Soon antibiotics may be switched on and off as readily as a light bulb, treating localized infections and potentially even cancer in the process. A team from the Karlsruhe Institute of Technology and the University of Kiev incorporated a photoswitchable molecule into an antibiotic so that its biological activity can be controlled with light of particular wavelengths. The researchers developed an amino acid analog by modifying a peptide mimetic based on a diarylethene scaffold. The diarylethenes are photoswitches: By reversible photoisomerization, the open form is turned into a closed form. An inactivated photoswitchable antibiotic was added to a bacterial field; after being partially covered with a mask, the area was exposed to light to activate the antibiotic. Courtesy of Angewandte Chemie. This amino acid analog was incorporated at several sites directly into the cyclic backbone of the annular peptide antibiotic gramicidin S. Biological activity of the resulting peptide mimetic could then be controlled within strict spatial and temporal limits with the help of UV and visible light. To demonstrate the modified antibiotic, the researchers treated a bacterial film with inactivated antibiotic and partially covered the area with a mask, then exposed it to light. As a result, the photoswitchable diarylethene was converted from a closed to an open form. Due to the structural modification induced, the entire substance molecule had a much higher antimicrobial effect. "In the future, such photoactivatable antibiotics might be used as smart therapeutic agents against local bacterial infections," said Anne S. Ulrich, director of the Institute for Biological Interfaces 2 and head of biochemistry at the Institute of Organic Chemistry at KIT. "Usual side effects can also be minimized by switching." Based on this strategy, new peptide-based agents could be developed to treat cancer, she added, as the newly developed photoactivatable building block could be applied in other peptide sequences. Switchable antibiotics could offer new options for the treatment of local infections, as they could reduce side effects. The research was published in Angewandte Chemie (doi: 10.1002/ange.201310019). For more information, visit: www.kit.edu.