Salubrinal induces HbF in human erythroid progenitors. (A) Differentiating erythroid progenitors were treated with 3 μM and 6 μM salubrinal (Sal) on days 15 and 18 of the culture. On day 20, cells were lysed and the proportions of HbA and HbF were determined by ion-exchange HPLC. These HPLC traces from a representative experiment reveal that Sal enhances HbF, as well as it reduces HbA compared with the untreated control. (B) The percentage of HbF was quantified in 5 independent experiments (3 different donors) comparing 3 μM and 6 μM Sal treatments to an untreated control. Sal dose-dependently increases the percentage of HbF. Error bars express ± standard error of the mean and P values were calculated using an unpaired two-tailed t test. (C) Equal numbers of cells were lysed on day 20 and hemoglobin concentrations were determined by measuring the absorbance at 415 nm. Sal treatments did not significantly reduce total hemoglobin content. Error bars represent ± standard error of the mean of 5 independent experiments (3 unique donors). P values were calculated using an unpaired two-tailed t test and were found to be nonsignificant (NS). The P value for 3 μM and 6 μM Sal compared with untreated was P = .26 and P = .32, respectively.