4.2. Growth Inhibition Assays

To test for lapatinib sensitivity, cells were seeded in 24-well plates and incubated for 24 h, then treated with varying concentrations of lapatinib (100, 150, 200, 250, 300, 400 or 500 nM, or 1 μM depending on the cell line) or with 100 nM of trastuzumab for 4 or 5 days (see legends for individual experimental details). Cells were trypsinized and counted using ViaCount (Millipore, Burlington, MA, USA) on the Guava EasyCyte (Millipore) in triplicate. Percentage growth inhibition was calculated relative to untreated controls.