PhenylketonuriaPhase 3NCT06971731
A Study of JNT-517 in Participants With Phenylketonuria (PKU)
A Phase 3 study testing JNT-517 in people with Phenylketonuria, run by Otsuka Pharmaceutical Development & Commercialization, Inc. at 26 sites in 10 countries.
Trial summary
This Phase 3 study will evaluate the safety, effectiveness, tolerability, and how the body processes JNT-517 in children, adolescents, and adults with phenylketonuria. Participants will be randomly assigned to receive either JNT-517 or placebo during an initial 6-week treatment period. Read more about this study
- Who is it for?
- Ages 4 years and older
- Conditions the study is for
- Phenylketonuria
- What is being tested?
- JNT-517
- Type of treatment
- Pill or oral medicine
- Could I receive a placebo?
- Yes, some participants may receive a placebo
- How many people
- 120 participants
- Where
- 26 sitesin 10 countries
- Study dates
- 20 Oct 2025to 1 Apr 2028
- Phase
- Phase 3
Key requirements
Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.
- Ages 4 years and older
- All sexes
- No healthy volunteers
- Child, Adult, Older adult
Who may be able to join
- Male or female participants aged 4 years or older.
- Diagnosed with phenylketonuria.
- Have phenylalanine levels that meet study requirements.
- Meet study-specific requirements regarding current treatment for phenylketonuria.
- Willing and able to follow study dietary requirements.
- Weigh at least 12.5 kilograms.
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- If able to become pregnant or father a child, willing to follow the study's contraception requirements.
- Any ongoing mental health condition must be stable before entering the study.
- Able to provide informed consent (or have consent provided by a parent or legal guardian, when applicable) and comply with study procedures.
Who cannot join
- Participants will be excluded from the study if any of the following criteria are met:
- Significant medical condition that, in the investigator's opinion, could make participation unsafe or interfere with study participation.
- Significant liver disease or impaired kidney function.
- Certain eye conditions, including significant cataracts.
- Active infection requiring medical evaluation.
- History of certain cancers within the past 5 years.
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- Allergy or hypersensitivity to JNT-517 or its ingredients.
- Prior treatment with JNT-517.
- Recent participation in another investigational study or receipt of an investigational treatment that does not meet study requirements.
- Use of medications that are not permitted during the study.
- Abnormal laboratory or heart test results that would make study participation inappropriate.
- Conditions that could affect the absorption of oral study medication.
- History of recent substance or alcohol abuse.
- Unwillingness to follow study requirements, including restrictions on intentional weight loss.
Trial locations and contacts
26 sites in 10 countries. Contact the study team or a site near you to ask about taking part.
26 sites in 10 countries
United States10 sites, 10 recruiting
- Recruiting
Ann & Robert H. Lurie Children's Hospital of Chicago
Chicago, Illinois, 60611
Otsuka Call Center, 844-687-8522, Otsuka-ProfessionalServices@otsuka-us.com
Erika Vucko
- Recruiting
University of Texas Southwestern
Dallas, Texas, 75390
Otsuka Call Center, 844-687-8522, Otsuka-ProfessionalServices@otsuka-us.com
Markey McNutt
- Recruiting
University of Florida (UF) Health Shands Hospital
Gainesville, Florida, 32608
Otsuka Call Center, 844-687-8522, Otsuka-ProfessionalServices@otsuka-us.com
Roberto Zori
- Recruiting
University of Texas Health (UTHealth) Science Center at Houston
Houston, Texas, 77030-1501
Otsuka Call Center, 844-687-8522, Otsuka-ProfessionalServices@otsuka-us.com
Hope Northrup
- Recruiting
University of California Los Angeles (UCLA) School of Medicine
Los Angeles, California, 90024
