Effect of KRN23, a Fully Human Anti-FGF23 Monoclonal Antibody, on Rickets in Children with X-linked Hypophosphatemia (XLH): 40-week Interim Results from a Randomized, Open-label Phase 2 Study
A. Linglart*a (Dr), T. Carpenterb (Dr), E. Imelc (Dr), A. Bootd (Dr), W. Höglere (Dr), R. Padidelaf (Dr), W. Van’t Hoffg (Dr), M. Whyteh (Dr), CY. Cheni (Dr), A. Skrinari (Dr), S. Agarwali (Dr), J. San Martini (Dr), A. Portalei (Dr)
a APHP, Le Kremlin-Bicêtre, FRANCE ; b Yale University School of Medicine, New Haven, Connecticut, ÉTATS-UNIS ; c Indiana University School of Medicine, Indianapolis, Indiana, ÉTATS-UNIS ; d University of Groningen, Groningen, PAYS-BAS ; e Birmingham Children's Hospital, Birmingham, ROYAUME-UNI ; f Royal Manchester Children's Hospital, Manchester, ROYAUME-UNI ; g Great Ormond Street Hospital, London, ROYAUME-UNI ; h Shriners Hospital for Children, St. Louis, Missouri, ÉTATS-UNIS ; i Ultragenyx Pharmaceutical Inc., Novato, California, ÉTATS-UNIS
* agnes.linglart@aphp.fr
Background: In XLH, high circulating FGF23 causes hypophosphatemia, rickets, and short stature.
Objective and hypotheses: To evaluate KRN23 effects on serum phosphate (Pi) level and rickets severity in XLH children in a Phase 2 study.
Method: 52 XLH children (ages 5-12 years, ≤Tanner 2) received KRN23 subcutaneously biweekly (Q2W) or monthly (Q4W). Serum Pi was measured at 2-week intervals. KRN23 dose was titrated (maximum 2mg/kg) targeting age-appropriate serum Pi concentrations. Rickets severity was assessed by the Thacher Rickets Severity Score (RSS) and Radiographic Global Impression of Change (RGI-C; ?3=worsening; +3=complete healing).
Results: The first 36 subjects had a mean 6.6 years of standard-of-care treatment before washout. KRN23 increased serum Pi from baseline in all subjects to near normal levels (mean increase 0.30 mmol/L at 38 weeks; p<0.001) and was more stable with Q2W dosing; hyperphosphatemia did not occur. KRN23 significantly improved RSS with greater improvements seen with Q2W dosing (44% reduction; p=0.0126) and particularly in higher-severity subjects (baseline RSS ≥1.5) (59% reduction; p<0.0001). Q2W dosing improved RGI-C by +1.6 (p<0.0001) with higher-severity subjects showing substantial healing (+2.0; p<0.0001). Most treatment-related adverse events (AE) were mild; transient injection site reactions occurred most frequently (39%). One child experienced a serious AE (fever/muscle pain) that improved and the child continues in the trial. No clinically meaningful changes occurred in serum/urine calcium, serum iPTH, or renal ultrasound.
Conclusion: KRN23 improved phosphorus homeostasis and rickets in children with XLH.
L’auteur a déclaré le(s) conflit(s) d’intérêt suivant(s) :
AL, TC, EI, EB, WH, RP, WvH et MW sont investigateurs de l'essai clinique phase 2 et ont reçu des honoraires investigateurs. CYC, AS, SA, JSM et AP sont employés par Ultragenyx.