The effect of a dimeric Affibody molecule (ZEGFR:1907)2 targeting EGFR in combination with radiation in colon cancer cell lines

The epidermal growth factor receptor (EGFR) is frequently overexpressedin colorectal cancer and is therefore an attractive target for treatment. (ZEGFR:1907)2is a newly developed dimeric affibody molecule with high affinity to the extracellularpart of EGFR. In this study, we evaluated the cytotoxic effects of (ZEGFR:1907)2in combination with external radiation and the possible inhibitory effects inthe EGFR signalling pathways in the colon cancer cell lines HT-29 and HCT116.The effects were compared with an EGFR antibody (cetuximab) and the tyrosine kinaseinhibitors (erlotinib and sunitinib). These cell lines are genotypically differentwith respect to e.g. KRAS and BRAF mutational status, recently shown to be ofclinical significance for therapeutic effects. Both cell lines express approximately100,000-150,000 EGFRs per cell but differ in the radiation response (HCT116, SF2=0.28and HT-29, SF2=0.70). Exposure to (ZEGFR:1907)2 produced a small, but significant,reduction in survival in HCT116 but did not affect HT-29 cells. Similar resultswere obtained after exposure to EGF and the EGFR antibody cetuximab. The EGFRtyrosine kinase targeting inhibitor erlotinib and the multi-tyrosine kinase inhibitorsunitinib reduced survival in both cell lines. However, none of the drugs hadany significant radiosensitizing effects in combination with radiation. Akt andErk are central proteins in the EGFR downstream signalling and in the cellularresponse to ionizing radiation. The activation of Akt (Ser 473) and Erk (Thr202/Tyr204)by radiation was both dose- and time-dependent. However the activation of EGFRwas not clearly affected by radiation. Neither (ZEGFR:1907)2 nor any of the otherdrugs were able to completely inactivate Akt or Erk. On the contrary, erlotinibstimulated Akt phosphorylation in both cell lines and in HCT116 cells Erk wasactivated. Overall the results illustrate the complexity in response to radiationand drugs in cells with differential phenotypic status.