Safety, Tolerability, Pharmacokinetics, and Preliminary Efficacy of BTX-9341 in Advanced and/or Metastatic Breast Cancer

June 4, 2025 updated by: Biotheryx, Inc.

A First-in-Human, Open-Label, Dose Escalation and Expansion Trial of BTX-9341 in Participants With Advanced and/or Metastatic Breast Cancer

The purpose of this study is to test BTX-9341 alone or in combination with fulvestrant (a currently marketed medication for breast cancer) in participants with advanced and/or metastatic hormone receptor positive (HR+)/human epidermal growth factor receptor 2 negative (HER2-) breast cancer. The study includes a dose escalation part (Part A) where small groups of participants will receive increasing doses of BTX-9341 or BTX-9341 + fulvestrant followed by a dose expansion part (Part B) where participants will receive the dose of BTX-9341 selected in Part A + fulvestrant.

Study Overview

Status

Recruiting

Conditions

Intervention / Treatment

Detailed Description

This first-in-human (FIH), Phase 1 study of BTX-9341 is multicenter, nonrandomized, and open-label to evaluate the safety, tolerability, pharmacokinetics (PK), and preliminary efficacy of BTX-9341 in participants with advanced and/or metastatic HR+/HER2 breast cancer. The study will include a dose escalation part (Part A) followed by a dose expansion part (Part B). During Part A, BTX-9341 will initially be dose escalated alone and then in combination with fulvestrant. A single combination therapy cohort of BTX-9341 + fulvestrant will be further explored in Part B. BTX-9341 will be administered orally in 28-day treatment cycles.

Study Type

Interventional

Enrollment (Estimated)

82

Phase

  • 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 Locations

  • United States
    • Minnesota
      • Rochester, Minnesota, United States, 55905
        • Recruiting
        • Biotheryx Investigative Site
        • Contact:
          • Biotheryx Investigative Site
    • Nebraska
      • Omaha, Nebraska, United States, 68130
        • Recruiting
        • Biotheryx Investigative Site
        • Contact:
          • Biotheryx Investigative Site
    • Texas
      • Houston, Texas, United States, 77030
        • Recruiting
        • Biotheryx Investigative Site
        • Contact:
          • Biotheryx Investigative Site
      • San Antonio, Texas, United States, 78229
        • Recruiting
        • Biotheryx Investigative Site
        • Contact:
          • Biotheryx Investigative Site
    • Utah
      • West Valley City, Utah, United States, 84119
        • Recruiting
        • Biotheryx Investigative Site
        • Contact:
          • Biotheryx Investigative Site
    • Virginia
      • Fairfax, Virginia, United States, 22031
        • Recruiting
        • Biotheryx Investigative Site
        • Contact:
          • Biotheryx Investigative Site

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

Ages Eligible for Study

  • Adult
  • Older Adult

Accepts Healthy Volunteers

No

Description

Inclusion Criteria:

  • Metastatic and/or locally advanced HR+/HER2- breast cancer (dose escalation: measurable disease and/or at least 1 lytic or mixed [lytic + sclerotic] bone lesion that can be assessed by CT or MRI or non-measurable disease [including bone lesions]; dose expansion: measurable disease)
  • Dose escalation: (a) received not more than 1 chemotherapy in the metastatic/advanced setting; (b) no limit to the lines of endocrine therapy (monotherapy or combination therapy) in the metastatic setting; (c) received CDK4/6 inhibitor therapy
  • Dose expansion: (a) received not more than 1 chemotherapy in metastatic/advanced setting; (b) received not more than 2 lines of endocrine therapy (monotherapy or combination therapy) and must have been on prior endocrine therapy for at least 6 months before progression; (c) received at most 2 lines of CDK4/6 inhibitor therapy (1 in the adjuvant setting and 1 in the metastatic setting) and must have been on prior CDK4/6 inhibitor therapy for at least 6 months

  • Acceptable hematologic function

    1. ANC ≥ 1500 per mL. Note: Use of growth-factors to maintain the ANC criterion is prohibited.
    2. Platelet count ≥ 100,000 per mL. Note: Use of transfusions or thrombopoietic agents to achieve the baseline platelet count criterion is prohibited.
    3. Hemoglobin ≥ 9.0 g/dL. Note: Packed red blood cell transfusion is allowed up to 14 days prior to trial entry.

