Description_x000D_ Biochem/physiol Actions_x000D_ GSK-A1 is an ATP site-targeting, highly potent and selective type III phosphatidylinositol 4-kinase PI4KA (PI4KIIIα) inhibitor (pIC50 = 8.5-9.8) that selectively downregulates cellular PtdIns(4)P, but not PtdIns(4,5)P2, level (HEK293 IC50 = 3 nM, complete depletion of HEK293 & COS-7 plasma membrane PtdIns(4)P by 100 nM post 10 min treatment) with much reduced potency toward PI4KB (pIC50 = 7.2-7.7), PI3KA/B/D/G (pIC50 = 7.3/7/7.1/7.8) or PI4K/2A/2B (pIC50 <5). GSK-A1 is a useful tool for probing PI4KA-dependent cellular processes and viral replication (typical culture treatment conc. range: 10-100 nM).