Phase 1 Study of CLR 125 in Triple Negative Breast Cancer

A Phase 1b, Open-Label Parallel Study Evaluating CLR 125 in Patients With Relapsed or Refractory Triple Negative Breast Cancer

The goal of this clinical trial is to evaluate the safety and efficacy of 3 different dose levels of CLR 125 in patients with advanced triple negative breast cancer. The main questions the study aims to answer are:

• What dose and regimen should be used in future trials of CLR 125 in patients with advanced triple negative breast cancer.
• What side effects do participants have when taking CLR 125.

Participants will:

• Have CLR 125 administered via infusion 4 times each cycle; repeated every 8 weeks.
• Visit the clinic once every 3 weeks for checkups and testing.
• Report any side effects or new medications.

Some participants may also receive one dose of CLR 131 to evaluate the amount of radiation delivered to various organs and to the tumor. These participants will:

• Have 4 scans completed over 2 weeks
• Have blood drawn 6 times over 2 weeks.

Study Overview

• Status: Recruiting
• Conditions: Breast Cancer
• Intervention / Treatment: Drug: Iopofosine I 131; Drug: CLR 125

Detailed Description

This study is designed to determine the recommended dose and regimen for future trials and to evaluate the safety and tolerability of CLR 125 at the selected doses in patients with advanced triple negative breast cancer. It will also determine the antitumor activity (treatment response by RECIST v1.1) through assessment of overall response rate, progression free survival, overall survival, duration of response and duration of clinical benefit of CLR 125 in patients with advanced triple negative breast cancer.

Total body, organ, and tumor dosimetry will be assessed in a select number of patients prior to CLR 125 dosing. At the conclusion of the study, total body, organ, and tumor dosimetry will be calculated for the intended patient population, to inform future studies.

Up to 60 evaluable patients will be enrolled.

• Study Type: Interventional
• Enrollment (Estimated): 60
• Phase: Phase 1

Contacts and Locations

• Study Contact: Name: Kate Oliver; Phone Number: 608-441-8120; Email: clinical@cellectar.com

Study Locations

• United States
  • Florida
    • Jacksonville, Florida, United States, 32224
      • Recruiting
      • Mayo Clinic Florida
      • Principal Investigator: Pooja Advani, MD
      • Contact: Clinical Trials Referral Office; Phone Number: 855-776-0015; Email: CancerTrials@mayo.edu
  • Maryland
    • Glen Burnie, Maryland, United States, 21061
      • Recruiting
      • United Theranostics
      • Principal Investigator: Babak Saboury, MD
      • Contact: Amanda Huggins; Phone Number: 667-HOPENOW; Email: clinicaltrial@unithera.com
  • Minnesota
    • Rochester, Minnesota, United States, 55905
      • Recruiting
      • Mayo Clinic Rochester
      • Principal Investigator: Karthik Giridhar, MD
      • Contact: Clinical Trials Referral Office; Phone Number: 855-776-0015; Email: CancerTrials@mayo.edu
  • New Jersey
    • Princeton, New Jersey, United States, 08540
      • Recruiting
      • United Theranostics
      • Contact: Amanda Huggins; Phone Number: 667-HOPENOW; Email: clinicaltrial@unithera.com
      • Principal Investigator: Munir Ghesani, MD

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: No

Description

Inclusion Criteria:

• Unequivocal TNBC histology [ER and PR less than 10% each and HER-2 negative].

• Patients that have progressed after at least one prior standard therapeutic regimen given alone or in combination (including, but not limited, to: chemotherapy, immunotherapy, sacituzumab govitecan-hziy, trastuzumab deruxtecan).

  • Patients who have received neo-adjuvant or adjuvant therapy must be at least one year from that treatment regimen.
• Patient is ≥ 18 years of age.
• ECOG performance status of 0 to 2.
• Life expectancy ≥ 6 months.

