Delivering Cytotoxic Radiation Directly to Cancer Cells

CLR 131 is a small-molecule, targeted Phospholipid Drug Conjugate™ (PDC) designed to deliver cytotoxic radiation directly and selectively to cancer cells. CLR 131 is our lead therapeutic PDC product candidate and is currently being evaluated in multiple Phase 2 and Phase 1 clinical studies.

U.S. Food and Drug Administration

An Investigational New Drug (IND) application was accepted by the U.S. Food and Drug Administration (FDA) in March 2014. In December 2014, the FDA granted orphan drug designation for CLR 131 for the treatment of multiple myeloma.

Market Opportunity

CLR 131 Targets Hematology

Multiple Myeloma

More than >59,000 patients are diagnosed with Multiple Myeloma annually, and this number is expected to nearly double by 2030.


The United States represents the largest portion of lymphoma patients, with more than 145,000 patients diagnosed annually.

CLR 131 Targets Pediatric Tumors

There are approximately 10,000 new pediatric cancer cases each year. Preclinical results of CLR 131 have shown a statistically significant increase in survival. CLR 131 has the potential to provide a new and unique therapy to roughly 50% of pediatric patients. 131I-metaiodobenzylguanidine (131I-MIBG) has been successfully utilized in pediatric radiotherapy for several decades as an off-label second line therapy in Neuroblastoma. The 131-I-MIBG data illustrate an extensive body of experience in pediatric oncology utilizing molecular radiopharmaceuticals. While CLR 131 differs from 131-I-MIBG in a variety of drug properties, the active moiety, 131-I is identical

CLR 131 Targets Head and Neck Cancer

Approximately 62,000 patients suffer from head and neck cancer each year.

In August 2016 the University of Wisconsin Carbone Cancer Center (UWCCC) was awarded a five-year Specialized Programs of Research Excellence (SPORE) grant from the National Cancer Institute to improve treatments and outcomes for head and neck cancer (HNC) patients. HNC is the sixth most common cancer in the world with approximately 56,000 new patients diagnosed every year in the United States. As a key component of this grant, the UWCCC researchers have tested CLR 131 in various animal HNC models, as well as initiating the first human clinical trial combining CLR 131 and external beam radiation in patients with recurrent HNC. The UWCCC is currently anticipated to initiate this clinical trial in 2018.

Clinical Trials

Phase 2 Study

Study Design

The Phase 2 study initiated in 2017 is intended to further define the clinical benefits of CLR 131 in multiple myeloma and other niche hematologic malignancies with high unmet clinical need. These niche hematologic malignancies include Chronic Lymphocytic Leukemia, Small Lymphocytic Lymphoma, Marginal Zone Lymphoma, Lymphoplasmacytic Lymphoma, and Diffuse Large B-Cell Lymphoma.

The study will be conducted in approximately 10-15 top cancer centers in the United States in patients with orphan-designated relapse or refractory hematologic cancers.

Study Goal

The study's primary endpoint is clinical benefit response (CBR), with additional endpoints of progression-free survival (PFS), median overall survival (mOS) and other markers of efficacy following a single 25 mCi/m2 dose of CLR 131, with the option for a second 25 mCi/m2 dose approximately 75-180 days later.

Approximately 50% of this study is covered by a $2,000,000 National Cancer Institute Fast-Track Small Business Innovation Research (SBIR) grant to further advance CLR 131.

Study Status


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Phase 1 Study

Study Design

The Phase 1 clinical study is a standard three-by-three dose escalation safety study in patients with relapse or refractory multiple myeloma. Multiple myeloma is an incurable cancer of the plasma cells and is the second most common form of hematologic cancers. This cancer type was selected for clinical, regulatory and commercial rationales, including multiple myeloma's highly radiosensitive nature, and continued unmet medical need in the relapse/refractory setting.

Study Goal

The primary goal of the Phase 1 study is to assess the compound's safety and tolerability in patients with relapsed or refractory multiple myeloma.

Study Results

The data monitoring committee determined that these results showed that a single 30-minute infusion of 31.25 mCi/m2 of CLR 131 was deemed safe and tolerated by the three patients in the cohort with one of those patients achieving a partial response (PR).

Posters & Publications

Gain a deeper understanding of our work with CLR 131 via our posters and scientific publications.

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