Expression Of Multidrug Resistance Research Articles

Dioscin Restores the Activity of the Anticancer Agent Adriamycin in Multidrug-Resistant Human Leukemia K562/Adriamycin Cells by Down-Regulating MDR1 via a Mechanism Involving NF-κB Signaling Inhibition

The purpose of this study was to investigate the ameliorating effect of dioscin (1) on multidrug resistance (MDR) in adriamycin (ADR)-resistant erythroleukemic cells (K562/adriamycin, K562/ADR) and to clarify the molecular mechanisms involved. High levels of multidrug resistance 1 (MDR1) mRNA and protein and reduced ADR retention were found in K562/ADR cells compared with parental cells (K562). Dioscin (1), a constituent of plants in the genus Discorea, significantly inhibited MDR1 mRNA and protein expression and MDR1 promoter and nuclear factor κ-B (NF-κB) activity in K562/ADR cells. MDR1 mRNA and protein suppression resulted in the subsequent recovery of intracellular drug accumulation. Additionally, inhibitor κB-α (IκB-α) degradation was inhibited by 1. Dioscin (1) reversed ADR-induced MDR by down-regulating MDR1 expression by a mechanism that involves the inhibition of the NF-κB signaling pathway. These findings provide evidence to support the further investigation of the clinical application of dioscin (1) as a chemotherapy adjuvant.

Egr-1 enhances drug resistance of breast cancer by modulating MDR1 expression in a GGPPS-independent manner

The multidrug resistance 1 (MDR1) gene product P-glycoprotein is an ATP-dependent efflux pump associated with chemotherapy failure in breast cancer. In the present study, we show that paclitaxel induces MDR1 expression in the MCF-7 breast cancer cell line in a MAPK/Egr-1-dependent manner. Paclitaxel exposure activated the Erk1/2/MAPK pathway and promoted the accumulation of the early response transcription factor Egr-1 in MCF-7 cells. Egr-1 binds to the GC element on the proximal MDR1 promoter to enhance MDR1 transcription. Loss of Egr-1 function in paclitaxel-resistant MCF-7 cells decreased MDR1 expression, whereas inhibiting Erk1/2 activity reduced both Egr-1 accumulation and MDR1 expression. These findings suggest that Erk1/2-induced Egr-1 accumulation activates MDR1 transcription and thereby induces the drug resistance observed in paclitaxel-resistant MCF-7 cells. Further mechanistic studies indicate that Egr-1 most likely does not induce the constitutive activation of Erk1/2 through its target gene geranylgeranyl diphosphate synthase (GGPPS), which regulates Ras prenylation. Indeed, our results suggest a novel pathway by which paclitaxel induces MDR1 expression, possibly illuminating a potential target pathway for the prevention of MDR1-mediated drug resistance.

MRP1 but Not MDR1 Is Associated with Response to Neoadjuvant Chemotherapy in Breast Cancer Patients

A major problem in the treatment of breast cancer is the development of resistance to chemotherapeutic agents. Although the role of multidrug resistance 1 (MDR1) and multidrug resistance associated protein 1 (MRP1) in inducing drug resistance in many cancers has been widely investigated the clinical significance of expression of these genes in breast cancer remains unclear and the data is still controversial. We investigated the expression of MDR1 and MRP1 in breast cancer patients as well as the possible correlation between MDR1 and MRP1 and clinical response to chemotherapy. In the present study, MDR1 and MRP1 gene expression were investigated by real time reverse transcription polymerase chain reaction (RT-PCR) assay in 54 breast cancer tumors and in corresponding adjacent normal tissues before neoadjuvant chemotherapy. The expression level of MDR1 and MRP1 were significantly higher in breast tumors than normal breast tissues. Although a significant relationship was found between the MRP1 expression and response to treatment no association was observed between MDR1 expression and response to treatment. MDR1 and MRP1 expression levels have been shown to be independent of tumor size, histological grade and the status of progesterone or estrogen receptor.

