Results showed the nanoparticles improved the contrast in both MRI and optical imaging, which is used during surgery.
This image shows a mouse brain tumour imaged using nanoparticles (left column) or conventional techniques (right column) combined with optical imaging and MRI. The nanoparticles give a clearer picture of the tumour, which is located at the back of the brain in the cerebellum. Photo: Courtesy by University of Washington.
"Brain cancers are very invasive, different from the other cancers. They will invade the surrounding tissue and there is no clear boundary between the tumour tissue and the normal brain tissue", stated lead author Miqin Zhang, a UW professor of materials science and engineering.
Being unable to distinguish a boundary complicates the surgery. Severe cognitive problems are a common side effect. "If we can inject these nanoparticles with infrared dye, they will increase the contrast between the tumour tissue and the normal tissue", Miqin Zhang stated. "So during the surgery, the surgeons can see the boundary more precisely. We call it 'brain tumour illumination or brain tumour painting. The tumour will light up."
Nano-imaging could also help with early cancer detection, Miqin Zhang said. Current imaging techniques have a maximum resolution of 1 millimeter (1/25 of an inch). Nanoparticles could improve the resolution by a factor of 10 or more, allowing detection of smaller tumours and earlier treatment.
Until now, no nanoparticle used for imaging has been able to cross the blood-brain barrier and specifically bind to brain-tumour cells. With current techniques doctors inject dyes into the body and use drugs to temporarily open the blood-brain barrier, risking infection of the brain.
The UW team surmounted this challenge by building a nanoparticle that remains small in wet conditions. The particle was about 33 nanometers in diameter when wet, about a third the size of similar particles used in other parts of the body.
Crossing the blood-brain barrier depends on the size of the particle, its lipid, or fat, content, and the electric charge on the particle. Miqin Zhang and colleagues built a particle that can pass through the barrier and reach tumours. To specifically target tumour cells they used chlorotoxin, a small peptide isolated from scorpion venom that many groups, including Miqin Zhang's, are exploring for its tumour-targeting abilities. On the nanoparticle's surface Miqin Zhang placed a small fluorescent molecule for optical imaging, and binding sites that could be used for attaching other molecules.
Future research will evaluate this nanoparticle's potential for treating tumours, Miqin Zhang said. She and colleagues already showed that chlorotoxin combined with nanoparticles dramatically slows tumours' spread. They will see whether that ability could extend to brain cancer, the most common solid tumour to affect children.
Merely improving imaging, however, would improve patient outcomes. "Precise imaging of brain tumours is phenomenally important. We know that patient survival for brain tumours is directly related to the amount of tumour that you can resect", stated co-author Richard Ellenbogen, professor and chair of neurological surgery at the UW School of Medicine. "This is the next generation of cancer imaging", he stated. "The last generation was CT, this generation was MRI, and this is the next generation of advances."
Other co-authors are Omid Veiseh, Conroy Sun, Chen Fang, Narayan Bhattarai, Jonathan Gunn of the UW's department of materials science and engineering; Forrest Kievit and Kim Du of UW bioengineering; Donghoon Lee of UW radiology; Barbara Pullar of the Fred Hutchinson Cancer Research Center; and Jim Olson of the Fred Hutchinson Cancer Research Center and Seattle Children's Hospital.
The research was funded by the National Institutes of Health, the Jordyn Dukelow Memorial Fund and the Seattle Children's Hospital Brain Tumour Research Endowment.