||BMS-599626 also inhibits the related receptor HER4, but with reduced potency with IC50 of 190 nM. BMS-599626 is identified as an ATP-competitive inhibitor for HER1 and as an ATP-noncompetitive inhibitor for HER2 with Ki of 2 nM and 5 nM, respectively. BMS-599626 inhibits the proliferation of tumor cells expressing high levels of HER1 and/or HER2, including Sal2, BT474, N87, KPL-4, HCC202, HCC1954, HCC1419, AU565, ZR-75-30, MDA-MB-175, GEO, and PC9 cells with IC50 of 0.24 μM, 0.31 μM, 0.45 μM, 0.38μM, 0.94 μM, 0.34 μM, 0.75 μM, 0.63 μM, 0.51 μM, 0.84 μM, 0.90 μM and 0.34 μM, respectively. While the proliferation of the ovarian tumor cell line A2780 and MRC5 fibroblasts, neither of which expresses HER1 or HER2, are not inhibited significant by BMS-599626.  A recent study shows that BMS-599626 significantly enhances the radiosensitivity of HN-5 cells expressing both EGFR and Her2 cell, by promoting cycle redistribution and inhibiting DNA repair.