Otsuka Call Center, 844-687-8522, Otsuka-ProfessionalServices@otsuka-us.com
Nicola Longo
- Recruiting
Vanderbilt University Medical Center
Nashville, Tennessee, 37232
Otsuka Call Center, 844-687-8522, Otsuka-ProfessionalServices@otsuka-us.com
Scott Ward
- Recruiting
University of Pittsburgh Medical Center (UPMC) - Children's Hospital of Pittsburgh
Pittsburgh, Pennsylvania, 15201
Otsuka Call Center, 844-687-8522, Otsuka-ProfessionalServices@otsuka-us.com
Gerard Vockley
- Recruiting
Oregon Health and Science University
Portland, Oregon, 97239
Otsuka Call Center, 844-687-8522, Otsuka-ProfessionalServices@otsuka-us.com
Cary Harding
- Recruiting
Utah Health - The University of Utah Hospital
Salt Lake City, Utah, 84112
Otsuka Call Center, 844-687-8522, Otsuka-ProfessionalServices@otsuka-us.com
Ashley Andrews
- Recruiting
University of South Florida
Tampa, Florida, 33606
Otsuka Call Center, 844-687-8522, Otsuka-ProfessionalServices@otsuka-us.com
Amarilis Sanchez-Valle
Australia3 sites, 3 recruiting
- Recruiting
Royal Adelaide Hospital
Adelaide, 5000
Otsuka Call Center, 844-687-8522, Otsuka-ProfessionalServices@otsuka-us.com
Drage Bratkovic
- Recruiting
Royal Melbourne Hospital
Parkville
Otsuka Call Center, 844-687-8522, Otsuka-ProfessionalServices@otsuka-us.com
Timothy Parkville
- Recruiting
Mater Health - Mater Hospital Brisbane
South Brisbane, 4104
Otsuka Call Center, 844-687-8522, Otsuka-ProfessionalServices@otsuka-us.com
Janelle Nisbet
Japan3 sites, 3 recruiting
- Recruiting
Nihon University Hospital
Chiyoda-ku
Otsuka Call Center, 844-687-8522, Otsuka-ProfessionalServices@otsuka-us.com
Mika Ishige
- Recruiting
Osaka Metropolitan University Hospital
Osaka
Otsuka Call Center, 844-687-8522, Otsuka-ProfessionalServices@otsuka-us.com
Takashi Hamazaki
- Recruiting
Fujita Health University
Toyoake
Otsuka Call Center, 844-687-8522, Otsuka-ProfessionalServices@otsuka-us.com
Yoko Nakajima
Germany2 sites, 2 recruiting
- Recruiting
Universitaetsmedizin der Johannes Gutenberg-Universitaet Mainz
Mainz
Otsuka Call Center, 844-687-8522, Otsuka-ProfessionalServices@otsuka-us.com
Julia Hennermann
- Recruiting
Universitätsklinikum Münster
Münster
Otsuka Call Center, 844-687-8522, Otsuka-ProfessionalServices@otsuka-us.com
Frank Rutsch
Netherlands2 sites, 2 recruiting
- Recruiting
Universitair Medisch Centra (AMC)- Amsterdam
Amsterdam
Otsuka Call Center, 844-687-8522, Otsuka-ProfessionalServices@otsuka-us.com
Mirjam Langeveld
- Recruiting
Beatrix Children's Hospital
Groningen
Otsuka Call Center, 844-687-8522, Otsuka-ProfessionalServices@otsuka-us.com
FrancJan Van Spronsen
Spain2 sites, 2 recruiting
- Recruiting
Hospital Universitario Ramón y Cajal
Madrid
Otsuka Call Center, 844-687-8522, Otsuka-ProfessionalServices@otsuka-us.com
Amaya Bélanger-Quintana
- Recruiting
Hospital Clinico Universitario de Santiago de Compostela
Santiago de Compostela
Otsuka Call Center, 844-687-8522, Otsuka-ProfessionalServices@otsuka-us.com
Alvaro Hermida
Canada1 site, 1 recruiting
- Recruiting
M.A.G.I.C Clinic
Calgary, Alberta, T2E 7H7
Otsuka Call Center, 844-687-8522, Otsuka-ProfessionalServices@otsuka-us.com
Aneal Khan
Czechia1 site, 1 recruiting
- Recruiting
Fakultní nemocnice Královské Vinohrady
Prague
Otsuka Call Center, 844-687-8522, Otsuka-ProfessionalServices@otsuka-us.com
Renáta Tyčová
France1 site, 1 recruiting
- Recruiting
Centre Hospitalier Régional Universitaire (CHRU) de Tours - Hôpital Bretonneau
Tours
Otsuka Call Center, 844-687-8522, Otsuka-ProfessionalServices@otsuka-us.com
Francois Maillot
Poland1 site, 1 recruiting
- Recruiting
Pomorski Uniwersytet Medyczny w Szczecinie
Szczecin
Otsuka Call Center, 844-687-8522, Otsuka-ProfessionalServices@otsuka-us.com
Maria Gizewska
About this study
Official title: 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
This Phase 3 study will evaluate the safety, effectiveness, tolerability, and how the body processes JNT-517 in children, adolescents, and adults with phenylketonuria.
