extranodal nasal natural killer (NK)/T-cell lymphoma (ENKL) type which occur worldwide, with a strong geographic predilection for Asian, Central and South American populations from Mexico, Peru, Argentina and Brazil, constituting 5% to 15% of lymphomas in these countries1. The clinical course is aggressive, and the prognosis is poor mainly due to the expression of P-glycoprotein, which actively exports several anticancer agents outside the lymphoma cells2,3. However, in recent years, novel therapeutic approaches improved the response to therapy and survival2. Based on this recent progress, nowadays this subtype is categorized as a lymphoma with intermediate prognosis, but the overall treatment results are not satisfactory4. This report represents the first Mexican case of relapsed ENKL refractory to multiple lines of treatment with successful response to radiotherapy, followed by pralatrexate as monotherapy.CaseThe patient is male, 30 years old with history of nasal congestion for 1 year, refractory to treatment. Who presented with B symptoms, nasal voice and mild malar edema. Imaging by PET showed SUV max of 13.8 in ethmoid, maxillar and sphenoid sinuses with mucosal thickening and septum fracture. Biopsy confirmed ENKL and immunochemistry was positive for CD3, CD20 and CD55.The initial treatment was made with 3 cycles of CHOEP, followed by 2 cycles of MTX + vorinostat + folinic acid; consolidation therapy with radiotherapy 25 sessions with 50 Gy and 4 cycles of VIPD. Control PET showed tumor reduction of 78% and 3 months later was negative, biopsy was also negative. Three months later presented headache and walking abnormalities. PET showed CNS tumor. Radiotherapy was initiated with whole brain plus sequential focal radiation boost in 20 sessions with 20 Gy; consolidation therapy with 2 cycles of 6 weeks with pralatrexate at 30 mg/m2. The diffusion weighted whole body imaging showed no signs of tumoral activity at any site.DiscussionThe nose and paranasal area including the upper aerodigestive tract are the most commonly affected sites of origin for ENKL, followed by skin and gastrointestinal tract1. In this case initially the patient presented nasal and paranasal disease. The most important issue considering the treatment of ENKL is the expression of P-glycoprotein, which mediates multi-drug resistance. Therefore, CHOP or other anthracycline based chemotherapy usually are not effective for ENKL3. For localized disease, radiotherapy together with chemotherapy is the standard approach. In disseminated ENKL, systemic chemotherapy remains the mainstay of treatment2. However, in recent years, novel agents have been identified for the treatment of ENKL. Chemotherapeutic agents not affected by P-glycoprotein, such as methotrexate4. This is why treatment with pralatrexate was initiated in this patient, representing the first experience in Mexico using pralatrexate on a patient with ENKL. The patient previously was heavily treated and with very poor prognosis due to CNS involvement, additional to the scarce therapeutic options and difficult access to health care system in Mexico. The patient showed favorable and rapid response to therapy. Currently the patient is in remission and waiting for bone marrow transplant. Pralatrexate appears to be a promising agent for consolidation therapy or as bridge therapy for those patients that will undergo on bone marrow transplant. 1.Suzuki R. Pathogenesis and treatment of extranodal natural killer/T-cell lymphoma. Semin Hematol 2014; 51: 42-512.Tse E, Kwong YL. How I treat NK/T-cell lymphomas. Blood 201320; 121: 4997-50053.Egashira M, Kawamata N, Sugimoto K, Oshimi K. P-glycoprotein expression on normal and abnormally expanded natural killer cells and inhibition of P-glycoprotein function by cyclosporine A and its analogue, PSC833. Blood 1999; 93: 599-6064.Jaccard A, Gachard N, Marin B, et al; GELA and GOELAMS Intergroup. Efficacy of L-asparaginase with methotrexate and dexamethasone (AspaMetDex regimen) in patients with refractory or relapsing extranodal NK/T-cell lymphoma, a phase 2 study. Blood 2011; 117: 1834-1839 DisclosuresEnrique:Alexion: Speakers Bureau; Janssen: Speakers Bureau; Amgen: Speakers Bureau; Celgene: Speakers Bureau; Mundipharma: Other: Subsidies for the costs of travel to the ASH annual meeting; Bristol-Myers Squibb: Speakers Bureau.