MRP1 but not MDR1 is associated with response to neoadjuvant chemotherapy in breast cancer patients.

A major problem in the treatment of breast cancer is the development of resistance to chemotherapeutic agents. Although the role of multidrug resistance 1 (MDR1) and multidrug resistance associated protein 1 (MRP1) in inducing drug resistance in many cancers has been widely investigated the clinical significance of expression of these genes in breast cancer remains unclear and the data is still controversial. We investigated the expression of MDR1 and MRP1 in breast cancer patients as well as the possible correlation between MDR1 and MRP1 and clinical response to chemotherapy. In the present study, MDR1 and MRP1 gene expression were investigated by real time reverse transcription polymerase chain reaction (RT-PCR) assay in 54 breast cancer tumors and in corresponding adjacent normal tissues before neoadjuvant chemotherapy. The expression level of MDR1 and MRP1 were significantly higher in breast tumors than normal breast tissues. Although a significant relationship was found between the MRP1 expression and response to treatment no association was observed between MDR1 expression and response to treatment. MDR1 and MRP1 expression levels have been shown to be independent of tumor size, histological grade and the status of progesterone or estrogen receptor.

Modulation of MDR1 and MRP3 Gene Expression in Lung Cancer Cells after Paclitaxel and Carboplatin Exposure

Carboplatin-paclitaxel is a reference regimen in the treatment of locally advanced or disseminated non-small cell lung cancer (NSCLC). This paper discusses the multidrug resistance developed with this drug combination, which is one of the major obstacles to successful treatment. In order to understand and overcome the drug resistance pattern of NSCLC after carboplatin plus paclitaxel exposure, levels of mRNA expression of multidrug resistance 1 (MDR1) and multidrug resistance-associated protein 3 (MRP3) were investigated in primary NSCLC cell lines (A-549 and A-427) and a metastasis-derived NSCLC cell line (NODO). Our results showed that exposure of the three NSCLC lines to plasma concentrations of paclitaxel (5 μM) produced an increase in MDR1 expression, while MRP3 showed no alteration in expression. By contrast, the same cells exposed to carboplatin plasma concentrations (30 μM) showed overexpression of MRP3. In these cells, MDR1 showed no expression changes. Interestingly, the combination of both paclitaxel and carboplatin caused increased expression of the MDR1 drug resistance gene rather than the individual treatments. These results suggest that carboplatin and paclitaxel may induce drug resistance mediated by MDR1 and MRP3, which may be enhanced by the simultaneous use of both drugs.

Effects of resveratrol on multidrug resistance in human retinoblastoma cells

Objective To observe the effect of resveratrol on multidrug resistance (MDR) in human retinoblastoma cells treated.Methods RB cells in logarithmic growth phase were divided into experimental group and control group.RB cells in experimental group were cultured with different concentrations of resveratrol (6.25, 12.50, 25.00, 50.00, 100.00 μmol/L) for 24 and 48 hours.The proliferation (absorbance value) was assayed using methyl thiazolyl tetrazolium (MTT).RB cells were cultured with 50.00 μmol/L resveratrol for 48 hours.The expressions of MDR-1,cyclooxygenase-2 (COX-2)、multidrug resistance-associated protein-1 (MRP-1),glutathione-S-transferases-π (GST-π) were determined by reverse transcription-polymerase chain reaction (RT-PCR) and Western blot.The RB cells of the control group were cultured with 0.5％ dimethyl sulfoxide.Results Compared with the control group,the absorbance value decreased in experimental groups (6.25,12.50,25.00,50.00 μmol/L) in a dose dependent manner (F=4.782,P＜0.05).The difference of absorbance value between 50.00 and 100.00μmol/L experimental groups was not significant (F=6.351,P＞0.05).Compared with the control group,the mRNA (t=9.170,5.758,4.152,4.638) and protein (t=3.848,5.955,4.541,3.514) expression levels of MDR-1,MRP1,COX-2,and GST-π decreased in the experimental group (P＜0.05).Conclusion Resveratrol can down-regulate the expression of MDR in RB cells. Key words: Retinoblastoma/ drug therapy; Drug resistance,multiple; Veratrum/drug effects