Participants will be randomly assigned to receive either JNT-517 or placebo during an initial 6-week treatment period. After this period, eligible participants will receive JNT-517 for an additional 46 weeks.
- Conditions
- Phenylketonuria
- Being tested
- JNT-517, JNT-517 Matching Placebo
- Keywords
- Phenylketonuria, PKU
- Medical subject headings
- Phenylketonurias
What participants receive
What participants receive. In a randomised study each person is assigned to one group by chance.
JNT-517Drug
JNT-517 orally
JNT-517 Matching PlaceboDrug
JNT-517 matching placebo orally
| Study group | Role | What they receive |
|---|---|---|
| JNT-517 - High Dose | Experimental | Participants will receive JNT-517 orally, twice daily (BID), with dosing determined by age, for 6 weeks in Period 1, followed by JNT-517 orally, BID for 46 weeks in Period 2. Receives: Drug: JNT-517 |
| JNT-517 - Low Dose | Experimental | Participants will receive JNT-517 orally, BID, with dosing determined by age, for 6 weeks in Period 1, followed by JNT-517 orally for 46 weeks in Period 2. Receives: Drug: JNT-517 |
| Placebo | Placebo comparator | Participants will receive JNT-517 matching placebo orally, BID for 6 weeks in Period 1, followed by JNT-517 orally, BID for 46 weeks in Period 2. Receives: Drug: JNT-517 Matching Placebo |
What is being measured
The primary outcome is the main question the study is designed to answer.
Absolute Change in Plasma Phenylalanine (Phe) From Baseline to the Mean of Weeks 2, 4, and 6 in the JNT-517 High Dose BID Dose Group at End of Period 1
Measured: Baseline to End of Period 1 (Week 6)
Secondary outcomes (28)
Percent Change in Plasma Phe From Baseline to the Mean of Weeks 2, 4, and 6 in the JNT-517 High Dose BID Group at End of Period 1
Measured: Baseline to End of Period 1 (Week 6)
Percentage of Participants Achieving Plasma Phe Less Than (<) 600 Micromoles per Liter (µmol/L) at End of Period 1 Among Participants With Baseline ≥600 µmol/L in the High Dose BID Group
Measured: Baseline to End of Period 1 (Week 6)
Percentage of Participants Achieving Plasma Phe <360 µmol/L at End of Period 1 in the High Dose BID Group
Measured: Baseline to End of Period 1 (Week 6)
Percentage of Participants Achieving Plasma Phe <600 µmol/L at End of Period 1 Among Participants With Baseline ≥600 µmol/L in the Low Dose BID Group
Measured: Baseline to End of Period 1 (Week 6)
Percentage of Participants Achieving Plasma Phe <360 µmol/L at End of Period 1 in the Low Dose BID Group
Measured: Baseline to End of Period 1 (Week 6)
Absolute Change in Plasma Phe From Baseline to the Mean of Weeks 2, 4, and 6 in the JNT-517 Low Dose BID Group at End of Period 1
Measured: Baseline to End of Period 1 (Week 6)
Percent Change in Plasma Phe From Baseline to the Mean of Weeks 2, 4, and 6 in the JNT-517 Low Dose BID Group at End of Period 1
Measured: Baseline to End of Period 1 (Week 6)
Change From Baseline in ADHD Rating Scale-5 (ADHD-RS-5) Inattentive Subscore in Participants With Baseline Inattentive Subscore More Than (>) 9 in the JNT-517 High Dose BID Group at End of Period 1
The ADHD-RS-5 Inattentive Subscore (sum of 9 inattentive items) ranges from 0 to 27, with higher scores indicating greater severity of inattentive symptoms. A decrease in the subscore represents an improvement in symptoms.
