– The prostaglandin E receptor 4 (EP4) is one of four G protein-coupled receptors that mediate the actions of prostaglandin E2. Binding of PGE2 to the EP4 receptor causes an increase in intracellular cyclic AMP, which plays important roles in bone formation and resorption, cancer, and atherosclerosis. KMN-80 is a substituted γ-lactam (pyrrolidinone) derivative of PGE1 that acts as a selective and potent agonist of EP4 with an IC50 value of 3 nM (IC50 = 1.4 μM for EP3 and > 10 μM for all other prostanoid receptors). In functional assays it has been shown to stimulate secreted alkaline phosphatase gene reporter activity in EP4-transfected HEK293 cells with an EC50 value of 0.19 nM, demonstrating >5,000 and 50,000-fold selectivity against EP2 and TP, respectively. KMN-80 can induce the differentiation of bone marrow stem cells from both young and aged rats into osteoblasts in vitro (EC50s = 20 and 153 nM, respectively) and exhibits favorable tolerability up to at least 10 μM, whereas the EP4 agonist L-902,688 is highly cytotoxic at similar concentrations in these cells. KMN-80 has been used to repair calvarial defects in an in vivo rat craniomaxillofacial reconstruction model (rate of reduction in defect size equivalent to BMP-2 treated rats) and to promote bone formation in a rat incisor tooth socket model.