A Phase 2 Trial of Imatinib Mesylate As Maintenance Therapy for Patients with Newly Diagnosed C-Kit Positive Acute Myeloid Leukemia (AML)

AbstractAbstract 3597The c-kit (CD117) receptor is expressed on > 10% blasts in 64% of de novo AMLs and mediates proliferation and anti-apoptotic effects. High c-kit levels correlate with a shorter time to relapse and decreased overall survival (OS). Imatinib mesylate (IM), a c-kit inhibitor, has activity against relapsed/refractory AML. The primary objective of this study was to determine whether adding maintenance IM for 1 yr after completion of standard induction (IT) and post-remission therapy (PRT) in patients (pts) with newly diagnosed c-kit+ AML improves relapse-free survival (RFS) compared to historical controls. Secondary objectives included: (1) assessing the feasibility of this approach; (2) evaluating outcomes based on c-kit expression (c-kit mean fluorescent intensity [MFI]); (3) determining whether c-kit expression correlates with AF1q gene and/or multi-drug resistance (MDR) gene expression. Methods:Pts were treated at Cleveland Clinic, Duke, Roswell Park, and University Hospitals of Cleveland from 2008 to 2012. IM was supplied by Novartis. Eligibility criteria included: pts age ≥ 18 yrs, AML in first complete remission (CR1), ≥ 20% c-kit+ blasts at diagnosis (dx), ECOG performance status 0–2. Cytogenetics (CG) were classified by CALGB 8461. Pts must have received IT (7+3 [continuous infusion cytarabine (C) and an anthracycline] or ADE [C, daunorubicin, etoposide]) and PRT (≥ 1 course for pts > 60 yrs; ≥ 2 courses for pts < 60 yrs). CR status was confirmed by bone marrow analysis prior to study enrollment. MDR expression was analyzed by immunohistochemistry on diagnostic samples (n=19); AF1q gene expression was analyzed by RT-PCR on RNA from available diagnostic pt samples (n=9) as previously described (Tse et al. Blood 2004; 104: 3058–63). C-kit MFI was calculated as the mean channel number (MCN) of the blasts/MCN autofluorescence using a CD45/orthogonal light scatter gate to isolate blasts. All pts received IM 600 mg/day for 12 months (mos) unless they experienced toxicity or disease progression. Dose modifications were made for Grades 2–4 non-hematologic toxicity and Grades 3–4 neutropenia and thrombocytopenia. Pts remaining off IM for > 4 wks were removed from treatment. Cumulative dose intensity was defined as the proportion of the total optimum dose administered over time. Results:Thirty-three pts were enrolled, with 32 pts having complete data. The median age was 54 yrs (range 19–81), median WBC at dx 22.13 K/μL (1.55–98.44), median peripheral blood blasts at dx 23.6% (range 0–85), and 44% were male. CG risk included: 47% (15) good, 31% (10) intermediate, and 22% (7) poor. The median c-kit % was 79.9, and median c-kit MFI 39.8 (range 6.5–120.1). Median AF1q expression was 9.59 (range 1.83–161.8.5). Eighty-four percent of pts had moderate or high levels of MDR expression (GSTP1, MDR1, LRP1, and/or MRP1); almost half (47%) had high expression. The majority of pts (74%, n=20) received PRT with high dose C (3 g/m2/dose × 6 doses/cycle). Pts received IM for a median of 4.0 mos (range 0.1–12.2), and the median daily dose was 600 mg. Twelve pts (38%) were dose reduced to 400 mg. Forty-five percent (13/29) of pts experienced grade 3 reactions possibly related to treatment, with the majority (31%) being myelosuppression. The most commonly reported adverse events were Grade 1/2 nausea and vomiting (72%), edema (59%), and fatigue (41%). Twelve pts (38%) discontinued treatment for adverse events. The median RFS survival is 18.8 mos, with a median follow-up of 19.1 mos (range 6.4–37.2). Estimated 2-yr OS is 62% ± 10%. Predictors of RFS included: age, WBC at dx, % peripheral blasts at dx, and CG risk. Dose intensity of IM did not correlate with outcome. AF1q and MDR expression did not correlate with c-kit MFI; although the number of pts with AF1q data was small. Of note, neither c-kit MFI nor AF1q expression were prognostic in this subset of pts treated with IM. With the exception of LRP1 expression (p=0.03), there was no correlation of MDR expression with RFS. Conclusions:Previous studies have demonstrated that c-kit MFI > 20.3 is an independent adverse prognostic factor for RFS and OS (median RFS 10.7 months). Considering the high c-kit MFI of pts in this study, the outcomes using IM maintenance are encouraging, and suggest that further study of this approach is warranted. Given the toxicities observed, reducing the dose of IM to 400 mg in the maintenance setting may be better tolerated. Disclosures:Advani:Novartis: Research Funding. Rizzieri:Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Kalaycio:Novartis: Research Funding, Speakers Bureau. Maciejewski:Novartis: Research Funding.

