Figure 3. The effect of lapatinib on the ¹²⁵I-EGF–A431 interaction.

The binding of ¹²⁵I-EGF to cultured A431 cells treated with complete medium (red), serum free medium (blue), 1 µM of lapatinib (A) or gefitinib (B) in complete medium (green) or 1 µM lapatinib (A) or gefitinib (B) in serum free medium (black) was measured in LigandTracer Grey. A) Lapatinib alters the kinetics of the interaction, as shown as a faster overall association rate and dissociation rate. In serum free medium, the difference between the first and second concentration (indicated by an arrow) is slightly less. B) Gefitinib increases the affinity, observed as a slower dissociation rate and small difference in signal height between the first and second concentration (arrow). The effect of gefitinib is larger in serum free medium.