a, EGFR levels in BT-474, MDA-MB-361, or HepG2 cells after incubation with 10–20 nM conjugates. b, Proliferation of HepG2 cells in the presence of EGF (200 ng ml−1) and 50 nM cetuximab or Ab-2. Cells were incubated with EGF and antibodies for 48 h, and proliferation measured using an MTS assay. Data are representative of three independent experiments (a). For b, data are mean ± s.e.m. of three independent experiments. P values were determined by unpaired two-tailed t-tests. Per cent control was calculated by densitometry and normalized to loading control.