Effect of cetuximab and fractionated irradiation on tumour micro-environment
Received 7 February 2010; received in revised form 4 July 2010; accepted 7 July 2010. published online 28 July 2010. Corrected Proof
Abstract
Background and purpose
Previous experiments have shown that application of the anti-EGFR monoclonal antibody C225 (cetuximab) improves local tumour control after irradiation in FaDu human squamous cell carcinoma (hSCC) due to the combined effect of decreased repopulation and improved reoxygenation. The present study investigates early changes of the pimonidazole hypoxic fraction of FaDu tumours and the expression and phosphorylation of the EGFR and its downstream signal transduction molecules after treatment with C225 alone or in combination with irradiation.
Material and methods
FaDu tumour xenografts were irradiated with up to 3×3Gy with or without additional C225 treatment and excised at different time points. Tumour hypoxia was evaluated using pimonidazole. EGFR expression and phosphorylation and intratumoural distribution of C225 were assessed by immunofluorescence analysis. Western blots were performed to evaluate expression and phosphorylation of EGFR, ErbB2, AKT and MAPK (ERK1/2).
Results
Hypoxia did not change during the 4days of treatment in the tumours treated with C225 alone or combined with irradiation. C225 treatment led to downregulation of the total EGFR in FaDu tumours, accompanied by a change of the spatial distribution of the receptor favouring the membranous expression. An induction of phosphorylation of the EGFR (tyr992, tyr1173) was observed with C225 alone or combined with irradiation. AKT phosphorylation was decreased, whereas MAPK phosphorylation remained unchanged. C225 membrane staining was homogeneously distributed over the whole tumour with no differences between hypoxic and non-hypoxic tumour cells.
Conclusion
Pimonidazole-hypoxia of FaDu tumours during the initial part of fractionated irradiation is not influenced by C225, indicating that external hypoxia markers may not be promising as biomarkers for tumour response to combined treatment. The downregulation of the total EGFR, but at the same time higher membrane staining, as well as the changes in downstream signal transduction molecules, warrants further investigation in other tumour models.
aDepartment of Radiation Oncology, Medical Faculty and University Hospital Carl Gustav Carus, Technische Universität Dresden, Germany
bOncoRay Center for Radiation Research in Oncology, Medical Faculty and University Hospital Carl Gustav Carus, Technische Universität Dresden, Germany
cExperimental Center, Medical Faculty and University Hospital Carl Gustav Carus, Technische Universität Dresden, Germany
dDepartment of Nuclear Medicine, Medical Faculty and University Hospital Carl Gustav Carus, Technische Universität Dresden, Germany
eDepartment of Radiation Oncology, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands
Corresponding author. Address: Department of Radiation Oncology, Medical Faculty Carl Gustav Carus, Technische Universität Dresden, Fetscherstr. 74, 01307 Dresden, Germany.
ABSTRACT
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