Effect of Src tyrosine kinase inhibition on the drug-resistance as well as MDR1 and LRP expression of the human cis-platinum-resistant lung cancer cell line A549/DDP

背景与目的本研究旨在探讨抑制Src酪氨酸激酶活性对人肺癌A549/DDP细胞耐药性及多药耐药蛋白（muti-drug resistance 1, MDR1）和肺耐药相关蛋白（lung resistance-related protein, LRP）表达的影响。方法以Src酪氨酸激酶抑制剂作用于A549/DDP细胞，应用Western blot法检测肿瘤细胞Src酪氨酸激活性的变化，CellTiter-Glo发光法检测肿瘤细胞药物敏感性的变化，流式细胞仪检测肿瘤细胞Rh-123含量变化，Western blot法和RT-PCR检测肿瘤细胞MDR1和LRP表达变化。结果Src酪氨酸激酶抑制剂可下调A549/DDP细胞中Src酪氨酸激活性，2.5 μM和10 μM Src酪氨酸激酶抑制剂作用肿瘤细胞后，肿瘤细胞药物敏感性提高，逆转倍数（reversal fold, RF）分别为1.59倍和2.10倍，肿瘤细胞中Rh-123含量分别提高了1.21倍和1.59倍，MDR1 mRNA表达分别是对照组的53.8%和27.5%，LRP mRNA表达分别是对照组的59.3%和21.4%，MDR1和LRP蛋白表达水平明显下降。结论抑制A549/DDP细胞中Src酪氨酸激酶活性可逆转肿瘤细胞多药耐药性，提高肿瘤细胞药物敏感性，其机制可能与降低细胞MDR1和LRP表达有关。

Tetrandrine enhances cytotoxicity of cisplatin in human drug-resistant esophageal squamous carcinoma cells by inhibition of multidrug resistance-associated protein 1

Multidrug resistance is one of the major causes limiting the efficacy of chemotherapeutic agents to control esophageal cancer. Herein, we investigated that the effect and mechanism of tetrandrine (TET) in the human esophageal squamous carcinoma cisplatin-resistant cell line YES-2/DDP. The human esophageal squamous carcinoma cisplatin-resistant cell line YES-2/DDP was isolated by stepwise selection in increasing concentrations of cisplatin. The CCK-8 method was carried out to measure the cell viability when cells were exposed to TET with or without cisplatin, and the IC50 and resistance index (RI) of cisplatin was then calculated. Real-time RT-PCR and western blotting were used to detect the mRNA and protein expression of multidrug resistance 1 (MDR1), multidrug resistance-associated protein 1 (MRP1) and breast cancer resistance protein (BCRP), respectively. Flow cytometry was adopted to determine CMFDA efflux and cell apoptosis, respectively. The resulting cell line YES-2/DDP was 16.4-fold resistant to cisplatin, the cytotoxicity of cisplatin to YES-2/DDP cells was enhanced by TET in a dose-dependent manner. Further, it was found that the expression of MDR1 and BCRP was similar in different treated cells. In contrast, the expression of MRP1 was markedly increased in YES-2/DDP cells, which was dose-dependently decreased by TET. In agreement with the results, MRP1 activity was also reversed by TET. In conclusion, TET possesses a reversal effect on drug resistance in YES-2/DDP cells through downregulation of MRP1, and has the potential to be an adjunct to chemotherapy for esophageal cancer.