• Patient must meet the following laboratory criteria:

  • Platelets ≥ 75,000/uL [75 x 10^9/L]
  • White blood cell (WBC) count ≥ 3000/uL
  • Absolute neutrophil count ≥ 1500/uL
  • Hemoglobin ≥ 9 g/dL
  • Estimated glomerular filtration rate ≥ 30 mL/min/1.73 m2 (as reported by the local lab)
  • Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) ≤ 2.5 × upper limit of normal (ULN)
  • Bilirubin < 1.5 × ULN
• At least one measurable lesion, as defined by RECIST v1.1, with longest diameter at baseline ≥ 10 mm (excluding lymph nodes, for which the short diameter must be ≥ 15 mm).
• Patients with known brain metastases must have completed any radiotherapy or systemic treatments for brain metastases prior to enrollment; by investigator assessment be considered stable with no new signs or symptoms for at least 1 month, and on a stable dose of steroids (unchanged for three weeks prior to registration or on a steroid tapering regimen).
• Patients must express willingness and ability to comply with scheduled study visits, treatment plans, laboratory tests, and other study procedures.
• Patient or their legally authorized representative must have the ability to understand and provide signed informed written consent before the initiation of any study-related procedures.
• Female patients of childbearing potential must have a negative pregnancy test within 24 hours of dosing.
• Women of childbearing potential must agree to use a highly effective method of contraception during the study and for 12 months following administration of the study drug. Highly effective methods of contraception include combined (estrogen and progestogen containing) hormonal contraceptives associated with inhibition of ovulation, progestogen-only hormonal contraception associated with inhibition of ovulation, intrauterine device, intrauterine hormone-releasing system, vasectomized partner, or sexual abstinence. Women who have undergone hysterectomy, bilateral oophorectomy, or bilateral tubal ligation, or are post-menopausal (no menses for 12 months without an alternative medical cause) are considered to be of non-childbearing potential.
• Men who are able to father a child must agree to use a condom during the study and for 12 months following administration of the study drug.

Exclusion Criteria:

• Antitumor systemic therapy or investigational therapy, within three-half-lives of the agent preceding study drug administration. NOTE: Patients participating in non-interventional clinical trials (i.e., non-drug) are allowed to participate in this trial.

  • Focal radiation (including palliative radiation) to non-target lesions should be completed at least 2 weeks prior to dosing.
  • For patients receiving CLR 125 after participation in the dosimetry phase, CLR 131 washout is not required prior to dosing with CLR 125.
• Prior targeted radiotherapy.

• Prior external beam radiation therapy resulting in greater than 20% of total bone marrow receiving greater than 20 Gy. For estimation purposes, the following bone marrow percentages can be used:

  • Vertebral bodies: Cervical 0.5%, thoracic 1%, lumbar 2% per vertebral body
  • Hemipelvis (ilium, acetabulum, ischium): 13% per side
  • Sacrum: 10%
  • Skull: 12%
  • Scapula: 5% per side
  • Ribs: 4% per side
  • Femur: 3% per side
• Ongoing Grade 2 or greater toxicities due to previous therapies, excluding alopecia, that in the opinion of investigator might be exacerbated by study treatment.
• Patients with prior or concurrent malignancy other than TNBC with the following exceptions, which must be fully treated with no evidence of disease for at least 2 years: non-melanoma skin cancers only requiring topical treatment or surgical excision; melanoma in situ; treated cervical carcinoma in situ; successfully treated prostate cancer.
• Any other concomitant serious illness or organ system dysfunction (including cardiac and pulmonary dysfunction) that in the opinion of the Investigator would either compromise patient safety or interfere with the evaluation of the safety of the test drug.
• Known history of human immunodeficiency virus or uncontrolled, serious, active infection.
• Pregnancy or breast-feeding

Study Plan

How is the study designed?

