"The M&M analogy is really a great one because it says you can put things on the outside and you can have something on the inside," Watkin said. "And in the case of gadolinium oxide, it's really a metallic ion."

Watkin said gadolinium oxide is a superb imaging agent because of its superparamagnetic properties - "meaning that they work well within a magnetic resonance imaging machine."


Its properties as an effective emitter of radiation sources also make it well-suited for use with a type of cancer therapy called neutron capture therapy.

"What it means," Watkin said, "is that these little particles capture the neutrons and emit alpha and gamma rays, and that energy - sent out from an accelerator - is what can be used to kill cancer cells.

"In looking at this, we both said, 'Holy ... cow!' These little gadolinium particles capture neutrons at four times a greater rate than boron, and yet boron is what is (currently) used for neutron capture. This means it (gadolinium oxide) is potentially a multimodal agent" ... in other words, "a contrast agent that would work with a number of different medical imaging techniques."

Among the most promising applications for using gadolinium oxide nanoparticles as a neutron capture therapy agent is in the treatment of brain tumors.

"Treating brain tumors - typically called glioblastomas - is very difficult," Watkin said. "Irradiating them is really difficult because you alter all kinds of tissues in the brain. And getting little bubbles like this or other kinds of contrast agents into the brain is difficult because the holes that allow plasma and other substances to flow through the brain are very small - about 25 nanometers. With such a small opening, you've got to have something pretty tiny to get in there. So these little gadolinium oxide particles can be really useful."

Watkin noted that another reason the researchers initially chose to investigate the effects of adding a dextran coating was because it makes it possible to "target" the nanoparticle.

"By that, we mean we put a ligand - an organic substance, such as a monoclonal antibody - on the outside that searches out in the bloodstream. Antibodies seek their antigens. So we target something to seek out a substance that's expressed by cells - cancer cells, in my work. Cancer cells express particular antigens to which an antibody attaches itself. So, if we put the appropriate glioblastoma antibody on the end of a particle, as it passes through the bloodstream it will attach to the tumor cell."

In experiments with other types of nanoparticles, Watkin has loaded the particles with cancer-fighting drugs such as Doxorubicin or Taxiter. He also is investigating using them to deliver genetic material such as RNA inhibitor.

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