GSK-A1 is an inhibitor of phosphatidylinositol 4-kinase IIIα (PI4KIIIα; IC50 = 3.16 nM). It is selective for PI4KIIIα over PI4KIIIβ, PI3Kα, PI3Kβ, and PI3Kδ (IC50s = >50 nM) but also inhibits PI3Kγ (IC50 = 15.8 nM). GSK-A1 decreases the levels of phosphatidylinositol 4-phosphate (PtdIns-(4)-P1) but not PtdIns-(4,5)-P2 in HEK293 cells expressing the angiotensin II type 1 (AT1) receptor (IC50 = 3 nM). GSK-A1 inhibits hepatitis C virus (HCV) genotype 1a and 1b replication.