Paired-label internalization of iso-[125I]SGMIB-5F7 (red bars) and [131I]MEGMIB-5F7GGC (black bars) in HER2-expressing SKOV-3 cells in vitro: A) percentage of radioactivity in efflux after 1, 2, 4 and 24 h incubation. B) percentage of radioactivity bound to cell surface after 1, 2, 4 and 24 h incubation. C) percentage of radioactivity internalized in the cells after 1, 2, 4 and 24 h incubation.