Synergistic In-Vitro Effects through Radiation and Blocking the Epidermal Growth Factor Receptor (EGFR) with the Monoclonal Antibody Cetuximab in Prostate Carcinoma Cell Line DU145

Abstract Background: The EGF-receptor is often overexpressed in advanced prostate carcinoma. In-vitro studies in prostate carcinoma cell-line DU145 demonstrated increased sensibilities to radiation with Cetuximab; in-vivo effects were not detected. Methods: In vitro, we analyzed the effect of radiation and Cetuximab in cell-lines DU145 and A431 (reference), using a proliferation assay, colony-forming unit assay, and Annexin-V apoptosis assay. We analyzed changes in the protein expression of pEGFR and pERK1/2 post-radiation and Cetuximab. Additionally, we investigated the impact of Cetuximab long-term treatment on the development of secondary-resistance-mutations. Results: DU145 cell counts were reduced by 44% after 4Gy (p=0.006) and by 55% after 4Gy and Cetuximab (p<0.001). The surviving fraction was 0.69 after 2Gy; 0.41, 4Gy; and 0.15, 6Gy (p<0,001). The additional Cetuximab-treatment did not significantly alter the impact on growth reduction or on the surviving fraction. After radiation and Cetuximab-treatment minor effects on the apoptotic cell-fraction in DU145 were detected. Using western blot, there were no pEGFR and pERK1/2 protein signals after Cetuximab-treatment. While no mutations of RAS, BRAF, PI3KCA and no amplifications of HER2 were detected, there were a TP53 mutation before and after long-term treatment with Cetuximab. Conclusion: Radiation inhibits cell-proliferation and colony-growth and induces apoptosis in DU145. Despite blocking EGFR-MAP-Kinase pathway with Cetuximab, no significant radiation-sensitizing-effect was detected. Cetuximab-treatment did not cause typical resistance mutations in DU145. Further research must clarify whether a combination of anti-EGFR therapeutics and immune-oncological approaches can increase the radiation-sensitizing-effect.