Efruxifermin (EFX) is an Fc-FGF21 fusion protein engineered to mimic the biological activity of fibroblast growth factor 21 (FGF21). FGF21 regulates multiple ,metabolic pathways and cellular processes. It is upregulated by anti-aging Calorie restriction (CR), and FGF21 overexpression extends lifespan. FGF21 is expression in the thymus declines with age, and transgenic overexpression of FGF21 retards thymic involution and reduces intrathymic lipid.

By delivering sustained and balanced signaling through FGF21’s receptors in the liver and adipose tissue, Efruxifermin is intended to inhibit lipolysis and de novo lipogenesis, which are core drivers of MASH. Interim results of the Phase II HARMONY trial, which evaluated Efruxifermin in patients with pre-cirrhotic MASH (fibrosis stages II or III),  were presented in March 2024. A Phase 2b study assessing Efruxifermin in patients with compensated cirrhosis due to NASH (fibrosis stage 4) was initiated in July 2021. Topline results from this study were presented in October 2023.