Can flavonoids from honey alter multidrug resistance?

Cancer is one of the deadly diseases that burdens the society since long-time. Although design of chemotherapy is well-advanced, still it could not prevent the cancer death by hundred percent. One of the major stumbling blocks for cancer chemotherapy is multidrug resistance (MDR) developed by cancer cells. Role of ABC family of transporter proteins is well recognized in MDR. P-glycoprotein (P-gp), member of ABC transporter family, has been described for drug resistance and a low bioavailability of drugs by pumping structurally unrelated drugs out of the cells at the cost of ATP hydrolysis. Recently various P-gp inhibitors (chemosensitizers) are studied extensively to reverse MDR. In this scenario, we propose honey with multitude of polyphenolic flavonoids as a plausible candidate for inhibiting the P-gp proteins. Common flavonoids of honey like chrysin, genistein, biochanin, quercetin, kaempferol, and naringenin have found to interact with P-gp transporters. Generally chemosensitizers bind with transmembrane domain (TMD) in the P-gp transporter but flavonoids are bi-functional in reversing the MDR. Flavonoids can inhibit the ATPases activity involved in drug efflux and also it may serve as substrates for P-gp transporters, thereby causing competitive inhibition towards other substrates. This dual-mode of flavonoids interaction with P-gp transporter enhances the therapeutic index. Hence we promulgate honey with rich flavonoid content as a potential candidate for reversing MDR. If our hypothesis is true, honey a novel chemosensitizer will reduce the huge amount invested in developing new chemosensitizers to overcome the burden of chemo-resistance.     

A role for P-glycoprotein in regulating cell growth and survival

Multidrug resistance (MDR) mediated by the adenosine triphosphate (ATP)-dependent drug efflux protein P-glycoprotein (P-gp), is a major obstacle to the successful treatment of cancer. P-gp is expressed in many types of cancers and the clinical success of chemotherapeutic treatment often correlates inversely with the level of P-gp expression. P-gp is a 170-180 kD cell-surface transporter protein and has historically been thought to confer resistance to chemotoxins by actively effluxing them from the cell. While there is little doubt that P-gp plays an important role as an efflux pump in conferring multidrug resistance, new evidence is mounting to suggest that in addition, P-gp may act as a general anti-apoptotic protein to increase the threshold for cell death. Effectively, P-gp may protect cells at two levels, firstly by decreasing the amount of toxins that accumulate in the cell, and secondly by blocking apoptotic pathways induced by toxins and cellular stress. Understanding how P-gp can regulate cell death could lead to novel therapies for the treatment of MDR tumors.     

Fungal ABC proteins: pleiotropic drug resistance, stress response and cellular detoxification.

A number of prominent genetic diseases are caused by mutations in genes encoding ATP-binding cassette (ABC) proteins (Ambudkar, Gottesmann, 1998). Moreover, several mammalian ABC proteins such as P-glycoprotein (P-gp) (Gottesman et al., 1995) and multidrug-resistance-associated proteins (MRPs) (Cole, Deeley, 1998) have been implicated in multidrug resistance (MDR) phenotypes of tumor cells highly resistant to many different anticancer drugs. The characteristics of MDR phenomena include the initial resistance to a single anticancer drug, followed by the development of cross-resistance to many structurally and functionally unrelated drugs. Similar mechanisms of MDR exist in pathogenic fungi, including Candida and Aspergillus (Vanden Bossche et al., 1998), and also in parasites such as Plasmodium and Leishmania (Ambudkar, Gottesmann, 1998), as well as in many bacterial pathogens (Nikaido, 1998). To dissect the mechanisms of MDR development and to elucidate the physiological functions of ABC proteins, many efforts have been made during the past decade. Importantly, yeast orthologues of mammalian disease genes made this unicellular eukaryote an invaluable model system for studies on the molecular mechanisms of ABC proteins, in order to better understand and perhaps improve treatment of ABC gene-related disease. In this review, we provide an overview of ABC proteins and pleiotropic drug resistance in the budding yeast Saccharomyces cerevisiae and the fission yeast Schizosaccharomyces pombe. Furthermore, we discuss the role of ABC proteins in clinical drug resistance development of certain fungal pathogens.     

