Burosumab for CSHS

An Open Label Trial to Assess the Safety and Efficacy of Burosumab in a Single Patient With Cutaneous Skeletal Hypophosphatemia Syndrome (CSHS)

Burosumab (also known as the drug, Crysvita®) is a fully human immunoglobulin G1 (IgG1) monoclonal antibody (mAb) that binds to and inhibits the activity of fibroblast growth factor 23 (FGF23), leading to an increase in serum phosphorus levels. This drug is already approved for use in patients with X-linked hypophosphatemia (XLH), but not for Cutaneous Skeletal Hypophosphatemia Syndrome (CSHS). It is hypothesized that burosumab may provide clinical benefit to a patient with CSHS due to the common underlying feature in this patient and in patients with XLH - abnormally elevated FGF23 in the context of low age -adjusted serum phosphorous levels.

Study Overview

• Status: Active, not recruiting
• Conditions: Cutaneous Skeletal Hypophosphatemia Syndrome (CSHS); Epidermal Nevus Syndrome
• Intervention / Treatment: Drug: Burosumab

Detailed Description

There are multiple disorders (each with a unique underlying cause) that result in unusually high circulating levels of FGF23, which in turn result in renal phosphate wasting and reduced (or aberrantly normal in relationship to elevated FGF23) levels of 1,25-dihydroxy vitamin D (1,25[OH]2D). Across these disorders the clinical symptoms are similar and often include osteomalacia (and, in children, rickets), muscle weakness, fatigue, bone pain, and fractures. Burosumab has been FDA-approved for one of these disorders, X-linked hypophosphatemia (XLH). In single- and repeat-dose clinical studies in subjects with XLH, subcutaneous (SC) administration of burosumab consistently increased and sustained serum phosphorus levels and tubular reabsorption of phosphate (TRP) and improved radiologic rickets, without a major impact on urine calcium levels. Positive results were also observed in a nonclinical pharmacology model of XLH. It is hypothesized that burosumab may provide clinical benefit in this patient due to the common underlying feature in this patient and in patients with XLH - abnormally elevated FGF23 in the context of low age -adjusted serum phosphorous levels.

• Study Type: Interventional
• Enrollment (Anticipated): 1
• Phase: Early Phase 1

Contacts and Locations

Study Locations

• United States
  • District of Columbia
    • Washington, District of Columbia, United States, 20010
      • Children's National Hospital

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Child; Adult; Older Adult
• Accepts Healthy Volunteers: No
• Genders Eligible for Study: All

Description

Inclusion Criteria:

In order to be eligible to participate in this study, an individual must meet all of the following criteria:

1. Patient has confirmed CSHS by physician diagnosis
2. Patient has confirmed FGF23 elevations in the context of a low fasting serum phosphorous < 2.5 mg/dL
3. Patient able to tolerate burosumab treatment
4. Have a corrected serum calcium level < 10.8 mg/dL
5. Have an eGFR >25 mL/min/1.73m2 (using CKD-EPI equation)
6. Must be willing in the opinion of the investigators, to comply with study procedures and schedule
7. Provide written informed consent by the subject or a Legal Authorized Representative (LAR) after the study has been explained and prior to any research related procedures begin
8. Must have a negative pregnancy test at Screening and be willing to have additional pregnancy tests during the study.
9. Must be willing to use a highly effective method of contraception for the duration of the study and for at least 12 weeks after the last dose of the study drug. Highly effective methods of contraception include: combined (estrogen and progestogen containing) hormonal contraception associated with inhibition of ovulation (e.g., oral, intravaginal, transdermal), progestogen-only hormonal contraception associated with inhibition of ovulation (e.g., oral, injectable, implantable), intrauterine device (IUD) or intrauterine hormone-releasing system (IUS), bilateral tubal occlusion, or sexual abstinence (i.e., refraining from heterosexual intercourse during the entire period of risk associated with the study treatments, when this is in line with the preferred and usual lifestyle of the subject)

Exclusion Criteria:

An individual who meets any of the following criteria will be excluded from participation in this study:

1. Concomitant use of active vitamin D (i.e. calcitriol) and/or exogenous phosphate supplementation during burosumab therapy. Subjects will be allowed over the counter Vitamin D should levels drop below <20 ng/ml
2. Blood phosphorus level within or above the normal range while not taking phosphate or active Vitamin D.
3. Severe renal impairment or end-stage renal disease, defined as an eGFR of less than 25 ml/min/1.73m2
4. The use or enrollment in studies using other investigational therapies including other monoclonal antibodies
5. Subject or Legally Authorized Representative not willing or not able to give written informed consent
6. In the investigator's opinion, the subject may not be able to meet all the requirements for study participation
7. History of hypersensitivity to burosumab excipients that in the opinion of the investigator, places the subject at an increased risk of adverse effects
8. Subject has a condition that in the opinion of the investigator could present a concern for subject safety or data interpretation.

