EGFR-targeted affibody–polyIC polyplex kills EGFR-overexpressing cancer cells without activating the EGFR

The epidermal growth factor receptor (EGFR) is aberrantly activated in many human epithelial cancers. This report presents the preparation, purification, and the anticancer potency of an anti-EGFR affibody (Z_{EGFR 1907’})-polyethylenimine (PEI)-polyIC complex (PPEA-polyplex). Surface plasmon resonance analysis showed that the Z_{EGFR 1907’} affibody binds tightly to full-length sEGFR with an average equilibrium dissociation constant, K_D, value of 6.74 nM. As expected the PPEA-polyplex does not activate the EGFR kinase, but kills tumor cells expressing medium to high levels of EGFR. The PPEA-polyplex stimulates the release of chemotactic cytokines (e.g., GRO-α, IFN-γ–inducible protein-10) and promoted PBMC-mediated bystander killing of non-treated tumor cells. The PPEA-polyplex also inhibited the growth of human epidermoid vulval carcinoma (A431) xenografts growing in immunocompromised nude mice. Both the in vitro and in vivo results indicate that PPEA-polyplexes have the potential to inhibit the growth of tumors which over-express the EGFR, including colon and breast cancer cells.