MK-0557

MK-0557 is a highly selective, orally available neuropeptide Y5 receptor antagonist with a K_i of 1.6 nM. IC50 & Target: Ki: 1.6 nM (Y5)^[1] 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^[2]. 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 body-weight gain at day 35^[2].