ClinicalTrials.gov record NCT06525636

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

Record copied from ClinicalTrials.gov: Oct 10, 2026AI summaries generated: Sep 28, 2026

A Multicenter, Open-label, Phase 1/2, Dose-escalation and Subsequent Safety Extension Study of Subcutaneous KK8123 in Adult Patients With X-linked Hypophosphatemia

StatusRecruitingThe study is currently enrolling participants. Only the study team can say whether a particular person can join.
Study typeInterventionalA study in which researchers assign participants to one or more interventions, such as a drug, procedure, device, behavioural programme or other approach, to measure their effects.
PhasePhase 1/2A study that combines safety and dose-finding (phase 1) with a first look at whether the treatment has an effect (phase 2).
Age18 years old to 65 years old
SexAll
LocationCanada, France, Germany, Spain, United States
AI summaryWhat this study is about, in plain languageShow ▾Hide ▴

AI-written from the registry record, not the study's own wording. May contain errors or omissions. Check the registry text on this page and the original record ↗ before acting on it.

This first-in-human, open-label Phase 1/2 study gives subcutaneous KK8123 to adults with X-linked hypophosphatemia to assess safety, tolerability, and how the drug behaves in the body. Part 1 is a sequential dose‑escalation period with planned treatment and observation; Part 2 is an optional safety extension. The study collects lab results, pharmacokinetic/pharmacodynamic data, imaging (echocardiogram, renal ultrasound), and adverse-event information over the study period.

What it is studying. The study is testing subcutaneous KK8123 in adults with X-linked hypophosphatemia to evaluate safety and tolerability, to measure pharmacokinetics (how the drug is processed by the body) and pharmacodynamics (its effect on serum phosphorus), and to collect related laboratory and imaging data including echocardiograms and renal ultrasound. It is a first‑in‑human, dose‑escalation investigation using single and multiple administrations.

What the researchers hope to learn. Scientific goals are to assess the safety and tolerability of KK8123, characterize its pharmacokinetics and pharmacodynamics, evaluate its effects on serum phosphorus, monitor laboratory and imaging changes (including heart and kidney imaging), and assess anti‑drug antibody responses.

What this study is about

The study's own summary, as published on ClinicalTrials.gov. Underlined terms have a short explanation.

A first-in-human study of KK8123 in adults with X-linked hypophosphatemia.

Interventions being studied

Being studied in this trial does not mean the treatment or procedure is approved or available for this condition.

Drug
  • KK8123

Eligibility

The criteria exactly as listed on ClinicalTrials.gov. Only the study team can say whether they apply to you.

Inclusion criteria

  • Part 1: Inclusion Criteria:
  • Male or female patients aged 18 to 65 years inclusive at the time of signing the ICF.
  • Body weight is at least 40 kg.
  • Diagnosed with XLH (as documented by the investigator).
  • Have a value of fasting serum phosphorus < 2.5 mg/dL (0.81 mmol/L) at Screening.
  • Have a value of renal TmP/GFR < 2.5 mg/dL (0.81 mmol/L) at Screening.
  • eGFR ≥ 60 mL/min (using the Chronic Kidney Disease Epidemiology Collaboration equation [Inker, 2021]) at Screening.
  • Have a corrected serum calcium level < 10.8 mg/dL (2.7 mmol/L) at Screening.
  • Provide a signed ICF.
  • Agree not to change diet and exercise regimen from one week prior to dosing to end of study.
  • Have a negative pregnancy test at Screening and be willing to have additional pregnancy tests during the study (female participants only).
  • If taking chronic pain medications (including narcotic pain medications/opioids), must be on a stable regimen for at least 21 days prior to the Screening visit, and be willing to maintain medications at the same stable dose(s) and schedule throughout the clinical trial. The dose must not exceed 60 mg oral morphine equivalents/day.
  • Be willing to use a method of contraception following local country guidelines while participating in the study and for 30 weeks after the last dose (all sexually active participants of childbearing potential).
  • Women of non-childbearing potential are defined as permanently sterile (i.e., due to tubal ligation at least one year before Screening, hysterectomy or bilateral oophorectomy) or postmenopausal (defined as at least 12 months post cessation of menses without an alternative medical cause).
  • Postmenopausal status of female participants will be confirmed with a Screening serum follicle-stimulating hormone level >40 mIU/mL.
  • 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.

