A Phase 1/1b Study of PRT13722 in Participants With Advanced HR+/HER2- Breast Cancer

November 5, 2026 updated by: Prelude Therapeutics Incorporated

A Phase 1/1b, First-in-Human, Open-Label, Multicenter Study to Evaluate the Safety, Tolerability, Pharmacokinetics, Pharmacodynamics, and Antitumor Activity of PRT13722, a KAT6A Protein Degrader, as Monotherapy and in Combination With Endocrine and Targeted Therapy in Adults With Locally Advanced or Metastatic HR-Positive, HER2-Negative Breast Cancer

This first-in-human, open-label, multicenter study will evaluate the safety, tolerability, pharmacokinetics, pharmacodynamics, and preliminary antitumor activity of PRT13722, an oral KAT6A protein degrader, in adults with locally advanced or metastatic Hormone receptor-positive, human epidermal growth factor receptor 2-negative (HR+/HER2-) breast cancer. PRT13722 will be evaluated as monotherapy and in combination with fulvestrant, abemaciclib plus fulvestrant, or imlunestrant to determine recommended dose(s) for expansion (RDE) and evaluate preliminary clinical activity.

Study Overview

Status

Status

Indicates the current recruitment status or the expanded access status.
Recruiting

Conditions

Conditions

The disease, disorder, syndrome, illness, or injury that is being studied. On ClinicalTrials.gov, conditions may also include other health-related issues, such as lifespan, quality of life, and health risks.

Intervention / Treatment

Intervention / Treatment

A process or action that is the focus of a clinical study. Interventions include drugs, medical devices, procedures, vaccines, and other products that are either investigational or already available. Interventions can also include noninvasive approaches, such as education or modifying diet and exercise.

Detailed Description

This is a first-in-human, open-label, multicenter, dose-escalation and dose-expansion study of PRT13722, a selective oral KAT6A protein degrader, in adults with locally advanced or metastatic HR-positive, HER2-negative breast cancer. The study will evaluate the safety, tolerability, dose-limiting toxicities, pharmacokinetics, pharmacodynamics, and preliminary antitumor activity of PRT13722 administered as monotherapy and in combination with fulvestrant, abemaciclib plus fulvestrant, or imlunestrant to determine recommended dose(s) for expansion and evaluate preliminary clinical activity.

The study is conducted in three parts:

Part 1: Monotherapy dose escalation and backfill cohorts. Part 2: Combination dose-escalation cohorts with fulvestrant, abemaciclib plus fulvestrant, and imlunestrant.

Part 3: Combination dose-expansion cohorts to further evaluate safety and preliminary efficacy at the selected dose levels.

Up to approximately 240 participants are planned for enrollment across the three parts of the study.

Study Type

Study Type

Describes the nature of a clinical study. Study types include interventional studies (also called clinical trials), observational studies (including patient registries), and expanded access.
Interventional

Enrollment (Estimated)

Enrollment

The number of participants in a clinical study. The "anticipated" enrollment is the target number of participants that the researchers need for the study.
242

Phase

Phase

The stage of a clinical trial studying a drug or biological product, based on definitions developed by the U.S. Food and Drug Administration (FDA). The phase is based on the study's objective, the number of participants, and other characteristics. There are five phases: Early Phase 1 (formerly listed as Phase 0), Phase 1, Phase 2, Phase 3, and Phase 4. Not Applicable is used to describe trials without FDA-defined phases, including trials of devices or behavioral interventions.
  • Phase 1

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Contact

Study Contact

The name and contact information for the person who can answer enrollment questions for a clinical study. Each location where the study is being conducted may also have a specific contact, who may be better able to answer those questions.

Study Locations

  • United States
    • Ohio
      • Maumee, Ohio, United States, 43537
        • Recruiting
        • Taylor Cancer Research Center

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Eligibility Criteria

The key requirements that people who want to participate in a clinical study must meet or the characteristics they must have. Eligibility criteria consist of both inclusion criteria (which are required for a person to participate in the study) and exclusion criteria (which prevent a person from participating). Types of eligibility criteria include whether a study accepts healthy volunteers, has age or age group requirements, or is limited by sex.

