Daunorubicin Efflux Research Articles

The involvement of multiple ABC transporters in daunorubicin efflux in Streptomyces coeruleorubidus.

Streptomyces genus produces a large number of antibiotics, which are always synthesized by specific biosynthetic gene clusters (BGCs). To resist autotoxicity, transporters encoded by genes located within BGC occasionally pump antibiotic along with transporter encoded by gene located outside BGC. Daunorubicin is an anthracycline antibiotic biosynthesized by Streptomyces species, playing a crucial role in the treatment of leukaemia. In existing studies, only one two-component ATP-binding cassette (ABC) transporter, encoded by drrA1-drrB1 (abbreviated as drrAB1) and located within the daunorubicin BGC, has been proven to extrude daunorubicin. In this work, two other two-component ABC transporters, encoded by drrAB2 and drrAB3 and located outside the cluster, were found to play the complementary role in daunorubicin efflux in S. coeruleorubidus. Disruption of three drrABs resulted in a 94% decrease in daunorubicin production. Furthermore, drrAB2 is regulated by the TetR family regulator DrrR1, responding to the intracellular accumulation of daunorubicin and suggesting its role in stress response and self-resistance. Although the homologues of DrrAB1 are only found in three anthracycline BGCs, the homologues of DrrAB2 and DrrAB3 are spread in many Streptomyces strains which do not contain any known anthracycline BGC. This indicates that DrrAB2 and DrrAB3 may recognize and extrude a broader range of substrates besides daunorubicin, thus playing a more extensive role in cellular detoxification.

Valproate modulates the activity of multidrug resistance efflux pumps, as a chemoresistance factor in gastric cancer cells.

Drug resistance is one of the most critical problems in gastric cancer therapy. This study was performed to investigate the valproic acid effects on the proliferation of sensitive and resistant cell lines of human gastric cancer, and to explore the mechanism of the agent on multi drug resistance and apoptosis genes. The cytotoxicity effect of valproic acid on the EPG85.257 and EPG85.257RDB cells was assessed by the MTT assay, and the IC50 concentration was evaluated. Apoptosis, genotoxicity, and drug resistance pump activity were evaluated using comet assay, Real-time PCR, and flow cytometry, respectively. Cell proliferation was assayed using a scratch test. Dose-dependent toxicity was recorded after treatment of cells with valproic acid. Valproic acid represented a significant growth inhibition on EPG85.257 cells with IC50 values of 5.84 µM and 4.78 µM after 48 h and 72 h treatment, respectively. In contrast, the drug-resistant counterpart represented 8.7 µM and 7.02 µM IC50 values after the same treatment time. Valproic acid induced PTEN, Bcl2, P53, Bax, P21, and caspase3 expression in EPG85.257 cells, whereas p21, p53, PTEN, and ABCB1 were overexpressed in EPG5.257RDB. Valproic acid hindered cell migration in both cell lines (P < 0.01). Valproate genotoxicity was significantly higher in the parent cells than in their resistant EPG85.257RDB counterparts. Valproate led to a 62% reduction in the daunorubicin efflux of the MDR1 pump activity. Valproate can affect drug resistance in gastric cancer via a unique mechanism independent of MDR1 expression.

Benzophenone Sulfonamide Derivatives as Interacting Partners and Inhibitors of Human P-glycoprotein.