Alopecurone B reverses doxorubicin-resistant human osteosarcoma cell line by inhibiting P-glycoprotein and NF-kappa B signaling

Doxorubicin (DOX) was first used in osteosarcoma in the early 1970s as a first-line antineoplastic drug. However, the occurrence of drug resistance in chemotherapeutic treatment has greatly restricted its use. When resistance to DOX treatment occurs, osteosarcoma may become not only resistant to the drug originally administered but also to a wide variety of structurally and mechanistically unrelated drugs. Thus, there is an urgent need to find ways of reversing DOX chemotherapy resistance in osteosarcoma. Plant-derived agents have great potential in preventing the onset of the carcinogenic process and enhancing the efficacy of conventional antitumor drugs. Alopecurone B (ALOB), a flavonoid, is isolated from Traditional Chinese Medicine Sophora alopecuroides L., and is reported to have potent inhibitory effect on multidrug resistance associated protein 1. In this study, a DOX-resistant osteosarcoma cell line (MG-63/DOX) was established by increasing the concentration gradient of DOX in a stepwise manner. MTT assay, flow cytometry analysis, dual-luciferase reporter gene assay, quantitative real-time polymerase chain reaction and Western blot analysis were applied to investigate the reversing effect of ALOB and its underlying mechanisms. The results indicated that ALOB mediated the resistance of MG-63/DOX cells to DOX by inhibiting P-glycoprotein function, transcription and expression. Besides, ALOB also enhanced the sensitivity of MG-63/DOX cells to other conventional chemotherapeutic drugs. Cell viability assay confirmed the reversing activity of ALOB. Furthermore, ALOB increased DOX-induced apoptosis at nontoxic concentration. In addition, ALOB showed inhibitory effect on NF-κB transcription in a DOX-independent manner. Furthermore, NF-κB signaling was suppressed by ALOB in an IKK-dependent manner. These studies not only demonstrate that ALOB is a potential agent for reversal of drug resistant cancers, but also testify that ALOB reverses multidrug resistance by inhibiting P-glycoprotein via NF-κB signaling.

Polymethyoxy Flavonoids: Possible Candidates for Overcoming Drug Resistance

The success of chemotherapy in cancer treatment is frequently limited by intrinsic or acquired multidrug resistance due to increased expression of a plasma membrane P-glycoprotein . P-glycoprotein is an ATP-dependent transporter that effluxes many lipophilic anticancer agents out of cells, thereby reducing intracellular drug concentration and results in cancer cell survival. It has been reported that certain kinds of natural compounds and their derivatives inhibit P-glycoprotein function, and overcome the multidrug resistance phenotype.

Tetrandrine Potentiates the Hypoglycemic Efficacy of Berberine by Inhibiting P-Glycoprotein Function

This study was designed to improve the absorption and hypoglycemic efficacy of berberine (BBR), which is a substrate of P-glycoprotein (P-gp), by combination with a P-gp inhibitor tetrandrine (Tet). Flow cytometry and LC-MS/MS were used to determine the cellular efflux or retention of chemicals. Pharmacokinetic study was performed in ICR mice following oral administration of the study compounds. The hypoglycemic efficacies of the compounds were evaluated in diabetic KK-Ay mice. In the in vitro experiments, Tet significantly inhibited the efflux and increased the uptake of P-gp substrates rhodamine-123 as well as BBR in MCF7/DOX cells and Caco-2 intestinal cells. Meanwhile, Tet greatly reduced the expression of P-gp in Caco-2 cells. The inhibition of BBR efflux by Tet was translated into improved pharmacokinetics in vivo. When co-administered, Tet dose-dependently increased the average maximum concentration (C(max)) and area under concentration-time curve (AUC₀₋₂₄) of BBR in mice. Tet itself had no impact on glucose metabolism. However, it greatly potentiated the hypoglycemic efficacy of BBR in diabetic KK-Ay mice. In addition, we found that Tet had moderate inhibitory effect on the catalytic activity of CYP3A4, which played a role in the bio-transformation of BBR, and this may also take part in the improvement of the pharmacokinetics of BBR. In summary, combination with P-gp inhibitors such as Tet can improve the pharmacokinetics and hypoglycemic efficacy of BBR greatly; this implicates a feasible strategy for exploring the therapeutic effects of BBR and other pharmaceuticals which are substrates of P-gp.

Evaluation of the biliary and brain distribution of technetium Tc 99m sestamibi in healthy dogs with the ABCB1 wildtype genotype before and after treatment with spinosad

To determine whether the reported drug-drug interaction between the flea medication spinosad and ivermectin is attributable to inhibition of P-glycoprotein by spinosad. 6 healthy adult dogs with the ABCB1 wildtype genotype. The study was conducted as a prospective, masked, randomized crossover design. Six dogs were allocated to 2 groups; each dog served as its own control animal. Dogs in one of the groups received spinosad at the manufacturer's recommended dose; the other group received no treatment. Forty-eight hours later, scintigraphic imaging of the head and abdomen were performed with the radiolabeled P-glycoprotein substrate methoxy-isobutyl-isonitrile (sestamibi) in both groups of dogs. After a washout period of 60 days, the dogs in each group received the alternate treatment, and scintigraphic imaging again was performed 48 hours later. Gallbladder-to-liver and brain-to-neck musculature ratios of technetium Tc 99m sestamibi were calculated for each dog and compared between treatments. No significant differences in gallbladder-to-liver or brain-to-neck musculature ratios were found between treatments. Results provided evidence that spinosad did not inhibit P-glycoprotein function 48 hours after spinosad was administered at the manufacturer's recommended dose. Further investigations will be necessary to elucidate the mechanism of the reported toxic interaction between spinosad and ivermectin.

