Project Summary/Abstract Inhibition of ceramide protects mice from death from the Radiation GI Syndrome (RGS). Administration of anti- ceramide single-chain Fv (scFv) 24 h post radiation exposure increases survival in intestinal stem cells and dramatically improves overall survival in mice. These data indicate that anti-ceramide scFv represents the first effective mitigator of lethal RGS. To advance the development of anti-ceramide scFv towards an Investigational New Drug application filing, we propose to 1) characterize the PK/PD relation with efficacy in mice; and 2) utilize PK/PD to select doses of anti-ceramide scFv to evaluate in a pilot efficacy study in a non- human primate (NHP) model of the RGS. Successful completion of the proposed aims will provide rationale for evaluation of anti-ceramide scFv safety in humans and full evaluation of efficacy in a larger powered NHP trial. Single-chain antibody fusion proteins are smaller derivatives of full length antibodies, and thus offer the advantage of rapid entering into the bloodstream efficacy and increased penetration into tissue compared to full-length antibodies, and from a product development standpoint these fusion proteins can be produced easily and at minimal cost. As such, a neutralizing anti-ceramide single-chain antibody fusion protein represents a promising candidate to fulfill the Project BioShield mandate for development of countermeasures to mitigate acute radiation syndromes within the first 24 h after a nuclear disaster.