Restoration of chemosensitivity by multifunctional micelles mediated by P-gp siRNA to reverse MDR

One of the main obstacles in tumor therapy is multiple drug resistance (MDR) and an underlying mechanism of MDR is up-regulation of the transmembrane ATP-binding cassette (ABC) transporter proteins, especially P-glycoprotein (P-gp). In the synergistic treatment of siRNA and anti-cancer drug doxorubicin, it is crucial that both the siRNA and doxorubicin are simultaneously delivered to the tumor cells and the siRNA can fleetly down-regulate P-g before doxorubicin inactivates the P-gp and is pumped out. Herein, a type of micelles comprising a polycationic PEI-CyD shell to condense the siRNA and hydrophobic core to package doxorubicin is reported. The structure of the polymer is determined by ¹H NMR, FT-IR, DSC, and XRD and the micelles are characterized by DLS, 2D-NOESY NMR, and TEM to study the self-assembly of the micelles with siRNA and drugs. In vitro studies demonstrate controlled release and temporal enhancement of the therapeutic efficacy of P-gp siRNA and doxorubicin. Release of siRNA down-regulates the mRNA and protein levels of P-gp in the MCF-7/ADR cell lines effectively and the accumulated doxorubicin facilitates apoptosis of the cells to reverse MDR. Moreover, in vivo research reveals that the siRNA and doxorubicin loaded micelles induce tumor cell apoptosis and inhibit the growth of MDR tumor. The western blotting and RT-PCR results illustrate that the synergistic treatment of siRNA and doxorubicin leads to efficient reduction of the P-gp expression as well as cell apoptotic induction in MDR tumors at a small dosage of 0.5 mg/kg. The micelles have large clinical potential in drug/RNAi synergistic treatment via restoration of the chemosensitivity in MDR cancer therapy.     

Potentiation of anti-epileptic drugs effectiveness by pyronaridine in refractory epilepsy

One of the major neurobiological mechanisms proposed in drug resistant epilepsy is removal of anti-epileptic drugs (AEDs) from the epileptogenic tissue through excessive expression of multi-drug efflux transporters such as P-glycoprotein (P-gp). P-gp, the encoded product of the human multi-drug resistance-1 (MDR-1; ABCB1) gene, is of particular clinical relevance in the emergence of multi-drug resistance (MDR), which may play an important role in preventing treatment response of some tumors and infectious diseases to chemotherapeutic agents and antibiotics. It has been shown that MDR-1 is over-expressed in brain tissue (hippocampal neurons) in patients with refractory temporal lobe epilepsy. For direct evidence that drug transporters such as P-gp are responsible for drug resistance, an experiment can be conducted to determine whether seizure control is improved when P-gp inhibitors are administered in addition to existing AEDs in patients with medically refractory epilepsy. In comparison with first and second-generation of P-gp inhibitors, third-generation inhibitors such as pyronaridine (PND) have advantages, such as higher potency and specificity for P-gp, lack of non-specific cytotoxicity, relatively long duration of action with reversibility, and good oral bioavailability. We suggest that a pilot study be conducted to determine whether adding of PND to existing AEDs decreases seizure frequency in patients with drug resistant epilepsy, and should this show promise, that a double-blind randomized controlled trial be designed to test the efficacy of PND.     

Roles of ligand and TPGS of micelles in regulating internalization,penetration and accumulation against sensitive or resistant tumor and therapy for multidrug resistant tumors

