Abstract/Project summary: TPI Df is a devastating untreatable childhood metabolic disease resulting in anemia, paralysis, irreversible brain damage and premature death. Numerous single amino acid substitutions in Triosephosphate Isomerase (TPI) are pathogenic and result in rapidly progressing multisystem disease. Importantly, all known pathogenic TPI Df mutations result in a protein that retains function and pathogenesis is known to result from increased turnover of the functioning protein by Protein Quality Control pathways (PQC). We have developed a human cellular TPI Df assay based on a cellular model of the “common” E104D mutation and implemented it for high-content, high-throughput imaging. We have used this model in a pilot screen and validated its utility to identify novel compounds that modulate mutant TPI protein levels in human cells. We propose to develop the assay to full HTS standards, conduct a screen of several relevant compound libraries, and identify first-in-class TPI Df small molecule therapies. We will validate hits in secondary assays for TPI stability and activity in TPI Df patient cells, prioritize them in a panel of in vitro toxicology and metabolic stability assays, examine structure activity relationships (SARs) of the lead compounds and substantially validate them in vivo using a recently developed mouse TPI Df model. Overall this project will discover and validate the first ever treatments for TPI Df that will provide the basis for clinical trials.