A new antibody that specifically targets cancer stem cells holds promise in treating an aggressive type of leukemia, researchers from Canada and Australia say.

The therapeutic molecule they created attacks a protein, CD123, on the surface of cancer stem cells, which sustain acute myeloid leukemia (AML).

This type of leukemia, a cancer of the white blood cells, is difficult to treat because it does not respond well to standard chemotherapy.

Earlier research has shown that cancer stem cells are resistant to chemotherapy — unlike the cancer cells that are generated by them — and since they survive such therapy, they can eventually cause a recurrence of the disease.

AML is the most common form of acute leukemia.

The antibody that targets the CD123 protein (IL-3 receptor alpha chain) on leukemia stem cells does not appear to affect normal blood cells, the researchers say in the study, published in the July 2 issue of the journal Cell Stem Cell.

CD123 is found in high levels on leukemia stem cells but not on normal blood cells.

On the basis of this experimental work, a Phase I clinical trial has been initiated to test safety and effectiveness in patients.

Leading the latest research is Dr. John Dick, senior scientist at the Ontario Cancer Institute, and associate professor Dr. Richard Lock of the Children's Cancer Institute Australia for Medical Research in Sydney.

Lock is leading the clinical trial in Australia that expands on research suggesting that antibodies targeting cancer stem cells significantly reduced the growth of human AML cells that had been transplanted into immune-deficient mice, a laboratory model that mimics the human disease, establishing the therapeutic potential of this type of therapy.