Isoforms of phospholipase D (PLD) cleave the head group from phospholipids, releasing the second messenger phosphatidic acid (PA), which can produce changes in Ras activation, cell spreading, stress fiber formation, chemotaxis, and membrane vesicle trafficking. FIPI is a derivative of halopemide which potently inhibits both PLD1 (IC50 = 25 nM) and PLD2 (IC50 = 20 nM).