Inhibition of autophosphorylation of epidermal growth factor receptor by a small peptide not employing an ATP-competitive mechanism.

Previously we found that short peptides surrounding major autophosphorylation sites of EGFR (VPEY(1068)INQ, DY(1148)QQD, and ENAEY(1173)LR) suppress phosphorylation of purified EGFR to 30-50% at 4000 microM. In an attempt to improve potencies of the peptides, we modified the sequences by substituting various amino acids for tyrosine or by substituting Gln and Asn for Glu and Asp, respectively. Among the modified peptides, Asp/Asn- and Glu/Gln-substitution in DYQQD (NYQQN) and ENAEYLR (QNAQYLR), respectively, improved inhibitory potencies. The inhibitory potency of NYQQN was not affected by the concentration of ATP, while that of QNAQYLR was affected. Docking simulations showed different mechanisms of inhibition for the peptides: inhibition by binding to the ATP-binding site (QNAQYLR) and inhibition by binding to a region surrounded by alphaC, the activation loop, and the catalytic loop and interfering with the catalytic reaction (NYQQN). The inhibitory potency of NYQQN for insulin receptor drastically decreased, whereas QNAQYLR inhibited autophosphorylation of insulin receptor as well as EGFR. In conclusion, NYQQN is not an ATP-competitive inhibitor and the binding site of this peptide appears to be novel as a tyrosine kinase inhibitor. NYQQN could be a promising seed for the development of anti-cancer drugs having specificity for EGFR.