Induction of DNA-double Strand Breaks via 90Y-DTPA-Cetuximab in Human Squamous Cell Carcinoma Cell Lines to establish EGFR directed Therapy for Tumour Inactivation

Backround:

Molecular targeting is a novel approach in radiotherapy with great potential to increase local tumour control. The epidermal growth factor receptor (EGFR) is a suitable target for such strategies, due to its overexpression in many solid tumours.
The aim of the project is an increased inactivation of tumour cells, including EGFR overexpressing metastases. Therefore the radioactive isotope 90Yttrium was bound to the EGFR directed antibody Cetuximab (C225). This allows a specific induction of DNA damage in EGFR overexpressing tumour cells with low side effects in normal tissue expressing low EGFR.
In this study double strand breaks (DSB) induced by ⁹⁰YDTPA-Cetuximab were determined. Therefore γH2AX foci formation in human squamous cell carcinoma cells of head and neck differing in EGFR expression were detected after treatment with ⁹⁰Y-DTPA-Cetuximab.

Summary & Conclusion:

• The binding of Cetuximab to cells depends on their membranous EGFR expression level.
• The chelator DTPA attached to the antibody Cetuximab reduces the affinity to EGFR about 30% compared to native Cetuximab. This effect can be avoided by using saturating concentrations of antibody.
• ⁹⁰Y-DTPA-Cetuximab induces DNA double strand breaks in human squamous cell carcinoma cell lines.
• The dose applied by ⁹⁰Y-DTPA-Cetuximab, and thereby the amount of DNA double strand breaks induced, depends on the time of treatment and seems to be related to the membranous EGFR expression.
• The repair of DNA double strand breaks in human squamous cell carcinoma cell lines shows comparable kinetics after treatment with ⁹⁰Y-DTPA-Cetuximab and irradiation with X-ray.

^__> ⁹⁰Y-DTPA-Cetuximab can be used to generate DNA-double strand breaks in human cell lines expressing high EGFR. The data shows that this EGFR directed targeting strategy using a radioactive labelled antibody has the potential to increase tumour control. Experiments in tumour model systems (respective xenografts) to investigate the therapeutic benefit (with and without external radiation) and possible side effects are currently done by our cooperation partners.
Acknowledgements
This project is supported by BMBF (02 NUK 006 C) & DFG (PAK-190)