There are several obstacles in the process of successful treatment of malignant tumors, including toxicity to normal cells, inefficiency of drug permeation and accumulation into the deep tissue of solid tumor, and multidrug resistance (MDR). In this work, we prepared docetaxel (DTX)-loaded hybrid micelles with DSPE–PEG and TPGS (TPGS/DTX-M), where TPGS serves as an effective P-gp inhibitor for overcoming MDR, and active targeting hybrid micelles (FA@TPGS/DTX-M) with targeting ligand of folate on the hybrid micelles surface offering active targeting to folate receptor-overexpressed tumor cells. A systematic comparative evaluation of these micelles on cellular internalization, sub-cellular distribution, antiproliferation, mitochondrial membrane potential, cell apoptosis and cell cycle, permeation and inhibition on 3-dimensional multicellular tumor spheroids, as well as antitumor efficacy and safety assay in vivo were well performed between sensitive KB tumors and resistant KBv tumors, and among P-gp substrate or not. We found that the roles of folate and TPGS varied due to the sensitivity of tumors and the loaded molecules in the micelles. Folate and folate receptor-mediated endocytosis played a leading role in internalization, permeation and accumulation for sensitive tumors and non-substrates of P-gp. On the contrary, TPGS played the predominant role which dramatically decreased the efflux of drugs both when the tumor is resistant and for P-gp substrate. These findings are very meaningful for guiding the design of carrier delivery system to treat tumors. The antitumor efficacy in xenograft nude mice model and safety assay showed that the TPGS/DTX-M and FA@TPGS/DTX-M significantly exhibited higher antitumor activity against resistant KBv tumors than the marketed formulation and normal micelles owing to the small size (approximately 20 nm), hydrophilic PEGylation, TPGS inhibition of P-gp function, and folate receptor-modified endocytosis, permeation and accumulation in solid tumor, as well as synergistic effects of DTX-induced cell division inhibition, growth restraint and TPGS-triggered mitochondrial apoptosis in tumor cells. In conclusion, folate-modified TPGS hybrid micelles provide a synergistic strategy for effective delivery of DTX into KBv cells and overcoming MDR.     

Delivery of siRNA by MRI-visible nanovehicles to overcome drug resistance in MCF-7/ADR human breast cancer cells

Multidrug resistance (MDR) is one of the major barriers in cancer chemotherapy. P-glycoprotein (P-gp), a cell membrane protein in MDR, also a member of ATP-Binding cassette (ABC) transporter, can increase the efflux of various hydrophobic anticancer drugs. In this study, polycation/iron oxide nanocomposites, were chosen as small interfering RNA (siRNA) carriers to overcome MDR through silencing of the target messenger RNA and subsequently reducing the expression of P-gp. Amphiphilic low molecular weight polyethylenimine was designed with different alkylation groups and alkylation degree to form various nanocarriers with clustered iron oxide nanoparticles inside and carrying siRNA through electrostatic interaction. A few optimized formulations can form stable nanocomplexes with siRNA and protect them from degradation during delivery, and lead to effective silencing effect that comparable to a commercial golden standard transfection agent, Lipofectamine 2000. Human breast cancer MCF-7/ADR cells can be vulnerable to doxorubicin treatment after the strong downregulation of P-gp through siRNA tranfection. Once transfected with these nanocomplexes, the cells displayed significant contrast enhancement against non-transfected cells under a 3T clinical MRI scanner. These nanocomposites also demonstrated their downregulation efficacy of P-gp in a MCF-7/ADR orthotopic tumor model in mice.     

P-glycoprotein in autoimmune diseases

Multidrug resistance-1 (MDR-1) is characterized by overfunction of P-glycoprotein (P-gp), a pump molecule that decreases intracellular drug concentration by effluxing them from the intracellular space. Broad ranges of structurally unrelated compounds are transported by P-gp, including antineoplastic agents, HIV protease inhibitors, prednisone, gold salts, methotrexate, colchicine as well as several antibiotics. In contrast, many other compounds such as calcium channel blockers (verapamil) and immunosupressors (cyclosporine-A) are able to inhibit P-gp function. The P-gp role in therapeutic failures has been extensively studied in cancer; however, there is little information regarding MDR-1 phenotype in autoimmune disorders. It has been reported that an increased number of lymphocytes are able to extrude P-gp substrates in rheumatoid arthritis, immune thrombocytopenic purpura and systemic lupus erythematosus, the patients with poor response to treatment being the ones that exhibit the highest values. This may be due, at least in part, to a simultaneous long-term usage of several drugs that induce P-gp function. Since abnormally activated cell compartments characterize autoimmune diseases, it is possible that those cells are the ones that exhibit drug resistance. The study of drug resistance mechanisms in autoimmunity may be helpful for the optimization of the current therapeutic schemes through their combination with low doses of P-gp inhibitors.     

