Drug Testers Think Small...continued
Glowing Cells
The testing system devised by Tsien also targets entire molecular pathways, but here the test unit is a single cell. "Ultimately we are trying to cure whole organisms, and the cell is the smallest unit that is genetically optimizable," says Tsien.
A company called Aurora Biosciences Corporation (La Jolla, Calif.) has licensed and patented many of Tsien’s inventions. Aurora’s aim is to test whether certain molecular pathways in the cell are on or off, by detecting whether the genes at the end of those pathways are on or off. The part of a cancer-causing gene that turns the gene on or off can be linked to any piece of DNA, so the new composite gene makes something that is easily detected. In this case that something is called beta-lactamase. Now if a drug turns off the cancer-causing pathway in the Aurora cells, it also turns off the production of beta-lactamase.
To detect beta-lactamase, Aurora uses Tsien’s inventions: custom-designed fluorescent molecules (or fluorophores). These molecules absorb high energy light waves (such as violet), and re-emit lower energy light (such as blue). The amount of blue light coming out can indicate the amount of fluorophore present.
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