AsPC-1 and BxPC-3 cells were plated at 200,000 cells/well and allowed to adhere overnight at 37 °C with 5% CO2. The cells were then co-incubated with either 10× (1 μg) or 25×, (2.5 μg) cold MEHD7945A, cetuximab, or DL3.6B and 89Zr-MEHD7945A [~0.5 μCi (0.0185 MBq), 100–125 ng] in 1 mL of complete media for 1 h at 37 °C with 5% CO2. Following incubation, the media was collected and the cells were rinsed with 1 mL 1× PBS twice. The cells were then lysed with 1 mL 1 M NaOH. All washes (media plus PBS, and alkaline) were collected in separate tubes and measured for counts using a gamma counter (Perkin Elmer). The %-bound activity was calculated as the ratio of the activity of the lysate and the total activity collected from the media, PBS, and base washes.