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

NCT06515470 | Recruiting Phase 1 DMC FDA Drug

• 1 other identifier: BTX-9341-101
• Study Type: interventional
• Target: 82
• Locations: 1 country
• Sites: 6

Brief Summary

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.

Conditions

Breast Cancer

Keywords

HR+/HER2-

Outcome Measures

Primary Outcomes (5)

• Safety and Tolerability 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)

  DLT rate in Cycle 1

  28 days

• Part A: Determine MTD/MED of BTX-9341 in monotherapy

  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

  Based on CTCAE v5.0 assessment of adverse events

  Approximately 18 months from study start

• Part B Combination Therapy: Objective Response (OR) rate

  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

Study Arms (3)

BTX-9341 (Part A)

EXPERIMENTAL

BTX-9341 capsule(s) administered orally once daily (QD) in 28-day cycles

Drug: BTX-9341

BTX-9341 + fulvestrant (Part A)

EXPERIMENTAL

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; Drug: Fulvestrant

BTX-9341 + fulvestrant (Part B)

EXPERIMENTAL

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: Fulvestrant; Drug: BTX-9341

Interventions

BTX-9341 DRUG

Daily oral dose in 28-day cycles until maximum tolerated dose (MTD) or maximum evaluable dose (MED) determined

BTX-9341 (Part A); BTX-9341 + fulvestrant (Part A)

Fulvestrant DRUG

500 mg intramuscular injections on Day 15 and then every 28 days

Also known as: Faslodex

BTX-9341 + fulvestrant (Part A); BTX-9341 + fulvestrant (Part B)

Eligibility Criteria

• Age: 18 Years+
• Sex: all
• Healthy Volunteers: No
• Age Groups: Adult (18-64), Older Adult (65+)

You may qualify if:

• 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
• ANC ≥ 1500 per mL. Note: Use of growth-factors to maintain the ANC criterion is prohibited.
• Platelet count ≥ 100,000 per mL. Note: Use of transfusions or thrombopoietic agents to achieve the baseline platelet count criterion is prohibited.
• Hemoglobin ≥ 9.0 g/dL. Note: Packed red blood cell transfusion is allowed up to 14 days prior to trial entry.
• Acceptable liver function
• Bilirubin ≤ 2.0 × institutional upper limit of normal (ULN) (or \< 3.0 × institutional ULN if Gilbert's disease is present)
• Alanine transaminase (ALT)/aspartate aminotransferase (AST) ≤ 3.0 × institutional ULN (≤ 5.0 × institutional ULN if liver metastases present)
• 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

You may not qualify if:

• 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

Sponsors & Collaborators

• Biotheryx, Inc.: lead

Study Sites (6)

Biotheryx Investigative Site

Rochester, Minnesota, 55905, United States

RECRUITING

Biotheryx Investigative Site

Omaha, Nebraska, 68130, United States

RECRUITING

Biotheryx Investigative Site

Houston, Texas, 77030, United States

RECRUITING

Biotheryx Investigative Site

San Antonio, Texas, 78229, United States

RECRUITING

Biotheryx Investigative Site

West Valley City, Utah, 84119, United States

RECRUITING

Biotheryx Investigative Site

Fairfax, Virginia, 22031, United States

RECRUITING

MeSH Terms

Conditions

Breast Neoplasms

Interventions

Fulvestrant

Condition Hierarchy (Ancestors)

Neoplasms by Site; Neoplasms; Breast Diseases; Skin Diseases; Skin and Connective Tissue Diseases

Intervention Hierarchy (Ancestors)

Estradiol; Estrenes; Estranes; Steroids; Fused-Ring Compounds; Polycyclic Compounds; Estradiol Congeners; Gonadal Steroid Hormones; Gonadal Hormones; Hormones; Hormones, Hormone Substitutes, and Hormone Antagonists

Study Officials

• Jeremy Barton, MD

  Chief Medical Officer

  STUDY DIRECTOR

Central Study Contacts

Danette Powell

CONTACT

858-354-1814; c-dpowell@biotheryx.com

Study Design

• Study Type: interventional
• Phase: phase 1
• Allocation: NON RANDOMIZED
• Masking: NONE
• Purpose: TREATMENT
• Intervention Model: SEQUENTIAL
• Sponsor Type: INDUSTRY
• Responsible Party: SPONSOR

Study Record Dates

• First Submitted: July 17, 2024
• First Posted: July 23, 2024
• Study Start: July 3, 2024
• Primary Completion (Estimated): September 30, 2027
• Study Completion (Estimated): December 31, 2027
• Last Updated: June 6, 2025

Record last verified: 2025-06

Data Sharing

• IPD Sharing: Will not share

Locations

US (6)