In recent decades, researchers have increasingly sought to develop bioinspired drug delivery carriers or nanoparticles that can bring medicines directly to problematic cells in the human body, such as tumors and inflamed tissues. But the approaches thus far have had prominent drawbacks, such as a complicated synthesis process, lack of control, and an inability to "hide" from the immune system and filtering organs.

An international team of researchers from Texas and Italy have now developed biomimetic proteolipid (consisting of proteins and lipids) vesicles that can not only pass by the immune system undetected, but also target inflamed tissues to deliver anti-inflammatory drugs. Described recently in Nature Materials , these drug-loaded "leukosomes" were able to reduce both systemic and local inflammation significantly better than the standard drug treatments available to date.

"With this technology, we can reduce the complexity of biology and incorporate it into a manmade technology that has highly controllable parameters," says study lead author Ennio Tasciotti, a molecular biologist with the Houston Methodist Research Institute. "These particles use the cells' own machinery to overcome the biological barrier."

Initially, Tasciotti explains, researchers developed bioinspired nanoparticle delivery systems from a bottom-up process, which involves creating larger structures out of small building blocks. Though this approach allows researchers to tightly control the properties of their final product, it requires a lengthy and troublesome synthesis to incorporate multiple biological components, which are necessary to reproduce the complex cellular membrane and better bypass the immune system.

To try to get around this, scientists began developing drug-delivery systems using top-down approaches. "We use cells and simplify the structure of the cell or use part of the cell itself to create a nanoparticle or drug-delivery system," Tasciotti explains. This approach, however, does not allow the scientists to really control the physical characteristics (such as size and homogeneity) of the system or the loading of different types of drugs.

Tasciotti and his colleagues instead combined the bottom-up and top-down approaches to create a leukosome-a liposome (vesicle made of a synthetic phospholipid bilayer) that is coated with proteins derived from the cellular membrane of leukocytes (white blood cells). "What we have created with this synthetic platform is a replica of an extra-cellular vesicle," Tasciotti says.

To create the leukosome, the researchers began by taking blood and extracting and purifying the membrane proteins from immune system cells, which would allow their platform to slip by the immune system untouched. They then assembled a mixture of cholesterol and synthetic choline-based phospholipids-specifically, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine, 1,2-distearoyl-sn-glycero-3-phosphocholine, and 1,2-dioleoyl-sn-glycero-3-phosphocholine-to mimic the physiologic composition of the cell membrane, and created thin films of the lipids using thin layer evaporation. "We found out that the immune system cells not only recognize proteins, but they also have a feeling for the type of lipids that are present," Tasciotti says. The team hydrated and enriched the films with proteins dispersed in phosphate-buffered saline, then created leukosome vesicles of uniform size (120 nm) by extruding the proteolipids through cellulose acetate membranes (with pore sizes of 200 nm) 10 times.

The researchers conducted a number of tests to better understand the properties of their leukosomes. They found that the leukosomes, even in high doses of 1,000 mg/kg and after repeated injections, did not cause an immune system or inflammatory response. "But the most surprising thing to me was that the leukosome was able to function in every single inflammatory pathological condition we've tested," Tasciotti says. Experiments showed that two proteins (LFA-1 and CD45) were strongly involved in finding and adhering to inflammatory tissues, but Tasciotti notes that the leukosomes have 342 distinct proteins, which are thought to have numerous functions unrelated to adhesion, such as immunomodulation, transport, and signaling, among others. Future work will tease out the other functions of the leukosome's proteins.

Tasciotti also conducted in vitro and in vivo tests to see how well the leukosomes delivered the anti-inflammatory drug dexamethasone (DXM), which was loaded into the vesicles during the film hydrating process. For the in vivo tests, they induced inflammation-with the hallmark symptoms of redness, water buildup (edema) and swelling, tissue thickening, and white blood cell accumulation-in mice ears by injecting the bacterial toxin lipopolysaccharide. Compared with regular liposomes, leukosomes accumulated into the inflamed ear 5 times and 8.5 times more at 1 hour and 24 hours after injection, respectively. Furthermore, compared with empty and DXM-loaded liposomes, and free DXM, DXM-loaded leukosomes significantly reduced the inflammation over time. Interestingly, empty leukosomes showed anti-inflammatory properties as well, revealing a novel scenario in which the proteolipid membrane has intrinsic therapeutic activity, Tasciotti notes.

"The reduction of the inflammatory process is not even comparable," Tasciotti says. "What we see is that all the animals treated with the leukosomes completely recovered from the treatment."

"Bioinspired strategies for drug delivery are gaining increasing attention since the early 2000s," says materials scientist Angel Concheiro at the University of Santiago de Compostela in Spain, who was not involved in the study. To develop these systems, he says, it is important to understand and apply the knowledge of how molecules are transported between cells and how they trigger specific responses through their various interactions. "Multidisciplinary teams able to converge biology, materials science, pharmaceutical technology, and clinic are required to bring bioinspired nanocarriers to reality," Concheiro says, adding that, given the leukosome's apparently safety and performance, the new study "represents a step-forward in the field."

Aside from further investigating the leukosome's properties, Tasciotti and his colleagues are studying the platform's ability to treat primary metastatic cancer, as well as cardiovascular inflammation and sepsis (a kind of systemic inflammation). If these studies are successful, leukosomes could easily be scaled up and translated to the clinic. "We took a lot of time to optimize them to make the synthetic route simple," Tasciotti says. "It's a product that can be replicated easily and every hospital can make."

Read the abstract in Nature Materials.