Human P-glycoprotein (P-gp) is a transmembrane protein that belongs to the ATPBinding Cassette (ABC) transporters family. Physiologically, it exports toxins out of the cell, however, its overexpression leads to the phenomena of Multidrug-Resistance (MDR) by exporting a diverse range of compounds, which are structurally and chemically different from each other, thus creating a hurdle in the treatment of various diseases including cancer. The current study was designed to screen benzophenone sulfonamide derivatives as a class of inhibitors and potential anticancer agents for P-gp. A total number of 15 compounds were evaluated. These compounds were screened in daunorubicin efflux inhibition assays using CCRF-CEM Vcr1000 cell line that overexpressed human P-gp. Cytotoxicity assay was also performed for active compounds 11, 14, and 13. These scaffolds were then docked in the homology model of human P-gp using mouse P-gp as a template (PDB ID: 4MIM) and the recently published Cryo Electron Microscopy (CEM) structure of human mouse chimeric P-gp to find their interactions with specified residues in the binding pocket. Analysis was performed using Labview VI and Graph pad prism version 5.0. Results revealed the potency of all these compounds in low nanomolar range whereas, compound 14 was found to be most active with IC50 value of 18.35nM±4.90 followed by 11 and 13 having IC50 values of 30.66nM±5.49 and 46.12nM±3.06, respectively. Moreover, IC50 values calculated for 14, 11 and 13 in cytotoxicity assay were found to be 22.97μM±0.026, 583.1μM±0.027 and 117.8μM±0.062, respectively. Docking results showed the interaction of these scaffolds in transmembrane helices (TM) where Tyr307, Tyr310, Tyr953, Met986 and Gln946 were found to be the major interaction partners, thus they might play a significant role in the transport of these scaffolds. Benzophenone sulfonamide derivatives showed IC50 values in low nanomolar range comparable to the standard inhibitor Verapamil, therefore they can be good inhibitors of P-gp and can serve as anticancer agents. Also, they have shown interactions in the transmembrane region sharing the same binding region of verapamil and zosuquidar.

Cyclin-dependent kinase inhibitors AZD5438 and R547 show potential for enhancing efficacy of daunorubicin-based anticancer therapy: Interaction with carbonyl-reducing enzymes and ABC transporters

Daunorubicin (DAUN) has served as an anticancer drug in chemotherapy regimens for decades and is still irreplaceable in treatment of acute leukemias. The therapeutic outcome of DAUN-based therapy is compromised by its cardiotoxicity and emergence of drug resistance. This phenomenon is often caused by pharmacokinetic mechanisms such as efflux of DAUN from cancer cells through ATP-binding cassette (ABC) transporters and its conversion to less cytostatic but more cardiotoxic daunorubicinol (DAUN-OL) by carbonyl reducing enzymes (CREs). Here we aimed to investigate, whether two cyclin-dependent kinase inhibitors, AZD5438 and R547, can interact with these pharmacokinetic mechanisms and reverse DAUN resistance. Using accumulation assays, we revealed AZD5438 as potent inhibitor of ABCC1 showing also weaker inhibitory effect to ABCB1 and ABCG2. Combination index analysis, however, shown that inhibition of ABCC1 does not significantly contribute to synergism between AZD5438 and DAUN in MDCKII-ABCC1 cells, suggesting predominant role of other mechanism. Using pure recombinant enzymes, we found both tested drugs to inhibit CREs with aldo-keto reductase 1C3 (AKR1C3). This interaction was further confirmed in transfected HCT-116 cells. Moreover, these cells were sensitized to DAUN by both compounds as Chou-Talalay combination index analysis showed synergism in AKR1C3 transfected HCT-116, but not in empty vector transfected control cell line. In conclusion, we propose AZD5438 and R547 as modulators of DAUN resistance that can prevent AKR1C3-mediated DAUN biotransformation to DAUN-OL. This interaction could be beneficially exploited to prevent failure of DAUN-based therapy as well as the undesirable cardiotoxic effect of DAUN-OL.

Dinaciclib, a cyclin-dependent kinase inhibitor, is a substrate of human ABCB1 and ABCG2 and an inhibitor of human ABCC1 in vitro

