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Vahedi S, Lusvarghi S, Pluchino K, Shafrir Y, Durell SR, Gottesman MM, Ambudkar SV. Mapping discontinuous epitopes for MRK-16, UIC2 and 4E3 antibodies to extracellular loops 1 and 4 of human P-glycoprotein. Sci Rep 2018; 8:12716. [PMID: 30143707 PMCID: PMC6109178 DOI: 10.1038/s41598-018-30984-8] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2018] [Accepted: 07/30/2018] [Indexed: 12/14/2022] Open
Abstract
P-glycoprotein (P-gp), an ATP-dependent efflux pump, is associated with the development of multidrug resistance in cancer cells. Antibody-mediated blockade of human P-gp activity has been shown to overcome drug resistance by re-sensitizing resistant cancer cells to anticancer drugs. Despite the potential clinical application of this finding, the epitopes of the three human P-gp-specific monoclonal antibodies MRK-16, UIC2 and 4E3, which bind to the extracellular loops (ECLs) have not yet been mapped. By generating human-mouse P-gp chimeras, we mapped the epitopes of these antibodies to ECLs 1 and 4. We then identified key amino acids in these regions by replacing mouse residues with homologous human P-gp residues to recover binding of antibodies to the mouse P-gp. We found that changing a total of ten residues, five each in ECL1 and ECL4, was sufficient to recover binding of both MRK-16 and 4E3 antibodies, suggesting a common epitope. However, recovery of the conformation-sensitive UIC2 epitope required replacement of thirteen residues in ECL1 and the same five residues replaced in the ECL4 for MRK-16 and 4E3 binding. These results demonstrate that discontinuous epitopes for MRK-16, UIC2 and 4E3 are located in the same regions of ECL1 and 4 of the multidrug transporter.
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Affiliation(s)
- Shahrooz Vahedi
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, 20892-4256, USA
| | - Sabrina Lusvarghi
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, 20892-4256, USA
| | - Kristen Pluchino
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, 20892-4256, USA
| | - Yinon Shafrir
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, 20892-4256, USA
| | - Stewart R Durell
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, 20892-4256, USA
| | - Michael M Gottesman
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, 20892-4256, USA
| | - Suresh V Ambudkar
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, 20892-4256, USA.
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Abstract
Gene amplification and/or overexpression of the c-erbB-2/HER2/neu tyrosine kinase are linked with poor prognosis in breast cancer. This is manifest in shorter disease-free intervals, increased risk of metastasis, and resistance to many types of therapy. The molecular mechanisms and signaling circuitry underlying these phenomena are now being elucidated. c-erbB-2, although having no known soluble ligand, is transactivated by heterodimerization with other family members (EGFR, c-erbB-3, c-erbB-4). Receptor activation potentiates tumor cell motility, protease secretion and invasion, and also modulates cell cycle checkpoint function, DNA repair, and apoptotic responses. Since it is expressed at low levels in normal adult tissues, c-erbB-2 is an ideal target for therapy. There is reason for optimism that agents targeting c-erbB-2 signaling will have profound and selective effects in breast cancer, either as single agents or more likely in combination with other therapeutic agents, to enhance their potency.
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Affiliation(s)
- S A Eccles
- CRC Centre for Cancer Therapeutics, Institute of Cancer Research, Sutton, Surrey, United Kingdom.
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Eccles SA. Cell biology of lymphatic metastasis. The potential role of c-erbB oncogene signalling. Recent Results Cancer Res 2001; 157:41-54. [PMID: 10857161 DOI: 10.1007/978-3-642-57151-0_5] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Lymphatic metastases are an important indicator of the malignancy of epithelial cancers. Empirical clinical observations associating specific genetic abnormalities with tumour progression, allied with basic laboratory investigations, are providing not only improved prognostic and diagnostic opportunities, but also a detailed understanding of the molecular machinery of metastasis. One such association--between the c-erbB oncogene family and metastasis--has proved particularly instructive. Functional links between over-expression (and occasionally mutational activation) of c-erbB-1 (EGFR) and c-erbB-2 and specific phenotypes of metastatic cells have been elucidated. Activated c-erbB oncogenes potentiate tumour cell adhesion to endothelial cells and upregulate VEGF, potentially facilitating angiogenesis and vascular invasion. In addition, cells over-expressing these oncogenes frequently show aberrant cell-cell and cell-matrix interactions, mediated by changes in integrin and cadherin function. Thirdly, both EGFR and c-erbB-2 signalling can significantly upregulate specific matrix metalloproteinases, key enzymes involved in angiogenesis and invasion. Finally, c-erbB receptors linked to the actin cytoskeleton and highly expressed on invadopodia, are thought to assist cell migration. Taken together, these observations suggest that such receptors can act as "master switches" in metastasis, whose activation co-ordinately controls events normally utilised in development, now subverted by the metastatic cell. As such, they represent ideal targets for therapeutic intervention.
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Affiliation(s)
- S A Eccles
- Section of Cancer Therapeutics, Institute of Cancer Research, Sutton, Surrey, UK
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Eccles SA. Monoclonal antibodies targeting cancer: 'magic bullets' or just the trigger? Breast Cancer Res 2001; 3:86-90. [PMID: 11250751 PMCID: PMC138676 DOI: 10.1186/bcr276] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2000] [Revised: 11/27/2000] [Accepted: 12/01/2000] [Indexed: 11/14/2022] Open
Abstract
The first monoclonal antibodies (mAbs) approved for cancer therapy are now in Phase II and III trials, but the critical mechanism(s) determining efficacy and response in patients are still largely undefined. Both the direct antigen-binding (Fab) and constant (Fc) regions of mAbs can contribute to their biological activity. However, Clynes et al (Nat Med 2000, 6:443) recently suggested that the latter (at least in experimental models) might be the dominant component in vivo, triggering host responses to destroy cancer cells. Those workers showed that in mice lacking 'activation' Fc receptors (Fc(gamma)RI and Fc(gamma)RIII), anti-tumour effects of certain mAbs were significantly reduced. In contrast, mice deficient in the 'inhibitory' receptor Fc(gamma)RIIB responded with tumour growth inhibition and enhanced antibody-dependent cellular cytotoxicity (ADCC). These observations suggest that mAbs might be engineered for preferential binding to Fc(gamma)RIII to maximise therapeutic benefit. However, further work is needed to establish a definitive cause-effect relationship in experimental models that are more clinically relevant, to determine whether human Fc(gamma)R isoforms behave in a similar fashion, and to confirm that therapeutic mAbs and host cells can adequately access solid tumour deposits to mediate effective ADCC in situ. Finally, the 'cost-benefit' ratio of such modified macromolecules will need to be measured against mini-mAb constructs, antisense oligonucleotides, peptidomimetics and emerging drugs capable of inhibiting key tumour cell signalling pathways.
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Affiliation(s)
- S A Eccles
- Institute of Cancer Research, Belmont, Sutton, Surrey, UK.
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