Exclusion criteria

  • Part 1: Exclusion Criteria:
  • For XLH participants previously treated with the applicable prior therapy, use within the protocol defined washout period 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 immediately prior to study treatment.
  • 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.
  • Part 2: Inclusion Criteria:
  • Completion of relevant cohort in Part 1 of the study.
  • Provide a signed informed consent after the nature of Part 2 of the study has been explained.
  • Body weight is at least 40 kg.
  • Negative pregnancy test at Screening of Part 2 and willing to have additional pregnancy tests until the end of the study (female participants only).
  • If taking chronic pain medications (including narcotic pain medications/opioids), must be on a stable regimen for at least 21 days prior to Week 0 of Part 2, and be willing to maintain medications at the same stable dose(s) and schedule throughout the study. The dose must not exceed 60 mg oral morphine equivalents/day.
  • Be willing to use a method of contraception following local country guidelines while participating in the study and for 30 weeks after the last dose (all sexually active participants of childbearing potential). Women of non-childbearing potential are defined as permanently sterile (i.e., due to tubal ligation at least one year before Screening, hysterectomy or bilateral oophorectomy) or postmenopausal (defined as at least 12 months post cessation of menses without an alternative medical cause). Postmenopausal status of female participants will be confirmed with a Week 0 serum follicle-stimulating hormone level >40 mIU/mL.
  • 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 all the assessments.
  • For participants who complete the Part 1 EoS visit more than 30 days before starting Part 2 Week 0, eGFR ≥ 60 mL/min at Screening.
  • For participants who complete the Part 1 EoS visit more than 30 days before starting Part 2 Week 0, have a corrected serum calcium level of < 10.8 mg/dl (2.7 mmol/L) at Screening.
  • Part 2: Exclusion Criteria:
  • Use of the applicable prior therapy 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.

Study description and what participation involves

The study's detailed description, as published on ClinicalTrials.gov.

Detailed description from the registry

Study 8123-001 is a Phase 1/2, multicenter, open-label, dose-escalation study to assess the safety, tolerability, PK and PD of KK8123, with an optional safety extension period. This study is comprised of a Screening Period followed by Part 1 and Part 2. The Screening Period will last up to 35 days (including obtaining informed consent). Part 1 is a Dose Escalation Period consisting of a nominal (planned) Treatment Period (all cohorts) followed by an Observation Period, and Part 2 is an optional Extension Period.

AI summaryWhat participation may involve, in plain languageShow ▾Hide ▴

AI-written from the registry record, not the study's own wording. May contain errors or omissions. Check the registry text on this page and the original record ↗ before acting on it.

After a screening period (up to 35 days), participants enter Part 1 (a dose-escalation treatment period with later observation); Part 2 is an optional extension. Participants receive subcutaneous injections of KK8123 and have regular safety and research assessments, including blood tests for drug levels and laboratory safety, electrocardiograms (ECGs), echocardiograms, renal ultrasound, vital‑sign checks, and hormone measurements (FSH, estradiol). Pregnancy tests are done at screening and during the study for people who can become pregnant, and participants of childbearing potential are asked to use contraception per the protocol. Safety (treatment-emergent adverse events and lab changes) and pharmacokinetics are monitored for up to about 48 weeks.

How the study is structured. Open‑label, non-randomized Phase 1/2 trial with sequential dose‑escalation cohorts. Part 1 enrolls participants into sequential low, mid, high, and mid‑high dose cohorts with a planned treatment period followed by observation. Part 2 is an optional extension using a mid‑high dose. KK8123 is given by subcutaneous administration and outcomes (safety labs, PK/PD measures, imaging, and adverse events) are followed for up to 48 weeks as reported in the registry.

Questions you could ask

These questions are suggestions for a conversation with the study team or your own clinician, not advice.

  • This is an early-phase study, mainly about safety and dose. What is already known about this treatment?
  • The listed sites are in Canada, France, Germany, Spain, United States. Is any of them reachable for me, and does the study help with travel?
  • Which of the eligibility criteria would need to be checked with tests before I could join?

