Better drugs will be designed once more is understood about receptor-ligand interactions and more information about targets is available from high-resolution studies of their properties in solution.

Subsequently, we monitored the ligand-dependent HER profiles based on receptor expression, phosphorylation, and dimerization in conjunction with measurements of cellular susceptibility to gefitinib.

There's a diverse range of responses that might occur, but that response is initiated by this simple chemical process of a ligand binding to a receptor.