Study of the Anti-FGF23 Antibody, Burosumab, in Adults With XLH

Phase 3CompletedNCT03920072

Kyowa Kirin Pharmaceutical Development Ltd35 enrolled

Overview

This is phase 3b open-label, international, multicenter study to continue to monitor the long-term safety and efficacy of burosumab in adult patients with XLH that participated in previous clinical trials with burosumab (UX023-CL303 / UX023-CL304).

XLH is a rare, genetic disorder that is serious, chronically debilitating and represents an unmet medical need. XLH is the most common inherited form of rickets and the most common inherited defect in renal tubular phosphate transport. XLH is transmitted as an X-linked dominant disorder. Mutations resulting in the loss of function of PHEX form the genetic basis for XLH. More than 300 different PHEX gene mutations have been identified in patients with XLH (PHEXdb); however, few definitive correlations have been observed between specific mutations and phenotypic severity. Patients with XLH have hypophosphatemia due to excessive serum FGF23 levels. FGF23 reduces serum phosphorus levels by two distinct mechanisms of action. The primary mechanism is to inhibit phosphate reabsorption in the proximal tubule of the kidney. The secondary mechanism is to decrease phosphate absorption by the small intestine through the inhibition of 1,25(OH)2D production in the kidney. Burosumab has the potential to block or reduce FGF23 action and improve phosphate homeostasis in XLH patients. Burosumab binds the amino-terminal domain of FGF23 that interacts with the FGF-binding portion of the combination FGFR1/Klotho receptor, preventing FGF23 from binding to and signaling from its receptor. Both intact and fragmented FGF23 polypeptides are immunoprecipitated with burosumab. By inhibiting FGF23, burosumab restores tubular reabsorption of phosphate (as measured by the ratio of renal tubular maximum reabsorption rate of phosphate to glomerular filtration rate \[TmP/GFR\]) from the kidney and increases the production of 1,25(OH)2D that also enhances intestinal absorption of phosphate. The dual action on kidney reabsorption and intestinal absorption improves serum phosphorus levels, which is expected to improve bone mineralization and reduce the diverse bone and non-bone manifestations associated with hypophosphatemia in XLH patients.

Study Type

INTERVENTIONAL

Allocation

Purpose

TREATMENT

Masking

NONE

Enrollment

Conditions

X-linked Hypophosphatemia

Interventions

BurosumabDRUG

Burosumab is a sterile, clear, colourless and preservative free solution supplied in single-use 5ml vials containing 1mL of burosumab at a concentration of 30mg/mL

Eligibility

Sex: ALLMin age: 18 YearsMax age: 70 Years

Medical Language ↔ Plain English

Inclusion Criteria: 1. Subjects who provide written informed consent after the nature of the study has been explained, and prior to any research-related procedures. 2. Subjects who participated in Study UX023-CL303 or UX023-CL304. Any subjects that did not complete Study UX023-CL303 or UX023-CL304 may be included on a case-by-case basis. Subjects' enrolment is not dependent on any response to Primary or Secondary endpoints in studies UX023-CL303 or UX023-CL304. 3. Willing to provide access to prior medical records for the collection of historical growth, biochemical and radiographic data, and disease history. 4. Must, in the opinion of the investigator, be willing and able to complete all aspects of the study, adhere to the study visit schedule and comply with the assessments. 5. Females of child-bearing potential must have a negative urine pregnancy test at Screening and be willing to have additional pregnancy tests during the study. Females considered not to be of child-bearing potential include those who have been in menopause for at least two years prior to Screening, or have had tubal ligation at least one year prior to Screening, or have had a total hysterectomy or bilateral salpingo-oophorectomy. If sexually active, male and female subjects must be willing to use one highly effective method of contraception for the duration of the study. Exclusion Criteria: 1. Hypocalcemia or hypercalcemia, defined as serum calcium levels outside the age-adjusted normal limits and deemed as clinically significant in the opinion of the investigator. 2. Presence of a concurrent disease or condition that would interfere with study participation or affect safety in the opinion of the investigator or Sponsor. 3. Use of any investigational product other than burosumab or investigational medical device within 30 days prior to Screening, or requirement for any investigational agent prior to completion of all scheduled study assessments. 4. Subjects with major protocol deviations in Study UX023-CL303 or UX023-CL304 which in the view of the investigator places the subject at high risk of poor treatment compliance or of not completing the study. 5. Subjects who discontinued treatment from Study UX023-CL303 or UX023-CL304 due to either a grade ≥3 treatment-related hypersensitivity reaction or a burosumab-related hypersensitivity reaction reported as a SAE.

Locations (10)

CHU de Bicetre

Le Kremlin-Bicêtre, France

Hopital Lariboisiere

Paris, France

Hopital Cochin

Paris, France

Outcomes

Primary Outcomes

Proportion of subjects achieving mean serum phosphorus levels above the LLN (2.5mg/dL[0.81mmol/L]), as averaged across dose cycles between baseline and their last administered dose.

To establish the effect of burosumab treatment on maintaining serum phosphorus levels to within normal range in adults with XLH.

Time frame: Serum phosphorous levels will be monitored from Screening and every 12 weeks until the end of the study, at approximately 144 weeks.

Secondary Outcomes

Effect of burosumab on pre-existing pseudofracture healing will be monitored by centrally read targeted X-Ray

Targeted radiography at locations pre-determined by the skeletal survey performed during UX023-CL303 or UX023-CL304 will be taken to monitor healing of pseudofractures and/or fractures.

Time frame: Targetted X-Rays at ongoing fracture sites will be taken at the End of Study Visit, approximately week 144.

Effect of burosumab on patients walking ability measured using the 6 Minute Walk Test.

Patient's motor function by sustained walking will be evaluated using the 6 Minute Walk Test. (6MWT). The percent predicted values for the 6MWT will be calculated using published normative data based on age, gender and height.

Time frame: The 6MWT will be measured at Baseline and then every 12 weeks for the first 48 weeks and then every 24 weeks for up to 144 weeks

Effect of burosumab on Patient mobility assessed using the Timed Up and Go Test (TUG).

The TUG assesses transitions during ambulatory activity incorporating strength, agility and dynamic balance assessments. The TUG score will be reported as the time (in seconds) that a subject takes to rise from a chair, walk three meters (approximately 10 feet), turn around, walk back to the chair and sit down.

Time frame: The TUG Test will be assessed at Baseline and then every 12 weeks for the first 48 weeks and then every 24 weeks for up to 144 weeks

Data from ClinicalTrials.gov

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