A First-in-human Study of KK8123 in Adults With X-linked Hypophosphatemia

Exclusion Criteria36

• For XLH patients previously treated with burosumab, use of burosumab within 7 months prior to ICF signature.
• Prior history of positive test for human immunodeficiency virus antibody, positive test for hepatitis B surface antigen, and/or hepatitis C virus antibody at Screening.
• History of hypersensitivity to any ingredient of any therapeutic monoclonal antibody.
• Have an active infection.
• Grade 3 or greater nephrocalcinosis as confirmed by renal ultrasound.
• Uncontrolled diabetes mellitus at Screening.
• History of known immunodeficiency.
• History of alcoholism or drug abuse.
• History of donation of blood within 60 days prior to Screening.
• Use of any IP or investigational medical device within 30 days prior to Screening, or requirement for any investigational agent prior to completion of all scheduled study assessments.
• Use of any therapeutic mAb within 90 days prior to Screening.
• Use of pharmacologically active vitamin D, its metabolites or analogs, oral phosphate for treatment of XLH, aluminum hydroxide antacids, acetazolamide, thiazide diuretics, and/or systemic corticosteroids within 14 days prior to Screening. If the participant takes any of these medications, a washout period of 14 days will be required after signing the ICF and before any other screeening assessments begin.
• Use of medication to suppress PTH (e.g., calcimimetics) within 2 months prior to Screening and for the duration of the study.
• Use of denosumab within 6 months prior to Screening.
• Use of oral bisphosphonates in the 2 years prior to Screening.
• Use of teriparatide or abaloparatide in the 2 months prior to Screening.
• Plasma iPTH ≥ 2.5 × ULN at Screening.
• Planned or recommended orthopedic surgery during the study.
• History of traumatic fracture or orthopedic surgery within 6 months prior to Screening.
• Participants who are lactating.
• Current active and symptomatic COVID-19 infection at Day -1.
• Presence or history of any condition that, in the view of the investigator, places the participant at high risk of poor treatment compliance or of not completing the study, or that would confound safety or interpretation of results.
• Use of burosumab following completion of Part 1 of the study.
• Have an active infection.
• Donation of blood within 60 days prior to Week 0 of Part 2.
• Use of any investigational product other than KK8123, or investigational medical device, within 30 days prior to Week 0 of Part 2, or requirement for any investigational agent prior to completion of all scheduled study assessments.
• Use of any therapeutic mAb other than KK8123 within 90 days prior to Week 0 of Part 2.
• Use of pharmacologically active vitamin D, its metabolites or analogs, oral phosphate for treatment of XLH, aluminum hydroxide antacids, acetazolamide, thiazide diuretics, and/or systemic corticosteroids within 14 days prior to Week 0 of Part 2.
• Use of medication to suppress PTH (e.g., calcimimetics) within 2 months prior to Week 0 of Part 2.
• Use of oral bisphosphonates following completion of Part 1 of the study.
• Use of teriparatide or abaloparatide in the 2 months prior to Week 0 of Part 2.
• Planned or recommended orthopedic surgery during the study.
• History of traumatic fracture or orthopedic surgery within 6 months prior to Week 0 of Part 2.
• Participants who are lactating.
• Current active and symptomatic COVID-19 infection, or a history of suffering any long-term sequalae from COVID-19 infection.
• Presence or history of any condition that, in the view of the investigator, places the participant at high risk of poor treatment compliance or of not completing the study.