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Growth and molecular interactions of the anti-EGFR antibody Cetuximab and the DNA cross-linking agent cisplatin in gefitinib-resistant MDA-MB-468 cells: New prospects in the treatment of triple-negative/basal-like breast cancer

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Three prominent hallmarks of triple-negative/basal-like breast carcinomas, a subtype of breast cancer gene phenotype associated with poor relapse-free and overall survival, are overexpression of the epidermal growth factor receptor (EGFR), hyperactivation of the MEK/ERK transduction pathway and high sensitivity to DNA-damaging agents. The cytotoxic interaction between EGFR inhibitors (monoclonal antibodies such as Cetuximab and small molecule tyrosine kinase inhibitors such as gefitinib) and DNA cross-linking agents (e.g. platinum derivatives) might represent a promising combination for the treatment of triple-negative/basal-like breast tumors that are dependent upon EGFR/MEK/ERK signaling. We evaluated the growth and molecular interactions of the anti-EGFR antibody Cetuximab (Erbitux®) and the DNA cross-linking agent cisplatin (cis-diammedichloroplatinum; CDDP) in the gefitinib-resistant MDA-MB-468 breast cancer cell line, an in vitro model system that shows many of the recurrent basal-like molecular abnormalities including ER-PR-HER2-negative status, TP53 deficiency, EGFR overexpression, PTEN loss and constitutive activation of the MEK/ERK pathway. Unlike other basal-like breast cancer models, MDA-MB-468 cells do not carry mutations of the key DNA repair gene BRCA1. Concurrent treatment with sub-optimal doses of Cetuximab significantly enhanced CDDP-induced apoptotic cell death. However, an isobologram-based mathematical assessment of the nature of the interaction revealed a loss of synergism when employing a high-dose of Cetuximab. Since BRCA1 depletion has been found to decrease DNA damage repair and cell survival in MDA-MB-468 cells when treated with DNA-damaging drugs, we employed ELISA-based quantitative analyses to measure BRCA1 protein levels in CDDP+/− Cetuximab-treated cells. Cetuximab as single agent was as efficient as CDDP at increasing BRCA1 protein expression. Interestingly, Cetuximab co-exposure significantly antagonized the ability of CDDP to up-regulate BRCA1 expression. Low-scale phosphor-proteomic approaches [i.e. phospho-receptor tyrosine kinase (RTK) and phospho-mitogen-activated protein kinases (MAPKs) Array Proteome Profiler™ capable of simultaneously identifying the relative levels of phosphorylation of 42 different RTKs and 23 different MAPKs and other serine/threonine kinases, respectively] revealed the ability of Cetuximab, as single agent, to paradoxically induce hyper-phosphorylation of EGFR while concomitantly deactivating p42/44 (ERK1/ERK2) MAPK. Unexpectedly, ELISA-based quantitative analyses of EGFR protein content demonstrated that simultaneous exposure to Cetuximab and optimal doses of CDDP completely depleted EGFR protein in MDA-MB-468 cells. Although these findings preclinically support, at least in part, ongoing clinical trials for ‘triple-negative/basal-like’ metastatic breast cancer patients who are receiving either Cetuximab alone versus Cetuximab plus carboplatin (http://www.clinicaltrials.gov/ct/show/NCT00232505), the unexpected ability of CDDP to promote a complete depletion of the Cetuximab target EGFR further suggests that treatment schedules, Cetuximab/CDDP doses and BRCA1 status should be carefully considered when combining anti-EGFR antibodies and platinum derivatives in triple-negative/basal-like breast carcinomas.
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Document Type: Research Article

Affiliations: Catalan Institute of Oncology (ICO), Dr Josep Trueta University Hospital of Girona, E-17007 Girona, Catalonia, Spain

Publication date: January 1, 2008

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  • The International Journal of Oncology provides an international forum for the publication of the latest, cutting-edge research in the broad area of oncology and cancer treatment. The journal accepts original high quality works and reviews on all aspects of oncology research including carcinogenesis, metastasis, epidemiology, chemotherapy and viral oncology. Through fair and efficient peer review, the journal is dedicated to publishing top tier research in the field, offering authors rapid publication as well as high standards of copy-editing and production. The International Journal of Oncology is published on a monthly basis in both print and early online.
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