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Therapeutic Effects of FGF23 c‐tail Fc in a Murine Preclinical Model of X‐Linked Hypophosphatemia Via the Selective Modulation of Phosphate Reabsorption
Authors:Kristen Johnson  Kymberly Levine  Joseph Sergi  Jean Chamoun  Rachel Roach  Jacqueline Vekich  Mike Favis  Mark Horn  Xianjun Cao  Brian Miller  William Snyder  Dikran Aivazian  William Reagan  Edwin Berryman  Jennifer Colangelo  Victoria Markiewicz  Cedo M Bagi  Thomas P Brown  Anthony Coyle  Moosa Mohammadi  Jeanne Magram
Affiliation:1. Center for Therapeutic Innovation, Pfizer, New York, USA;2. Drug Safety Research and Development, Pfizer, Groton, USA;3. Comparative Medicine, Pfizer, Groton, USA;4. Department of Biochemistry and Molecular Pharmacology, New York University School of Medicine, New York, USA
Abstract:Fibroblast growth factor 23 (FGF23) is the causative factor of X‐linked hypophosphatemia (XLH), a genetic disorder effecting 1:20,000 that is characterized by excessive phosphate excretion, elevated FGF23 levels and a rickets/osteomalacia phenotype. FGF23 inhibits phosphate reabsorption and suppresses 1α,25‐dihydroxyvitamin D (1,25D) biosynthesis, analytes that differentially contribute to bone integrity and deleterious soft‐tissue mineralization. As inhibition of ligand broadly modulates downstream targets, balancing efficacy and unwanted toxicity is difficult when targeting the FGF23 pathway. We demonstrate that a FGF23 c‐tail‐Fc fusion molecule selectively modulates the phosphate pathway in vivo by competitive antagonism of FGF23 binding to the FGFR/α klotho receptor complex. Repeated injection of FGF23 c‐tail Fc in Hyp mice, a preclinical model of XLH, increases cell surface abundance of kidney NaPi transporters, normalizes phosphate excretion, and significantly improves bone architecture in the absence of soft‐tissue mineralization. Repeated injection does not modulate either 1,25D or calcium in a physiologically relevant manner in either a wild‐type or disease setting. These data suggest that bone integrity can be improved in models of XLH via the exclusive modulation of phosphate. We posit that the selective modulation of the phosphate pathway will increase the window between efficacy and safety risks, allowing increased efficacy to be achieved in the treatment of this chronic disease. © 2017 American Society for Bone and Mineral Research.
Keywords:FIBROBLAST GROWTH FACTOR 23  X‐LINKED HYPOPHOSPHATEMIA  1,25D  PHOSPHATE  OSTEOMALACIA
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