P-glycoprotein expression in non-Hodgkin's lymphomas of human immunodeficiency virus infected patients

Multidrug resistance (MDR) is a challenge in cancer treatment. One of the most studied mechanisms is P-glycoprotein (P-gp), which acts as a drug efflux pump, with decreased intracellular accumulation of drugs. It still needs to be clarified whether P-gp expression has a significant impact on non-Hodgkin's lymphoma treatment response, but a poor outcome has been reported in patients with positive P-gp expression. AIDS-related lymphomas have aggressive behavior, and although a complete response could be achieved, relapse is not uncommon. In an attempt to determine a possible relationship between MDR and poor outcome in this population, histologic samples obtained from 45 non-Hodgkin's lymphoma HIV-infected patients without previous cytotoxic therapy were submitted to immunohistochemical analysis using monoclonal antibody C494 specific for the MDR-1 isoform of P-gp. Samples from 27 patients (60%) were positive. Response to treatment (P=0.02) and overall survival (P=0.001) were significantly lower in patients with positive P-gp expression. In patients having achieved complete remission, the median disease-free survival (DFS) was not reached; the mean DFS was 57.2 months with DFS rates of 72.9% in three years. Our results show that P-gp is expressed before treatment of non-Hodgkin's lymphoma of HIV patients, and is related to poor response to treatment and overall survival.     

Synergistic effect of folate-mediated targeting and verapamil-mediated P-gp inhibition with paclitaxel -polymer micelles to overcome multi-drug resistance

Multidrug resistance (MDR) in tumor cells is a significant obstacle for successful cancer chemotherapy. Overexpression of drug efflux transporters such as P-glycoprotein (P-gp) is a key factor contributing to the development of tumor drug resistance. Verapamil (VRP), a P-gp inhibitor, has been reported to be able to reverse completely the resistance caused by P-gp. For optimal synergy, the drug and inhibitor combination may need to be temporally colocalized in the tumor cells. Herein, we investigated the effectiveness of simultaneous and targeted delivery of anticancer drug, paclitaxel (PTX), along with VRP, using DOMC-FA micelles to overcome tumor drug resistance. The floate-functionalized dual agent loaded micelles resulted in the similar cytotoxicity to PTX-loaded micelles/free VRP combination and co-administration of two single-agent loaded micelles, which was higher than that of PTX-loaded micelles. Enhanced therapeutic efficacy of dual agent micelles could be ascribe to increased accumulation of PTX in drug-resistant tumor cells. We suggest that the synergistic effect of folate receptor-mediated internalization and VRP-mediated overcoming MDR could be beneficial in treatment of MDR solid tumors by targeting delivery of micellar PTX into tumor cells. As a result, the difunctional micelle systems is a very promising approach to overcome tumor drug resistance.     

P glycoprotein and multidrug resistance]

Drug resistance has been shown to be associated with the expression of P-glycoprotein (P-gp), the product of mdr-1 gene. One of the suggested mechanisms for the phenomenon called Multidrug Resistance (MDR) is related to the overexpression and amplification of the mdr-1 gene. The product of this gene is called P-gp and it has been considered as a potential marker for drug resistance. Transfection of the mdr-1 gene into drug-sensitive cells confers the role of mdr-1 gene in developing MDR phenotype. Structural analysis of homologous cDNA, responsible for production of transport proteins, from: MDR cell lines, bacteria and yeast, revealed high similarity. Molecular structure analysis indicate that P-gp has nucleotide binding sites. It has been established that P-gh has an internal ATP-ase activity, thus it can act as energy dependent transport protein. The expression of P-gp has been found in neoplastic and normal tissues (as adrenal glands, kidney, liver, pancreas, jejunum and large intestine), as well as in several cell lines which have been induced to become resistant to cytostatics. The aim of present study was to review the role of P-gp expression in laboratory and clinic.     

