New pill could help control PKU – phase 3 trial now recruiting

NCT ID NCT06971731

Disease control Sponsor: Otsuka Pharmaceutical Development & Commercialization, Inc. Source: ClinicalTrials.gov ↗

First seen Jun 27, 2026 · Last updated Jul 09, 2026 · Updated 2 times

Summary

This study tests an experimental oral drug, JNT-517, for adults with phenylketonuria (PKU), a genetic condition that causes harmful buildup of phenylalanine (Phe). About 120 adults will receive either JNT-517 or a placebo for 6 weeks, then all will receive JNT-517 for nearly a year. The goal is to see if the drug safely lowers blood Phe levels and helps manage the disease.

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Study facts

What this study's own registry entry says, in plain language.

Phase

Phase 3

Large-scale testing in a bigger group. Usually the last step before a treatment can be approved.

Participants

About 120 people

The number the study aims to enrol. It can still change while the study runs.

Started

Oct 2025

Expected to finish

Apr 2028

An estimate. End dates often move.

Lead sponsor

A company

The lead sponsor is a pharmaceutical, biotech, or medical-device company.

Who can take part

This study's own entry requirements. Only the study team can say for certain whether you qualify.

Ages

18 years and older

Sex

Anyone

Healthy volunteers

Not accepted

This study is not open to healthy volunteers. The entry requirements below say who it is open to.

Show the full entry requirements

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: 1. Males and females ≥18 years of age on Day 1 2. Clinical diagnosis of PKU 3. Average of at least 3 plasma Phe levels (after \>4-hour fast) during Screening period of ≥360 μmol/L 4. Not on pegvaliase within 4 weeks prior to Screening 5. 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. 6. 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 7. Body weight \>40 kilograms (kg) 8. If biologically female of childbearing potential: 1. Must have a negative serum pregnancy test at Screening and a negative urine pregnancy test by Day 1 2. 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 3. 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 4. Must refrain from donating ova during the course of the study and for 30 days after the last dose of the study drug. 9. If a biologically female not of childbearing potential or postmenopausal, defined as follows: 1. Has had surgical sterilization (hysterectomy, bilateral oophorectomy, or bilateral salpingectomy) 2. Has had amenorrhea for minimum of 1 year with confirmation by levels of follicle stimulating hormone testing 3. 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 10. 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. 11. 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. 12. 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: * Exclusion Criteria Participants will be excluded from the study if any of the following criteria are met: 1. 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 2. Positive for hepatitis B or C or human immunodeficiency virus 3. 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 4. Any history of significant liver disease 5. 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 6. Any surgical or medical conditions that may affect study drug absorption, distribution, metabolism, or excretion 7. Estimated glomerular filtration rate (eGFR) \<60 mL/min/1.73 m2 by 2021 Chronic Kidney Disease Epidemiology Collaboration formula 8. 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. 9. 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 10. History of drug/alcohol abuse in the last year 11. 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 12. 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. 13. Current, recent, or suspected active viral or bacterial infection within 2 weeks prior to and during the Screening Period 14. Unable to tolerate oral medication or have a condition that would interfere with the absorption of JNT-517 15. Allergy to JNT-517 or any component of the investigational product 16. 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 \[mm\^3\]).

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Conditions

The condition(s) this trial relates to.

phenylketonuria

As listed by the trial registrant

The condition terms exactly as the trial's registrant entered them.

Phenylketonuria

How to take part

Only the study team decides who joins. These are the ways to reach them.

The places running it

26 sites in 10 countries. The list below names each one and where it is.
The official record

ClinicalTrials.gov lists the study team's own contact details, including names and phone numbers. We don't republish those.

Open the record ↗
A doctor treating you

A doctor who knows your case can contact a study site on your behalf, and can tell you whether this study is worth pursuing at all.

Contacts and locations

Locations

Ann & Robert H. Lurie Children's Hospital of Chicago
RECRUITING

Chicago, Illinois, 60611, United States
Beatrix Children's Hospital
RECRUITING

Groningen, Netherlands
Centre Hospitalier Régional Universitaire (CHRU) de Tours - Hôpital Bretonneau
RECRUITING

Tours, France
Fakultní nemocnice Královské Vinohrady
RECRUITING

Prague, Czechia
Fujita Health University
RECRUITING

Kutsukake-cho, Japan
Hospital Clinico Universitario de Santiago de Compostela
RECRUITING

Santiago de Compostela, Spain
Hospital Universitario Ramón y Cajal
RECRUITING

Madrid, Spain
M.A.G.I.C Clinic
RECRUITING

Calgary, Alberta, T2E 7H7, Canada
Mater Health - Mater Hospital Brisbane
RECRUITING

South Brisbane, 4104, Australia
Nihon University Hospital
RECRUITING

Chiyoda-ku, Japan
Oregon Health and Science University
RECRUITING

Portland, Oregon, 97239, United States
Osaka Metropolitan University Hospital
RECRUITING

Osaka, Japan
Pomorski Uniwersytet Medyczny w Szczecinie
RECRUITING

Szczecin, Poland
Royal Adelaide Hospital
RECRUITING

Adelaide, 5000, Australia
Royal Melbourne Hospital
RECRUITING

Parkville, Australia
Universitaetsmedizin der Johannes Gutenberg-Universitaet Mainz
RECRUITING

Mainz, Germany
Universitair Medisch Centra (AMC)- Amsterdam
RECRUITING

Amsterdam, Netherlands
University of California Los Angeles (UCLA) School of Medicine
RECRUITING

Los Angeles, California, 90024, United States
University of Florida (UF) Health Shands Hospital
RECRUITING

Gainesville, Florida, 32608, United States
University of Pittsburgh Medical Center (UPMC) - Children's Hospital of Pittsburgh
RECRUITING

Pittsburgh, Pennsylvania, 15201, United States
University of South Florida
RECRUITING

Tampa, Florida, 33606, United States
University of Texas Health (UTHealth) Science Center at Houston
RECRUITING

Houston, Texas, 77030-1501, United States
University of Texas Southwestern
RECRUITING

Dallas, Texas, 75390, United States
Universitätsklinikum Münster
RECRUITING

Münster, Germany
Utah Health - The University of Utah Hospital
RECRUITING

Salt Lake City, Utah, 84112, United States
Vanderbilt University Medical Center
RECRUITING

Nashville, Tennessee, 37232, United States

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