Recruiting
Phase 1

PRT13722, Fulvestrant, Abemaciclib

Sponsor:

Prelude Therapeutics Incorporated

Code:

NCT07905001

Conditions

Breast Cancer

Hormone-receptor-positive Breast Cancer

HER2-negative Breast Cancer

HR-positive Breast Cancer

HR+/HER2- Breast Cancer

Eligibility Criteria

Sex: All

Age: 18+

Healthy Volunteers: Not accepted

Interventions

PRT13722

Fulvestrant

Abemaciclib

Imlunestrant

Study Details

Brief summary:

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.

Conditions

Breast Cancer

Hormone-receptor-positive Breast Cancer

HER2-negative Breast Cancer

HR-positive Breast Cancer

HR+/HER2- Breast Cancer

Study ID

NCT07905001

Start date

Nov 16, 2026

Status verified date

Oct, 2026

Completion date

Oct 31, 2029

Anticipated

Primary completion date

Oct 31, 2028

Anticipated

Eligibility Criteria

Eligibility Criteria

Sex: All

Age: 18+

Healthy Volunteers: Not accepted

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 Design

Enrollment

242 participants

Anticipated

Allocation

Non randomized

Intervention Model

Sequential

Primary purpose

Treatment

Interventions and Outcome Measures

Arms

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.

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.

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.

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.

Interventions

PRT13722

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

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).

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.

Imlunestrant

Imlunestrant is an approved oral SERD administered once daily.

Primary outcome measure

  • Dose limiting toxicity of PRT13722 (Parts 1A and 2) [ Time Frame: 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 ]
  • Preliminary Antitumor Activity: Objective Response Rate (Parts 1B and 3) [ Time Frame: Through study completion, an average of 2 years ]

Central Contacts and Locations

Central contacts

Study Contact (Please Do Not Disclose Personal Information)

See Emailclinicaltrials@preludetx.com

Locations

Taylor Cancer Research Center

Recruiting

Maumee, Ohio, United States, 43537

More Information

Sponsor

Prelude Therapeutics Incorporated

Last update posted

Nov 9, 2026

Last verified

Oct, 2026

Keywords

  • Breast Cancer
  • Hormone-receptor-positive Breast Cancer
  • HER2-negative Breast Cancer
  • HR-positive Breast Cancer
  • HR+/HER2- Breast Cancer
  • Locally Advanced Breast Cancer
  • Locally Advanced or Metastatic HR+/HER2- Breast Cancer
  • Metastatic Breast Cancer
  • PRT13722
  • Abemaciclib
  • Fulvestrant
  • Imlunestrant
  • KAT6A

Trial information was received from ClinicalTrials.gov and was last updated on 2026-11-10. This information was provided to ClinicalTrials.gov by Prelude Therapeutics Incorporated on 2026-11-09. Recruitment status is synced daily from ClinicalTrials.gov and may not reflect the sponsor's current status. Confirm during your call.