The ROR1 pathway holds great promise in terms of generating a new wave of first-in-class, targeted cancer therapies for patients with a number of cancers, including leukemia, lymphoma, and solid tumors such as ovarian and breast cancers.

— Dr. Thomas J. Kipps, University of California San Diego —

Zilovertamab (formerly called cirmtuzumab or UC-961) is currently being evaluated in combination with ibrutinib in the Phase 2 portion of a study in patients with mantle cell lymphoma (MCL) and chronic lymphocytic leukemia (CLL). Additional investigator-initiated studies include a Phase 1b clinical trial of zilovertamab in combination with paclitaxel for the treatment of women with HER2-negative metastatic or locally advanced, unresectable breast cancer, as well as a Phase 2 clinical trial of zilovertamab in combination with venetoclax, a Bcl-2 inhibitor, in patients with relapsed/refractory CLL.

Monoclonal Antibody Targeted to ROR1

Zilovertamab is a first-in-class humanized monoclonal antibody that binds with high affinity to a biologically important epitope on ROR1 (Receptor-tyrosine kinase-like Orphan Receptor 1). ROR1 is a type 1 transmembrane protein, essential for fetal development, that is expressed on the plasma membrane with an extracellular domain that is essential for ligand binding and signal transduction. Zilovertamab binds to many different types of cancer cells, but does not recognize most normal adult tissues.

ROR1 is a Survival Factor for Many Cancers

Tumor cells that express ROR1 have tumor-initiating features that are associated with a dedifferentiated oncogenic state. When expressed by hematologic malignancies such as mantle cell lymphoma (MCL) and chronic lymphocytic leukemia (CLL), ROR1 acts as a receptor for the tumor growth factor Wnt5a. When zilovertamab binds to ROR1, it blocks Wnt5a activation, induces differentiation of the tumor cells, and inhibits tumor cell proliferation, migration and survival. Early clinical data indicates that zilovertamab synergizes with ibrutinib (marketed as IMBRUVICA® with $2,968 million in U.S. revenues in 2018) as a potential combination treatment for CLL and MCL.

Unmet Need in CLL and MCL

CLL and MCL are cancers of B-cells that can cause disabling constitutional symptoms; lymph node and/or spleen/liver enlargement, and bone marrow infiltration, causing marrow failure, immune deficiency, morbidity, and early mortality. Approximately 21,000 and 4,200 persons respectively  are diagnosed with CLL/SLL and MCL annually in the United States.  There are currently no curative therapies. Patients with CLL or MCL generally require successive rounds of therapy and often develop refractory disease.

Ibrutinib (IMBRUVICA®) is an orally administered inhibitor of Bruton’s tyrosine kinase, that has become a standard of care in the modern treatment of CLL and MCL. However, most patients with CLL achieve only a partial response with ibrutinib, which then must be administered continuously, resulting in a greater potential for side effects, an enhanced health care burden for patients, and substantial therapeutic costs. The proportion of patients with CLL who achieve a complete response to ibrutinib after 12 months of therapy is below 10%. In previously treated patients with MCL, rates of complete response range from 12.5% to 23%, even with long-term, continuous therapy. Resistance to ibrutinib eventually develops in many patients with CLL and the great majority of patients with MCL. An agent that increases the complete response rate of CLL and MCL to ibrutinib is urgently needed.

Collaboration with University of California San Diego and CIRM

Zilovertamab was developed at the University of California in San Diego based on the pioneering scientific research of Thomas Kipps, MD, Ph.D., and his colleagues at the Moores Cancer Center. Oncternal holds an exclusive worldwide license to develop and commercialize antibodies recognizing ROR1. The development of zilovertamab has been supported by the California Institute for Regenerative Medicine (CIRM), in recognition of the role of ROR1 conferring stem cell-like properties to the cancer cells that express it.

We are enrolling patients:

  • With relapsed/refractory mantle cell lymphoma (MCL) for a Phase 1b/2 study of zilovertamab in combination with ibrutinib
  • With chronic lymphocytic leukemia (CLL) for a Phase 2 clinical study of zilovertamab in combination with venetoclax, a Bcl-2 inhibitor 
  • With Ewing sarcoma for a Phase 1 study of ONCT-216, our small-molecule inhibitor of ETS-family transcription factor oncoproteins, in combination with vincristine
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