Preface: the concept and consequences of multidrug resistance

The problem of multidrug resistance (MDR) in human cancers led to the discovery 30 years ago of a single protein P-glycoprotein (P-gp), capable of mediating resistance to multiple structurally diverse drugs. P-gp became the archetypal eukaryotic ABC transporter gene, and studies of P-gp and related ABC transporters in both eukaryotes and bacteria have led to a basic mechanistic understanding of the molecular basis of MDR. Particular milestones along the way have been the identification of the homology between P-gp and bacterial transport proteins, the purification and functional reconstitution of P-gp into synthetic lipid systems, and the development of targeted therapies that attempt to overcome MDR by inhibiting P-gp. This preface places into this context some of the less well-explored themes developed in the MDR field, particularly various alternative models of P-gp action, evidence for parallel physiological roles for P-gp, and the unusual relationship between the substrate recognition capabilities of ABC transporters and their evolutionary history.     

Chemoprotection and selection by chemotherapy of multidrug resistance-associated protein-1 (MRP1) transduced cells

Utilization of chemotherapy for treatment of tumors is mainly limited by its hematological toxicity. Because of the low level expression of drug resistance genes, transduction of hematopoietic progenitors with multidrug resistance 1 (MDR1) or multidrug resistance-associated protein 1 (MRP1) genes should provide protection from chemotherapy toxicity. Successful transfer of drug resistance genes into hematopoietic cells might allow the administration of higher doses of chemotherapy and, therefore, increase regression of chemosensitive tumors. In addition, this approach can be used to select in vivo transduced cells by their enrichment after administration of cytotoxic drugs. Our group has studied the potential value of MRP1 to protect hematopoietic cells. The interest in the use of MRP1 as an alternative to MDR1 gene transfer for bone marrow protection lies in its different modulation. Indeed, classical P-gp reversal agents, tested in clinic to decrease MDR1 tumor resistance, have little or no effect on MRP1 function. This would allow, in the same patient, the use of reversal agents to decrease P-gp tumor resistance without reversing bone marrow protection of the transduced hematopoietic cells provided by MRP1. We constructed two different MRP1-containing vectors with either the Harvey retroviral long terminal repeat (LTR) or phosphoglycerate kinase (PGK) as promoters and generated ecotropic producer cells. MRP1 transduced fibroblasts were more resistant to doxorubicin, vincristine, and etoposide and their chemoprotection was increased after selection with chemotherapeutic agents in the presence of glutathione, a co-factor for MRP1 function. Lethally irradiated mice were engrafted with bone marrow (BM) cells transduced with MRP1 vectors (PGK promoter). We demonstrated that high expression of MRP1 in murine hematopoietic cells reduces doxorubicin-induced leukopenia and mortality. In addition, in vivo selection of MRP1-transduced BM cells was achieved following doxorubicin administration and allowed a better chemoprotection after the second chemotherapy cycle.     

P-glycoprotein (P-gp) function in T cells: implications for organ transplantation

P-glycoprotein (P-gp), a member of the adenosine triphosphate (ATP)-binding cassette (ABC) family of transporter molecules, is responsible for maintaining low intracellular concentrations of a variety of extracellular compounds and xenobiotics, and for transport of various intracellular molecules. Many drugs are P-gp substrates and intracellular concentrations of these agents may be critical for drug action. Experience in oncology indicates that repeated exposure to P-gp substrate cytotoxic drugs leads to the selection of drug-resistant tumor cells that overexpress P-gp. Since immunosuppressive agents such as cyclosporine, tacrolimus, sirolimus and corticosteroids are substrates for P-gp and since T-cells also express P-gp, it is conceivable that an analogous mechanism exits for therapy-resistant graft rejection. As will be discussed in this article, P-gp may interfere with the response to immunosuppressive therapy through several distinct mechanisms, and as such may represent an attractive therapeutic target.     

