This is an R01 application in response to RFA-AI-13-013 Partnerships for Biodefense (R01). Rickettsioses represent some of the most devastating human infections. These tick-borne diseases are caused by obligately intracellular bacteria of the genus Rickettsia, including typhus fever (Rickettsia prowazekii), an NIAID Category B Priority pathogen. It has been forecasted that temperature increases due to global climate change will lead to more widespread incidence of rickettsioses. In addition, a high infectivity and severe illness after inhalation make rickettsiae potential bioterrorism threats. Although rickettsil infections can be controlled by appropriate broad-spectrum antibiotic therapy if diagnosed early, up to 20% of misdiagnosed or untreated and 5% of treated Rocky Mountain spotted fever (RMSF) cases result in a fatal outcome. In fact, a fatality rate as high as 32% has been reported in hospitalized patients with Mediterranean spotted fever. Strains of R. prowazekii resistant to tetracycline and chloramphenicol have been developed in laboratories. Therefore, novel mechanism-based treatments are urgently needed. Our recent studies reveal that exchange protein directly activated by cAMP (Epac1) plays an important role in rickettsiosis. Deletion of Epac1 gene in mice protects them from fatal rickettsioses. Most importantly, we have developed first-in-class, small-molecule Epac specific-inhibitors (ESIs). Using these ESIs, we have further demonstrated that pharmacological inhibition of Epac in vivo recapitulates the Epac1-null phenotype: wild-type mice treated with an ESI are protected from fatal rickettsioses. These results indicate that Epac1 is a novel therapeutic target for potentially fatal rickettsiosis. In te present proposal, we will design, synthesize and optimize the lead candidates discovered in our laboratory for the discovery and development of more potent and specific ESIs with minimal toxicity, desired pharmacokinetic (PK) and pharmacodynamic (PD) properties. Optimized ESIs will be further analyzed for preclinical testing for efficacy and safety to identify drug candidate in animal models in vivo for the development of effective therapeutics for rickettsioses.