Importance of inducible multidrug resistance 1 expression in HL-60 cells resistant to gemtuzumab ozogamicin

Resistance to gemtuzumab ozogamicin (GO) hampers the effective treatment of refractory acute myeloid leukemia (AML). To clarify the mechanism of resistance to GO, HL-60 cells were persistently exposed to GO in order to establish GO-resistant HL-60 (HL-60/GOR) cells. Multidrug resistance 1 (MDR-1) was strongly expressed in HL-60/GOR cells, but not in HL-60 cells. Although withdrawal of GO after the chronic exposure of HL-60/GOR cells to this compound gradually decreased MDR-1 expression to trace levels, reintroducing GO restored high MDR-1 expression in HL-60/GOR cells, but not in HL-60 cells. These results indicate that HL-60/GOR cells acquired the ability to induce MDR-1 expression in response to GO. U0126, a MEK1/2 inhibitor, prevented GO-inducible MDR-1 expression and abrogated GO resistance in HL-60/GOR cells. These results suggest that in the clinical use of GO, inducible MDR-1 expression in tumor cells should be investigated before treatment with GO. If the cells are positive then MEK1/2 inhibitors may be effective in overcoming resistance to GO.

Reversal effect of Tween-20 on multidrug resistance in tumor cells in vitro

Multidrug resistance (MDR) is a major barrier for chemotherapy of many cancers. Non-ionic surfactants have great potential to reverse the MDR by preventing onset or delay progression of the carcinogenic process. However, the role of Tween-20 in the development of MDR remains unknown. The aim of this study was to explore the reversal effect and potential mechanism of Tween-20 on tumor cells in vitro. Alamar Blue assay was used to examine the reversal index of Tween-20 to vincristine (VCR), doxorubicin (DOX) and 5-fluorouracil (5-FU) in KBv200, HepG2/R and Bel-7402/5-FU, respectively. Morphological change was determined by Gimsa and Hoechst 33258 staining. The acumulation of DOX was confirmed by spectrofluorimetric assay. Cell cycle analysis was performed using flow cytometry. The mRNA and protein expression levels of MDR were assessed by semiquantitative RT-PCR and dot blot, respectively. The results showed that Tween-20 at concentrations of 0.0025%, 0.005%, 0.01% had little cytotoxicity. When combined with the cancer drugs, it significantly promoted the sensitivity of MDR cells. Fluorescence staining confirmed that the percentage of apoptotic cell increased when combined with Tween-20. This notion was further supported by the observation that Tween-20 treatment potentiated VIN-induced G2/M arrest of the cell cycle. Furthermore, Tween-20 treatment increased significantly intracellular accumulation of DOX. RT-PCR and dot blot revealed that Tween-20 could downregulate the expression of MDR and P-glycoprotein. Low concentrations of Tween-20 can efficiently reverse the multidrug resistance phenotype by enhancing accumulation of the anticancer drugs. The potential mechanism may be via inhibiting the multidrug-resistant gene expression.

