ALK activity is essential for the proliferation of ALK⁺ ALCL cells in culture.ALK⁺ ALCL cell lines (Karpas-299, SR-786, Sup-M2, and Sudhl-1) and ALK^- cells (K562) were seeded on 96-well plates and treated with compounds at indicated concentrations for 48 hours. Viable cells were detected with MTS assay. The values presented are the average of relative cell numbers from 2 independent experiments with standard error. The effects of compounds on ALK tyrosine phosphorylation in ALCL cells are shown, in which the ALCL cells were treated with compounds at indicated concentrations for 2 hours and phospho- and total NPM-ALK were detected by immunoblotting as described in “Materials and methods.”