The ability of gallate and pyrogallol moieties of catechins to inhibit P-glycoprotein function

The role of structure–activity relationships in the ability of catechins to inhibit P-glycoprotein (P-gp) function was investigated with respect to gallate and pyrogallol moieties. Experiments using octyl derivatives of gallic acid indicated that the gallate moiety required the catechol group and a neighboring carbonyl group to inhibit P-gp. On the other hand, the pyrogallol moiety appeared to require three hydroxyl groups to inhibit P-gp, according to comparisons between (−)-epicatechin gallate (ECG) and (−)-epigallocatechin gallate (EGCG). The difference in the number of hydroxyl groups that gallate or pyrogallol moieties required for P-gp inhibition, was due to the presence of a carbonyl group. The P-gp inhibition by catechins was restricted by their hydrophobicity. The pyrogallol moiety of EGC did not appear to inhibit P-gp because of its low hydrophobicity. The P-gp inhibitory activity of EGCG was speculated to be increased by the addition of long carbon chains to the C3″of gallate moieties.

Inhibition of P-glycoprotein function by tannic acid and pentagalloylglucose

We studied the effects of tannic acid and 1(beta),2,3,4,6-penta-O-galloyl-D-glucose (pentagalloylglucose), one of the components of tannic acid, on the P-glycoprotein (P-gp) function in multidrug-resistant P-gp over-expressing KB-C2 cells. Both tannic acid and pentagalloylglucose markedly elevated the accumulation of P-gp substrates, rhodamine 123 and daunorubicin, by inhibiting their efflux. A 19-fold increase in cellular rhodamine 123 was observed for tannic acid at 60 microM (85 microg mL(-1)) and a 21-fold increase was observed for pentagalloylglucose at 100 microM (94 microg mL(-1)). The increasing effects of these compounds in the accumulation were much larger than that of (-)epigallocatechin-3-O-gallate (EGCG), which has been revealed to have a prominent inhibitory effect on P-gp compared with other flavonoids. Analysis of verapamil-stimulated ATPase activity in membrane vesicles expressing human P-gp suggested that inhibition of P-gp function by tannic acid and pentagalloylglucose was at least partly due to ATPase inhibition of P-gp. The findings also suggested that the presence of a large number of galloyl groups in polyphenols strengthens the interaction with regulatory regions in P-gp.

Inhibition of P-glycoprotein function by tea catechins in KB-C2 cells.

We studied the effects of tea catechins, (-)-epicatechin (EC), (-)-epigallocatechin (EGC), (-)-epicatechin gallate (ECG), and (-)-epigallocatechin gallate (EGCG) on the P-glycoprotein (P-gp) function in multidrug-resistant P-gp over-expressing KB-C2 cells. EC did not have any effects on cellular accumulation of P-gp substrates, rhodamine-123 and daunorubicin, but the other catechins increased the accumulation in the order of EGC < ECG < EGCG. The effects of EGCG were larger than those of verapamil and quercetin. Since these catechins inhibited the efflux of P-gp substrates, the elevation of substrate accumulation seemed to be induced by the inhibition of the efflux transporter. The results showed that the inhibitory effects of the catechins did not depend on their total hydrophobicity, but significantly depended on their chemical structure. The presence of the galloyl moiety on the C-ring markedly increased the n-octanol/PBS partition coefficients of the catechins and their activity on P-gp. On the other hand, the presence of the trihydric pyrogallol group as the B-ring decreased the partition coefficients but increased the activity on P-gp, compared with the action of the corresponding catechins with a dihydric catechol B-ring.

Pharmacokinetic Interaction between Nifedipine and Coenzyme Q10 in Rats: A New Type of Drug-Supplement Interaction