Suppression of BCRP Expression and Restoration of Sensitivity to Chemotherapy in Multidrug-Resistant Hepatocellular Carcinoma Cell Line HEPG2/ADM by RNA Interference

Breast cancer resistance protein (BCRP) is an ATP-binding cassette multidrug transporter that confers resistance to various anticancer drugs like Adriamycin. Overexpression of BCRP confers multidrug resistance (MDR) in hepatocellular carcinoma cells and is a frequent impediment to successful chemotherapy. We evaluated a new approach using RNA interference for the specific knockdown of BCRP in hepatocellular carcinoma cells. To overcome the BCRP-mediated atypical multidrug drug resistance, one small interfering RNA construct (RNAi) targeting one special region of BCRP gene were designed to inhibit the atypical MDR expression by transfecting them into HepG2/ADM cell lines. We found that the overexpression of BCRP gene was suppressed efficiently by the introduction of small interfering RNA, which caused sequence specific gene silence. The level of BCRP mRNA reduced to 22.55% after transfected by pSUPER-BCRPs compared with those of the controls. Similarly, the level of BCRP decreased too. Furthermore, the sensitivity to Adriamycin of pSUPER-BCRPs-treated HEPG2/ADM cells is increased 3.55-fold compared to their control (p<0.05). The relative reverse rate of HepG2/ADM cell to Adriamycin is 72.2%. These data indicated that pSUPER-BCRPs could modulate MDR and may present a new approach to overcome BCRP-mediated drug resistance in HEPG2/ADM cells. It may reverse multidrug resistance phenotype and therefore provide promising therapeutic modalities in the treatment of hepatocellular carcinoma.

Conditional Replication Adenovirus Sensitizes A549 Cancer Cell to Cisplatin

Objective: The aim of the study was to improve the therapeutic effect for lung cancer using a synergetic strategy of adenovirus-based gene therapy combined with chemotherapy. Methods: A conditional replication adenovirus(CRAd) was employed to treat the A549 lung cancer cells and cisplatin-resisted A549(A549-DDP) cells. In vitro MTS / PMS assay were used to evaluate the cell viability. PCR were used to detect expression of Coxsackie receptor (CAR) and Multidrug resistance(MDR) gene. The in vivo anti-tumor effect of CRAd and cisplatin was evaluated using a subcutaneous mouse model. Results: The CRAd sensitizes A549 cancer cells to cisplatin. The mechanism of enhanced cell growth inhibition is associated with the increased CAR and MDR expression. Conclusion: Our approach is better than the conventional gene therapy and chemotherapy strategy.

Hypoxia-induced increases in A549/CDDP cell drug resistance are reversed by RNA interference of HIF-1α expression

This study aimed to investigate the effects of knocking down hypoxia-inducible factor-1α (HIF-1α) through RNA interference on hypoxia-induced increases in drug resistance in A549/CDDP cells, and to study the underlying mechanisms. A small interfering RNA (siRNA) eukaryotic expression vector targeting HIF-1α was constructed and transfected into A549/CDDP cells treated with hypoxia. The mRNA and protein levels of HIF-1α, multidrug resistance-1 (MDR1), and multidrug resistance-associated protein (MRP) were determined by reverse transcription polymerase chain reaction (RT-PCR) and immunocytochemistry. Cell viability following treatment with cisplatin was determined by MTT assay. Hypoxia increased the resistance of A549/CDDP cells to cisplatin and this effect was reversed by the siRNA inhibition of HIF-1α expression. Expression of HIF-1α siRNA also downregulated HIF-1α, MDR1 and MRP mRNA, and protein expression in A549/CDDP cells treated with hypoxia (p<0.05). Hypoxia-induced resistance of A549/CDDP cells to cisplatin is reversed by the siRNA inhibition of HIF-1α expression. This effect may be mediated by a decreased expression of MDR1 and MRP.

