A study published Friday in the journal Cell Stem Cell reported results from the first-in-human phase 1 clinical trial of an experimental monoclonal antibody-based drug. The potential new drug is proved to have measurably inhibited chronic leukemia cancer (CLL) cells' ability to self-renew and resisted their terminal differentiation and senescence.

CLL is the most common form of blood cancer in adults, resulting in a progressive and deadly overabundance of white blood cells, called lymphocytes. "In this trial, we treated 26 patients with relapsed CLL with increasing amounts of cirmtuzumab, which we found was exceptionally well-tolerated. Patients received only a short-course of treatment and this appeared to halt disease progression, allowing most patients to forego any additional therapy for more than eight months," said Michael Choi, assistant clinical professor at the University of California (UC) San Diego School of Medicine and first author of the paper.

"This is noteworthy as the patients who enrolled in the trial had leukemia that was getting worse and causing disruption of normal blood production or other clinical problems," said Choi.

Cirmtuzumab targets a molecule called ROR1 that normally is used only by embryonic cells during early development, but which is abnormally exploited by cancer cells to promote tumor growth and metastasis. Metastasis is responsible for 90 percent of all cancer-related deaths. Because ROR1 is not used by normal adult cells, scientists believe it is a unique marker of cancer cells in general and cancer stem cells in particular. The cancer stem cells often elude or become resistant to cancer therapies, allowing treated cancers to recur, according to the researchers. ROR1 appears to drive tumor growth and disease spread and scientists think that presents an excellent novel target for anti-cancer therapy. Choi and his colleagues described the results of the clinical trial and their findings that treatment with cirmtuzumab can block the capacity of ROR1 to drive tumor growth, self-renewal and metastasis.

"The next step is to pursue a phase 2 trial with more patients that will inform us more specifically about how and how well the treatment works," said the paper's co-senior author Catriona Jamieson, deputy director of UC San Diego Moores Cancer Center.