P-glycoprotein (P-gp) function in T cells: implications for organ transplantation

P-glycoprotein (P-gp), a member of the adenosine triphosphate (ATP)-binding cassette (ABC) family of transporter molecules, is responsible for maintaining low intracellular concentrations of a variety of extracellular compounds and xenobiotics, and for transport of various intracellular molecules. Many drugs are P-gp substrates and intracellular concentrations of these agents may be critical for drug action. Experience in oncology indicates that repeated exposure to P-gp substrate cytotoxic drugs leads to the selection of drug-resistant tumor cells that overexpress P-gp. Since immunosuppressive agents such as cyclosporine, tacrolimus, sirolimus and corticosteroids are substrates for P-gp and since T-cells also express P-gp, it is conceivable that an analogous mechanism exits for therapy-resistant graft rejection. As will be discussed in this article, P-gp may interfere with the response to immunosuppressive therapy through several distinct mechanisms, and as such may represent an attractive therapeutic target.     

TPGS-stabilized NaYbF4:Er upconversion nanoparticles for dual-modal fluorescent/CT imaging and anticancer drug delivery to overcome multi-drug resistance

Multi-drug resistance (MDR) is a major cause of failure in cancer chemotherapy. Tocopheryl polyethylene glycol 1000 succinate (TPGS) has been extensively investigated for overcoming MDR in cancer therapy because of its ability to inhibit P-glycoprotein (P-gp). In this work, TPGS was for the first time used as a new surface modifier to functionalize NaYbF₄:Er upconversion nanoparticles (UNCPs) and endowed the as-prepared products (TPGS-UCNPs) with excellent water-solubility, P-gp inhibition capability and imaging-guided drug delivery property. After the chemotherapeutic drug (doxorubicin, DOX) loading, the as-formed composites (TPGS-UCNPs-DOX) exhibited potent killing ability for DOX-resistant MCF-7 cells. Flow-cytometric assessment and Western blot assay showed that the TPGS-UCNPs could potently decrease the P-gp expression and facilitate the intracellular drug accumulation, thus achieving MDR reversal. Moreover, considering that UCNPs process efficient upconversion emission and Yb element contained in UCNPs has strong X-ray attenuation ability, the as-obtained composite could also serve as a dual-modal probe for upconversion luminescence (UCL) imaging and X-ray computed tomography (CT) imaging, making them promising for imaging-guided cancer therapy.     

Effects of fluoroquinolone treatment on MDR1 and MRP2 mRNA expression in Escherichia coli-infected chickens

Current knowledge about the expression of ABC transport proteins suggests that their expression is regulated by a variety of factors, including pathological conditions, and in particular inflammatory reactions to infection. As ABC transporters are major determinants of absorption, distribution and excretion of many antimicrobials, modulation of their activity may result in increased or decreased tissue levels of drugs, affecting the efficacy of treatment. As fluoroquinolones have been identified as modulators and substrates of a number of drug transporters, we evaluated the effect of danofloxacin mesylate and enrofloxacin treatment on the levels of expression of MDR1 and MRP2 mRNAs in the intestines and livers of broilers with experimentally induced colibacillosis. MDR1 mRNA expression was significantly decreased in infected animals and was partly restored over 5 days of treatment with orally administered danofloxacin mesylate or enrofloxacin. Changes in the level of expression of MRP2 mRNA were less prominent. The study suggests that the treatment of colibacillosis with fluoroquinolones, which resulted in a significant clinical improvement of the animals, also restored the expression of drug transporters. This is of clinical importance as these ABC transporters significantly contribute to the functionality of important biological barriers, protecting the bird and specific tissues from pathogens and bacterial toxins.     