Quantitative Membrane Protein Expression at the Blood–Brain Barrier of Adult and Younger Cynomolgus Monkeys

Cynomolgus monkey has been used as a model for the prediction of drug disposition in human brain. The purpose of this study was to clarify protein expression levels of membrane proteins affecting drug distribution to brain, such as transporters, receptors, and junctional proteins, in cynomolgus monkey brain microvessels by using liquid chromatography tandem mass spectrometory. In adult monkeys, three ATP-binding cassette transporters (multidrug resistance 1 (MDR1), breast cancer resistance protein (BCRP), and multidrug resistance protein 4 (MRP4)), six solute carrier transporters (glucose transporter 1 (GLUT1), GLUT3/14, monocarboxylate transporter 1 (MCT1), MCT8, organic anion transporting polypeptide 1A2, and equilibrative nucleoside tranporter 1), two junctional proteins (claudin-5 and vascular endothelial cadherin), and two receptors (insulin receptor and low-density lipoprotein receptor-related protein 1) were detected. Comparison of the expression levels with those in mouse, which we reported previously, revealed a pronounced species difference. BCRP expression in monkey was greater by 3.52-fold than that in mouse, whereas MDR1 and MRP4 expression levels in monkey were lower by 0.304- and 0.180-fold, respectively, than that in mouse. This study also investigated the developmental changes in expression of membrane proteins in neonate and child monkeys. Expression of MDR1 was similar in neonate and adult monkeys, whereas in rat, P-glycoprotein expression was reported to be significantly lower in brain microvessels of neonate as compared with adult rat. These results will be helpful to understand and predict brain concentrations of drugs in different species and at different ages of primates. © 2011 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 100:3939–3950, 2011

Expression of P-glycoprotein, Cyclin D1 and Ki-67 in Acute Lymphoblastic Leukemia: Relation with Induction Chemotherapy and Overall Survival.

Previous studies showed that non-cycling cells have a higher multidrug resistance (MDR) expression, which may be down-regulated by proliferation induction. Triggering these cells into proliferation down-regulates high MDR expression. The aim of this study was to determine the expression of P-glycoprotein (PGP) and cell cycle parameters (cyclin D1 and Ki-67) in acute lymphoblastic leukemia (ALL) at diagnosis, and to evaluate the correlation between the expressions of each marker, and the clinical significance of such expression with response to induction chemotherapy and overall survival. A total of 78 newly diagnosed ALL patients were enrolled in our study. PGP, cyclin D1 and Ki-67 were determined by flow cytometry. PGP expression was encountered in 10/78 (12.8%) of ALL cases. Cyclin D1 and Ki-67 were expressed in 16/77 (20.6%) and 27/76 (34.6%) of ALL cases, respectively. None of the parameters were associated with response to induction chemotherapy and overall survival. Based on the current analysis, we conclude that a joint immunophenotypic evaluation of PGP and cell cycle parameters like that adopted in this study is unlikely to reveal mechanisms of multidrug resistance associated with the clinical outcome.

Various doses of fractioned irradiation modulates multidrug resistance 1 expression differently through hypoxia-inducible factor 1α in esophageal cancer cells

To evaluate the effect of different regimen of radiotherapy on multidrug resistance 1 (MDR1) expression and analyze the role hypoxia-inducible factor 1α (HIF1α) played in the whole process. Fifty-four cell lines established from 96 esophageal cancer biopsy samples were given various doses of fractioned irradiation. The mRNA and protein levels of HIF1α and MDR1 post-irradiation were measured by quantitative reverse transcription-polymerase chain reaction and Western blot analysis, respectively. HIF1α-siRNA was used to verify the effect of HIF1α on radiation-mediated MDR1 modulation. In esophageal cancer cells surviving 28 Gy irradiation (2 Gy/f, 14 fractions), MDR1 mRNA expression increased 65.27 ± 5.58%, and HIF1α was elevated by 27.21 ± 2.25%. Interestingly, their expression decreased by 54.38 ± 11.53% and 32.08 ± 4.75% after 7 Gy irradiation (0.5 Gy/f, 14 fractions). HIF1α expression showed a positive correlation with MDR1 expression in the whole process (P < 0.05). Silencing of HIF1α decreased MDR1 expression and blocked changes in MDR1 and HIF1α expression induced by fractioned irradiation. These results indicate that MDR1 is differentially modulated by different doses of fractionated radiation, which should be taken into account when combining radiotherapy and chemotherapy for patients with esophageal cancer.