Dinaciclib is a novel cyclin-dependent kinase inhibitor (CDKI) with significant activity against various cancers in vitro and in vivo. ABC efflux transporters play an important role in drug disposition and are responsible for multidrug resistance in cancer cells. Inhibitors and substrates of these transporters may participate in pharmacokinetic drug–drug interactions (DDIs) that alter drug disposition during pharmacotherapy. To assess such risks associated with dinaciclib we evaluated its possible effects on efflux activities of ABCB1, ABCC1 and ABCG2 transporters in vitro. Monolayer transport, XTT cell proliferation, ATPase and intracellular accumulation assays were employed. Here, we show that the transport ratio of dinaciclib was far higher across monolayers of MDCKII-ABCB1 and MDCKII-ABCG2 cells than across MDCKII parental cell layers, demonstrating that dinaciclib is a substrate of ABCB1 and ABCG2. In addition, overexpression of ABCB1, ABCG2 and ABCC1 conferred resistance to dinaciclib in MDCKII cells. In ATPase assays, dinaciclib decreased stimulated ATPase activity of ABCB1, ABCG2 and ABCC1, confirming it has interactive potential toward all three transporters. Moreover, dinaciclib significantly inhibited ABCC1-mediated efflux of daunorubicin (EC50=18μM). The inhibition of ABCC1 further led to a synergistic effect of dinaciclib in both MDCKII-ABCC1 and human cancer T47D cells, when applied in combination with anticancer drugs. Taken together, our results suggest that ABC transporters can substantially affect dinaciclib transport across cellular membranes, leading to DDIs. The DDIs of dinaciclib with ABCC1 substrate chemotherapeutics might be exploited in novel cancer therapies.

Abstract 172: Adipocytes decrease daunorubicin concentration in acute lymphoblastic leukemia cells

Abstract Obesity is associated with increased cancer incidence and mortality. Adipose tissue has been shown to play a role in several types of cancer, including acute lymphoblastic leukemia (ALL). We have demonstrated that murine ALL cells actively migrate into adipose tissue in mice, and that adipocytes protect ALL cells from daunorubicin (DNR) in vitro. We have further shown that media cultured by both adipocytes and ALL cells together (ALCM) can protect ALL cells from DNR. We hypothesize that adipocytes protect ALL cells from DNR by decreasing ALL cell intracellular drug accumulation. Human pre B ALL cells (BV173) were co-cultured with 3T3-L1 adipocytes using a transwell system. Intracellular DNR was visualized using con-focal fluorescence microscopy at various time points in leukemia cells during DNR treatment. Drug uptake in leukemia cells treated with DNR and co-cultured with adipocytes was measured by flow cytometry. By preloading cells with DNR, drug efflux assays were also performed with ALL cells. Gene expression of ABCB1a and cell surface expression of MDR1 were quantified using qPCR and flow cytometry, respectively, in ALL cells co-cultured with adipocytes. After 72 hours of DNR treatment, there were significantly more viable BV173 cells in the transwells placed over adipocytes than those over fibroblasts (290,000± 60,500 vs. 108,000± 13,000, p=0.008, n=4). Co-culture with adipocytes was associated with a lower intracellular DNR in BV173 cells. After 4 hours, DNR was 30% lower, and by 24 hours intracellular DNR was 80% less (n=1). However, co-culturing ALL cells with adipocytes was not associated with a significant increase in efflux rate of DNR from preloaded BV173 (half-life = 36±13 vs. 31±9 min., p=0.23, n=3). The mRNA expression of ABCB1a, the gene encoding MDR1, was increased in BV173 cells (130% increase, n=1) co-cultured with adipocytes for 24 hours. However, we did not detect an increase in surface MDR1 expression in BV713 co-cultured with adipocytes. We then tested whether adipocyte-secreted factors would cause efflux of DNR from ALL cells. There was a tendency for DNR efflux rate to be higher in BV173 cells cultured in ALCM (half-life = 36±13 vs. 27±10 min., p=0.08, n=3). Further investigation is needed to confirm this effect. These findings demonstrate that adipocytes may protect ALL cells from daunorubicin treatment in part by decreasing intracellular drug accumulation. However, it is not clear whether this effect is due to altered uptake, efflux, or intracellular drug action. Citation Format: Xia Sheng, Jonathan Tucci, James Behan, Steven D. Mittelman. Adipocytes decrease daunorubicin concentration in acute lymphoblastic leukemia cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 172. doi:10.1158/1538-7445.AM2014-172

Progesterone–adenine hybrids as bivalent inhibitors of P-glycoprotein-mediated multidrug efflux: Design, synthesis, characterization and biological evaluation

Bivalent ligands were designed on the basis of the described close proximity of the ATP-site and the putative steroid-binding site of P-glycoprotein (ABCB1). The syntheses of 19 progesterone–adenine hybrids are described. Their abilities to inhibit P-glycoprotein-mediated daunorubicin efflux in K562/R7 human leukemic cells overexpressing P-glycoprotein were evaluated versus progesterone. The hybrid with a hexamethylene linker chain showed the best inhibitory potency. The efficiency of these progesterone-adenine hybrids depends on two main factors: (i) the nature of the linker and (ii) its attachment point on the steroid skeleton.

