Inhibition Of ABC Transporters Research Articles

Inhibition of breast cancer resistance protein (ABCG2) in human myeloid dendritic cells induces potent tolerogenic functions during LPS stimulation.

Breast cancer resistance protein (ABCG2), a member of the ATP-binding cassette transporters has been identified as a major determinant of multidrug resistance (MDR) in cancer cells, but ABC transporter inhibition has limited therapeutic value in vivo. In this research, we demonstrated that inhibition of efflux transporters ABCG2 induced the generation of tolerogenic DCs from human peripheral blood myeloid DCs (mDCs). ABCG2 expression was present in mDCs and was further increased by LPS stimulation. Treatment of CD1c+ mDCs with an ABCG2 inhibitor, Ko143, during LPS stimulation caused increased production of IL-10 and decreased production of pro-inflammatory cytokines and decreased expression of CD83 and CD86. Moreover, inhibition of ABCG2 in monocyte-derived DCs (MDDCs) abrogated the up-regulation of co-stimulatory molecules and production of pro-inflammatory cytokines in these cells in response to LPS. Furthermore, CD1c+ mDCs stimulated with LPS plus Ko143 inhibited the proliferation of allogeneic and superantigen-specific syngenic CD4+ T cells and promoted expansion of CD25+FOXP3+ regulatory T (Treg) cells in an IL-10-dependent fashion. These tolerogenic effects of ABCG2 inhibition could be abolished by ERK inhibition. Thus, we demonstrated that inhibition of ABCG2 in LPS-stimulated mDCs can potently induce tolerogenic potentials in these cells, providing crucial new information that could lead to development of better strategies to combat MDR cancer.

ABCG2 AND MDR PROMOTE BRAINSTEM GLIOMAGENESIS AND LIMIT THE EFFICACY OF DASATINIB IN A DIFFUSE INTRINSIC PONTINE GLIOMA (DIPG) MOUSE MODEL

BACKGROUND: DIPG is an incurable tumor that arises in the brainstem of children. Our laboratory generates murine DIPGs by expressing PDGF-B and deleting p53 in nestin progenitors of the neonatal brainstem using the RCAS/tv-a system. Dasatinib, an inhibitor of PDGFR-A and SRC activation, has been evaluated in clinical trials for children with DIPG but with disappointing results. As dasatinib is a substrate of the ABC transporters ABCG2 and MDR, we hypothesized that ABCG2 and MDR may limit the efficacy of dasatinib in DIPG. METHODS: We generated murine DIPGs driven by PDGF-B and p53 loss in ABC WT (ABCG2+/+; MDRa+/+; MDRb+/+) and ABC KO (ABCG2-/-; MDRa-/-; MDRb-/-) mice. Next, we investigated whether dasatinib is efficacious in ABC KO and ABC WT DIPG-bearing mice. We treated ABC WT DIPG-bearing mice with dasatinib alone, elacridar (a dual ABCG2/MDR inhibitor) alone, and dasatinib in combination with elacridar. We also measured dasatinib levels in the tumor and plasma of all of the different tumor cohorts. Lastly, we evaluated the blood-brain-barrier (BBB) of our DIPG mouse model with Dextran Texas Red. RESULTS: Surprisingly, we observed a significant difference in tumor latency between untreated ABC KO and untreated ABC WT mice in this PDGF-B; p53 deficient DIPG model. Median survival of DIPG-bearing ABC KO was longer than DIPG-bearing ABC WT: 43 days vs. 34 days respectively (p = 0.02). We observed that dasatinib almost doubled the survival of DIPG-bearing mice in the ABC KO model: 44 days vs. 80 days (p = 0.0004). Dasatinib modestly prolonged survival in ABC WT mice: 33 days vs. 42 days (p < 0.0001). Co-treatment with elacridar significantly increased the efficacy of dasatinib in the ABC WT model 42 days vs. 59 days (p < 0.0001). However, elacridar alone did not significantly prolong survival in the ABC WT mice 33 days vs. 34 days (p = 0.38). Pharmacokinetic analysis demonstrated that genetic ablation of the ABC transporters or inhibition of ABC transporters with elacridar significantly increased dasatinib delivery into normal brain but not into tumor. Dextran Texas Red studies demonstrated a disrupted BBB in DIPG models independent of ABC transporters. CONCLUSIONS: 1. ABC transporters promote brainstem gliomagenesis 2. ABC transporters regulate dasatinib delivery into normal brain but not into the tumor as BBB is disrupted in our DIPG mouse model 3. ABC transporter activity limits the efficacy of dasatinib in vivo. Our results suggest that ABCG2 and MDR inhibitors may have a therapeutic role in the treatment of DIPG. SECONDARY CATEGORY: Preclinical Experimental Therapeutics.

