Fig. 2. Selection of canertinib resistant cells. Tu-2449 cells were treated with canertinib for 10 days. The drug was replenished in the growth medium in 24 hour intervals by half-medium change. After 10 days, drug treatment was discontinued for three days. Cell growth was microscopically monitored after 1, 3, 5, 7, 9 and 13 days. The upper panel shows different fields while the lower panel shows the same field. Magnification, 40×. Drug treatment selects for small cell colonies with higher cell density.