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This may be of interest to Wesley because, although the focus is primarily on cancer, the flip side of the same process seems to have implications for MS. Tryptophan has also been discussed on this forum, (I'm sure somebody said Turkey is a good source):

Contact: Wolf Frommer
wfrommer@stanford.edu
650-325-1521 x208
Carnegie Institution

Scientists discover how cancer may take hold
Stanford, CA-- A team, led by researchers at the Carnegie Institution,* has found a key biochemical cycle that suppresses the immune response, thereby allowing cancer cells to multiply unabated. The research shows how the biomolecules responsible for healthy T-cells, the body’s first defenders against hostile invaders, are quashed, permitting the invading cancer to spread. The same cycle could also be involved in autoimmune diseases such as multiple sclerosis. The work is published in the September 25, 2007, issue of PLoS Biology.

The scientists used special molecular “nanosensors” for the work. “We used a technique called fluorescence resonance energy transfer, or FRET, to monitor the levels of, tryptophan, one of the essential amino acids human cells need for viability,” explained lead author Thijs Kaper. “Humans get tryptophan from foods such as grains, legumes, fruits, and meat. Tryptophan is essential for normal growth and development in children and nitrogen balance in adults. T-cells also depend on it for their immune response after invading cells have been recognized. If they don’t get enough tryptophan, the T-cells die and the invaders remain undetected.”

The scientists looked at the chemical transformations that tryptophan undergoes as it is processed in live human cancer cells. When tryptophan is broken down in the cancer cells, an enzyme (dubbed IDO) forms molecules called kynurenines. This reduces the concentration of tryptophan in the local tissues and starves T-cells for tryptophan. A key finding of the research was that a transporter protein (LAT1), present in certain types of cancer cells, exchanges tryptophan from the outside of the cell with kynurenine inside the cell, resulting in an excess of kynurenine in the body fluids, which is toxic to T-cells.

“It’s double trouble for T-cells,” remarked Wolf Frommer. “Not only do they starve from lack of tryptophan in their surroundings, but it is replaced by the toxic kynurenines, which wipes T-cells out.”

The scientists think that this cycle may be also be involved in cells involved in certain autoimmune diseases. In these cases the cells may not be able to take up or convert enough tryptophan. Without enough of the amino acid or the IDO enzyme to convert tryptophan, the cells cannot produce enough kynurenine. Lacking kynurenine, the body’s own T-cells cannot be kept in check, so they rebel and attack the body.

The FRET system detects metabolites such as sugars and amino acids using a biosensor tag. A protein is genetically fused to tags at opposite ends of a molecule. The tags are made from different colors of the jellyfish green fluorescent protein (GFP). When a metabolite binds to the biosensor, it changes the shape of the sensor’s backbone, altering the position of the fluorescent tags. When a specific wavelength of light activates one tag, it fluoresces. When the metabolite causes the tags to move close together, the other tag will also fluoresce—resonating like a tuning fork. This system allows the scientists to visually track the location and concentration of certain biochemicals.

“Our FRET technology with the novel tryptophan nanosensor has an added bonus,” said Thijs. “It can be used to identify new drugs that could reduce the ability of cancer cells to uptake tryptophan or their ability to degrade it. We believe that this technology could be a huge boost to cancer treatment.”


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Carnegie holds certain patent rights related to this discovery, as well as other related inventions in the FRET area. Interested individuals should contact Gary Kowalczyk at 202-939-1118, or gkowalczyk@ciw.edu.

Researchers on this project are Thijs Kaper, Carnegie Institution’s Department of Plant Biology; Loren Looger, formerly at Carnegie Institution’s Department of Plant Biology now at Janelia Farm; Hitomi Takanaga, Carnegie Institution’s Department of Plant Biology; Michael Platten ,University Hospital of Heidelberg; Lawrence Steinman, Stanford University; and Wolf Frommer, Carnegie Institution’s Department of Plant Biology.

www.carnegieinstitution.org

The Carnegie Institution of Washington, a private nonprofit organization, has been a pioneering force in basic scientific research since 1902. It has six research departments: the Geophysical Laboratory and the Department of Terrestrial Magnetism, both located in Washington, D.C.; The Observatories, in Pasadena, California, and Chile; the Department of Plant Biology and the Department of Global Ecology, in Stanford, California; and the Department of Embryology, in Baltimore, Maryland

Interesting post. Seems the cancer cells are grabbing up the tryptophan and starving any T cells that come into the area. It might have parallels in autoimmune diseases but with multiple sclerosis there would probably be something else going on that would bring the T cells into the area in the first place.

The article mentions FRET assays. This assay type is easy, consistent, and fairly cheap so FRET adapts easily to our robotic work where we are screening 10s of thousands of small molecules to try to find new potential drug candidates. We use variations of FRET in the cancer drug discovery projects I work on. One technique we use a lot has coumarin as the excitor fluorophore and fluorescein as the emitter fluorophore. Unfortunately, when you are testing 10s of thousands of compounds to find potential new drugs, some of them have coumarin-like or fluorescein-like structures so they can emit light on their own, self-fluorescence. So you need a secondary assay (probably more expensive) that doesn't involve fluorescence to really analyze these compounds. Some of the interesting part of my job is trying to figure out which assay type (FRET, fluorescence intensity, fluorescence polarization, etc.) will work best against a particular protein target. And then getting the assay to work well enough to use it on the robots (automated liquid handlers really but that doesn't sound as exciting as saying robots). Sometimes when I am reading about MS, I see mention of some of the target proteins we are looking at for cancer, particularly in signalling cascades from receptors to the nucleus. I keep hoping that, besides finding good drugs for cancer, there might be applications in autoimmune diseases too.

I'm off to Chicago next week with my wife who is attending a pathology conference there. It will be a vacation for me. I am going to spend the days at Starbucks or some cubby hole in the hotel writing my latest version of my autoimmune disease theory. I haven't published anything on it since 2005 and I have some new ideas to add to it. I've just needed to get away from work so I can focus and organize it into something presentable.

Wesley