ClinicalTrials.gov record NCT06971731

A Study of JNT-517 in Participants With Phenylketonuria (PKU)

Record copied from ClinicalTrials.gov: Oct 10, 2026AI summaries generated: Sep 6, 2026

A Phase 3, Double-Blind, Randomized, Two-Period, Multicenter, Placebo-Controlled, Efficacy and Safety Study of JNT-517 for the Treatment of Participants With Phenylketonuria

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 3A later-stage study, usually with more participants, designed to give stronger evidence about how well a treatment works and how safe it is. It often compares the treatment with standard care or a placebo, and results may support an application for approval.
Age18 years old and older
SexAll
LocationAustralia, Canada, Czechia, France, Germany, Japan, Netherlands, Poland, 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 Phase 3, randomized, masked study tests oral JNT-517 in adults (18+) with PKU. The first part is a roughly 6-week blinded comparison of JNT-517 versus placebo (about a 2-in-3 chance to receive JNT-517). In the second part, continuing participants receive one of two doses of JNT-517 for about 46 weeks; total participation can be up to ~400 days including screening.

What it is studying. The study is testing the safety, tolerability, pharmacokinetics (how the drug is processed in the body), and the effect of oral JNT-517 on blood phenylalanine (Phe) levels and related outcomes in adults with PKU. It compares JNT-517 to placebo during an initial 6-week period, then studies longer-term use of two JNT-517 doses over about 46 weeks.

What the researchers hope to learn. To evaluate whether oral JNT-517 affects plasma phenylalanine levels, to assess safety and tolerability, to measure pharmacokinetics, and to collect data on neurocognitive measures and dietary protein outcomes related to PKU treatment.

What this study is about

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

The goal of this Phase 3, randomized study is to assess the safety, efficacy, tolerability, and pharmacokinetics (PK) of oral JNT-517 in adults (18 years of age or older) with PKU. Participants will receive either JNT-517 or placebo and will be blinded to their treatment assignment. Participants will have a 2 in 3 (or approximately 67%) chance of receiving JNT-517 during the first part of the study which will last approximately six weeks. During the second part of the study every participant who continues in the study will receive one of two doses of JNT-517 for an additional 46 weeks. The study requires a screening period of up to 35 days to ensure dietary stabilization and amino acid levels required to meet study eligibility. In total, participation in the study could last for up to 400 days. Participants will: Take 75 mg JNT-517 or 150 mg JNT-517, or a placebo BID (2x per day) for approximately 365 days; Visit the clinic or have a mobile health nurse visit your home for checkups and tests; Collect urine sample at home and bring to clinic on specified days; Keep a food diary 3 days before each study visit

