PHA-E is a natural product extracted from red kidney beans, and it has been 
reported to induce cell apoptosis by blocking EGFR in lung cancer cells. Because 
EGF is the major in vivo competitor to PHA-E in clinical application, PHA-E must 
be proved that has better affinity to EGFR than EGF. This study would focus on 
how PHA-E tightly bind to EGFR and the results would compare with EGF. The 
adhesion force, measured by AFM, between EGFR and PHA-E was 207.14±74.42 pN that 
was higher than EGF (183.65±86.93 pN). The equilibrium dissociation constant of 
PHA-E and EGF to EGFR was 2.4 10(-9)±1.4 10(-9) and 7.3 10(-8)±2.7 10(-8), 
respectively, that could evaluate binding affinity. The result showed that 
binding affinity of PHA-E to EGFR was one order higher than EGF to EGFR. In the 
results of flow cytometer and confocal microscope, we found binding efficiency 
of EGF to EGFR was decrease as the concentration of PHA-E increased. In the 
analysis of Western blot, treatment of A-549 cells with PHA-E resulted in a 
dose-dependent decrease in EGFR phosphorylation. In conclusion, we found that 
PHA-E had better adhesion force and binding affinity to EGFR than that of the 
EGF. The interaction between PHA-E and EGFR could block EGF binding and then 
inhibit EGFR phosphorylation. PHA-E could be developed into a new target 
molecule for lung cancer treatment that could be immobilized on the drug carrier 
to guide therapeutic particles to the tumor site.