Heat Is on Cancer

Invisibly small engineered particles are being recruited as the newest and smallest soldiers in the war on cancer, helping scientists "cook" deadly tumors while leaving surrounding tissues cool.

Scientists at Rice University and Nanospectra Biosciences in Houston started with minuscule, seashell-shaped specks of silica -- each about 1/30 the size of a red blood cell and coated with an extremely thin layer of gold. The atomic structure of these "nanoshells" is such that they absorb infrared rays and then convert that energy into intense heat.

The team injected about 20 billion of the nanoshells into the bloodstreams of each of seven mice that had 1/8-inch tumors growing under their skin. During the next six hours, as the researchers had predicted, the nanoshells gathered preferentially in and around the tumors, because blood vessels around tumors tend to be leaky. Then the team exposed the tumors to three minutes of laser-generated infrared light, which harmlessly penetrates living tissues.

Tumor temperatures quickly shot up to 122 degrees Fahrenheit -- hot enough to fry the cancer cells. Three months later, those mice were alive and apparently cancer-free. Their counterparts in a control group, which got exposed to infrared rays without the nanoshell injections, all succumbed to their cancers in less than three weeks.

The treatment will require many further studies before proving worthy of human testing. The long-term toxicity of the particles has yet to be assessed, and it's not clear how well the approach would work on deeply buried tumors. But the strategy shows "great promise," the team concluded in the June 25 issue of the journal Cancer Letters.

-- Rick Weiss

An Old Moon Close Up

Phoebe is a craggy-faced contrarian of a moon, old and beaten up from billions of years of collisions with meteors and other celestial detritus and from moving in the wrong direction in the outer limits of Saturn's gravitational reach.

Last week, NASA scientists presented the first research results from data gathered by the spacecraft Cassini as it flew by Phoebe on its way to going into orbit around Saturn on Wednesday.

Planetary scientist Torrence Johnson, of NASA's Jet Propulsion Laboratory, said in a telephone interview that Phoebe -- only 137 miles in diameter -- is formed of ice, rock and carbon compounds.

Its composition is probably similar to the planet Pluto, Neptune's moon Triton and the comets beyond -- objects hurled into the outer reaches of the solar system during its formation about 4.5 billion years ago, Johnson said.

Phoebe most likely got left behind, captured by Saturn into an orbit in the opposite direction of most solar system objects. Most satellites, formed from the gas and dust rings that surrounded young planets, move in the same direction as their host's rotation and orbit.

"We think it happened early, because when Saturn had gas and dust, there was drag and collisions that could slow Phoebe down," Johnson said.

-- Guy Gugliotta

When Neurons Get Fired

When an animal touches something, it stimulates a chain of nerve cells running from the body surface to the spinal cord to the brain. This system is capable of recording a huge variety and intensity of sensations. Amazingly, however, it all occurs through the firing -- or lack of firing -- of these neurons.

How that firing, in electrical pulses called "action potentials," records sensory information is a mystery that neuroscientists have been slowly figuring out over 50 years. Last week, a team of researchers at the University of Maryland School of Medicine reported in the journal Science that they had taken a large step forward.

Lauren M. Jones, a graduate student working with Asaf Keller, studied neurons hard-wired into the whisker follicles of rats. In those animals, whiskers are nearly as important as eyes in perceiving their surroundings.

Certain neurons only fire when a whisker is moved in one direction but not in a different one -- a fact known for a long time. What Jones discovered is how that information is encoded in the timing of a cell's firing.

Previously, neuroscientists believed the key variable was the frequency of firing. This suggested that the brain somehow counted the number of times a cell fired for, say, a second, and then computed the average time between firings.

The Maryland researchers showed that the timing of action potentials in relationship to each other -- and not simply their overall frequency -- is also highly specific to the stimulus.

This means that when a neuron fires 50 times over two seconds in response to a whisker movement, the amount of information about the movement that a single nerve cell can pick up is much greater. Each of those 50 action potentials has a temporal relationship to the ones right before and after it that, it turns out, can carry information about the intensity of the stimulus, speed of its change and subtle changes in its direction.

-- David Brown

Six images that Cassini captured have been put together to create this mosaic of Phoebe.