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Rainbow X-Ray Vision (video)
March 13, 2003

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Interviewee: Sanford Simon, Rockefeller University.

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Produced by Ann Marie Cunningham

Copyright © ScienCentral, Inc., with additional footage courtesy Sanford Simon

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For anyone who’s diagnosed with cancer, doctors often prescribe radiation and chemotherapy. But some tumors resist these standard treatments. Right now researchers don’t know why, because it’s been very difficult to learn how cells actually work.

As this ScienCentral News video reports, one scientist has come up with a better tool for figuring out why some tumors don’t surrender to medicine’s arsenal.

Bright Lights off Broadway

At Rockefeller University in New York City, biologist Sanford Simon is studying living cells, to find out why some cells organize themselves into tumors that resist standard cancer treatments. Until recently, he says, scientists had to study cell organization by looking at cross sections of dead tissue on slides under a microscope. “It was as if you wanted to study heart beat and blood circulation, but you only looked at cadavers,” Simon recalls. “You had no sense of the heart moving or blood flowing through veins.”

Biologists tried to follow the movements and interactions inside cells by staining their components with fluorescence. But the only fluorescent stains available didn’t come in a wide range of clear colors. Even more problematic, they bleached away in less than a minute. According to Simon, it was impossible to follow how a cell worked—only to get “a very brief glimpse of a cell at work during a few seconds.”

Then, in the early 1980s, a Russian physicist who was working on miniature semiconductors saw a byproduct of his work fall to the bottom of his test tube. These were quantum dots, minute crystals made of two metals, selenium and cadmium. Each quantum dot is only about the size of an average molecule, and can emit a neon-bright color when it is struck by ultraviolet light. Depending on size, quantum dots’ colors span the entire spectrum visible in a rainbow.

Biologists immediately recognized that quantum dots offered distinct advantages for studying cell organization. Inside a cell, quantum dots give off very clear, sharp colors—for an indefinite period of time. However, “in science,” Simon points out, “it’s very easy to come up with an idea. It’s much harder to figure out how to make that idea work in practice.”

Quantum dots’ cadmium core is highly poisonous, and physicists had been using the dots in a solution of chloroform, which also can be toxic. So biologists spent the next decade working on coatings and other solutions that would allow them to fix quantum dots onto cell components, without killing off the cells they wanted to study.

Today, Simon says, he has the means to use quantum dots safely. Because they remain stable inside cells, without fading or decaying, they have accelerated his work considerably. Most recently, he has found that if he starves particular cells of their nutrients, they herd together and concentrate themselves. Their behavior under stress may provide him with clues to the reasons why some tumors resist bombardment with radiation and chemotherapy.

Simon's work was funded by the National Institutes of Health (NIH), National Science Foundation (NSF), and the American Cancer Society.

by Ann Marie Cunningham

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