A Study to Evaluate the Safety and Efficacy of JNT-517 in Participants With Phenylketonuria (PKU)

NCT ID: NCT06971731

Last Updated: 2026-01-21

Basic Information

• Recruitment Status: RECRUITING
• Clinical Phase: PHASE3
• Total Enrollment: 120 participants
• Study Classification: INTERVENTIONAL
• Study Start Date: 2025-10-20
• Study Completion Date: 2027-10-01

Brief Summary

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

Conditions

Phenylketonuria

Study Design

• Allocation Method: RANDOMIZED
• Intervention Model: PARALLEL
• Primary Study Purpose: TREATMENT
• Blinding Strategy: QUADRUPLE

Study Groups

Drug: JNT-517 - 150 mg BID (Tablet)

Group Type: EXPERIMENTAL

JNT-517 Tablet

Intervention Type: DRUG

JNT-517: 150 mg BID

Drug: JNT-517 - 75 mg BID (Tablet)

Group Type: EXPERIMENTAL

JNT-517 Tablet

Intervention Type: DRUG

JNT-517: 75 mg BID

Placebo - BID

One-third (1/3) of participants in the study will be assigned to placebo BID during Treatment Period Part 1. After 6 weeks, these participants will transition to Treatment Period Part 2 and receive JNT-517 at 150 mg BID for 46 weeks.

Group Type: PLACEBO_COMPARATOR

Placebo Tablet: BID

Intervention Type: DRUG

Placebo Tablet: BID

Interventions

JNT-517 Tablet

JNT-517: 75 mg BID

Intervention Type: DRUG

JNT-517 Tablet

JNT-517: 150 mg BID

Intervention Type: DRUG

Placebo Tablet: BID

Placebo Tablet: BID

Intervention Type: DRUG

Eligibility Criteria

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 >45 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

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 (Appendix A)

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 (Appendix A) 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 mg/dL is exclusionary-Hemoglobin <11.0 g/dL (<110.0 g/L)-White blood cell count >ULN-Platelets <150 × 109/L (<150,000/mm3)

• Minimum Eligible Age: 18 Years
• Eligible Sex: ALL
• Accepts Healthy Volunteers: No

Sponsors

Otsuka Pharmaceutical Development & Commercialization, Inc.

INDUSTRY

Sponsor Role: lead

Responsible Party

Responsibility Role: SPONSOR

Locations

University of Florida (UF) Health Shands Hospital

Gainesville, Florida, United States

Site Status: RECRUITING

Vanderbilt University Medical Center

Nashville, Tennessee, United States

Site Status: RECRUITING

University of Texas Southwestern

Dallas, Texas, United States

Site Status: RECRUITING

University of Texas Health (UTHealth) Science Center at Houston

Houston, Texas, United States

Site Status: RECRUITING

Utah Health - The University of Utah Hospital

Salt Lake City, Utah, United States

Site Status: RECRUITING

Royal Adelaide Hospital

Adelaide, , Australia

Site Status: RECRUITING

Mater Health - Mater Hospital Brisbane

South Brisbane, , Australia

Site Status: RECRUITING

Beatrix Children's Hospital

Groningen, , Netherlands

Site Status: RECRUITING

Countries

United States; Australia; Netherlands

Central Contacts

Otsuka Call Center

Role: CONTACT

otsuka-professionalservices@otsuka-us.com

844-687-8522

Facility Contacts

Roberto Zori

Role: primary

Scott Ward

Role: primary

Markey McNutt

Role: primary

Hope Northrup

Role: primary

Ashley Andrews

Role: primary

Drage Bratkovic

Role: primary

Janelle Nisbet

Role: primary

FrancJan Van Spronsen

Role: primary

Other Identifiers

JNT517-301

Identifier Type: -

Identifier Source: org_study_id