Resveratrol Modulates Expression of ABC Transporters in Non-Small Lung Cancer Cells: Molecular Docking and Gene Expression Studies

Multidrug resistance is one of the most common causes of relapse in cancer chemotherapy. Inhibition of ABC transporters to reverse MDR is a prominent approach to enhance the efficacy of cancer chemotherapy. We investigated the effect of resveratrol (RSV) on the membrane transport function and the expression of proteins involved in the multidrug resistance in NCI-H460 cells. The molecular interactions of RSV with P-gp were analyzed by Schrodinger software. The membrane transport function and cell cycle distribution were measured using flow cytometry. The mRNA expression level of MDR1, LRP, MRP2, ABCC1, ABCC2 and ABCC3 genes were detected by qRT-PCR and BCRP expression was detected by western blot analysis. In silico docking studies revealed that RSV possesses greater binding affinity with TMD region of P-gp. In this study, RSV pretreatment significantly enhanced Paclitaxel (PTX) antiproliferative effect in NCI-H460 cells. The rhodamine 123 drug efflux studies revealed that there was a significant transport function inhibition by RSV treatment and moderate transport function inhibition by PTX. Further, RSV treatment significantly decreased the mRNA expression levels of various ABC transporters genes. Furthermore, expression of BCRP was found to be down-regulated during RSV treatment. It was also found that this enhanced anticancer efficacy of RSV was associated with PTX-induced cell arrest in the G2/M phase of cell cycle. Interestingly, we observed significantly enhanced antiproliferative effect, transport function inhibition and downregulation of ABC transporters in RSV-PTX combination group. This might be due to additive or synergistic effect of RSV with PTX in NCI-H460 cells. Thus, the present findings illustrate the modulatory role of RSV on PTX sensitization in relatively resistant NCI-H460 cells.

ABC transporter activity linked to radiation resistance and molecular subtype in pediatric medulloblastoma

BackgroundResistance to radiation treatment remains a major clinical problem for patients with brain cancer. Medulloblastoma is the most common malignant brain tumor of childhood, and occurs in the cerebellum. Though radiation treatment has been critical in increasing survival rates in recent decades, the presence of resistant cells in a substantial number of medulloblastoma patients leads to relapse and death.MethodsUsing the established medulloblastoma cell lines UW228 and Daoy, we developed a novel model system to enrich for and study radiation tolerant cells early after radiation exposure. Using fluorescence-activated cell sorting, dead cells and cells that had initiated apoptosis were removed, allowing surviving cells to be investigated before extensive proliferation took place.ResultsIsolated surviving cells were tumorigenic in vivo and displayed elevated levels of ABCG2, an ABC transporter linked to stem cell behavior and drug resistance. Further investigation showed another family member, ABCA1, was also elevated in surviving cells in these lines, as well as in early passage cultures from pediatric medulloblastoma patients. We discovered that the multi-ABC transporter inhibitors verapamil and reserpine sensitized cells from particular patients to radiation, suggesting that ABC transporters have a functional role in cellular radiation protection. Additionally, verapamil had an intrinsic anti-proliferative effect, with transient exposure in vitro slowing subsequent in vivo tumor formation. When expression of key ABC transporter genes was assessed in medulloblastoma tissue from 34 patients, levels were frequently elevated compared with normal cerebellum. Analysis of microarray data from independent cohorts (n = 428 patients) showed expression of a number of ABC transporters to be strongly correlated with certain medulloblastoma subtypes, which in turn are associated with clinical outcome.ConclusionsABC transporter inhibitors are already being trialed clinically, with the aim of decreasing chemotherapy resistance. Our findings suggest that the inhibition of ABC transporters could also increase the efficacy of radiation treatment for medulloblastoma patients. Additionally, the finding that certain family members are associated with particular molecular subtypes (most notably high ABCA8 and ABCB4 expression in Sonic Hedgehog pathway driven tumors), along with cell membrane location, suggests ABC transporters are worthy of consideration for the diagnostic classification of medulloblastoma.

Discovering Natural Product Modulators to Overcome Multidrug Resistance in Cancer Chemotherapy

Multidrug resistance caused by the overexpression of ABC drug transporters is a major obstacle in clinical cancer chemotherapy. For several years, it appeared that direct inhibition of ABC transporters would be the cheapest and most efficient way to combat this problem. Unfortunately, progress in finding a potent, selective inhibitor to modulate ABC transporters and restore drug sensitivity in multidrug-resistant cancer cells has been slow and challenging. Candidate drugs should ideally be selective, potent and relatively non-toxic. Many researchers in recent years have turned their attention to utilizing natural products as the building blocks for the development of the next generation of inhibitors, especially after the disappointing results obtained from inhibitors of the first three generations at the clinical trial stage. The first step is to discover natural substances (distinct from the first three generation inhibitors) that are potent, selective and relatively non-toxic in order to be used clinically. Here, we present a brief overview of the prospect of using natural products to modulate the function of ABC drug transporters clinically and their impact on human physiology and pharmacology.