Interventions being studied

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

Drug
  • JNT-517 Tablet
  • Placebo Tablet: BID

Eligibility

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

Inclusion criteria

  • Males and females ≥18 years of age on Day 1
  • Clinical diagnosis of PKU
  • Average of at least 3 plasma Phe levels (after >4-hour fast) during Screening period of ≥360 μmol/L
  • Not on pegvaliase within 4 weeks prior to Screening
  • If on sapropterin or large neutral amino acids, such as PheBloc®, NeoPhe®, and PreKunil® at Screening, must be on a stable dose 4 weeks prior to Screening and for the entire study duration.
  • Willing and able to maintain a stable diet in Phe and total protein (intact protein and medical food protein) and able to adjust diet through the duration of the study according to the Dietary Management Guidelines
  • Body weight >40 kilograms (kg)
  • If biologically female of childbearing potential:
  • Must have a negative serum pregnancy test at Screening and a negative urine pregnancy test by Day 1
  • Must practice sexual abstinence, or if involved in any sexual intercourse that could lead to pregnancy, must agree to use 2 highly effective contraceptive methods from Screening until at least 30 days after the last study drug administration
  • If taking estrogen- or progesterone-based oral contraceptives, must agree to use 2 other highly effective methods of contraception or must agree to sexual abstinence during the study
  • Must refrain from donating ova during the course of the study and for 30 days after the last dose of the study drug.
  • If a biologically female not of childbearing potential or postmenopausal, defined as follows:
  • Has had surgical sterilization (hysterectomy, bilateral oophorectomy, or bilateral salpingectomy)
  • Has had amenorrhea for minimum of 1 year with confirmation by levels of follicle stimulating hormone testing
  • Has not achieved menarche (has not had first menstrual period). If a female achieves menarche during the study, she will need to follow the contraception requirement for females of childbearing potential
  • If biologically male, must practice sexual abstinence, or if involved in any sexual intercourse that could lead to pregnancy, must agree to use highly effective contraceptive methods from Day 1 until at least 30 days after the last study drug administration and must refrain from donating sperm during the course of the study and for 30 days after the last dose of the study drug NOTE: No restrictions are required for biological males who have undergone a documented vasectomy at least 4 months prior to Screening. If the vasectomy procedure is not documented or was performed less than 4 months prior to Screening, males must follow the same contraception as for non-vasectomized participants.
  • Participants with psychiatric illness must be well-controlled for the last 6 months prior to the Screening visit and if on medication, on stable medications for the last 3 months.
  • Capable of giving signed informed consent or parent/legal guardian to provide informed consent and the participant to give assent and confirm able to comply with study procedures

Exclusion criteria

  • Participants will be excluded from the study if any of the following criteria are met:
  • Any acute or uncontrolled chronic medical condition that would prevent the participant from complying with the procedures or place the participant at risk if they participate in the study
  • Positive for hepatitis B or C or human immunodeficiency virus
  • Any history of malignancy of any organ system (other than non-melanoma skin cancer or in situ cervical cancer), treated or untreated, within the past 5 years, regardless of whether there is evidence of local recurrence or metastases
  • Any history of significant liver disease
  • Any history of cataracts or more than minimal cataracts observed during the Screening ophthalmologic examination. Minimal cataracts are defined as changes similar to lens opacities classification system III (LOCS III), lens grade C1, N1 or P1
  • Any surgical or medical conditions that may affect study drug absorption, distribution, metabolism, or excretion
  • Estimated glomerular filtration rate (eGFR) <60 mL/min/1.73 m2 by 2021 Chronic Kidney Disease Epidemiology Collaboration formula
  • Participation in another investigational drug trial within 30 days or, if known, 5 half-lives of the investigational drug (whichever is longer). For gene therapy or editing trials, participants must have received the intervention >6 months prior to Screening visit and with stable plasma Phe in the past 2 months prior to Screening visit.
  • Alcohol consumption within 5 days of randomization and/or unwilling to limit to 1 alcoholic drink per day until after the 6-month study visit
  • History of drug/alcohol abuse in the last year
  • Use of any medications that are inhibitors or inducers of cytochrome P450 (CYP3A4) or inhibitors of the transporter P-glycoprotein (P-gp) within 4 weeks prior to randomization and unwilling and/or unable to avoid these medications throughout the treatment duration
  • Use of any medications that are substrates of breast cancer resistance protein (BCRP), multidrug and toxin extrusion (MATE)1, or MATE2-K within 4 weeks prior to randomization and unwilling and/or unable to avoid these medications throughout the treatment duration NOTE: Participants will be permitted to continue with estrogen- or progesterone-based oral contraceptives, but must agree to use 2 other methods of contraception, where at least 1 must be highly effective, or must agree to sexual abstinence during the study.
  • Current, recent, or suspected active viral or bacterial infection within 2 weeks prior to and during the Screening Period
  • Unable to tolerate oral medication or have a condition that would interfere with the absorption of JNT-517
  • Allergy to JNT-517 or any component of the investigational product
  • Any of the following laboratory values at the Screening visit: -Alanine aminotransferase or aspartate aminotransferase values >1.5× the upper limit of normal (ULN)-Total bilirubin ˃ULN unless history of Gilbert Syndrome and then total bilirubin >4 milligrams per deciliter (mg/dL) is exclusionary-Hemoglobin <11.0 grams per deciliter (g/dL) [<110.0 grams per liter (g/L)]-White blood cell count >ULN-Platelets <150 × 10\^9/Liter (L) (<150,000/cubic millimeters [mm\^3]).