Induction of dendritic cells with multidrug resistance from K562/MDR1 cells

To induce the differentiation of K562/MDR1 cells into dendritic cells (DC) with multidrug resistance property. K562/MDR1 cells and K562 cells were cultured in the presence of GM-CSF and IL-4 to generate DC and matured by TNF-α. On d14 K562/MDR1-DC and K562-DC cells were harvested and the expressions of CD1a, CD83, CD80, CD86, HLA-ABC and HLA-DR were assessed by flow cytometry (FCM). The antigen presentation function of K562/MDR1-DC and K562-DC was determined by allogenic mixed lymphocyte reaction (Allo-MLR). The expression of P-glycoprotein and the intracellular accumulation of daunorubicin (DNR) were detected by FCM. The sensitivity of K562/MDR1-DC and K562-DC cell to vincristine, adriamycin was measured using MTT assay. Both K562/MDR1 and K562 cells were differentiated into dendritic cells in the presence of cytokine cocktails, showing the morphologic and immunophenotypic characteristics of DC. K562/MDR1-DC more markedly enhanced proliferation of allogeneic lymphocytes in MLR than K562-DC. High level expression of P-glycoprotein and efflux of DNR were demonstrated in K562/MDR1-DC. K562/MDR1-DC showed multidrug resistance property, with higher IC(50) to VCR and ADM than that of K562-DCs. K562/MDR1 cells can be differentiated into DC with the presence of cytokines, the induced K562/MDR1-DC cells express high level of P-glycoprotein and acquire the multidrug resistance property.

Amonafide: a potential role in treating acute myeloid leukemia

Introduction: Amonafide is a novel topoisomerase II (Topo II) inhibitor and DNA intercalator that induces apoptotic signaling by blocking the binding of Topo II to DNA. Amonafide retains cytotoxic activity even in the presence of P-glycoprotein (Pgp)-mediated multi-drug resistance (MDR), a major contributor to clinical treatment failure.Areas covered: In vitro, Pgp-mediated transport (efflux) of amonafide from myeloblasts obtained from patients with secondary acute myeloid leukemia (sAML) was significantly less than efflux of daunorubicin. Amonafide has shown efficacy in patients with sAML, as well as in patients with poor prognostic characteristics such as older age and unfavorable cytogenetics, all associated with MDR. Improved antileukemic activity is observed when amonafide is given together with cytarabine, rather than as monotherapy, with a complete remission rate of ∼ 40% in a recent Phase II trial in sAML. The efficacy of amonafide was maintained among poor-risk subsets of patients, including older patients and patients who had previous myelodysplastic syndrome or previous leukemogenic therapy. The safety profile was acceptable and manageable.Expert opinion: Amonafide plus cytarabine may have clinical utility in patients with sAML and in other poor-risk subgroups of acute myeloid leukemia (AML). Ongoing trials will help define the role for amonafide in the treatment of poor-risk AML.