Ages Eligible for Study

18 years and older (Adult, Older Adult)

Accepts Healthy Volunteers

No

Genders Eligible for Study

All

Description

Inclusion Criteria:

  • Willing and able to comply with all scheduled visits, treatment plan, laboratory tests, lifestyle considerations (including contraception requirements), and other study procedures.
  • histological or cytological diagnosis of locally advanced or metastatic HR-positive/HER2-negative breast cancer
  • Disease progression following prior standard therapy and eligible for the assigned study cohort
  • Measurable or evaluable disease per RECIST v1.1
  • Willingness to provide tumor tissue for biomarker analyses
  • Eastern Cooperative Oncology Group performance status of 0-1
  • Negative serum or urine pregnancy test and agree to use highly effective contraception or maintain true abstinence.
  • Adequate organ function and bone marrow reserves (hematology, renal, and hepatic)

Exclusion Criteria:

  • Untreated, symptomatic, or unstable brain metastases
  • Symptomatic visceral disease at risk of imminent life-threatening complications
  • Uncontrolled infection or significant concurrent medical conditions
  • Clinically significant cardiovascular disease or prolonged QT syndrome
  • Pregnancy or breastfeeding
  • Prior treatment with a KAT6-targeting agent
  • Recent anticancer therapy, radiotherapy, or major surgery
  • Use of prohibited concomitant medications, including strong CYP3A4 inhibitors or inducers, proton pump inhibitors, P-gp inhibitors or inducers, and breast cancer resistance protein inhibitors
  • Participation in another interventional clinical study
  • Any condition that would interfere with study participation or evaluation of study results

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

  • Primary Purpose: Treatment
  • Allocation: Non-Randomized
  • Interventional Model: Sequential Assignment
  • Masking: None (Open Label)

Arms and Interventions

Participant Group / Arm

Participant Group / Arm

A group or subgroup of participants in a clinical trial that receives a specific intervention/treatment, or no intervention, according to the trial's protocol.
Intervention / Treatment

Intervention / Treatment

A process or action that is the focus of a clinical study. Interventions include drugs, medical devices, procedures, vaccines, and other products that are either investigational or already available. Interventions can also include noninvasive approaches, such as education or modifying diet and exercise.
Experimental: PRT13722 Monotherapy

Participants receive PRT13722 once daily as monotherapy. This arm includes dose-escalation (Part 1A) and backfill cohorts (Part 1B) evaluating PRT13722 in participants with locally advanced or metastatic HR-positive, HER2-negative breast cancer to support the selection of RDE.
Drug: PRT13722

PRT13722 is an investigational oral drug administered once daily at the assigned dose level.
Experimental: PRT13722 + Fulvestrant

Participants receive PRT13722 once daily in combination with fulvestrant. This study includes a dose-escalation (Part 2A) in participants with locally advanced or metastatic HR-positive, HER2-negative breast cancer followed by dose-expansion (Part 3A) at the RDE.
Drug: PRT13722

PRT13722 is an investigational oral drug administered once daily at the assigned dose level.

Drug: Fulvestrant

Fulvestrant is an approved selective estrogen receptor degrader (SERD) administered on Cycle 1 Day 1, Cycle 1 Day 15, Cycle 2 Day 1, then once monthly as an intramuscular injection into the buttocks (gluteal muscle).
Experimental: PRT13722 + Abemaciclib + Fulvestrant

Participants receive PRT13722 once daily in combination with abemaciclib and fulvestrant. This study includes a dose-escalation (Part 2B) in participants with locally advanced or metastatic HR-positive, HER2-negative breast cancer followed by dose-expansion (Part 3B) at the RDE.
Drug: PRT13722

PRT13722 is an investigational oral drug administered once daily at the assigned dose level.

Drug: Fulvestrant

Fulvestrant is an approved selective estrogen receptor degrader (SERD) administered on Cycle 1 Day 1, Cycle 1 Day 15, Cycle 2 Day 1, then once monthly as an intramuscular injection into the buttocks (gluteal muscle).

Drug: Abemaciclib

Abemaciclib is an approved oral cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitor administered twice daily and used in combination with endocrine therapy for HR-positive, HER2-negative breast cancer.
Experimental: PRT13722 + Imlunestrant

Participants receive PRT13722 once daily in combination with imlunestrant. This study includes a dose-escalation (Part 2C) in participants with locally advanced or metastatic HR-positive, HER2-negative breast cancer followed by dose-expansion (Part 3C) at the RDE.
Drug: PRT13722

PRT13722 is an investigational oral drug administered once daily at the assigned dose level.

