LONG-TERM DOSING

The particle's ability to stick to the artery wall contributed to one of its main potential clinical benefits: steady, long-term dosing.

Although it's too early to know how successful the treatment could be, Chan says by lengthening the polymer chain you could slow down the release of the anti-proliferative drug.

"In blood, particles are eroding slowly, and the chain is being cut, and the drug is being released," she explains. "If you can get a really long chain, you might have a very slow and low drug release."

Currently, the team has gotten dosing to a steady drip over around 12 days.

"In order to be competitive or potentially useful, it needs to be able to release over at least a couple of days or a week," Chan adds.

FATTY COATING

Critical to keeping the nanoburr sticking and circulating in the blood for a long time is another aspect of its structure: its protective fatty and chemical coatings.

The body's natural defenses will quickly muster attacks against foreign particles. To ensure this doesn't happen with the burrs, the researchers sheathe them in soy lecithin, a fatty substance, and coat them with polyethylene glycol (PEG). PEG, being so inert and hydrophilic, is able to evade much of the body's defenses, and has become the substance of choice in designing nanoparticles for medical applications, according to Chan. Studies begun in the early '90s have shown that "with PEG, you can increase circulation [of a polymeric nanoparticle] from five minutes to days," she explains. "PEG is the holy grail of polymeric nanoparticles."

FIGHTING TUMORS

Although the current study tested the nanoburrs on arteries, Chan says they could also have a role in fighting tumors.

"Most tumors have really poor, irregular and leaky vasculature," Chan notes. Nanoburrs could preferentially target the pockets between damaged layers of the arteries recruited by tumors, letting them slip into the leaky vessels while bearing a cancer-killing drug as payload.


UPCOMING STUDIES

Before testing the burrs' chances against cancer, Chan is hoping to try the effectiveness of the technique in blocking restenosis in animals. In the current study, when the nanoburr was injected in rats, the researchers replaced paclitaxel, the anti-proliferative drug used in stents, with a fluorescent dye so they could easily image how well it stuck to injured arteries. Now they want to see how the nanoburr actually works by comparing treatment with a drug-bearing nanoparticle to one with a sham saline solution.

"I think there are a lot of options right now," Chan says.


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