Hhat inhibition reduces proliferation of HER2 amplified cells. A-C, BT474 (A), MDA-MB-453 (B), and SK-BR3 (C) cells were cultured for 6 days in the presence of DMSO, RU-SKI 43 alone or in combination with indicated concentrations of lapatinib. Cell numbers were quantified and normalized to vehicle treated cells (100 x (drug/vehicle). Bars represent mean ± SD (n = 3) for all panels. Each experiment was performed using three separate passages of cells in triplicate. *P ≤ 0.05; **P ≤ 0.01; ***P ≤ 0.001; ****P ≤ 0.0001; Student’s t test.