MK-0557 is a highly selective, orally available neuropeptide Y5 receptor antagonist with a K i of 1.6 nM. In Vitro Neuropeptide Y (NPY) is a potent orexigenic neuropeptide, and antagonism of NPY Y1 and NPY Y5 receptors (NPYxR) is considered a potentially important anti-obesity drug target. MK-0557 has a K i =1.3 nM at the human NPY5R, with similar affinities at rhesus, mouse, and rat NPY5R. MK-0557 has no significant binding to the human NPY1R, NPY2R, NPY4R, or mouse NPY6R at concentrations of 10 μM. MCE has not independently confirmed the accuracy of these methods. They are for reference only. In Vivo MK-0557 antagonizes the effects of the NPY5R-selective agonist on body-weight gain and hyperphagia in C57BL/6J mice and significantly suppresses the body-weight gain in diet-induced obese (DIO) mice. When lean mice on regular chow are switched to a medium high-fat diet (4.2 kcal/g) and treated with MK-0557 at 30 mg/kg PO QD, MK-0557 causes a 40% reduction in\nbody-weight gain at day 35. MCE has not independently confirmed the accuracy of these methods. They are for reference only. Form:Solid IC50& Target:NPY Y 5 receptor