People with rheumatoid arthritis often take potent medicines that relieve their pain but have damaging side-effects. An alternative approach could see the medicines given in a form that is activated when people shine red light on their affected joints, allowing them to take lower doses.
The system has only been tested in mice, so is likely to be several years away from use, but some of the different elements have been shown to work separately in people.
In rheumatoid arthritis, the immune system attacks the joints, so it is often treated with injections of an anti-inflammatory steroid drug called dexamethasone, which dampens the immune response. But there are side-effects of long-term use, including weaker bones.
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An alternative would see people have a blood sample taken so their red blood cells could be extracted and turned into a delivery vehicle, an established experimental technique for getting drugs into the body.
In this case, the technique would be used to deliver molecules of dexamethasone joined to molecules of vitamin B12, which are then loaded on to the red blood cells by bathing them in a weak salt solution. The person would then need to have their blood cells returned to them in a transfusion.
Once in the blood, the drug-B12 compound is too large to pass through pores in the membrane of red blood cells. But if it is exposed to red light, the bond between B12 and dexamethasone is broken. By itself, dexamethasone is small enough to pass out of the red blood cells and enter the blood.
The idea is people could shine a red light on their hands, for instance, as this wavelength penetrates about 10 centimeters through flesh. “You want the drug in this place in your body, and that’s where we are giving it,” says Emilia Zywot at the University of North Carolina at Chapel Hill.
When Zywot and her colleagues tested the strategy on mice with an inflamed paw, commonly used as a model of arthritis, the red light therapy relieved their joint inflammation equally as well as injections of ordinary dexamethasone but at one third of the drug dose. The at the conference in San Diego this month.
If the same results are seen in human trials, people might need a red blood cell infusion about once a month, and then could treat their painful joints with red light at home, as needed, says Zywot.
The approach could be used with other medicines that need to be targeted at certain parts of the body, as long as the technique for binding the medicine to the B12 molecule doesn’t damage it, says Zywot. But it wouldn’t work for internal organs as the light wouldn’t penetrate far into the body. It could also be done using donor red blood cells as long as they are of the right blood group.
Robert Langer at the Massachusetts Institute of Technology in Boston says trying to develop locally targeted drugs is a growing area. “The holy grail is localising delivery with something like an antibody. But using an external force like light is fairly attractive.”
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