The cytotoxicity of a conjugate composed of human epidermal growth factor and eosinophil cationic protein

Background: Conventional targeted therapy with foreign proteins is highly immunogenic. In this study, we developed targeted therapy composed of human endogenous proteins and evaluated its efficacy in vitro. Materials and Methods: Human epidermal growth factor (EGF) was chemically linked to human eosinophil cationic protein (ECP). The cytotoxicity of the EGF-ECP conjugate was evaluated by MTT assay. Results: The conjugate showed dose-dependent cytotoxicity on EGF receptor (EGFR) -overexpressing BT-20 cells with an IC₅₀ of 1.5 × 10^-7 M, whereas the IC₅₀ of ECP alone was almost 10 M. The conjugate had no detectable cytotoxicity against EGF receptor-deficient H69 cells. Excess EGF protected BT-20 cells from the cytotoxicity of the conjugate. Comparing the cytotoxicity and the level of EGFR expression, the cytotoxicity of the conjugate was positively correlated with the level of EGFR expression of each cell line. Conclusion: Conjugates composed solely of human proteins might be useful with less immunogenicity and less toxicity than the conventional immunotoxins for targeted therapy.