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  • MDM2 antagonist nutlin-3a reverses mitoxantrone resistance by inhibiting breast cancer resistance protein mediated drug transport. 21459080

    Breast cancer resistance protein (BCRP; ABCG2), a clinical marker for identifying the side population (SP) cancer stem cell subgroup, affects intestinal absorption, brain penetration, hepatobiliary excretion, and multidrug resistance of many anti-cancer drugs. Nutlin-3a is currently under pre-clinical investigation in a variety of solid tumor and leukemia models as a p53 reactivation agent, and has been recently demonstrated to also have p53 independent actions in cancer cells. In the present study, we first report that nutlin-3a can inhibit the efflux function of BCRP. We observed that although the nutlin-3a IC(50) did not differ between BCRP over-expressing and vector control cells, nutlin-3a treatment significantly potentiated the cells to treatment with the BCRP substrate mitoxantrone. Combination index calculations suggested synergism between nutlin-3a and mitoxantrone in cell lines over-expressing BCRP. Upon further investigation, it was confirmed that nutlin-3a increased the intracellular accumulation of BCRP substrates such as mitoxantrone and Hoechst 33342 in cells expressing functional BCRP without altering the expression level or localization of BCRP. Interestingly, nutlin-3b, considered virtually inactive in disrupting the MDM2/p53 interaction, reversed Hoechst 33342 efflux with the same potency as nutlin-3a. Intracellular accumulation and bi-directional transport studies using MDCKII cells suggested that nutlin-3a is not a substrate of BCRP. Additionally, an ATPase assay using Sf9 insect cell membranes over-expressing wild-type BCRP indicated that nutlin-3a inhibits BCRP ATPase activity in a dose-dependent fashion. In conclusion, our studies demonstrate that nutlin-3a inhibits BCRP efflux function, which consequently reverses BCRP-related drug resistance.
    Tipo de documento:
    Referencia
    Referencia del producto:
    MAB4155P

  • Flow cytometry-based approach to ABCG2 function suggests that the transporter differentially handles the influx and efflux of drugs. 15517563

    BACKGROUND: To better characterize the function of the ABCG2 transporter in vitro, we generated three cell lines (MXRA, MXRG, and MXRT) stably expressing ABCG2 after transfection of wild-type ABCG2 and two mutants (R482G and R482T), respectively. METHODS: ABCG2 expression and function were analyzed by flow cytometry using monoclonal antibodies, a variety of fluorescent substrates, and a series of potential inhibitors of the transporter. RESULTS: ABCG2 expression was detected in all cell lines. The cell lines effluxed mitoxantrone (MXR), but only the mutants effluxed rhodamine 123 (Rho123), SYTO13, doxorubicin, and daunorubicin. After incubation with MXR, intracellular accumulations were 9- and 22-fold higher in MXRA than in MXRT and MXRG cells, respectively, suggesting that ABCG2 also modulates the influx rate of the drug. Flow cytometry kinetic studies of MXR efflux showed that MXRG cells effluxed 50% of the drug at a faster rate than MXRA and MXRT cells (t50: 15.3 min vs. 27.8 and 44.5 min, respectively). MXRG cells also extruded Rho123 and SYTO13 at a faster rate than MXRT cells. ABCG2-mediated transport was inhibited by fumitremorgin C, cyclosporine A, and PSC-833, but not by verapamil or probenecid. MXRG cells displayed the highest level of resistance to MXR, doxorubicin, and daunorubicin in the cytotoxicity assays. CONCLUSIONS: Glycine mutations at position 482 have a significant impact on ABCG2 function by modifying its substrate specificity and its influx/efflux rates. This study also demonstrates that flow cytometry constitutes a powerful tool for the kinetic analysis of ABC transporters.
    Tipo de documento:
    Referencia
    Referencia del producto:
    MAB4155
    Nombre del producto:
    Anti-BCRP1 Antibody, clone 5D3

  • Multidrug resistance mediated by the breast cancer resistance protein BCRP (ABCG2). 14576842

    Observations of functional adenosine triphosphate (ATP)-dependent drug efflux in certain multidrug-resistant cancer cell lines without overexpression of P-glycoprotein or multidrug resistance protein (MRP) family members suggested the existence of another ATP-binding cassette (ABC) transporter capable of causing cancer drug resistance. In one such cell line (MCF-7/AdrVp), the overexpression of a novel member of the G subfamily of ABC transporters was found. The new transporter was termed the breast cancer resistance protein (BCRP), because of its identification in MCF-7 human breast carcinoma cells. BCRP is a 655 amino-acid polypeptide, formally designated as ABCG2. Like all members of the ABC G (white) subfamily, BCRP is a half transporter. Transfection and enforced overexpression of BCRP in drug-sensitive MCF-7 or MDA-MB-231 cells recapitulates the drug-resistance phenotype of MCF-7/AdrVp cells, consistent with current evidence suggesting that functional BCRP is a homodimer. BCRP maps to chromosome 4q22, downstream from a TATA-less promoter. The spectrum of anticancer drugs effluxed by BCRP includes mitoxantrone, camptothecin-derived and indolocarbazole topoisomerase I inhibitors, methotrexate, flavopiridol, and quinazoline ErbB1 inhibitors. Transport of anthracyclines is variable and appears to depend on the presence of a BCRP mutation at codon 482. Potent and specific inhibitors of BCRP are now being developed, opening the door to clinical applications of BCRP inhibition. Owing to tissue localization in the placenta, bile canaliculi, colon, small bowel, and brain microvessel endothelium, BCRP may play a role in protecting the organism from potentially harmful xenobiotics. BCRP expression has also been demonstrated in pluripotential "side population" stem cells, responsible for the characteristic ability of these cells to exclude Hoechst 33342 dye, and possibly for the maintenance of the stem cell phenotype. Studies are emerging on the role of BCRP expression in drug resistance in clinical cancers. More prospective studies are needed, preferably combining BCRP protein or mRNA quantification with functional assays, in order to determine the contribution of BCRP to drug resistance in human cancers.
    Tipo de documento:
    Referencia
    Referencia del producto:
    MAB4155
    Nombre del producto:
    Anti-BCRP1 Antibody, clone 5D3

