Scientists at Stanford University have developed a new laser therapy that destroys
cancer cells but leaves healthy ones unharmed. The new, non-invasive treatment
is described in a study published in the Aug. 1 online edition of the Proceedings
of the National Academy of Sciences (PNAS).
"One of the longstanding problems in medicine is
how to cure cancer without harming normal body tissue," says
Hongjie Dai, an associate professor of chemistry
at Stanford and co-author of the study. "Standard
chemotherapy destroys cancer cells and normal cells
alike. That's why patients often lose their hair
and suffer numerous other side effects. For us, the
Holy Grail would be finding a way to selectively
kill cancer cells and not damage healthy ones."
For the PNAS experiment, Dai and his colleagues
used a basic tool of nanotechnology--carbon nanotubes,
synthetic rods that are only half the width of a
DNA molecule. Thousands of nanotubes could easily
fit inside a typical cell.
"An interesting property of carbon nanotubes is
that they absorb near-infrared light waves, which
are slightly longer than visible rays of light and
pass harmlessly through our cells," Dai says. But
shine a beam of near-infrared light on a carbon nanotube,
and the results are dramatic. Electrons in the nanotube
become excited and begin releasing excess energy
in the form of heat.
In the experiment, Stanford researchers found that
if they placed a solution of carbon nanotubes under
a near-infrared laser beam, the solution would heat
up to about 158 degrees F (70 C) in two minutes.
When nanotubes were placed inside cells and radiated
by the laser beam, the cells were quickly destroyed
by the heat. However, cells without nanotubes showed
no effects when placed under near-infrared light.
"It's actually quite simple and amazing," Dai observes. "We're
using an intrinsic property of nanotubes to develop
a weapon that kills cancer."
To assure that only diseased cells were destroyed
in the experiment, the scientists had to find a way
to selectively deliver carbon nanotubes into cancer
cells and not into healthy ones. Dai and his co-workers
achieved this by performing a bit of biochemical
trickery. Unlike normal cells, the surface of a cancer
cell contains numerous receptors for a vitamin known
as folate. The researchers decided to coat the nanotubes
with folate molecules, which would only be attracted
to diseased cells with folate receptors.
The experiment worked as predicted. Most of the
folate-coated nanotubes ended up inside cancer cells,
bypassing the normal cells--like Trojan horses crossing
the enemy line. Once the nanotubes were planted inside,
the researchers shined the near-infrared laser on
the cancer cells, which soon heated up and died.
"Folate is just an experimental model that we used," Dai
says. "In reality, there are more interesting ways
we can do this. For example, we can attach an antibody
to a carbon nanotube to target a particular kind
of cancer cell."
One example is lymphoma, or cancer of the lymphatic
system. Like many cancers, lymphoma cells have well-defined
surface receptors that recognize unique antibodies.
When attached to a carbon nanotube, the antibody
would play the role of a Trojan horse. Dai and Dean
Felsher, a lymphoma researcher in the Stanford School
of Medicine, have begun a collaboration using laboratory
mice with lymphoma. The researchers want to determine
if shining near-infrared light on the animal's skin
will destroy lymphatic tumors, while leaving normal
"It's a really interesting idea," says Felsher,
an assistant professor of medicine and of pathology. "For
a long time people have thought about ways to target
cancer cells, and this is a very promising technique."
Researchers at Rice University recently conducted
a similar experiment on mice with cancerous tumors.
Instead of carbon nanotubes, the Rice team injected
the tumors with gold-coated nanoshells and exposed
the animals to near-infrared light for several minutes.
The tumors disappeared within 10 days without damaging
any healthy tissue.
Dai points out that the carbon nanotubes also can
be delivered to diseased cells by direct injection. "In
breast cancer, for example, there might come a time
when we inject nanotubes into the tumor and expose
the breast to near-infrared light," he says. This
benign therapy could potentially eliminate months
of debilitating chemotherapy and radiation treatment,
"The laser we used is a 3-centimeter beam that's
held like a flashlight," he notes. "We can take the
beam and put anywhere we want. We can shine it on
a local area of the skin or inside an internal organ
using a fiber-optic device."
Dai has applied for a patent on the procedure through
Stanford's Office of Technology Licensing (OTL).
He also has patented another technique that uses
pulses of near-infrared light to shake the DNA molecule
loose from the carbon nanotube after they've entered
the cell. The idea is to use the nanotube to deliver
therapeutic molecules of DNA, RNA or protein directly
into the cell nucleus to fight various infections
"Nanotechnology has long been known for its applications
in electronics," Dai concludes. "But this experiment
is a wonderful example of nanobiotechnology--using
the unique properties of nanomaterials to advance
biology and medicine."
Dai's graduate student, Nadine Wong Shi Kam, is
lead author of the PNAS study. Other co-authors are
Michael O'Connell, a former postdoctoral fellow in
the Department of Chemistry, and graduate student
Jeffrey A. Wisdom in the Department of Applied Physics.
The study was partly supported by the National Science
Foundation Center on Polymer Interfaces and Macromolecular
Assemblies, a research partnership among Stanford,
IBM Almaden Research Center, University of California-Davis
and University of California-Berkeley.
By Mark Shwartz
Hongjie Dai, Department of Chemistry: 650-723-4518, firstname.lastname@example.org
The study, "Carbon Nanotubes as Multifunctional
Biological Transporters and Near-Infrared Agents
for Selective Cancer Cell Destruction," will be posted
on the PNAS website ( www.pnas.org )
the week of Aug. 1. Images are available at http://newsphotos.stanford.edu (slug "nanotube").
Relevant Web URLs:
Proceedings of the
National Academy of Sciences
NCI Alliance for nanotechnology in Cancer
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