Divergent Effects of Nitric Oxide Donors on the Biliary Efflux Transporters in Isolated Perfused Rat Livers: Nitric Oxide-Independent Inhibition of ABC Transporters by Sodium Nitroprusside

Rhodamine 123 (RH-123) and its glucuronidated metabolite (RH-Glu) are excreted into the bile via the ABC efflux transporters P-glycoprotein (P-gp) and multidrug resistance-related protein type 2 (Mrp2), respectively. In this study, we investigated the short-term (2 h) effects of a low or high concentration of nitric oxide (NO) donors sodium nitroprusside (SNP) and isosorbide dinitrate (ISDN) on the hepatobiliary disposition of RH-123 and its metabolite in an isolated perfused rat liver model. Additionally, the effects of ISDN on the hepatobiliary disposition of 5 (and 6)-carboxy-2', 7'- dichlorofluorescein (CDF), a specific marker of Mrp2, were investigated in the same model. Whereas SNP caused a substantial (85-90%) reduction in the P-gp- and Mrp2-mediated transport of RH-123 and RH-Glu, respectively, ISDN did not affect either of these transporters. However, ISDN reduced the biliary recovery of RH-Glu, most likely because of inhibition of the formation of the metabolite. Further studies showed that the effects of SNP on these transporters are due to a substantial (88%) depletion of hepatic ATP levels by this NO donor. Additionally, studies using CDF revealed an almost identical hepatobiliary disposition of this Mrp2 marker in the presence or absence of ISDN. It is concluded that short-term exposure of rat livers to NO does not affect the functions of the efflux transporters P-gp and Mrp2. The observed inhibitory effects of SNP on the functions of both P-gp and Mrp2 are via an NO-independent mechanism.

Chrysin blocks topotecan-induced apoptosis in Caco-2 cells in spite of inhibition of ABC-transporters

ATP-driven efflux pumps such as phosphoglycoprotein-170 (P-gp), multidrug-resistance-associated protein-2 (MRP-2), or breast cancer resistance protein (BCRP) play a crucial role in limiting the efficacy of tumor pharmacotherapy. Selected flavonoids have been suggested to inhibit individual efflux-transporters and to act therefore as multidrug-resistance reversing agents. In the present study it is shown that the flavonoid chrysin acts as a potent inhibitor of P-gp, MRP-2, and BCRP in Caco-2 colon carcinoma cells. As a consequence, cells accumulated higher rates of the apoptosis-inducing chemotherapeutic topotecan in the presence of chrysin, even though under these conditions the expression of the transporters was markedly increased. Interestingly, in spite of the enhanced cellular drug accumulation the topotecan-induced apoptosis, assessed according to DNA-fragmentation, chromatin condensation, and by determination of sub-G1 peaks using fluorescence-assisted-cell sorting (FACS), was potently inhibited by chrysin. Suggested transport-independent apoptosis inhibiting activities of ATP-binding cassette (ABC)-transporters, such as the inhibition of caspases, were shown to be necessary for the inhibition of topotecan-induced apoptosis and were found to be associated with stabilization of β-catenin especially in the cytosol. Inhibition of topotecan-induced intracellular acidification, however, was proven not to prevent caspase-activation and apoptosis. In conclusion, our studies show that chrysin in spite of raising the cellular concentrations of topotecan potently inhibits the apoptosis-inducing activities of the anti-tumor drug. Inhibition of caspase-activation was identified as the underlying mechanism and is suggested to be caused by transport-independent functions of ABC-transporters.

Effect of proton pump inhibitor co-medication on imatinib disposition: A healthy volunteer study

