A new way to deliver drugs with pinpoint targeting:

Most pharmaceuticals must either be ingested or injected into the body to do their work. Either way, it takes some time for them to reach their intended targets, and they also tend to spread out to other areas of the body. Now, researchers at MIT and elsewhere have developed a system to deliver medical treatments that can be released at precise times, minimally-invasively, and that ultimately could also deliver those drugs to specifically targeted areas such as a specific group of neurons in the brain.

The new approach is based on the use of tiny magnetic particles enclosed within a tiny hollow bubble of lipids (fatty molecules) filled with water, known as a liposome. The drug of choice is encapsulated within these bubbles and can be released by applying a magnetic field to heat the particles, allowing the drug to escape from the liposome and into the surrounding tissue.

The findings are reported in the journal Nature Nanotechnology in a paper by MIT postdoc Siyuan Rao, Associate Professor Polina Anikeeva, and 14 others at MIT, Stanford University, Harvard University, and the Swiss Federal Institute of Technology in Zurich.

  

"We wanted asystem that could deliver a drug with temporal precision, and could eventually target a particular location," Anikeeva explains. "And if we don't want it to be invasive, we need to find a non-invasive way to trigger the release."Magnetic fields, which can easily penetrate through the body—as demonstrated by detailed internal images produced by magnetic resonance imaging, or MRI—were a natural choice. The hard part was finding materials that could be triggered to heat up by using a very weak magnetic field (about one-hundredth the strength of that used for MRI), to prevent damage to the drug or surrounding tissues", Rao says.

Rao came up with the idea of taking magnetic nanoparticles, which had already been shown to be capable of being heated by placing them in a magnetic field and packing them into these spheres called liposomes. These are like little bubbles of lipids, which naturally form a spherical double layer surrounding a water droplet. When placed inside a high-frequency but low-strength magnetic field, the nanoparticles heat up, warming the lipids and making them undergo a transition from solid to liquid, which makes the layer more porous—just enough to let some of the drug molecules escape into the surrounding areas. When the magnetic field is switched off, the lipids re-solidify, preventing further releases. Over time, this process can be repeated, thus releasing doses of the enclosed drug at precisely controlled intervals.

The drug carriers were engineered to be stable inside the body at the normal body temperature of 37 degrees Celsius, but able to release their payload of drugs at a temperature of 42 degrees. "So we have a magnetic switch for drug delivery," and that amount of heat is small enough "so that you don't cause thermal damage to tissues," says Anikeeva, who holds appointments in the departments of Materials Science and Engineering and the Brain and Cognitive Sciences. In principle, this technique could also be used to guide the particles to specific, pinpoint locations in the body, using gradients of magnetic fields to push them along, but that aspect of the work is an ongoing project. For now, the researchers have been injecting the particles directly into the target locations and using the magnetic fields to control the timing of drug releases. "The technology will allow us to address the spatial aspect," Anikeeva says, but that has not yet been demonstrated.

Source Credit: Nano Magazine.