  • Acceptable liver function

    1. Bilirubin ≤ 2.0 × institutional upper limit of normal (ULN) (or < 3.0 × institutional ULN if Gilbert's disease is present)
    2. Alanine transaminase (ALT)/aspartate aminotransferase (AST) ≤ 3.0 × institutional ULN (≤ 5.0 × institutional ULN if liver metastases present)
    3. Alkaline phosphatase ≤ 2.5 × institutional ULN (≤ 5.0 × institutional ULN if bone or liver metastases present)
  • Able and willing to sign informed consent
  • Meets all study requirements in the opinion of the Investigator

Exclusion Criteria:

  • RB1 (retinoblastoma) gene mutation
  • Symptomatic visceral disease
  • Clinical evidence or history of central nervous system metastasis
  • Abnormalities in coagulation, such as bleeding diathesis, or treatment with anticoagulants precluding injections of fulvestrant or luteinizing hormone-releasing hormone (LHRH) agonist

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
Intervention / Treatment
Experimental: BTX-9341 (Part A)
BTX-9341 capsule(s) administered orally once daily (QD) in 28-day cycles
Drug: BTX-9341
Daily oral dose in 28-day cycles until maximum tolerated dose (MTD) or maximum evaluable dose (MED) determined
Drug: BTX-9341
Daily oral dose in 28-day cycles using dose determined in Part A
Experimental: BTX-9341 + fulvestrant (Part A)
BTX-9341 capsule(s) administered orally QD in 28-day cycles and fulvestrant intermuscular injections on Day 15 and then once every 28 days
Drug: BTX-9341
Daily oral dose in 28-day cycles until maximum tolerated dose (MTD) or maximum evaluable dose (MED) determined
Drug: BTX-9341
Daily oral dose in 28-day cycles using dose determined in Part A
Drug: Fulvestrant
500 mg intramuscular injections on Day 15 and then every 28 days
Other Names:
  • Faslodex
Experimental: BTX-9341 + fulvestrant (Part B)
BTX-9341 capsule(s) administered orally QD in 28-day cycles and fulvestrant intermuscular injections on Day 15 and then once every 28 days
Drug: BTX-9341
Daily oral dose in 28-day cycles until maximum tolerated dose (MTD) or maximum evaluable dose (MED) determined
Drug: BTX-9341
Daily oral dose in 28-day cycles using dose determined in Part A
Drug: Fulvestrant
500 mg intramuscular injections on Day 15 and then every 28 days
Other Names:
  • Faslodex

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Safety and Tolerability of BTX-9341
Time Frame: Up to 28 days after last dose of BTX-9341
Frequency and severity, incidence of treatment-emergent and treatment-related adverse events using NCI-CTCAE v5.0
Up to 28 days after last dose of BTX-9341
Part A: Number of Participants With Dose Limiting Toxicities (DLTs)
Time Frame: 28 days
DLT rate in Cycle 1
28 days
Part A: Determine MTD/MED of BTX-9341 in monotherapy
Time Frame: Approximately 1 year from study start
Based on CTCAE v5.0 assessment of adverse events
Approximately 1 year from study start
Part A: Determine MTD/MED of BTX-9341 in combination therapy
Time Frame: Approximately 18 months from study start
Based on CTCAE v5.0 assessment of adverse events
Approximately 18 months from study start
Part B Combination Therapy: Objective Response (OR) rate
Time Frame: Approximately 18 months from start of Part B
OR is the confirmed complete response (CR) or partial response (PR) according to Response Evaluation Criteria in Solid Tumor (RECIST) version 1.1 as determined by Investigator assessment
Approximately 18 months from start of Part B

Collaborators and Investigators

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

Sponsor

Biotheryx, Inc.

Investigators

  • Study Director: Jeremy Barton, MD, Chief Medical Officer

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 (Actual)

July 3, 2024

Primary Completion (Estimated)

September 30, 2027

Study Completion (Estimated)

December 31, 2027

Study Registration Dates

First Submitted

July 17, 2024

First Submitted That Met QC Criteria

July 17, 2024

First Posted (Actual)

July 23, 2024

Study Record Updates

Last Update Posted (Actual)

June 6, 2025

Last Update Submitted That Met QC Criteria

June 4, 2025

Last Verified

June 1, 2025

More Information

Terms related to this study

Keywords

Additional Relevant MeSH Terms

Other Study ID Numbers

  • BTX-9341-101

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

NO

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

Yes

Studies a U.S. FDA-regulated device product

No

product manufactured in and exported from the U.S.

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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