Synthesis and Reversal Efficacy of Magnetic Nanoparticles Coloaded with Daunorubicin and 5-Bromotetrandrin

AbstractAbstract 4945Owing to serious side effects and multidrug resistance (MDR), systematic chemotherapy is limited in cancer treatment. On the one hand, most of side effects are result from non-selective for target cells of antitumor drugs. On the other hand, the main mechanism of MDR is the overexpression of P-glycoprotein (P-gp). Design and exploitation of novel clinical chemotherapy formulation with dual functional properties of targeted therapy and reversal of drug resistance is a promising approach in tumor therapy. Nanoparticles drug delivery system has been shown to improve cancer therapy by increased drug delivery to target sites because of the enhanced permeability and retention effect (EPR). In the present studies, we developed a new formulation, which magnetic nanoparticles (MNPs) coloaded with daunorubicin (DNR) and 5-bromotetrandrin (Br Tet), an anticancer drug and a MDR reversal agent, and studied the in vitro antitumor efficacy. The drug encapsulation efficiency of DNR and Br Tet (alone or in combination) in MNPs was 62–83%. The release of DNR and Br Tet from nanoparticles was sustained. The DNR and Br Tet loaded MNPs (DNR-Br Tet-MNPs) are provided with good magnetic responsibility. The drugs in combination incorporated in MNPs displayed well synergistic cytotoxicity in the MDR leukemia K562/A02 cells. Fluorescence intensity of intracellular DNR detection demonstrated that DNR-Br Tet-MNPs could be endocytosed by K562/A02 cells and sustained releasing DNR intracellular. The results of RT-PCR and western blot demonstrated that the expressions of MDR1 mRNA and G-pg of K562/A02 cells are decreased by treated with DNR-Br Tet-MNPs after 48 h. It was concluded that the antitumor efficacy of DNR-Br Tet-MNPs was due to the inhibition of Br Tet to P-gp and reducing the efflux of DNR. Our DNR-Br Tet-MNPs could be of high clinical value in the target treatment of many resistant tumors, such as haematologic malignancies. Disclosures:No relevant conflicts of interest to declare.

Screening for Chemosensitizers from Natural Plant Extracts through the Inhibition Mechanism of P-glycoprotein

ABSTRACT − P-gp plays a critical role in drug disposition and represents a mechanism for the development of multidrugresistance. Flavonoids, a major class of natural compounds widely present in foods and herbal products, have been shownto inhibit P-gp. Therefore, the aim of this study was to identify new candidate chemosensitizers by screening various plantextracts. The ability of natural plant extracts to inhibit P-gp activity was assessed by measuring cellular accumulation of cal-cein AM, daunorubicin and vincristine in P-gp overexpressing MDCKII-MDR1 cells. Among more than 800 plant extracts,eight were found to inhibit P-gp activity. Curcuma aromatica extract produced greatest inhibition, followed by Curcumalonga and Dalbergia odorifera extracts. Extracts of Aloe ferox, Curcuma zedoariae rhizome, Zanthoxylum planispinum, andAgeratum conyzoides showed moderate inhibitory effects. Curcumin and quercetin exhibited similar inhibition of P-gp-mediated efflux of daunorubicin and vincristine, and flavones had a lesser effect. When chemosensitizing effect was eval-uated by measuring daunorubicin sensitivity to MDCKII-MDR1 cells in the presence of natural plant extracts, Curcuma aro-matica showed the most potent chemosensitizing effect based on daunorubicin cytotoxicity. In conclusion, natural plantextracts such as Curcuma aromatica can potently inhibit P-gp activity and may have potential as a novel chemosensitizers. Key words

Functional study of the novel multidrug resistance gene HA117 and its comparison to multidrug resistance gene 1