Drug: Imlunestrant

Imlunestrant is an approved oral SERD administered once daily.

What is the study measuring?

Primary Outcome Measures

Primary Outcome Measures

In a clinical study's protocol, the planned outcome measure that is the most important for evaluating the effect of an intervention/treatment. Most clinical studies have one primary outcome measure, but some have more than one.
Outcome Measure
Measure Description
Time Frame
Dose limiting toxicity of PRT13722 (Parts 1A and 2)
Time Frame: Through cycle 1 (28 days)

Incidence of dose limiting toxicities, defined according to protocol-specified criteria
Through cycle 1 (28 days)
Incidence of Treatment-Emergent Adverse Events [Safety and Tolerability] of PRT13722 as monotherapy and in combination (Parts 1A and 2)
Time Frame: Through study completion, an average of 2 years

Safety and tolerability assessed by the number of participants with treatment-emergent adverse events, serious adverse events, adverse events leading to dose modification, treatment interruption, or treatment discontinuation, and clinically significant laboratory abnormalities. Adverse events and selected laboratory abnormalities will be graded according to National Cancer Institute Common Terminology Criteria for Adverse Events (NCI CTCAE), Version 6.0
Through study completion, an average of 2 years
Preliminary Antitumor Activity: Objective Response Rate (Parts 1B and 3)
Time Frame: Through study completion, an average of 2 years

Proportion of patients with best overall response of either complete response or partial response, as assessed by the investigator per RECIST v1.1
Through study completion, an average of 2 years

Secondary Outcome Measures

Secondary Outcome Measures

In a clinical study's protocol, a planned outcome measure that is not as important as the primary outcome measure for evaluating the effect of an intervention but is still of interest. Most clinical studies have more than one secondary outcome measure.
Outcome Measure
Measure Description
Time Frame
Preliminary Antitumor Activity: Objective Response Rate (Parts 1A and 2)
Time Frame: Through study completion, an average of 2 years

Proportion of patients with best overall response of either complete response or partial response, as assessed by the investigator per RECIST v1.1
Through study completion, an average of 2 years
Duration of Response
Time Frame: Through study completion, an average of 2 years

Time from first documented response to disease progression as assessed by the investigator per RECIST v1.1, or death, whichever comes first.
Through study completion, an average of 2 years
Clinical Benefit Response
Time Frame: Through study completion, an average of 2 years

Proportion of patients with a best overall response of complete response, partial response, or durable stable disease (24 weeks or longer), as assessed by the investigator per RECIST v1.1
Through study completion, an average of 2 years
Progression-Free Survival
Time Frame: Through study completion, an average of 2 years

Time from the date of first dose of investigational product to the date of first documented disease progression, as assessed by the investigator per RECIST v1.1, or death due to any cause
Through study completion, an average of 2 years
Overall Survival
Time Frame: Through study completion, an average of 2 years

Time from the date of first dose of investigational product to death due to any cause
Through study completion, an average of 2 years
Incidence of Treatment-Emergent Adverse Events [Safety and tolerability] of PRT13722 as Monotherapy and in Combination (Parts 1B and 3)
Time Frame: Through study completion, an average of 2 years

Safety and tolerability will be evaluated by incidence of adverse events leading to dose modifications, treatment interruptions, treatment discontinuations, and clinically significant laboratory abnormalities graded according to NCI CTCAE, Version 6.0
Through study completion, an average of 2 years
Maximum Observed Plasma Concentration (Cmax)
Time Frame: Cycle 1 Day 1, Cycle 1 Day 15, and Cycle 2 Day 1 (each cycle is 28 days)

Maximum observed plasma concentration will be calculated using non-compartmental analysis
Cycle 1 Day 1, Cycle 1 Day 15, and Cycle 2 Day 1 (each cycle is 28 days)
Time To Maximum Concentration (Tmax)
Time Frame: Cycle 1 Day 1, Cycle 1 Day 15, and Cycle 2 Day 1 (each cycle is 28 days)

Time to maximum concentration will be calculated using non-compartmental analysis
Cycle 1 Day 1, Cycle 1 Day 15, and Cycle 2 Day 1 (each cycle is 28 days)
Terminal Elimination Half-life (T1/2)
Time Frame: Cycle 1 Day 1 (each cycle is 28 days)

