Protein-Protein Interaction Activates and Fuels Leukemia Cell Growth

Building upon previous research, scientists at University of California, San Diego School of Medicine and UC San Diego Moores Cancer report that a protein called Wnt5a acts on a pair of tumor-surface proteins, called ROR1 and ROR2, to accelerate the proliferation and spread of chronic lymphocytic leukemia (CLL) cells, the most common form of blood cancer in adults.

They note, however, that these effects of Wnt5a were blocked by a humanized monoclonal antibody specific for ROR1, called cirmtuzumab (or UC-961), which inhibited the growth and spread of CLL cells in both cell lines and mouse models of leukemia. 

Although the findings are made with leukemia cells, researchers said the study has implications for patients with other cancers, including solid-tissue tumors. ROR1 and ROR2 are considered “orphan receptors,” which are expressed primarily during embryonic development. The expression of these proteins, particularly ROR1, becomes suppressed during fetal development and is negligible on normal adult tissues. However, CLL and many solid tissue cancers re-express these orphan receptors.

“Our findings show that ROR1 and ROR2 team up to stimulate tumor cell growth and metastasis in response to Wnt5a, which appears over-expressed in patients with CLL and can act as a survival/growth factor for leukemia cells. By blocking the capacity of Wnt5a to stimulate tumor cells, cirmtuzumab can inhibit the growth and spread of cancer cells,” said senior author Thomas J. Kipps, MD, PhD, Evelyn and Edwin Tasch Chair in Cancer Research and deputy director for research at Moores Cancer Center.

“We now have better insight into how cirmtuzumab works against leukemia cells. This should help find better ways to treat patients who have other cancers with cirmtuzumab, which currently is being evaluated in a phase I clinical trial for patients with CLL.”