ALK inhibition leads to inhibition of colony formation and enhanced caspase activity in ALK⁺ ALCL cells. (A) ALK⁺ ALCL cells were treated with indicated concentrations of CEP compounds for 24 hours. The cells were diluted with 0.65% agar in culture medium with or without compounds and seeded on 35-mm³ culture dishes at density of 2 × 10³/dish. The plates were cultured until individual colonies were formed. The values presented are the average of relative colony numbers from 2 independent assays with standard error. (B) ALK⁺ ALCL cells (Karpas-299 and Sudhl-1) or ALK^- cells (K562) were seeded on 96-well plates and treated with CEP compounds at indicated concentrations for 24 hours. Caspase 3/7 activity was quantitated with apo-one homogenous caspase 3/7 assay kit. The values presented are the average of relative caspase 3/7 activities from 3 individual samples with standard error.