Nanomedicine's Promise Is Anything but Tiny

[Guest guest]

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. Stupp and 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.

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 " photo-thermal nano-shells, " little creations of 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.

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