BackgroundThe novel gene HA117 is a multidrug resistance (MDR) gene expressed by all-trans retinoic acid-resistant HL-60 cells. In the present study, we compared the multidrug resistance of the HA117 with that of the classical multidrug resistance gene 1 (MDR1) in breast cancer cell line 4T1.MethodsTransduction of the breast cancer cell line 4T1 with adenoviral vectors encoding the HA117 gene and the green fluorescence protein gene (GFP) (Ad-GFP-HA117), the MDR1 and GFP (Ad-GFP-MDR1) or GFP (Ad-GFP) was respectively carried out. The transduction efficiency and the multiplicity of infection (MOI) were detected by fluorescence microscope and flow cytometry. The transcription of HA117 gene and MDR1 gene were detected by reverse transcription polymerase chain reaction (RT-PCR). Western blotting analysis was used to detect the expression of P-glycoprotein (P-gp) but the expression of HA117 could not be analyzed as it is a novel gene and its antibody has not yet been synthesized. The drug-excretion activity of HA117 and MDR1 were determined by daunorubicin (DNR) efflux assay. The drug sensitivities of 4T1/HA117 and 4T1/MDR1 to chemotherapeutic agents were detected by Methyl-Thiazolyl-Tetrazolium (MTT) assay.ResultsThe transducted efficiency of Ad-GFP-HA117 and Ad-GFP-MDR1 were 75%-80% when MOI was equal to 50. The transduction of Ad-GFP-HA117 and Ad-GFP-MDR1 could increase the expression of HA117 and MDR1. The drug resistance index to Adriamycin (ADM), vincristine (VCR), paclitaxel (Taxol) and bleomycin (BLM) increased to19.8050, 9.0663, 9.7245, 3.5650 respectively for 4T1/HA117 and 24.2236, 11.0480, 11.3741, 0.9630 respectively for 4T1/MDR1 as compared to the control cells. There were no significant differences in drug sensitivity between 4T1/HA117 and 4T1/MDR1 for the P-gp substrates (ADM, VCR and Taxol) (P < 0.05), while the difference between them for P-gp non-substrate (BLM) was statistically significant (P < 0.05). DNR efflux assay confirmed that the multidrug resistance mechanism of HA117 might not be similar to that of MDR1.ConclusionsThese results confirm that HA117 is a strong MDR gene in both HL-60 and 4T1 cells. Furthermore, our results indicate that the MDR mechanism of the HA117 gene may not be similar to that of MDR1.

Design, synthesis and evaluation of progesterone–adenine hybrids as bivalent inhibitors of P-glycoprotein-mediated multidrug efflux

Steroidal bivalent ligands were designed on the basis of the described closer proximity of the ATP-site and the putative steroid-binding site of P-glycoprotein (ABCB1). The syntheses of seven progesterone–adenine hybrids were described. Their abilities to inhibit P-glycoprotein-mediated daunorubicin efflux in K562/R7 human leukemic cells overexpressing P-glycoprotein were evaluated versus progesterone.

Daunorubicin efflux in Streptomyces peucetius modulates biosynthesis by feedback regulation

Streptomyces peucetius self-resistance genes drrA and drrB encode membrane-associated proteins that function like an ABC transporter for the efflux of daunorubicin and to maintain a constant subinhibitory physiological concentration of the drug within the cell. In this study, the drrA and drrB operons were disrupted for investigating drug production, self-resistance and regulation. The drrA-drrB null mutant was highly sensitive to daunorubicin. A 10-fold decrease in drug production was observed in the null mutant compared with the wild-type strain. We propose that the absence of a drug-specific efflux pump increases the intracellular concentration of daunorubicin, which is sensed by the organism to turn down drug production. Quantitative real-time PCR analysis of the mutant showed a drastic reduction in the expression of the key regulator dnrI and polyketide synthase gene dpsA. However, the expression of regulatory genes dnrO and dnrN was increased. Feedback regulation based on the intracellular daunorubicin concentration is discussed.

Activators of P‐glycoprotein: Structure–Activity Relationships and Investigation of their Mode of Action

P-glycoprotein (P-gp), a 170 kDa plasma membrane protein, is one of the most relevant ABC transporters involved in the development of multidrug resistance (MDR). Understanding its mechanism of transport as well as its interactions with various substrates are basic requirements for the development of adequate therapeutic approaches to overcome this kind of resistance against a broad spectrum of structurally unrelated cytostatic drugs. P-gp modulators (activators) that exert various effects on the intracellular accumulation of distinct P-gp substrates are useful tools for investigating the interactions between multiple drug binding sites of this transport protein. In this study, a series of 27 different imidazobenzothiazoles and imidazobenzimidazoles structurally related to the known P-gp activators QB102 and QB11 was designed, and their modulating properties were investigated. Most of them were able to stimulate P-gp-mediated efflux of daunorubicin and rhodamine 123 in a concentration-dependent manner, but some compounds also displayed weak inhibitory effects. Additionally, P-gp-mediated efflux of vinblastine and colchicine was inhibited by several compounds. Therefore, we concluded that the novel compounds bind to the H site of P-gp and activate the efflux of specific substrates of the R site in a positive cooperative manner, whereas binding of H-type substrates is inhibited competitively. This hypothesis is confirmed by the observation that the modulators do not influence hydrolysis of ATP or its affinity toward P-gp.

