What's the News: Researchers have developed a new, more targeted way to deliver cancer-fighting drugs, in which some nanoparticles zero in on a tumor, then summon another type of nanoparticles that actually dispense the drug. This method, detailed in a new study published online by Nature Materials, piggybacks on the body's underlying biochemistry, using the chain of events that makes blood clot to call the drug-bearing nanoparticles to the site. How the Heck:
The nanoparticles that home in on the tumor are tiny gold nanorods, which can penetrate the blood vessels surrounding the tumor. (The blood vessels surrounding tumors, which grow rapidly as the tumor expands, tend to be more porous than blood vessels elsewhere in the body, letting the nanoparticles target tumors in particular.)
The researchers then shone light onto the gold nanorods. This heated the nanorods slightly, causing just enough damage to the tumor tissue to trigger the body's clotting process.
When the body senses damage to a blood vessel, it starts a biochemical chain reaction---called a cascade---to repair the injury. At the end of the cascade, strands of a molecule called fibrin come together, helping to form a clot.
The second nanoparticle is clad in bits of proteins that bind to fibrin. This particle also carries the chemotherapy drug, so when it binds to the fibrin, it delivers the drug to the tumor.
In a test of the method in mice, the scientists found that forty times more of the drug reached tumors in mice given both nanoparticles, compared to mice given a treatment without this scout-then-surge approach. The tumors in the former group---but not the latter---stopped growing.
What's the Context:
One of the big problems in drug delivery is how to get as much of the drug as possible to the tumor (or other disease site). Some nanoparticles already passively target tumors by taking advantage of their more permeable blood vessels, while others actively target tumors by binding to particular proteins there. This drug delivery system uses the passive-targeting mechanism as a starting point, but has the added advantage of a second wave of particles that further zero in on the tumor.
Several challenges remain before the drug is ready for use in people, particularly ensuring that the nanoparticles trigger blood clots only in tumors, not elsewhere in the body.
Reference: Geoffrey von Maltzahn et al. "Nanoparticles that communicate in vivo to amplify tumour targeting." Nature Materials, published online before print June 19, 2011. DOI:10.1038/nmat3049Image: Gary Carlson