Efruxifermin, a long‐acting Fc‐fusion FGF21 analogue, reduces body weight gain but does not increase sympathetic tone or urine volume in Sprague Dawley rats

Background and Purpose Analogues of fibroblast growth factor 21 (FGF21) demonstrate diverse metabolic benefits in preclinical models of type 2 diabetes, dyslipidaemia and non‐alcoholic steatohepatitis (NASH), but clinical responses with different analogues are inconsistent. Efruxifermin is an Fc‐FGF21 fusion protein with prolonged half‐life and enhanced receptor affinity compared with native human FGF21. Efruxifermin is in clinical trials for the treatment of non‐alcoholic steatohepatitis. Experimental Approach Efruxifermin was administered weekly to male and female Sprague Dawley rats for 4 or 26 weeks. Body and organ weights, macroscopic and microscopic pathology, clinical chemistry, blood cytology and serum and urine biomarkers were analysed to characterize the pharmacodynamics of efruxifermin and to investigate potential non‐clinical toxicities following chronic administration of supra‐pharmacological doses of efruxifermin. Key Results Efruxifermin significantly reduced body weight gain after 4 and 26 weeks, despite increasing food intake. Changes in tissue pathology, clinical chemistry and serum biomarkers generally appeared to be associated with weight loss, except for a significant decrease in urine volume in both males and females without perturbed electrolyte balance. Markers of sympathetic activation, urinary corticosterone and ratio of adrenal‐to‐body weight were unchanged. Conclusion and Implications Efruxifermin attenuated body weight gain, consistent with other FGF21 analogues. In contrast to at least one other FGF21 analogue, efruxifermin decreased rather than increased urine volume. The absence of an increase in sympathetic tone in rats mirrors the unchanged salivary cortisol and systemic blood pressure following efruxifermin treatment in humans.