For more than two decades, researchers have tried to develop a
light-activated cancer therapy that could replace standard chemotherapy,
which is effective but causes serious negative side effects. Despite
those efforts, they've struggled to come up with a light-activated
approach that would target only cancer cells.
Now scientists at the National Cancer Institute
have developed a possible solution that involves pairing
cancer-specific antibodies with a heat-sensitive fluorescent dye. The
dye is nontoxic on its own, but when it comes into contact with
near-infrared light, it heats up and essentially burns a small hole in
the cell membrane it has attached to, killing the cell.
Light touch: Researchers treated the tumor on the right-hand side
of this mouse’s body with a light-activated therapy. The top image is
before treatment; the bottom is after.
To target the tumor cells, the researchers used antibodies that bind
to proteins that are overexpressed in cancer cells. "Normal cells may
have a hundred copies of these antibodies, but cancer cells have
millions of copies. That's a big difference," says Hisataka Kobayashi, a molecular imaging researcher at the National Cancer Institute and the lead author of the new study, published this week in Nature Medicine. The result is that only cancer cells are vulnerable to the light-activated cascade.
The researchers tested the new treatment in mice and found that it reduced tumor growth and prolonged survival.
There are a few kinks to work out before the system can be adapted
for humans, though. For instance, the researchers couldn't test the
treatment's effect on large tumors, since killing off too many cells at
once caused cardiovascular problems in the mice. Finding the right
cancer-cell markers to pair with the dye may also prove difficult. For
example, HER-2, one of the proteins targeted in the study, is only
expressed in 40 percent of breast-cancer cells in humans.
Still, the lack of toxicity associated with the treatment is a huge advantage, says Karen Brewer,
a chemist at Virginia Tech who also works on light-activated cancer
therapies. "What's interesting about this study is that they're applying
a traditional method of targeting cancer cells to a light-activated
treatment," she says. "This is really where the field is headed."
The dye used in the study offers another bonus because it lights
up—allowing clinicians to track the treatment's progress with
fluorescence imaging. In the mice, the fluorescence visibly declined in
tumor cells a day after administration of the near-infrared light.
Kobayashi suspects the approach could also prove valuable as a secondary
therapy by helping surgeons label cancer cells that may remain after a
tumor has been excised. "It could help clean up the tumor cells that are
harder for surgeons to get to," he says.
By Erica Westly
From Technology Review
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