Measured: Baseline to End of Period 1 (Week 6)
Change From Baseline in Dietary Phe Intake While Achieving Plasma Phe <360 µmol/L at the End of Period 2 in Participants Receiving High Dose BID Group and Participating in the Diet Normalization
Measured: Baseline to end of Period 2 (Week 52)
Number of Participants With Treatment-Emergent Adverse Events and Serious Treatment-Emergent Adverse Events in Periods 1 and 2
Measured: From first dose of the study drug through Week 56
Percentage of Participants With More Than or Equal to (≥) 30 Percent (%) and ≥50% Reduction From Baseline in Plasma Phe at Week 6
Measured: Baseline to End of Period 1 (Week 6)
Percentage of Participants Achieving Plasma Phe Less Than (<) 120 µmol/L at End of Period 1 in the High Dose BID and Low Dose BID Groups
Measured: End of Period 1 (Week 6)
Absolute Change in Plasma Phe From Baseline to Weeks 2, 4, and 6 of Period 1 in the JNT-517 High Dose BID and Low Dose BID Groups
Measured: Baseline to End of Period 1 (Week 6)
Percent Change in Plasma Phe From Baseline to Weeks 2, 4, and 6 of Period 1 in the JNT-517 High Dose BID and Low Dose BID Groups
Measured: Baseline to End of Period 1 (Week 6)
Percentage of Participants Achieving Plasma Phe <600 µmol/L Among Participants With Baseline ≥600 µmol/L in the JNT-517 High Dose BID and Low Dose BID Dose Groups at the End of Period 2
Measured: Baseline to End of Period 2 (Week 52)
Percentage of Participants Achieving Plasma Phe <360 µmol/L in the JNT-517 High Dose BID and Low Dose BID Dose Groups at the End of Period 2
Measured: End of Period 2 (Week 52)
Percentage of Participants Achieving Plasma Phe <120 µmol/L in the JNT-517 High Dose BID and Low Dose BID Dose Groups at the End of Period 2
Measured: End of Period 2 (Week 52)
Absolute Change From Baseline in Plasma Phe in the JNT-517 Low Dose BID and High Dose BID Dose Groups During Period 2
Measured: Baseline to End of Period 2 (Week 52)
Percent Change From Baseline in Plasma Phe in the JNT-517 Low Dose BID and High Dose BID Dose Groups During Period 2
Measured: Baseline to End of Period 2 (Week 52)
Percentage of Participants With ≥30% and ≥50% Reduction From Baseline in Plasma Phe During Period 2
Measured: Baseline to End of Period 2 (Week 52)
Change From Baseline in Cambridge Neuropsychological Test Automated Battery (CANTAB) Stop Signal Reaction Time at End of Period 1
The CANTAB Stop Signal Task measures response inhibition. Stop Signal Reaction Time (SSRT) reflects the time required to inhibit a response, with longer times indicating poorer inhibitory control. A decrease from baseline indicates improvement.
Measured: Baseline to End of Period 1 (Week 6)
Change From Baseline in ADHD-RS-5 Inattentive Subscore in Participants With Baseline Inattentive Subscore > 9 in the JNT-517 Low Dose BID Group at End of Period 1
The ADHD-RS-5 Inattentive Subscore (sum of 9 inattentive items) ranges from 0 to 27, with higher scores indicating greater severity of inattentive symptoms. A decrease in the subscore represents an improvement in symptoms.