We examined pharmacokinetic (PK) and pharmacodynamic (PD) interactions between coenzyme Q10 (CoQ10) and nifedipine (NFP), which is a popular medicine for treating hypertension, and elucidated possible mechanisms for the interaction between CoQ10 and NFP in rats. The mean plasma concentrations of NFP in rats after the oral administration of NFP (1 mg/kg) with CoQ10 (75 mg/kg) were increased over the study period and the area under the plasma concentration-time curve (AUC), showed a 1.47-fold increase compared with that of the control. Rats that received NFP with CoQ10 showed a continuous decrease in the mean blood pressure over the study period compared with the control. There were no significant changes in the PK parameters of NFP after intravenous administration (1 mg/kg) between with and without oral CoQ10 pretreatment, and also no significant changes in the intestinal excretion of rhodamine 123 (Rho123) or NFP between with and without CoQ10 were found. In contrast, the portal plasma concentration of NFP after intra loop administration in the presence of CoQ10 (75 mg/kg) showed a 1.6-fold increase in the AUC value compared with that of the control. As for physicochemical properties, the partition coefficient of NFP showed a marked increase in the presence of CoQ10 over 10 mg/ml in the organic phase (n-hexane). From on an analysis of the absorbance spectrum, CoQ10 showed a shift towards a longer wavelength in hydrophobic environments with NFP, suggesting that CoQ10 reacts with NFP to form a charge-transfer complex due to a pi-cloud between them. In conclusion, it was found that CoQ10 increases the oral bioavailability of NFP and that this interaction between NFP and CoQ10 is not caused by metabolism via cycochrome P450 (CYP) 3A in the liver or intestine or by the inhibition of P-glycoprotein function, by the physicochemical interaction between them. Therefore, the solubility of NFP in a hydrophobic environment could be enhanced by forming a chargetransfer complex with CoQ10, and it is considered that NFP deviating from a charge-transfer complex may migrate to the blood circulation from the intestinal tract. This mechanism of interaction is considered a new type of drugsupplement interaction.

Effects of farnesyl transferase inhibitor in anti-tumor and multidrug resistance

Farnesyl transferase inhibitor (FTI) is a new class of agents, the targets of which are the tumor proliferation and signal transduction pathway. FTI can exert antitumour activity via inhibiting proteins farnesyled modification including Ras, inducing apoptosis and inhibiting angiogenesis. FTI can reverse muhidrug resistance(MDR) through inhibition of P-glycoprotein function. Key words: Neoplasms; Drug resistance, neoplasm; Enzyme inhibitors

Characterization of β‐adrenoceptor antagonists as substrates and inhibitors of the drug transporter P‐glycoprotein1

Transporter proteins such as P-glycoprotein are major determinants of intracellular drug concentrations. Moreover, inhibition or induction of transporters is an important mechanism underlying drug interactions in humans. However, very little is known whether beta-adrenoceptor antagonists are substrates and/or inhibitors of P-glycoprotein. Therefore, we investigated the P-glycoprotein-mediated transport of propranolol, metoprolol, bisoprolol, carvedilol and sotalol in P-glycoprotein-expressing Caco-2 monolayers and inhibition of P-glycoprotein-mediated digoxin transport by the beta-adrenoceptor antagonists. A significant inhibition of polarized, basal to apical drug transport by the P-glycoprotein inhibitor PSC-833 was observed for bisoprolol (0.5 and 5 microm) and carvedilol (0.5 microm). Moreover, propranolol and carvedilol inhibited P-glycoprotein-mediated digoxin transport with IC(50) values of 24.8 and 0.16 microm, respectively, whereas metoprolol and sotalol had no effect. Bisoprolol significantly inhibited directional digoxin transport at 50 and 250 microm by 31% and 44%, respectively. Taken together, P-glycoprotein is likely to be one determinant of bisoprolol and carvedilol disposition in humans. In addition, the beta-adrenoceptor antagonists propranolol and carvedilol significantly inhibit P-glycoprotein function thereby possibly contributing to drug interactions in humans (e.g. digoxin-carvedilol and cyclosporine-carvedilol).

Inhibition of P-Glycoprotein Function by Several Antidepressants may not Contribute to Clinical Efficacy

In many depressive patients the negative feedback mechanism of the HPA (hypothalamic-pituitary-adrenocortical) axis is impaired. It has been suggested that antidepressants inhibit membrane glucocorticoid transporters like P-Glycoprotein (Pgp) and hence enhance the intracellular glucocorticoid concentration, leading to an increased glucocorticoid-receptor mediated gene transcription and therefore to normalization of the function of the HPA axis. The aim of this study is to investigate inhibition of Pgp by several different antidepressants. We characterized the inhibitory potencies of the antidepressants in two in vitro assays by using calcein-AM as Pgp substrate. The two different cell-systems expressing Pgp were: 1. PBCEC (porcine brain capillary endothelial cells) as model for the blood-brain-barrier, and 2. A human lymphocytic leukaemia cell line CEM and the multi-drug-resistant (MDR) cell line VLB-100, expressing Pgp as model for the human protein. All of the antidepressants tested inhibit the transport of calcein-AM by Pgp in the micromolecular range. Because this inhibition is only seen at concentrations above therapeutically relevant plasma levels, their effect my not play a role for the mechanism of action of the antidepressants tested.