Diatrizoate, Iopromide and Iotrolan Enhanced Cytotoxicity of Daunorubicin in Multidrug Resistant K562/adr Cells: Impaired the Mitochondrial and Inhibited the P-Glycoprotein Function

Multidrug resistance was an obstacle in cancer chemotherapy because the cells decreased their intracellular drug accumulation by energy-dependent compounds efflux pumps such as P-glycoprotein (P-gp). This study observed some iodinated radiographic contrast media, diatrizoate, iopromide and iotrolan affected the cellular energetic state and the kinetics of P-gp in drug-sensitive K562 and drug resistant K562/adr cell lines using spectrophotometer and spectrofluorometer. By colorimetric MTT assay, it was found that contrast media (0-3500 μM) had no effect on both K562 and K562/adr cell viabilities, but in co-treatment with daunorubicin (DNR), diatrizoate decreased cell viability in K562/adr cells by decreasing ICso of DNR from 610.7 ±74.5 nM to 360±108.9 nM. The change in cellular energetic state was studied using rhodamine B as a probe to estimate mitochondrial membrane potential (ΔΨm). The results showed that 3500 μM diatrizoate decreased ΔΨm from 162.2±0.3 mV to 86.9±9.9 mV in K562/adr cells. The kinetics of P-gp-mediated efflux of DNR could be reduced by diatrizoate from 0 (no inhibition) to 0.65±0.11. This inhibition could be partially prevented in co-incubation with 20 nM concanamycin A or 10 μM cytochalasin B. Among the three molecules, diatrizoate showed the best efficiency. It could be proposed for further studies that diatrizoate could be used as MDR identification or MDR imaging and also acted as MDR sensitizing agent in cancer treatments.

Selective modulation of P-glycoprotein activity by steroidal saponines from Paris polyphylla

Bio-guided fractionation of the roots of Paris polyphylla (Trilliaceae), based on inhibition of P-glycoprotein-mediated daunorubicin efflux in K562/R7 cell line, led to isolation and identification of the three saponins 3-O-Rha(1-->2)[Ara(1-->4)]Glc-pennogenine, gracillin and polyphyllin D, and the two ecdysteroids 20-hydroxyecdysone and pinnatasterone. These compounds were tested for multidrug reversion on P-glycoprotein (ABCB1) with both drug-selected and transfected cell lines, and also on Breast Cancer Resistance Protein (BCRP/ABCG2). By contrast to a weak efficiency on BCRP, the three saponins displayed significant effects as inhibitors of P-glycoprotein-mediated drug efflux.

Flurazepam inhibits the P-glycoprotein transport function: An insight to revert multidrug-resistance phenotype

P-glycoprotein mediated drug transport may lead to a multidrug resistance phenotype often associated with a poor response to the successful treatment of a variety of human disorders. Several agents have been found to modulate P-glycoprotein drug resistance, most probably by blocking its transport function. The aim of this study was to examine the effects of some benzodiazepines (bromazepam, chlordiazepoxide, diazepam and flurazepam) able to bind to P-glycoprotein in proteoliposomes on its transport function and ATPase activity in the human cancer cell line, KB-V1. The toxicity of the benzodiazepines drugs towards KB-V1 cells was first evaluated and the non toxic drugs concentrations were used to assess the drug efflux and the ATPase activity. Using the flow cytometry approach, the accumulation and efflux of daunorubicin were followed by measuring the daunorubicin associated geometric mean fluorescence intensity. Vanadate was employed as a comparative inhibitory compound. Flurazepam was able to inhibit the daunorubicin efflux in 80%. ATPase activity determined by a colorimetric assay revealed that flurazepam inhibits the P-glycoprotein enzymatic activity, indicating coupling between drug transport and ATP hydrolysis. Bromazepam, chlordiazepoxide and diazepam behaved as activators of the P-glycoprotein ATPase activity, suggesting a role as transported substrates and did not interfere in the daunorubicin transport.

