Science Concentrates DRUG DELIVERY
Getting red blood cells to carry drugs Researchers store drugs in red blood cells as vitamin B-12 conjugates and release them with light Red blood cells, the most numerous type of cell in the body, can act as light-activated drug delivery vehicles, according to a new study. The technique traps drugs in the cells, where they could circulate for the cells’ four-month lifetimes. Red or infrared light shone on a patient’s skin or through an inserted fiber optic could release the trapped
drugs when and where they are needed. In the technique, David S. Lawrence of the University of North Carolina, Chapel Hill, and coworkers first covalently attach a drug and a fluorescent molecule to cobalamin, the core structure of vitamin B-12 (Angew. Chem. Int. Ed. 2016, DOI: 10.1002/ anie.201609731). The conjugates enter red
Red blood cell
Drug Drug
N N
N
N N
N
O
Drug
Photolysis
Co N
Bloodstream
N
Co N N
O O
O N
HN
N
HN
Energy transfer
HN
HN O
O
N+
N+
Drug N
Light
N
A drug-fluorophore-cobalamin conjugate (depicted schematically here) gets trapped in a red blood cell (left). Light releases the drug, which can then exit the cell (right).
blood cells passively when the cells’ pores are expanded in a low-salt buffer. But they can’t leave when the cells are in normal buffer or in the blood. Red or near-infrared light, which can pass through tissue, excites the fluorescent group. This energy is then transferred to cobalamin’s corrin macrocycle, initiating a photolytic reaction. The reaction cleaves the drug from the complex. Because the drug is membrane permeable, it can exit the red blood cell to become biologically active in the patient’s bloodstream. Conjugates with different fluorescent groups could allow selective release of multiple drugs at different wavelengths. The technique has so far been tested only in isolated red blood cells. In a treatment situation, a doctor would obtain red blood cells from a patient, load them with drug conjugates, and then re-infuse the cells. Vladimir R. Muzykantov of the University of Pennsylvania, an expert in red blood cell-based drug delivery, comments that “drug delivery by red blood cells has been studied before in animals and is currently being tested in patients. But the level of precision and versatility of the new approach for controlled release of agents from red blood cell carriers is fascinating.” The next steps, he says, would be to test the approach in animals and the clinic. The UNC group has started to test the strategy to treat autoimmune diseases and cancer in animals. Lawrence also founded Iris Biomed, in Chapel Hill, N.C., to commercialize the technology—STU BORMAN
WATER
A new solar-powered device that takes the salt and minerals out of saltwater works at a higher efficiency than other similar devices (Proc. Nat. Acad. Sci. 2016, DOI: 10.1073/ pnas.1613031113). This type of portable, solar-based technology could be a boon for those living in remote areas without clean drinking water. Scientists are devoting much attention to the development of solar-powered desalination devices because traditional methods for removing salt from saltwater are based on reverse osmosis and use large
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amounts of energy. Typical solar-powered desalinators aren’t very efficient—often only 30 to 45% of the energy they take in from sunlight results in water vapor generation. This is in part because their solar absorbers, which heat water to evaporation, are in direct contact with the bulk saltwater, which sucks away large amounts of the heat. To mitigate this energy loss, solar desalinators often require additional heat input from external thermal sources or extra help from optical sunlight concentrators. Now, Jia Zhu, Xiuqiang Li, Weichao Xu,
and colleagues at the University of Nanjing have developed a device that employs a thermal insulator. A folded graphene oxide absorber sits on top of the polystyrene foam insulator, which in turn floats on the bulk saltwater. Water from the bulk solution gets taken up by two-dimensional channels in a cellulose film that’s wrapped around the insulator before making contact with the heated absorber. The insulator keeps heat from dissipating into the bulk water. The device has an efficiency of 80%.—ELIZABETH WILSON
ADAPTED FROM ANGEW. CHEM. INT. ED.
Solar device desalinates water efficiently
