Each of the 64 primary hits was subjected to primary validation for ISRE activity over a broader range of concentrations of drug and IFN-b (0-15 U/ml). Among the primary and confirmed screening hits, idarubicin hydrochloride ranked highest in potency for enhancing ISRE activity (i.e., idarubicin exhibited a significant effect at a lower concentration than other compounds). During the ISRE validation, we found that idarubicin caused a concentrationdependent increase in ISRE activity over a range of IFN-b treatment concentrations, with highly significant effects as low as 25 nM idarubicin in combination with 15 U/ml IFN-b ( Figure 5A) .