Terminal elimination half-life will be calculated using non-compartmental analysis
Cycle 1 Day 1 (each cycle is 28 days)
Area under the plasma concentration versus time curve (AUC)
Time Frame: Cycle 1 Day 1, Cycle 1 Day 15, and Cycle 2 Day 1 (each cycle is 28 days)

Area under the plasma concentration-time curve will be calculated using non-compartmental analysis
Cycle 1 Day 1, Cycle 1 Day 15, and Cycle 2 Day 1 (each cycle is 28 days)
Steady State Trough Concentrations
Time Frame: Cycle 1 Day 15, and Cycle 2 Day 1 (each cycle is 28 days)

Steady state trough concentrations will be calculated using non-compartmental analysis
Cycle 1 Day 15, and Cycle 2 Day 1 (each cycle is 28 days)

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

Sponsor

The organization or person who initiates the study and who has authority and control over the study.
Prelude Therapeutics Incorporated

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Estimated)

Study Start

The actual date on which the first participant was enrolled in a clinical study. The "anticipated" study start date is the date that the researchers think will be the study start date.
November 16, 2026

Primary Completion (Estimated)

Primary Completion

The date on which the last participant in a clinical study was examined or received an intervention to collect final data for the primary outcome measure. Whether the clinical study ended according to the protocol or was terminated does not affect this date. For clinical studies with more than one primary outcome measure with different completion dates, this term refers to the date on which data collection is completed for all the primary outcome measures. The "anticipated" primary completion date is the date that the researchers think will be the primary completion date for the study.
October 31, 2028

Study Completion (Estimated)

Study Completion

The date on which the last participant in a clinical study was examined or received an intervention/treatment to collect final data for the primary outcome measures, secondary outcome measures, and adverse events (that is, the last participant's last visit). The "anticipated" study completion date is the date that the researchers think will be the study completion date.
October 31, 2029

Study Registration Dates

First Submitted

First Submitted

The date on which the study sponsor or investigator first submitted a study record to ClinicalTrials.gov. There is typically a delay of a few days between the first submitted date and the record's availability on ClinicalTrials.gov (the first posted date).
October 15, 2026

First Submitted That Met QC Criteria

First Submitted That Met QC Criteria

The date on which the study sponsor or investigator first submits a study record that is consistent with National Library of Medicine (NLM) quality control (QC) review criteria. The sponsor or investigator may need to revise and submit a study record one or more times before NLM's QC review criteria are met. It is the responsibility of the sponsor or investigator to ensure that the study record is consistent with the NLM QC review criteria.
October 23, 2026

First Posted (Actual)

First Posted

The date on which the study record was first available on ClinicalTrials.gov after National Library of Medicine (NLM) quality control (QC) review has concluded. There is typically a delay of a few days between the date the study sponsor or investigator submitted the study record and the first posted date.
October 29, 2026

Study Record Updates

Last Update Posted (Actual)

Last Update Posted

The most recent date on which changes to a study record were made available on ClinicalTrials.gov. There may be a delay between when the changes were submitted to ClinicalTrials.gov by the study's sponsor or investigator (the last update submitted date) and the last update posted date.
November 9, 2026

Last Update Submitted That Met QC Criteria

Last Update Submitted That Met QC Criteria

The most recent date on which the study sponsor or investigator submitted changes to a study record that are consistent with National Library of Medicine (NLM) quality control (QC) review criteria. It is the responsibility of the sponsor or investigator to ensure that the study record is consistent with the NLM QC review criteria.
November 5, 2026

Last Verified

Last Verified

The most recent date on which the study sponsor or investigator confirmed the information about a clinical study on ClinicalTrials.gov as accurate and current. If a study with a recruitment status of recruiting; not yet recruiting; or active, not recruiting has not been confirmed within the past 2 years, the study's recruitment status is shown as unknown.
October 1, 2026

More Information

Terms related to this study

Keywords

Additional Relevant MeSH Terms

Other Study ID Numbers

Other Study ID Numbers

Identifiers or ID numbers other than the NCT number that are assigned to a clinical study by the study's sponsor, funders, or others. These numbers may include unique identifiers from other trial registries and National Institutes of Health grant numbers.
  • PRT13722-01
  • 2026-527825-37-00 (Ctis)

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

Yes

Studies a U.S. FDA-regulated device product

No

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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