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| Stephen C. Miller, PhD |
In an exciting new study, researchers at UMass Medical School have developed luciferin amides – a new class of molecules that are exclusively activated by the widely pursued drug target, fatty acid amide hydrolase (FAAH). Once activated, they become substrates for firefly luciferase, resulting in a bioluminescent glow. These imaging probes enable the highly selective and sensitive bioluminescence detection of FAAH activity in live cells and mice, and improve the ability to image in the brain. The study was published in the Journal of the American Chemical Society.
“By using the light of the firefly to make the mouse glow only when FAAH is active, we can identify inhibitors – potential drugs – simply by taking pictures of the glowing mice,” said Stephen C. Miller, PhD, associate professor of biochemistry and molecular pharmacology. “This approach represents several major advances that will be of great and immediate interest to a broad range of researchers.”
Many imaging probes work well in purified protein assays, but lack the specificity needed for use in cells or mice. Using the newly developed luciferin amides, researchers will now be able to image the activity of a single enzyme in a highly complex environment. “This is the Holy Grail for molecular sensors,” said Dr. Miller. “We are no longer confined to evaluating inhibitors in a lab assay – we can see where and when they inhibit in the living animal.”
Miller added that this approach makes it easy to detect small molecule inhibitors that can cross the blood-brain barrier. “We can literally see whether inhibitors are able to block light emission from the brain,” he said.
Finally, Miller found that luciferin amides have great promise for imaging other events in the brain. Conventional bioluminescence imaging relies on the ability of a small molecule from the firefly, known as D-luciferin, to reach the enzyme firefly luciferase. When they meet, light is produced. “But it’s hard for D-luciferin to get into the brain,” said Miller. The new luciferin amides do a much better job, even when 1,000-fold lower doses are used. “We were excited to find that luciferin amides improve brain delivery, and endogenous FAAH activity unmasks the luciferins for imaging in the brain,” said Miller.
These powerful advances were driven by molecular-level insight into how luciferase works, and the functional requirements and properties of luciferins. Firefly luciferase is closely related to enzymes that act on fatty acids, and this new approach takes advantage of the inherent fatty acid mimicry of luciferins to target FAAH. By only changing a single atom – replacing an oxygen atom with a nitrogen one – Miller and colleagues were able to create these FAAH-specific probes that work in vivo.
“The tools we have developed will aid the translation of small molecule inhibitors into live animal models, help determine the structural features that are important to cross the blood-brain barrier, and broadly and immediately enhance the power and scope of noninvasive in vivo bioluminescence imaging,” said Miller.
The work was supported by the National Institutes of Health (NIH).
Related links on UMassMedNow:
UMMS researchers show fruit flies have latent bioluminescence
