Download Nanomedicine`s Promise Is Anything but Tiny

Nanomedicine's Promise Is Anything
but Tiny
By Rick Weiss
Washington Post Staff Writer
Monday, January 31, 2005; Page A08
It was a small wedding. Very small. But big changes are coming from the marriage of
medicine and nanotechnology, the new branch of science that deals with things a few
millionths of an inch in size.
Think "tiny medicine," and you probably think "Fantastic Voyage," the 1966 movie (and
Isaac Asimov book) about a minuscule medical crew submarining through a patient's
circulatory system. In fact, some nanomedicine experts foresee a day when invisibly
small robots will cruise through the body looking for signs of disease -- albeit without the
added attraction of a neoprene-clad Raquel Welch
"Nanobots" remain imaginary for now, but a number of other futuristic nanodevices are
already proving their potential in animal and human experiments. More than 60 drugs and
drug delivery systems based on nanotechnology, and more than 90 medical devices or
diagnostic tests, are already being tested, according to NanoBiotech News, a weekly
newsletter that tracks the field. These examples, drawn from recent scientific
publications, offer a glimpse of just how small the field of medicine is getting.
Quantum Dot Diagnostics
Quantum dots, also known as "qdots," are bits of material -- silicon, for example -- that
are so tiny they are in some cases just a few atoms across. Illuminated by ultraviolet light,
they glow very brightly with a specific hue that depends on their size: qdots with
diameters of about 2 nanometers (billionths of a meter) glow bright green, for example; 5
nanometer dots glow brilliant red.
Scientists are already using quantum dots as research tools to help them understand how
proteins, DNA and other biological molecules catch rides on the various transportation
systems inside cells. First they coat some qdots with a material that makes the dots attach
specifically to the molecule they want to track, then they inject those coated dots into
cells growing in laboratory dishes. Once the dots grab their targets, researchers simply
watch the trails of colored light to see where they go.
Qdots shine brighter and longer than conventional dyes used to illuminate the inner
workings of cells. And by coating different size qdots so each attaches to a different kind
of molecule, scientists can track the movements of many substances in a cell at once by
following the various color trails.
Now scientists are developing qdots not just for basic research but to diagnose diseases.
There are scores of proteins and other substances in the body that are early indicators of
disease but which are difficult to detect with current technologies. While qdots and other
nanomaterials have not been proved safe for use in the body, they are clearly capable of
spotting diseases in blood or tissue specimens. Qdots that bind to proteins unique to
cancer cells, for example, can literally bring tumors to light.
Nursing Neurons With Nanogels
Injured nerves do not regenerate easily, and the little healing that does occur is often
inhibited by scar tissue formation. Samuel Stupp and John Kessler at Northwestern
University in Chicago are using nanotechnology to overcome those hurdles.
They made tiny rod-like molecules called amphiphiles, each of which is capped by a
cluster of amino acids known to spur the growth of neurons and prevent scar tissue
formation. The molecules are designed to remain suspended in a few drops of liquid until
they come in contact with living cells. At that point they spontaneously arrange
themselves like spokes in a wheel, and then further assemble into spaghetti-like
nanofibers a few thousandths the thickness of a human hair. The nerve-healing amino
acids end up arranged nicely on the fibers' surface.
The nanofibers turn the liquid in which they are suspended into a therapeutic gel, which
in experiments with cultured cells spurred neuron growth and inhibited scar formation.
Moreover, rats and mice that got injections of the liquid a day after spinal cord injuries
were more likely to recover the ability to walk than untreated animals.
The team has also made self-assembling nanofibers bearing amino acids involved in bone
healing, which have speeded the recovery of rodents with severe bone injuries.
Blood Test in a Nanotube
Among the more curious creations of nanotechnology are carbon nanotubes -- hollow
tubes about 1/100,000th the diameter of a human hair, made of interwoven carbon atoms.
Because the laws of physics get strange at those scales, they display bizarre electrical and
optical properties.
Michael Strano of the University of Illinois and his colleagues are among many scientists
developing biomedical applications for nanotubes. They coated the tubes with an enzyme
that, in the presence of sugar, makes hydrogen peroxide, which in turn triggers a flow of
electrons into the tiny tubes. The electrons make the tubes glow when they are exposed to
infrared light -- a reaction unique to nanotubes.
Thousands of these nanotubes can be packed into a hair-like capsule the size of a splinter,
which can be painlessly implanted under the skin. The result: a quick and easy way to
measure blood sugar. Simply shine infrared light on the tiny implant and then measure,
with a handheld device, the intensity of the glow. Strano envisions coated nanotubes
being used as implantable biosensors to get continuous readings of a number of medically
important measures, such as cholesterol or hormone levels, without ever having to get a
drop of blood from the body.
Frying Tumors
One of the best ways to destroy a tumor is to burn it. But that is difficult to do without
frying nearby healthy tissue, especially when the tumor is deep in the body. Enter "photothermal nano-shells," little creations of Jennifer West at Rice University in Houston.
The shells are gold-coated spheres about 130 nanometers in diameter, which means about
15,000 of them could line up across the head of a pin. Metallic spheres of that size are
very good at absorbing "near infrared" light -- a variant of the kind of light emitted by
television remote controls -- that can harmlessly penetrate several inches into the body.
When West and her colleagues infused her nanoshells into the bloodstreams of mice with
cancer, the spheres traveled through the circulatory system and then concentrated around
the animals' tumors -- a fortuitous result of the fact that blood vessels tend to be leaky
near tumors. Then the team exposed the animals to the near infrared light. The
nanospheres quickly absorbed that energy and heated up to about 122 degrees Fahrenheit,
cooking the tumors but leaving surrounding tissues unharmed.
Months later, the animals were still cancer-free.
"We can easily get them even hotter than that," West said of the spheres, which later get
eliminated by the immune system.
With nearly $10 billion slated for investment in nanotech research this year,
nanomedicine is sure to get hotter as well.