Study description and what participation involves

The registry record has no detailed description beyond the summary above.

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 up to a 35-day screening (including fasting blood tests to confirm Phe levels and diet stabilization), participants will be randomized and take an oral tablet twice daily for about 365 days (one of two doses of JNT-517 or placebo during the first ~6 weeks; thereafter continuing participants receive one of two JNT-517 doses for ~46 weeks). Visits include clinic checkups (or visits by a mobile health nurse), regular blood draws to measure plasma Phe and safety labs, home urine collection on specified days, and keeping a 3-day food diary before study visits. Pregnancy tests and contraceptive requirements apply, and participants must limit alcohol and avoid certain medications during treatment as specified by the study. Total participation could last up to about 400 days.

How the study is structured. Interventional, randomized, parallel-group study with masking (quadruple-masked). Part 1: a ~6-week, blinded comparison of JNT-517 (two dose levels) versus placebo; participants are assigned randomly (about two-thirds chance to receive active drug in Part 1). Part 2: a longer treatment period (~46 weeks) in which participants receive one of two doses of JNT-517. Dosing is twice daily (BID); placebo is used only in the first period per the registry record.

Questions you could ask

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

  • Some participants receive a placebo. How is that decided, and what happens for placebo-group participants when the study ends?
  • The listed sites are in Australia, Canada, Czechia, France, Germany, Japan, Netherlands, Poland, 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 phenylketonuria

Clinical trials38 trials listed for phenylketonuriaEvery trial the registry lists for phenylketonuria, with recruitment status, phase and sites, updated from ClinicalTrials.gov.See all trials →Research updatesWhat changed in phenylketonuria researchLatest monthly update: September 2026. Includes: Diet supply gaps. New research summarized each month in plain language, with links to every source paper.Read the latest update →

Important dates

Study start
Oct 20, 2025
Primary completion
Mar 1, 2028 (estimated)
Study completion
Apr 1, 2028 (estimated)
Target enrollment
120 participants (estimated)
Last updated on registry
Jul 8, 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
Otsuka Pharmaceutical Development & Commercialization, 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 (26)

Terms used on this page · explanations by MedicalUpdates.ai

randomized
Participants are assigned to the study groups by chance, like a coin toss, rather than chosen by the doctor or the participant. This is done so the groups are comparable.
pharmacokinetics
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.
placebo
A treatment that looks like the study treatment but contains no active ingredient. Some participants receive it instead of the study treatment, usually without knowing which they got.
blinded
Who does not know which intervention a participant is receiving. It can apply to participants, the people giving the treatment, those assessing results, or those analysing the data.
screening period
The checks done before enrolment to see whether a person qualifies, such as tests, scans or a review of medical history.
stable dose
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.
study drug
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.
informed consent
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.
legal guardian
A person who is legally allowed to make decisions, including consent to research, on behalf of someone who cannot consent for themselves.
assent
A child's or dependent adult's agreement to take part, given alongside the formal consent of a parent or legal representative.
Estimated glomerular filtration rate
A blood-test estimate of how well the kidneys are filtering. Lower numbers mean reduced kidney function; many studies set a minimum value.
5 half-lives
The time it takes for the amount of a drug in the body to fall by half. 'Five half-lives' is often used as the point at which a previous drug has essentially left the body.
upper limit of normal
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.
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.
Exclusion Criteria
The conditions that rule a person out even if they meet the inclusion criteria, for example other illnesses, certain medicines or pregnancy.

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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