More on X-linked hypophosphatemia

Clinical trials5 trials listed for X-linked hypophosphatemiaEvery trial the registry lists for X-linked hypophosphatemia, with recruitment status, phase and sites, updated from ClinicalTrials.gov.See all trials →Research updatesWhat changed in X-linked hypophosphatemia researchLatest monthly update: September 2026. Includes: Burosumab outcomes. New research summarized each month in plain language, with links to every source paper.Read the latest update →

Important dates

Study start
Oct 9, 2024
Primary completion
May 21, 2029 (estimated)
Study completion
May 21, 2029 (estimated)
Target enrollment
39 participants (estimated)
Last updated on registry
Sep 21, 2026
Data verified
Oct 10, 2026

Sponsor and research team

The lead sponsor funds and oversees the trial. A pharmaceutical or biotech company sponsor typically means the study is testing that company's drug or device; a hospital, university, or government agency usually indicates investigator-initiated or publicly funded research.

Lead sponsor
Kyowa Kirin Co., Ltd.
Collaborators
  • Kyowa Kirin, Inc.

Central study contact

If you're interested in participating, the central contact can answer general questions about the study — including eligibility requirements and how to find a recruiting site near you. Actual eligibility is determined by the site's medical team.

Participating sites (10)

Terms used on this page · explanations by MedicalUpdates.ai

first-in-human
The first study in which a treatment is given to people. Safety is the main question and the number of participants is usually small.
Inclusion Criteria
The conditions a person must meet to be considered for the study, for example a confirmed diagnosis, an age range or a test result.
ICF
The process of explaining a study, including its risks and what participation involves, so that a person can decide freely whether to take part. Consent is usually documented in writing, and a participant can choose to leave the study later.
at Screening
The checks done before enrolment to see whether a person qualifies, such as tests, scans or a review of medical history.
GFR
A blood-test estimate of how well the kidneys are filtering. Lower numbers mean reduced kidney function; many studies set a minimum value.
stable regimen
A dose that has not changed for a defined period before the study starts. Studies may require this so that background treatment is relatively stable when study measurements begin.
childbearing potential
Studies often ask participants who could become pregnant, or could father a child, to use contraception during the study and for a period afterwards, because the effect of the treatment on a pregnancy is unknown.
Exclusion Criteria
The conditions that rule a person out even if they meet the inclusion criteria, for example other illnesses, certain medicines or pregnancy.
prior therapy
Treatment a person has already had for the condition. A 'line of therapy' is one course of treatment; studies often require, or limit, the number of prior lines.
washout period
A period during which a participant stops a previous treatment before starting the study treatment, so the earlier treatment does not affect the results.
investigational
A treatment that is being tested and has not been approved for this use. It may be approved for a different condition. Being studied does not mean it works or is available outside the study.
corticosteroids
Steroid medicines, such as prednisone, that reduce inflammation. Studies often require a stable dose at entry or measure whether the study treatment allows the dose to be reduced.
× ULN
The highest value of a blood test that a laboratory considers normal. Criteria such as '≤ 3 × ULN' mean the result must be no more than three times that value.
cohort
A group of people who share a characteristic, such as a diagnosis, and are studied together. 'Prospective' means they are followed forward from enrolment; 'retrospective' means existing records are reviewed.
open-label
No masking is used, so the assigned intervention is not deliberately hidden from participants or study staff.
dose-escalation
Groups of participants receive increasing doses of a treatment, one group after another, to find a dose that can be given safely.
PK
How the body absorbs, distributes, breaks down and removes a drug. It is studied by measuring drug levels or related substances at set times after a dose.
extension period
A continuation study in which participants who completed an earlier study can keep receiving the treatment, usually with everyone knowing what they are given.

The study record on this page is reproduced from ClinicalTrials.gov, a database of the U.S. National Library of Medicine, where it was submitted by the study sponsor. MedicalUpdates.ai does not own this content, is not affiliated with or endorsed by ClinicalTrials.gov, NIH, or the U.S. Government, and does not verify the record. Plain-language notes, the glossary and the questions above are added by this site; text in the boxes marked "AI summary" was written by an AI model and may contain errors. Registry records change over time. Check the original record for the current version and discuss eligibility or participation with a qualified healthcare professional.

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