Difference of Drug-Resistance between Single-Factor Resistance Cell Line K562/MDR1 Transfected with mdr1 Gene and Multi-Factor Resistance Cell Line K562/A02 Induced by Doxorubicin.

Objective To study difference of drug-resistance between single-factor resistance cell line K562/MDR1 transfected with mdr1 gene and multi-factor resistance cell line K562/A02 induced by doxorubicin.Methods Retroviral virions carrying the complete sequence of mdr1 gene cDNA were produced and infected drug-sensitive leukemia cell line K562 and mdr1 single-factor resistance cell line K562/MDR1 was established. The difference of drug-resistance between K562/MDR1 and K562/A02, a kind of multi-factor resistance cell line induced by doxorubicin, was studied by checking the expression of mdr1 gene and Pgp, daunorubicin efflux rate, MTT drug sensitivity to chemotherapeutic drug. Lentiviral vector encoding shRNA which targeted MDR1 gene was transfected into two kinds of cell lines and effect of RNAi on reversing drug resistance was detected.Results The results of Q-PCR and flow cytometry demonstrated that there were high expression of mdr1 mRNA and Pgp in both kinds of drug-resistance cell lines and no difference between them. The function of Pgp detected by daunorubicin efflux rate is higher in K562/MDR1 (90.93%) than K562/A02 (78.67%). The results of MTT test showed that IC50 of K562/MDR1 and K562/A02 is 0.55 and 1.22μmol/L respectively and this confirmed that drug-resistance in K562/A02 is higher than that in K562/MDR1. After RNA interference, the expression of the mdr1 gene and Pgp in K562/MDR1 markedly was down-regulated and the drug resistance was restored and IC50 is 0.16μmol/L, similar to K562 sensitive cell line. The expression of the mdr1 gene and Pgp in K562/A02 markedly was downregulated too, and drug resistance to anticancer drug is reduced to some extent but IC50 is 0.56μmol/L, it is still higher than that in sensitive cell line.Conclusion Drug-resistance in K562/A02 induced by anticancer-drug was made of many factors and it is more resistance to anticancer-drug than that in K562/MDR1 caused by mdr1 gene. Due to only mdr1 resistance, K562/MDR1 is better cell model to make mdr1/Pgp research.

Chemogenomic Analysis Identifies Geldanamycins as Substrates and Inhibitors of ABCB1

A prerequisite for geldanamycin (GA, NSC122750) to targeting heat shock protein 90 and inhibiting tumor growth is sufficient intracellular drug accumulation. We hypothesized that membrane transporters on tumor cells determine at least in part the response to GA analogues. To facilitate a systematic study of chemosensitivity across a group of GA analogues with similar chemical structures, we correlated mRNA expression profiles of most known transporters with growth inhibitory potencies of compounds in 60 tumor cell lines (NCI-60). We subsequently validated the gene-drug correlations using cytotoxicity and transport assays. Geldanamycin analogues displayed a range of negative correlations coefficients with ABCB1 (MDR1, or P-glycoprotein) expression. Suppressing ABCB1 in multidrug resistant cells (NCI/ADR-RES and K562/DOX) and ABCB1-transfected cells (BC19) increased sensitivity to GA analogues, as expected for substrates. Moreover, ABCB1-mediated efflux of daunorubicin in K562/DOX cells could be blocked markedly by GA analogues in a dose-dependent fashion. The IC(50) values (half-maximum inhibition of daunorubicin efflux) were 5.5, 7.3 and 12 muM for macbecin II (NSC330500), 17-AAG (NSC330507) and GA, respectively. These observations demonstrate that GA analogues are substrates as well as inhibitors of ABCB1, suggesting that drug interactions between GA analogues and other agents that are ABCB1 substrates may occur via ABCB1 in normal or tumor cells.