The EGFR and HER3 protein expression were determined by SDS-PAGE using the Invitrogen XCell SureLock system. Briefly, proteins were extracted from cell pellets with RIPA buffer and protease and phosphatase inhibitors (HALT, ThermoFisher). Fifteen micrograms of protein were resolved by 4–12% SDS-PAGE and transferred to membrane. After blocking with 5% milk in TBS-0.1% Tween-20, membrane was incubated with anti-EGFR-XP (D38B1, Cell Signaling), anti-HER3-XP (D22C5, Cell Signaling), or anti-β-Actin (mAbcam 8226, Abcam) antibody overnight at 4 °C. After incubation with secondary antibody (anti-mouse HRP or anti-rabbit HRP, Amersham) the membrane was visualized by Ammersham ECL (GE Life sciences) and read using a ChemiDoc imaging system (Bio-Rad) and analyzed using image lab touch software 2.2 (Bio-Rad).