(a) ABP 980, trastuzumab (EU) and trastuzumab (US) show similar inhibition of pAKT phosphorylation in breast cancer cells. Graphs show the percent inhibition compared with an untreated control for 3 sets of side-by-side comparisons of unique lots. Each point is a mean of 4 replicates (±SE). Abbreviations: Ab antibody, pAKT phospho-AKT, trastuzumab (EU) EU authorized trastuzumab, trastuzumab (US) FDA licensed trastuzumab. (b) ABP 980, trastuzumab (EU) and trastuzumab (US) mediate similar HER2 internalization in breast cancer cells. Representative experiment showing fluorescence intensity histogram overlays displaying grouped comparisons between 3 antibody sources and each with 3 respective lots, i.e., EU lot (blue), US lot (grey), and ABP 980 lot (red), at either 4 °C or 37°C. The x axis represents pHrodo™ Red signal fluorescence intensity, and the y-axis represents normalized cell frequency. (c) Representative experiment showing single plane confocal micrographs of SK-BR-3 cells treated with pHrodo™ Red-conjugated ABP980, trastuzumab (US) or trastuzumab (EU) at 4°C or 37°C for 4 h. Internalized antibody appears as red fluorescent vesicles, suggesting internalization of the pHrodo Red-conjugated trastuzumab antibodies. Bottom panel images represent digital zooms from their respective original picture. Imaged with a 20×, 0.75 NA objective; excitation with a 561 nm laser, emission filter of 580/20. Abbreviations: Trastuzumab (EU) or EU EU authorized trastuzumab, trastuzumab (US) or US FDA licensed trastuzumab.