BMS 599626 dihydrochloride is a potent and selective EGFR and ErbB2 inhibitor. BMS-599626 inhibited HER4 (IC50: 190 nM). In Sal2, N87, and GEO tumor cells, BMS-599626 inhibited phosphorylation of HER1 and HER2 in a dose-dependent way and inhibited cell proliferation. In AU565 breast cancer cells, BMS-599626 (1μM) inhibited HER1/HER2 heterodimer formation. In tumor cells that forming HER1/HER2 heterodimers, BMS-599626 inhibited heterodimerization [1][2].