Design Details

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

Number of Arms

4

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Other: Dosimetry Phase; Iopofosine I 131 (CLR 131) will be administered at 10 mCi on day 1 for approximately 15 patients for imaging purposes.	Drug: Iopofosine I 131; Investigational radiopharmaceutical product intended for IV administration.; Other Names: CLR 131
Experimental: Treatment Phase: CLR 125 Arm 1; CLR 125 administered at 65 mCi/m2 fractionated over four doses (day 1, 2, 8, and 9) in each 8-week cycle; patient will receive up to 4 cycles.	Drug: CLR 125; Investigational radiopharmaceutical product intended for IV administration.
Experimental: Treatment Phase: CLR 125 Arm 2; CLR 125 will be administered at 125 mCi/m2 fractionated over four doses (day 1, 2, 8, and 9) in each 8-week cycle; patient will receive up to 3 cycles.	Drug: CLR 125; Investigational radiopharmaceutical product intended for IV administration.
Experimental: Treatment Phase: CLR 125 Arm 3; CLR 125 will be administered at 190 mCi/m2 fractionated over four doses (day 1, 2, 8, and 9) in each 8-week cycle; patient will receive up to 2 cycles.	Drug: CLR 125; Investigational radiopharmaceutical product intended for IV administration.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Dose Determination for CLR 125	Identify the recommended Phase 2 dose and regimen of CLR 125 in advanced TNBC patients	57 days after initiation of last cycle (each cycle is 57 days)
Number of adverse events related to study treatment (CLR 125)	Adverse Events are graded per NCI CTCAE v5.0	Assessed throughout the study through 1 year following completion of treatment.

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Efficacy Evaluation for Overall Response Rate	To determine the overall response (ORR) rate as assessed by RECIST v1.1.	57 days after initiation of last cycle (each cycle is 57 days)
Efficacy Evaluation for Progression Free Survival	To determine the therapeutic activity defined as Progression Free Survival (PFS) using Kaplan Meier estimator.	Assessed throughout the study through 1 year following completion of treatment
Efficacy Evaluation for Overall Survival	To determine the therapeutic activity defined as Overall Survival (OS) using Kaplan Meier estimator.	Assessed throughout the study through 1 year following completion of treatment
Evaluation for Duration of Response	To determine the therapeutic activity defined as Duration of Response (DOR) using Kaplan Meier estimator.	Assessed throughout the study through 1 year following completion of treatment
Efficacy Evaluation for Duration of Clinical Benefit	To determine the therapeutic activity defined as Duration of Clinical Benefit (DOCB) using Kaplan Meier estimator.	Assessed throughout the study through 1 year following completion of treatment.

Other Outcome Measures

Outcome Measure	Measure Description	Time Frame
Dosimetry Evaluation for Total Body and Normal Organs	To determine total body and organ radiation dosimetry, together, of iopofosine I 131 (CLR 131) in advanced TNBC patients	1 hour post-infusion and concluding 11 days post-initial imaging
Tumor Dosimetry Evaluation of iopofosine I 131 (CLR 131)	Determine the tumor dosimetry of iopofosine I 131 (CLR 131) in advanced TNBC patients.	1 hour post-infusion and concluding 11 days post-initial imaging

Collaborators and Investigators

• Sponsor: Cellectar Biosciences, Inc.
• Investigators: Study Director: Jarrod Longcor, Cellectar Biosciences

Study record dates

Study Major Dates

• Study Start (Actual): December 5, 2025
• Primary Completion (Estimated): February 1, 2028
• Study Completion (Estimated): July 1, 2029

Study Registration Dates

• First Submitted: November 13, 2025
• First Submitted That Met QC Criteria: December 16, 2025
• First Posted (Actual): December 31, 2025

Study Record Updates

• Last Update Posted (Actual): June 3, 2026
• Last Update Submitted That Met QC Criteria: June 1, 2026
• Last Verified: December 1, 2025

More Information

Terms related to this study

• Keywords: triple negative breast cancer
• Additional Relevant MeSH Terms: Neoplasms by Site; Neoplasms; Skin Diseases; Breast Diseases; Skin and Connective Tissue Diseases; Breast Neoplasms; Triple Negative Breast Neoplasms; CLR1404
• Other Study ID Numbers: DCL-25-003

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