Metformin inhibits P‐glycoprotein expression via the NF‐κB pathway and CRE transcriptional activity through AMPK activation

The expression of P-glycoprotein (P-gp), encoded by the multidrug resistance 1 (MDR1) gene, is associated with the emergence of the MDR phenotype in cancer cells. We investigated whether metformin (1,1-dimethylbiguanide hydrochloride) down-regulates MDR1 expression in MCF-7/adriamycin (MCF-7/adr) cells. MCF-7 and MCF-7/adr cells were incubated with metformin and changes in P-gp expression were determined at the mRNA, protein and functional level. Transient transfection assays were performed to assess its gene promoter activities, and immunoblot analysis to study its molecular mechanisms of action. Metformin significantly inhibited MDR1 expression by blocking MDR1 gene transcription. Metformin also significantly increased the intracellular accumulation of the fluorescent P-gp substrate rhodamine-123. Nuclear factor-κB (NF-κB) activity and the level of IκB degradation were reduced by metformin treatment. Moreover, transduction of MCF-7/adr cells with the p65 subunit of NF-κB induced MDR1 promoter activity and expression, and this effect was attenuated by metformin. The suppression of MDR1 promoter activity and protein expression was mediated through metformin-induced activation of AMP-activated protein kinase (AMPK). Small interfering RNA methods confirmed that reduction of AMPK levels attenuates the inhibition of MDR1 activation associated with metformin exposure. Furthermore, the inhibitory effects of metformin on MDR1 expression and cAMP-responsive element binding protein (CREB) phosphorylation were reversed by overexpression of a dominant-negative mutant of AMPK. These results suggest that metformin activates AMPK and suppresses MDR1 expression in MCF-7/adr cells by inhibiting the activation of NF-κB and CREB. This study reveals a novel function of metformin as an anticancer agent.

Variation of MDR proteins expression and activity levels according to clinical status and evolution of CML patients

The involvement of the multidrug resistance (MDR) mediated by ABC transporter proteins P-glycoprotein (Pgp) and multidrug resistance-associated protein-1 (MRP1) overexpressions in patients with chronic myeloid leukemia (CML) are not completely understood. Pgp and MRP1 expressions and activity were analyzed in samples from 158 patients with chronic myeloid leukemia (CML). Using flow cytometry, Pgp expression was more frequently observed in early chronic (P = 0.00) and in advanced (P = 0.02) CML phases when it was compared to MRP1 expression. Variation of MDR expression and activity were observed during the CML evolution in patients previously treated with interferon and imatinib. In the K562-Lucena cell line, Pgp positive, imatinib caused an enhancing in Pgp expression at protein and mRNA levels, whereas in the Pgp negative cell line, this drug was capable of decreasing MDR1/Pgp mRNA levels. Our result emphasizes the importance of understanding the different aspects of MDR status in patients with CML when they are under investigation in determining imatinib resistance.

Involvement of MyoD and PEA3 in regulation of transcription activity of MDR1 gene

Overexpression of multidrug resistance 1 (MDR1) in cancer remains one of the major causes for the failure of chemotherapy. In the present study, we found that MyoD and PEA3 could activate P-glycoprotein (P-gp) expression in SGC7901 cells. Knockdown of MyoD and PEA3 attenuated MDR1 expression and increased the sensitivity of multidrug resistant cancer cells to cytotoxic drugs that were transported by P-gp in SGC7901/VCR cells. MyoD or PEA3 could bind to the E-box and PEA3 sites on the MDR1 promoter and activate its transcription. The regulation of MDR1 expression by MyoD and PEA3 may provide potential ways to overcome MDR in cancer treatment.