Harvard Scientists Test Stem Cells in Fight Against Melanoma

Study Targets Cancer Stem Cells in Mice; Published in Recent Issue of Nature

Melanoma, a lethal human skin cancer, can be suppressed in mice by targeting cancer stem cells, according to a report from several Harvard authors in the Jan. 17 issue of Nature magazine.

This finding lends support to the controversial belief that therapy should focus on rooting out these cancer stem cells—single cells that can give rise to a tumor and cause remission following treatment.

Melanoma is an aggressive skin cancer that currently has no effective therapies for the late stages of its development, said Markus H. Frank ’89, an assistant professor of pediatrics and the senior author of the study.

According to the National Cancer Institute, almost 60,000 new cases were diagnosed in the United States in 2007, and there were over 8,000 deaths last year as a result of the cancer.

In the recent study, Frank and his colleagues discovered a marker for the most fertile and tenacious cells in melanoma tumors.

Cells containing a certain protein, called ABCB5, could divide limitlessly into every type of cell in the tumor.

After injecting melanoma-infected mice with antibodies that bind specifically to ABCB5, Frank and his colleagues found that tumors in eight of the 11 test subjects were gone.

In comparison, all 28 mice who were not given the antibodies developed new tumors as the cancer cells spread to other parts of their bodies.

“The significance of our study lies in understanding that, if we can identify the relatively few cells that cause melanoma virulence and target them for destruction, we would have hope for an effective treatment for this and other forms of cancer,” said co-author George F. Murphy, a professor of pathology at Harvard Medical School.

David T. Scadden, a co-director of the Harvard Stem Cell Institute who was not involved in the study, said that the results are an important step forward in cancer therapy.

“I think that this is the first evidence of being able to specifically target a cancer stem cell,” Scadden said. “The study shows that targeting them might actually matter.”

Despite the findings, there is skepticism that this therapeutic approach will work in human patients with melanoma.

“Human cells are considered foreign for the mouse, so you can get an immune response just because of this,” said Kornelia Polyak, a Medical School professor and researcher at the Dana-Farber Cancer Institute.

Polyak also said that more work needs to be done before cancer therapy can focus solely on targeting cancer stem cells.

“Most people—including myself—believe that to eliminate the tumor, one has to kill both the stem-like and the more differentiated cancer cells, but we may need to use approaches that are specific for each,” Polyak said.

For Frank and his colleagues, the next phase is to bring the research from mice to humans.

But according to Frank, even in ideal circumstances, it would still take two to three years before a drug targeting cancer stem cells could be tested on humans.

—Staff writer Kevin C. Leu can be reached at kleu@fas.harvard.edu.

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