Statement of Purpose: mRNA-mediated protein replacement represents a promising concept for the treatment of liver disorders. Children born with fumarylacetoacetate hydrolase (FAH) mutations suffer from hepatorenal tyrosinemia type I resulting in renal dysfunction, liver failure, neurological impairments, and cancer. Protein replacement therapy using FAH mRNA offers tremendous potential to treat Hepatorenal Tyrosinemia Type I (HT-1), but is currently hindered by the development of efficacious mRNA carriers that can function in diseased livers. Structure-guided, rational optimization of 5A2-SC8 mRNA-loaded dendrimer lipid nanoparticles (mDLNPs) increased delivery potency of FAH mRNA, resulting in functional FAH protein and sustained normalization of body weight and liver function in FAH
knockout mice. Optimization using luciferase mRNA produced DLNP carriers that were efficacious at mRNA doses as low as 0.05 mg/kg in vivo. mDLNPs transfected >44% of all hepatocytes in the liver, yielded high FAH protein levels (0.5 mg/kg mRNA), and were well tolerated in a knockout mouse model with compromised liver function. Genetically engineered FAH
mice treated with FAH mRNA mDLNPs had statistically equivalent levels of TBIL, ALT, and AST compared to wild type C57BL/6 mice and maintained normal weight throughout the month-long course of treatment. This study provides a framework for the rational optimization of LNPs to improve delivery of mRNA broadly and introduces a specific and viable DLNP carrier with translational potential to treat genetic diseases of the liver.