  • Epidermal differentiation and loss of clonal growth potential of human limbal basal epithelial progenitor cells during intrastromal invasion. 21527382

    Intrastromal invasion by limbal basal epithelial progenitor cells in explant cultures is associated with epithelial-mesenchymal transition. It remains unclear whether intrastromal invasion is contingent on culturing conditions and whether invaded cells retain their progenitor status and original lineage.Human limbal explants were cultured on various culture substrates, with or without air-lifting (AL), and subjected to hematoxylin and eosin staining and immunostaining to pan-cytokeratins, p63α, ΔNp63, Pax6, CK10, and CK12. Single cells obtained by trypsin/EDTA from dispase-isolated epithelial sheets from both the outgrowth and the surface epithelium, or by collagenase from the remaining stroma, were seeded on 3T3 feeder layers.Intrastromal invasion was verified in all seven explant cultures by positive pan-cytokeratin staining. Immunofluorescence staining revealed that invaded epithelial cells were positive for p63α and ΔNp63, with or without nuclear staining of Pax6. Double immunostaining to CK10 and CK12 revealed that squamous metaplasia induced by AL was noted on the surface epithelium but not in intrastromally invaded epithelial cells. On 3T3 feeder layers, both the outgrowth and the surface epithelium yielded significant numbers of holoclones and meroclones positive to ΔNp63 but negative to CK10 and CK12. In contrast, intrastromally invaded epithelial cells generated only paraclones negative to ΔNp63 and CK12 but positive to CK10 regardless of culturing conditions.Intrastromal invasion by limbal basal epithelial progenitor cells is universal in all explant culture conditions, explaining why there is a gradual decline of outgrowth potential. Alteration of the limbal stromal niche leads invaded epithelial cells to adopt an epidermal fate.
    Tipo de documento:
    Referencia
    Referencia del producto:
    Múltiplo
    Nombre del producto:
    Múltiplo

  • Enhanced wound healing, kinase and stem cell marker expression in diabetic organ-cultured human corneas upon MMP-10 and cathepsin F gene silencing. 24255036

    Diabetic corneas overexpress proteinases including matrix metalloproteinase-10 (M10) and cathepsin F (CF). Our purpose was to assess if silencing M10 and CF in organ-cultured diabetic corneas using recombinant adenovirus (rAV)-driven small hairpin RNA (rAV-sh) would normalize slow wound healing, and diabetic and stem cell marker expression.Sixteen pairs of organ-cultured autopsy human diabetic corneas (four per group) were treated with rAV-sh. Proteinase genes were silenced either separately, together, or both, in combination (Combo) with rAV-driven c-met gene overexpression. Fellow control corneas received rAV-EGFP. Quantitative RT-PCR confirmed small hairpin RNA (shRNA) silencing effect. Ten days after transfection, 5-mm epithelial wounds were made with n-heptanol and healing time recorded. Diabetic, signaling, and putative stem cell markers were studied by immunofluorescence of corneal cryostat sections.Proteinase silencing reduced epithelial wound healing time versus rAV-enhanced green fluorescent protein (EGFP) control (23% for rAV-shM10, 31% for rAV-shCF, and 36% for rAV-shM10 + rAV-shCF). Combo treatment was even more efficient (55% reduction). Staining patterns of diabetic markers (α₃β₁ integrin and nidogen-1), and of activated epidermal growth factor receptor and its signaling target activated Akt were normalized upon rAV-sh treatment. Combo treatment also restored normal staining for activated p38. All treatments, especially the combined ones, increased diabetes-altered staining for putative limbal stem cell markers, ΔNp63α, ABCG2, keratins 15 and 17, and laminin γ3 chain.Small hairpin RNA silencing of proteinases overexpressed in diabetic corneas enhanced corneal epithelial and stem cell marker staining and accelerated wound healing. Combined therapy with c-met overexpression was even more efficient. Specific corneal gene therapy has a potential for treating diabetic keratopathy.
    Tipo de documento:
    Referencia
    Referencia del producto:
    Múltiplo
    Nombre del producto:
    Múltiplo