Ex vivo competitive binding assay. A digital autoradiograph of AsPC-1 tumor sections displayed saturable, concentration-dependent binding of 89Zr-MEHD7945A upon addition of 100-fold excess cold MEHD7945A. (A) A non-linear regression analysis and Scatchard plot of 89Zr-MEHD7945A plotted against the amount of bound ligand shows the Bmax ~ 336 fmol/mg and a KD ~ 0.51 nM (B).