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Cancer Nanotech

Cancer Nanotech

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Think small—really small. Nanotechnology employs devices with dimensions of one to 1,000 nanometers. To put this in perspective, consider the following: a nanometer is 1/80,000th the width of a human hair; it is the length of 10 hydrogen atoms placed end to end; and it is less than one third the height of a single twist on a strand of DNA. At these sizes it is no wonder that scientists have seized upon nanotechnology for myriad medical applications. After all, the human body is built upon a foundation of nature-made nanostructures—genes, proteins, cells—that may be best approached on their own scale. Cancer is the key area of medical nanotechnology research. In the not too distant future, dozens of intriguing nanodevices such as the nanotubes at left may transform cancer diagnosis, treatment, and prevention.—Lexi Krock

Nanotubes are hollow cylinders made of carbon atoms. Doctors could someday use them as miniscule syringes for injecting cells with drugs from within the body, or as nanoscale diagnostic probes the patient would never feel. They can also be filled and sealed, forming test tubes or potential drug delivery devices. Here, an array of nanotubes engage in what their creators at the Oak Ridge National Laboratory call "impalefection," the capturing of genetic materials by impaling cells (a hamster's ovary cells in this case). In the future, nanotubes could help identify DNA mutations associated with a risk of cancer.

This glowing silica nanowire is wrapped around a single strand of human hair. It looks delicate—it is about five times smaller than a virus—but it is several times stronger than spider silk. Researchers have developed coated nanowires that bind to certain proteins that can indicate the presence of prostate cancer before conventional tests can. Other potential applications for nanowires include the early sensing of breast and ovarian malignancies. Nanowires are so small that doctors could one day implant them into the body as permanent health detectives that continuously monitor molecular levels.

The honeycomb mesh behind this tiny carbon cantilever is the surface of a fly's eye. Cantilevers are beams anchored at only one end. In the nanoworld, they function as sensors ideal for detecting the presence of extremely small molecules in biological fluids. Arrays of nanocantilevers coated with antibodies, for example, will bend from the changes in surface tension when substrates that signal a malignancy bind to it. Simply by monitoring whether or not such nanocantilevers are bent, specialists may someday be able to identify the presence of cancer molecules that today are difficult to detect.

Nanoshells are hollow silica spheres covered with gold. Scientists can attach antibodies to their surfaces, enabling the shells to target certain cells such as cancer cells. In mouse tests, Naomi Halas's research team at Rice University directed infrared radiation through tissue and onto the shells, causing the gold to superheat and destroy tumor cells while leaving healthy ones intact. Technicians can control the amount of heat with the thickness of the gold and the kind of laser. Nanoshells could one day also be filled with drug-containing polymers. Heating them would cause the polymers to release a controlled amount of the drug. Human trials using gold nanoshells are slated to begin in a couple of years.

Quantum Dots
Quantum dots are miniscule semiconductor particles that can serve as signposts of certain types of cells or molecules in the body. They can do this because they emit different wavelengths of radiation depending on the type of cadmium used in their cores: cadmium sulfide for ultraviolet to blue, cadmium selenide (seen here) for most of the visible spectrum, and cadmium telluride for the far red and near-infrared. (A dot's size determines its precise color within each range.) A polymer coating enables researchers to attach molecules such as antibodies that will seek out and attach to tumors and other targeted cells. The coating also shields nearby cells from the cadmium's toxicity. The different colors of quantum dots provide a powerful tool for labeling and monitoring multiple cells and molecules simultaneously.

Nanopores have cancer research and treatment applications. Engineered into particles, they are holes that are so tiny that DNA molecules can pass through them one strand at a time, allowing for highly precise and efficient DNA sequencing. As a DNA strand moves through a nanopore, scientists can monitor each "letter" on it, deciphering coded information, including mutations associated with cancer. By engineering nanopores into the surface of a drug capsule that are only slightly larger than the medicine's molecular structure, drug manufacturers can also use nanopores to control the rate of a drug's diffusion in the body.

Gold Nanoparticles
These nanoparticles, seen in a transmission electron micrograph image, are similar in structure to nanoshells, but they have a solid core. Researchers at Northwestern University are using gold nanoparticles to develop ultrasensitive detection systems for DNA and protein markers associated with many forms of cancer, including breast and prostate cancer. The scientists can release swarms of nanoparticles linked to a host of cancer-related antibodies. The nanoparticles can hunt for hundreds of different cancer targets simultaneously. Their tests with cancer molecules in solution revealed that gold nanoparticles are up to one million times as sensitive as conventional cancer-detection approaches.

Liposomes—tiny pouches made of lipids, or fat molecules, surrounding a water core—were the first type of nanoparticles widely used for clinical cancer treatment. Several different kinds of liposomes are also widely employed against infectious diseases and can deliver certain vaccines. During cancer treatment they encapsulate drugs, shielding healthy cells from their toxicity, and prevent their concentration in vulnerable tissues such as those of a patient's kidneys and liver. Liposomes can also reduce or eliminate certain common side effects of cancer treatment such as nausea and hair loss.

These crystalline particles are a form of carbon atom whose molecular architecture is arranged in a soccer ball-like structure. Also known as buckyballs, they were discovered in 1985 among the detritus of laser-vaporized graphite. Unlike other molecules that have applications as cancer drug delivery vehicles, fullerenes don't break down in the body and are excreted intact. This trait can be important for some cancer treatment compounds that are dangerous to healthy cells. For example, fullerene drug delivery particles that contain radioactive atoms would allow for the complete removal of radiation from the body following treatment.

This fascinating particle holds significant promise for cancer treatment. Its many branches allow other molecules to easily attach to its surface. Researchers at the University of Michigan have fashioned dendrimers into sophisticated anti-cancer machines carrying five chemical tools—a molecule designed to bind to cancer cells, a second that fluoresces upon locating genetic mutations, a third to assist in imaging tumor shape using X-rays, a fourth carrying drugs released on demand, and a fifth that would send a signal when cancerous cells are finally dead. The creators of these dendrimers have had successful tests with cancer cells in culture and plan to try them in living animals soon.

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