Measured: Baseline to End of Period 1 (Week 6)
Change From Baseline in CANTAB Stop Signal Reaction Time During Period 2
The CANTAB Stop Signal Task measures response inhibition. SSRT reflects the time required to inhibit a response, with longer times indicating poorer inhibitory control. A decrease from baseline indicates improvement.
Measured: Baseline to End of Period 2 (Week 52)
Change From Baseline in ADHD Rating Scale-5 (ADHD-RS-5) Inattentive Subscore in Participants with Baseline Inattentive Subscore >9 in the JNT-517 High Dose BID and Low Dose BID Dose Groups During Period 2
The ADHD Rating Scale-5 (ADHD-RS-5) Inattentive Subscore (sum of 9 inattentive items) ranges from 0 to 27, with higher scores indicating greater severity of inattentive symptoms. A decrease in the subscore represents an improvement in symptoms.
Measured: Baseline to End of Period 2 (Week 52)
Change From Baseline in Adult Self-rating Scale (ASRS) for Attention Deficit Hyperactivity Disorder in Participants Aged ≥12 years at Screening in Both JNT 517 Dose Groups During Periods 1 and 2
The ASRS has 18 questions covering two dimensions: attention deficits and hyperactive/impulsive behavior. Responses are rated on frequency using options like 'never,' 'rarely,' 'sometimes,' 'often,' or 'very frequently.' Each item scores from 0 (no problem) to 4 (most severe). The total ASRS score is the sum of all item scores ranging from 0 to 72, and higher scores indicate a high likelihood of ADHD.
Measured: From first dose of the study drug through Week 56
Change From Baseline in Dietary Protein Intake While Maintaining Plasma Phe <360 µmol/L
Measured: Baseline to End of Period 2 (Week 52)
Percentage of Participants Achieving Recommended Dietary Allowance (RDA) for Natural Intact Protein Intake While Maintaining Plasma Phenylalanine <360 µmol/L
Measured: End of Period 2 (Week 52)
Percentage of Participants Achieving Two Times the RDA for Natural Intact Protein Intake Consistent With an Unrestricted Diet While Maintaining Plasma Phenylalanine <360 µmol/L
Measured: End of Period 2 (Week 52)
Timeline
From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.
- First posted14 May 2025
- Study start20 Oct 2025
- Primary completion1 Mar 2028 (estimated)
- Study completion1 Apr 2028 (estimated)
Resources
- Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
- Other trials for PhenylketonuriaStudies of the same condition, open and under way.
- More trials run by Otsuka Pharmaceutical Development & Commercialization, Inc.The sponsor's other registered studies.
- What the trial phases meanHow a treatment moves from first tests in people to approval.
More details
For doctors and researchers: how the study is designed, who runs it, and its registry IDs.
Study design
- Study type
- Interventional
- Phase
- Phase 3
- Primary purpose
- Treatment
- Allocation
- Randomised
- Intervention model
- Parallel groups
- Masking
- Quadruple blind
- Who is masked
- Participant, Care provider, Investigator, Outcomes assessor
- Enrolment
- 120 participants (estimated)
Sponsor and investigators
- Sponsor type
- Industry (pharma, biotech, devices)
- Responsible party
- Sponsor
IDs, dates and publications
- ClinicalTrials.gov ID
- NCT06971731
- Sponsor's protocol ID
- JNT517-301
- Other IDs
- 2024-519554-37-00, 1011258
- Status last verified
- Oct 2026
- First submitted
- 7 May 2025
- Last updated
- 21 Oct 2026
- Results posted
- No
- Data monitoring committee
- No
- FDA-regulated drug
- Yes
- FDA-regulated device
- No
- Individual data sharing
- Yes: Anonymized Individual participant data (IPD) that underlie the results of this study will be shared with researchers to achieve aims pre-specified in a methodologically sound research proposal. Small studies with less than 25 participants are excluded from data sharing.