Curtailing FGF19’s mitogenicity by suppressing its receptor dimerization ability

As a physiological regulator of bile acid homeostasis, FGF19 is also a potent insulin sensitizer capable of normalizing plasma glucose concentration, improving lipid profile, ameliorating fatty liver disease, and causing weight loss in both diabetic and diet-induced obesity mice. There is therefore a major interest in developing FGF19 as a therapeutic agent for treating type 2 diabetes and cholestatic liver disease. However, the known tumorigenic risk associated with prolonged FGF19 administration is a major hurdle in realizing its clinical potential. Here, we show that nonmitogenic FGF19 variants that retain the full beneficial glucose-lowering and bile acid regulatory activities of WT FGF19 (FGF19 WT ) can be engineered by diminishing FGF19's ability to induce dimerization of its cognate FGF receptors (FGFR). As proof of principle, we generated three such variants, each with a partial defect in binding affinity to FGFR (FGF19 ΔFGFR ) and its coreceptors, i.e., βklotho (FGF19 ΔKLB ) or heparan sulfate (FGF19 ΔHBS ). Pharmacological assays in WT and db/db mice confirmed that these variants incur a dramatic loss in mitogenic activity, yet are indistinguishable from FGF19 WT in eliciting glycemic control and regulating bile acid synthesis. This approach provides a robust framework for the development of safer and more efficacious FGF19 analogs.