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CLR 131

Phase 1

Head and Neck Cancer | Small molecule | Oncology |Cellectar Biosciences, Inc.|Last Updated: Mar 18, 2026

Success Probability

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Market & Valuation

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Trial Design

UNCONTROLLEDDMCBiomarker
Total Trials1
Total Enrollment12

FDA Designations

No designations recorded

Clinical trial landscape

CLR 131 · 3 trials · 10 indications

Phase 1 3
NCT04105543CLR 131 Combined With Radiation for Head and Neck CancerHead and Neck Cancer
COMPLETED12 Analytics
NCT05610891Novel Targeted Radiotherapy in Pediatric Patients With Inoperable Relapsed or Refractory HGGHigh-Grade Glioma
ACTIVE NOT_RECRUITING50 Analytics
NCT03478462Dose Escalation Study of CLR 131 in Pediatric Relapsed/Refractory Malignant Tumors Including Neuroblastoma and SarcomasPediatric Solid Tumor
ACTIVE NOT_RECRUITING30 Analytics
PHASE1COMPLETED
CLR 131 Combined With Radiation for Head and Neck Cancer
Head and Neck CancerUnlock trial analytics
PHASE1ACTIVE NOT_RECRUITING
Novel Targeted Radiotherapy in Pediatric Patients With Inoperable Relapsed or Refractory HGG
High-Grade GliomaUnlock trial analytics
PHASE1ACTIVE NOT_RECRUITING
Dose Escalation Study of CLR 131 in Pediatric Relapsed/Refractory Malignant Tumors Including Neuroblastoma and Sarcomas
Pediatric Solid TumorUnlock trial analytics

Study Endpoints

Primary Endpoints

Incidence of Treatment Related Adverse Events
up to 18 weeks

Incidence of adverse events assessed using Common Terminology Criteria for Adverse Events (CTCAE) version 5.0. Adverse Events Grading (1 = mild, 2 = moderate, 3 = severe, 4 = life threatening, and 5 = death)

Summary of Adverse Events Possibly Related to Treatment
up to 18 weeks

Adverse Events Grading (1 = mild, 2 = moderate, 3 = severe, 4 = life threatening, and 5 = death)

Safety Evaluation of CLR 131
Assessed throughout the study to 1-year post-infusion follow-up period

Will be assessed by physical examination, performance status, vital signs, laboratory changes over time, and adverse events. Evaluations will use a nonparametric Wilcoxon Signed Rank test and a linear mixed effects modeling will be conducted to evaluate longitudinal changes.

Efficacy Evaluation for Progression Free Survival
Day 84 post-infusion follow-up period through 3 years following completion of treatment.

To determine the therapeutic activity defined as Progression Free Survival (PFS) using Kaplan Meier estimator. PFS is defined as the time from arm assignment until disease progression or death.

Number of participants with dose limiting toxicities (DLT)
up to 64 days

DLT will be assessed by physical examination, vital signs, and laboratory values

Secondary Endpoints

CLR 131 Tumor Uptake Via SPECT/CT Imaging
Up to 8 days
Median Radiation Treatment Time
up to 14 weeks
Number of Dose Delays
up to 14 weeks
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Study Design & Arms

AllocationNA
MaskingNONE
ModelSINGLE_GROUP
PurposeTREATMENT

Treatment Arms

ArmTypeDescription
CLR 131 Dose EscalationEXPERIMENTALEnrollment will start at dose level 1 (first 4 participants). Participants will receive 2 doses of CLR 131 intravenously with the first dose on day 1 followed by the second dose on day 8. Dose Level -1 (de-escalation dose, if toxicities warrant) = 12.5 mCi/m\^2 Dose Level 1 (beginning dose) = 15.6 mCi/m\^2 Dose Level 2 (escalation dose) = 18.75 mCi/m\^2 Dose escalation will proceed with no limiting toxicities at each level (maximum of 8 participants at each dose level). With maximum tolerated dose confirmed, an expansion phase will proceed.
Pediatric High-Grade Glioma PatientsEXPERIMENTALTwo dosing cohorts will be explored; patients in the first arm will receive two doses, 20 mCi/m2 each, separated by 14 days for two cycles, with a third optional cycle. Patients in the second arm will receive two doses, 10 mCi/m2 each, separated by 14 days for three cycles with a fourth optional cycle.
CLR 131EXPERIMENTALCLR 131 intravenous administration

Interventions

NameTypeDescription
CLR 131DRUGCLR 131 is a radiopharmaceutical dosed intravenously over a period of approximately 30 minutes, dose will be based on total body surface area calculated from actual body weight and height
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Eligibility Criteria

Age Range18 Years to N/A
SexALL
Healthy VolunteersNo
Study Sites2

Inclusion Criteria: * Participant must be informed of the investigational nature of the study and must be able to sign a written informed consent. * Participants with histologically or cytologically confirmed solid malignancy that has recurred in the head and neck (above the clavicles) region, e.g....

Countries:United StatesCanadaAustralia
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Frequently asked questions about CLR 131

What is CLR 131 used for?

CLR 131 is an investigational small molecule being studied for use in oncology, specifically for high-grade glioma, head and neck cancer, and pediatric solid tumors. It is currently in Phase 1 clinical trials for these indications.

How does CLR 131 work?

CLR 131 is a radiotherapeutic small molecule that delivers radiation directly to cancer cells. It is designed to target and destroy malignant cells while sparing healthy tissue, though the specific molecular target has not been disclosed.

Who is developing CLR 131?

CLR 131 is being developed by Cellectar Biosciences, Inc., a biopharmaceutical company traded on the NASDAQ under the ticker symbol CLRB. The company is conducting Phase 1 clinical trials for this investigational drug.

What phase is CLR 131 in?

CLR 131 is in Phase 1 clinical development. It is an investigational drug and has not been approved by the FDA. All ongoing and completed studies are early-stage trials focused on safety and dosing.

What clinical trials is CLR 131 in?

CLR 131 is being studied in three Phase 1 trials. NCT03478462 is a dose escalation study in pediatric patients with relapsed or refractory malignant tumors. NCT04105543 combines CLR 131 with radiation for head and neck cancer. NCT05610891 evaluates CLR 131 in pediatric patients with inoperable relapsed or refractory high-grade glioma.

Is CLR 131 being studied in pediatric patients?

Yes, CLR 131 is being studied in pediatric patients. Two of its Phase 1 trials focus on children: NCT03478462 enrolls patients aged 2 years and older with solid tumors, and NCT05610891 enrolls patients aged 10 years and older with high-grade glioma.