2503 Background: Imatinib mesylate, a potent inhibitor of Bcr-Abl and c-kit tyrosine kinases, is widely used to treat gastrointestinal stromal tumors and Philadelphia chromosome-positive leukemias. Imatinib often causes gastric upset and is therefore frequently administered with a proton pump inhibitor (PPI). Yet, the resulting elevated gastric pH, delayed gastric emptying, and inhibition of ABC transporters in the gut could change imatinib absorption, thereby affecting the therapeutic effectiveness of imatinib. To test this hypothesis, we sought to define the effect of PPI on the plasma pharmacokinetics of imatinib. Methods: 11 healthy subjects (6 M, 5 F; 21–56 years) were enrolled in a 2-period, open-label, randomized cross-over, fixed- sequence study. In one period, they received a single 400 mg dose of imatinib p.o., in the other, 40 mg omeprazol daily for five days followed by a single 400 mg dose of imatinib p.o.. The periods were separated by a wash-out period of ≥ 14 days. Plasma samples from 0–72 h after dosing were obtained. Plasma concentrations of imatinib and its active metabolite CGP74588 were determined with an LC-MS assay and data were analyzed non-compartmentally. The study was powered to detect a 30% difference in imatinib AUC with 80% power and a 5% type I error. Results: See Table . Conclusions: This study demonstrates that the use of PPI to treat imatinib-induced gastric upset does not significantly affect imatinib plasma AUC. Support: Novartis; NIH/NCRR/CTSA Grant UL1 RR024153 [Table: see text] [Table: see text]

Therapeutic Potential of RNA Interference in Drug-Resistant Cancers

Resistance including multidrug resistance to chemotherapy is a common clinical problem in patients suffering from cancer. Multidrug resistance is often mediated by overexpression of transmembrane xenobiotic transport molecules belonging to the superfamily of ATP-binding cassette (ABC)-transporters. Inhibition of ABC-transporters by low-molecular weight compounds in cancer patients has been extensively investigated in clinical trials, but the results have been disappointing. Thus, alternative experimental therapeutic strategies for overcoming multidrug resistance are under investigation. These include the application of RNA interference (RNAi) technology. Various RNAi strategies were applied to reverse multidrug resistance in different tumor models in vitro and in vivo. Results and conclusions of these RNAi studies as well as their potential impact for the development of potential RNAi therapeutics will be discussed.

Transbilayer movement of ceramide in the plasma membrane of live cells

Ceramide (Cer) is the precursor for sphingolipids and functions as a second messenger in a variety of cellular processes including apoptosis. However, no direct target of Cer leading to apoptosis has been identified. Understanding the movement and trafficking of Cer is important for fully understanding Cer signaling. In this study, we identified, for the first time, the transbilayer movement of Cer in the plasma membrane (PM) of living cells. We developed a new method to monitor transbilayer Cer movement using ceramide kinase activity. To produce Cer on the extracellular leaflet of the PM, bacterial sphingomyelinase (SMase) was added to rat basophilic leukemia cells. Interestingly, the dramatic elevation of ceramide 1-phosphate (C1P), the product of CerK, was observed following the increase of Cer induced by SMase treatment. Since we determined that both the protein and catalytic activity of CerK exists in the intracellular compartment, the all conversion of Cer to C1P by CerK should be occur intracellularly. This result indicates the rapid transbilayer movement of Cer from the outer leaflet to the inner leaflet of the PM of living cells. Furthermore, protease digestion of membrane proteins, inhibition of ABC transporters (by glibencramide) and of cation channels (by carbonyl cyanide m-chlorophenylhydrozone), and modification of cholesterol content did not affect the transbilayer movement of Cer. Thus, this movement might occur spontaneously. Our findings indicate not only Cer movement in the PM, but also identify an intrinsic property of Cer enabling Cer signaling.

Leukemic CD34+CD38- Cells Display Conserved Differential Expression of Many ATP Binding-Cassette Transporter Genes.

In most cases of acute myeloid leukemia (AML) CD34+CD38− cells are considered to be stem cells, responsible for the maintenance and relapse of AML. ATP binding cassette transporters function in the extrusion of xenobiotics and chemotherapeutical compounds, and may be involved in therapy resistance. Elucidation of mechanisms conferring drug resistance to CD34+CD38− cells is essential to provide novel targets for stem cell eradication in AML. We studied gene expression of all 45 transmembrane ABC transporters (the complete ABCA, B, C, D and G family) in human hematopoietic CD34+CD38− cells and more committed CD34+CD38+ progenitor cells, from healthy donors and patients with non-hematological diseases (N=11) and AML patients (N=11). Gene expression was assessed using a novel real-time RT-PCR approach with micro fluidic cards. In normal CD34+CD38− cells 36 ABC transporters were expressed, 22 of these displayed significant higher expression in the CD34+CD38− cell fraction compared to the CD34+CD38+ cell fraction. In addition to the known stem cell transporters (ABCB1, ABCC1 and ABCG2) these differential expressed genes included many members not previously associated with stem cell biology. In AML the ABC transporter expression profile was largely conserved, including expression of all 13 known drug transporters. These data suggest an important role for many ABC transporters in hematopoietic stem cell biology. In addition, the preferential expression of a high number of drug transport related transporters predicts that broad spectrum inhibition of ABC transporters is likely to be required for CD34+38− stem cell eradication in AML. This approach will, apart from affecting the leukemic stem cells, equally affect the normal stem cells.