Reversal of multidrug resistance by co-delivery of paclitaxel and lonidamine using a TPGS and hyaluronic acid dual-functionalized liposome for cancer treatment

Multidrug resistance (MDR) remains the primary issue in cancer therapy, which is characterized by the overexpressed P-glycoprotein (P-gp)-included efflux pump or the upregulated anti-apoptotic proteins. In this study, a D-alpha-tocopheryl poly (ethylene glycol 1000) succinate (TPGS) and hyaluronic acid (HA) dual-functionalized cationic liposome containing a synthetic cationic lipid, 1,5-dioctadecyl-N-histidyl-l-glutamate (HG2C₁₈) was developed for co-delivery of a small-molecule chemotherapeutic drug, paclitaxel (PTX) with a chemosensitizing agent, lonidamine (LND) to treat the MDR cancer. It was demonstrated that the HG2C₁₈ lipid contributes to the endo-lysosomal escape of the liposome following internalization for efficient intracellular delivery. The TPGS component was confirmed able to elevate the intracellular accumulation of PTX by inhibiting the P-gp efflux, and to facilitate the mitochondrial-targeting of the liposome. The intracellularly released LND suppressed the intracellular ATP production by interfering with the mitochondrial function for enhanced P-gp inhibition, and additionally, sensitized the MDR breast cancer (MCF-7/MDR) cells to PTX for promoted induction of apoptosis through a synergistic effect. Functionalized with the outer HA shell, the liposome preferentially accumulated at the tumor site and showed a superior antitumor efficacy in the xenograft MCF-7/MDR tumor mice models. These findings suggest that this dual-functional liposome for co-delivery of a cytotoxic drug and an MDR modulator provides a promising strategy for reversal of MDR in cancer treatment.     

Multi-drug resistance in the treatments of autoimmune diseases]

Although corticosteroids and immunosuppressants are widely used for the treatments of autoimmune diseases such as systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA), we often experience patients who are resistant to these treatments. P-glycoprotein (P-gp) of membrane transporters, a product of the multiple drug resistance (MDR)-1 gene, plays a pivotal role in the acquisition of drug resistance. However, the relevance of MDR-1 and P-gp to resting and activated lymphocyte, major targets of the treatments in autoimmune diseases, remains unclear. We found that peripheral lymphocytes in patients with SLE and RA express P-gp on the surface and its expression is highly correlated with disease activity. P-gp on lymphocytes is induced by activation with cytokines such as IL-2, IL-4 and TNF-alpha, resulting in active efflux of corticosteroids from cytoplasm of lymphocytes, which mechanisms could lead to drug-resistance and high disease activity. However, the addition of P-gp antagonists such as ciclosporin A and inhibitors of P-gp synthesis successfully reduce efflux of corticosteroids from lymphocytes in vitro and these results imply that P-gp antagonists and P-gp synthesis inhibitors could work in order to overcome drug-resistance in vivo. Therefore, we propose that measurement of P-gp on lymphocytes is useful marker to indicate drug resistance and requirement of antagonists and/or intensive treatments to overcome drug resistance in active SLE and RA patients.     

沉默miR-21对子宫内膜癌顺铂耐药细胞株Ishikawa/DDP的影响

目的:观察沉默miR-21对子宫内膜癌顺铂耐药细胞株Ishikawa/DDP的影响.方法:以Lipofectamine 2000介导miR-21抑制剂转染Ishikawa/DDP细胞株,同时设置阴性组和耐药组.采用反转录PCR检测miR-21、多药耐药基因MDR1、促凋亡基因Bax和抗凋亡基因Bcl-2的表达.采用蛋白印迹法检测多药耐药蛋白P-gp、促凋亡蛋白Bax和抗凋亡蛋白Bcl-2的表达.采用噻唑蓝比色法检测细胞对顺铂的敏感性.采用流式细胞术检测细胞凋亡情况.结果:与耐药组和阴性组比较,抑制剂组miR-21,MDR1和Bcl-2 mRNA表达显著下调(P＜0.0l),而Bax mRAN表达显著上调(P＜0.00l);抑制剂组P-gp和Bcl-2蛋白表达显著低下调(p＜0.05),而Bax蛋白表达显著上调(P＜0.001).与耐药组和阴性组比较,顺铂对抑制剂组的IC50值显著(P＜0.001);顺铂对抑制剂组细胞的诱导凋亡率显著增加(P＜0.00l).结论:沉默miR-21可显著提高Ishikawa/DDP细胞株对顺铂的敏感性,并促进细胞凋亡,其具体机制可能与下调MDR1,P-gp和Bcl-2表达,以及上调Bax表达有关.