Studies of 4 HDAC inhibitors that failed to induce γ gene expression. (A) Effects on cell numbers. Notice that all compounds are cytotoxic in the concentrations that failed to induce the γ gene promoter. SW183 (▪), SW187 (▤), SW188 (•), and SW189 (). (B) Induction of erythroblast maturation as detected by measurements of benzidine-positive GM979 cells. SW183 (▪), SW187 (▤), SW188 (•), and SW189 (). Error bars indicate SEM.