CAY10594 is a Phospholipase D (PLD) inhibitor. PLD is an enzyme that cleaves the head group from phospholipids, producing the second messenger phosphatidic acid. Two mammalian isoforms of PLD (PLD1 and PLD2) have been identified, with multiple splice variants of each. Although the two isoforms share functional and structural features, they are regulated differently and apparently serve distinct biological roles. CAY10594 is a potent PC-PLD2 inhibitor|in vitro|(IC|50|= 140 nM). It also inhibits PC-PLD1 at higher concentrations (IC|50|= 5.1 μM). CAY10594 strongly inhibits the invasive migration of breast cancer cells in transwell assays, suggesting that PLD might be a useful target in blocking tumor cell invasion.