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: N/A
• Interventional Model: Single Group Assignment
• Masking: None (Open Label)

Number of Arms

1

Arms and Interventions

Participant Group / Arm

Intervention / Treatment

Experimental: Burosumab; Burosumab, which is FDA-approved for X-linked hypophosphatemic rickets, will be given monthly, for a total of 12 months and titrated to achieve a target fasting serum phosphorus level within normal range for age. The chosen starting dose of burosumab will be 0.3 mg/kg given SQ Q4W. The maximum dose allowed in this protocol is 2.0 mg/kg. Burosumab will be administered via subcutaneous (SC) route.

Drug: Burosumab; Burosumab, the investigational product, is a recombinant human IgG1 monoclonal antibody targeting FGF23. It is supplied as a sterile, clear, colorless and preservative-free solution and is administered via subcutaneous injection.; Other Names: Crysvita

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Serum Phosphorus change	Change from baseline over 52 weeks in serum phosphorus with burosumab treatment.	52 weeks

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Changes in 1,25(OH)2-Vitamin D	Changes from baseline over 52 weeks in 1,25(OH)2-Vitamin D	52 weeks
Changes in tubular reabsorption of phosphate (TRP)	Changes from baseline over 52 weeks in tubular reabsorption of phosphate (TRP)	52 weeks
Changes in TmP/GFR (the ratio of renal tubular maximum phosphate reabsorption rate to glomerular filtration rate	Changes from baseline over 52 weeks in TmP/GFR (the ratio of renal tubular maximum phosphate reabsorption rate to glomerular filtration rate	52 weeks
Biomechanical Marker	Effect of burosumab over 52 weeks on biochemical marker of bone turnover that reflects osteomalacia severity: alkaline phosphatase (ALP).	52 weeks
6-minute walk test	Change in walking capacity over 52 weeks as assessed by 6-Minute Walk Test (6MWT)	52 weeks
Sit-to-Stand test (STST)	Change in proximal muscle function over 52 weeks as assessed by the Sit-to-Stand test (STST)	2 weeks
Brief Pain Inventory (BPI)	Change in Patient/parent-Reported Outcomes over 52 weeks as assessed by Brief Pain Inventory (BPI)	52 weeks
Brief Fatigue Inventory (BFI)	Change in Patient/parent-Reported Outcomes over 52 weeks as assessed by Brief Fatigue Inventory (BFI)	52 weeks
SF36 item short health survey (SF-36)	Change in Patient/parent-Reported Outcomes over 52 weeks as assessed by SF36 item short health survey (SF-36)	52 weeks
PROMIS Pain Intensity	Change in Patient/parent-Reported Outcomes over 52 weeks as assessed by PROMIS Pain Intensity instrument. Pain is rated on a scale of 0-10 where 0 represents no pain and 10 represents the worst possible pain.	52 weeks
PROMIS Pain Interference	Change in Patient/parent-Reported Outcomes over 52 weeks as assessed by PROMIS Pain Interference instrument. Responses are aggregated and converted to a T-score from 0-100 where 50 is the mean and every 10 is one standard deviation from the mean.	52 weeks
PROMIS Physical Function with Mobility Aid	Change in Patient/parent-Reported Outcomes over 52 weeks as assessed by PROMIS Physical Function with Mobility Aid instrument. Responses are aggregated and converted to a T-score from 0-100 where 50 is the mean and every 10 is one standard deviation from the mean.	52 weeks
PROMIS Fatigue	Change in Patient/parent-Reported Outcomes over 52 weeks as assessed by PROMIS Fatigue instrument. Responses are aggregated and converted to a T-score from 0-100 where 50 is the mean and every 10 is one standard deviation from the mean.	52 weeks

Collaborators and Investigators

• Sponsor: Laura Tosi
• Collaborators: Children's National Research Institute; Ultragenyx Pharmaceutical Inc
• Investigators: Principal Investigator: Laura Tosi, MD, Children's National Health System

Study record dates

Study Major Dates

• Study Start (Actual): July 1, 2019
• Primary Completion (Anticipated): October 30, 2022
• Study Completion (Anticipated): March 1, 2023

Study Registration Dates

• First Submitted: February 13, 2019
• First Submitted That Met QC Criteria: June 19, 2019
• First Posted (Actual): June 21, 2019

Study Record Updates

• Last Update Posted (Actual): March 7, 2022
• Last Update Submitted That Met QC Criteria: March 4, 2022
• Last Verified: March 1, 2022

More Information

Terms related to this study

• Keywords: CSHS; Cutaneous Skeletal Hypophosphatemia Syndrome; Epidermal Nevus Syndrome
• Additional Relevant MeSH Terms: Pathologic Processes; Metabolic Diseases; Nervous System Diseases; Neoplasms by Histologic Type; Neoplasms; Disease; Congenital Abnormalities; Nevi and Melanomas; Abnormalities, Multiple; Neurocutaneous Syndromes; Phosphorus Metabolism Disorders; Nevus; Syndrome; Hypophosphatemia; Nevus, Sebaceous of Jadassohn
• Other Study ID Numbers: IRB 11746

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: Yes
• Studies a U.S. FDA-regulated device product: No