Many lipids and their derivatives are potent ligands for cellular receptors. The action of lipid second messengers is regulated by lipases and related enzymes that limit the lifetime and sphere of action of these bioactive molecules. The products of these hydrolytic reactions can themselves be second messengers and precursors to other bioactive molecules. For example, the serine hydrolase monoacylglycerol lipase (MAGL) is responsible for limiting the lifetime and sphere of action of the endocannabinoid 2-arachidonoylglycerol (2-AG) and for generating the fatty acid product, arachidonic acid. Inhibitors of these enzymes are potential therapeutics for the treatment of pain, anxiety, addiction, inflammation, and a myriad of diseases where inflammation or lipid regulation play central roles. However, the tools currently available for the evaluation of serine hydrolase activity and inhibition are primarily limited to use in vitro. In this grant, we will develop luminogenic sensors for serine hydrolases (Aim 1), and apply them to the imaging of serine hydrolase activity in live cells and identification of novel inhibitors for this class of enzymes (im 2). Finally, we will perform real-time imaging of serine hydrolase activity in vivo, to determine where and when these enzymes are active, and how the action of drug pumps affect the tissue distribution of small molecule inhibitors of their function (Aim 3).