A Novel Fc-FGF21 With Improved Resistance to Proteolysis, Increased Affinity Toward β-Klotho, and Enhanced Efficacy in Mice and Cynomolgus Monkeys

Fibroblast growth factor (FGF) 21 is a natural hormone that modulates glucose, lipid, and energy metabolism. Previously, we engineered an Fc fusion FGF21 variant with two mutations, Fc-FGF21 (RG), to extend the half-life and reduce aggregation and in vivo degradation of FGF21. We now describe a new variant developed to reduce the extreme C-terminal degradation and improve the binding affinity to b-Klotho. We demonstrate, by introducing one additional mutation located at the C terminus of FGF21 (A180E), that the new molecule, Fc-FGF21(RGE), has gained many improved attributes. Compared with Fc-FGF21(RG), Fc-FGF21(RGE) has similar in vitro potency, preserves b-Klotho dependency, and maintains FGF receptor selectivity and cross-species reactivity. In vivo, Fc-FGF21(RGE) showed reduced susceptibility to extreme C-terminal degradation and increased plasma levels of the bioactive intact molecule. The circulating half-life of intact Fc-FGF21(RGE) increased twofold compared with that of Fc-FGF21(RG) in mice and cynomolgus monkeys. Additionally, Fc-FGF21(RGE) exhibited threefold to fivefold enhanced binding affinity to coreceptor b-Klotho across mouse, cynomolgus monkey, and human species. In obese and diabetic mouse and cynomolgus monkey models, Fc-FGF21(RGE) demonstrated greater efficacies to Fc-FGF21(RG), resulting in larger and more sustained improvements in multiple metabolic parameters. No increased immunogenicity was observed with Fc-FGF21(RGE). The superior biophysical, pharmacokinetic, and pharmacodynamic properties, as well as the positive metabolic effects across species, suggest that further clinical development of Fc-FGF21(RGE) as a metabolic therapy for diabetic and/or obese patients may be warranted.