James Hainfeld and Daniel Slatkin of Nanoprobes Inc. and Henry Smilowitz of the University of Connecticut Health Center began by injecting cancer cells into the mice, followed by a salt solution containing gold nanoparticles. Two minutes later, the mice were irradiated with high-energy (250 kilovolts) X-rays.

The team found that the combination of nanoparticles followed by X-ray treatment reduced the size of the tumours, or completely eradicated them, whereas tumours that had received only X-ray therapy continued to grow. The gold nanoparticles had no therapeutic effect on their own. Hainfeld and co-workers also found that the one-year survival rate for the combined treatment was 86%, compared with 20% for X-ray therapy alone, and zero for nanoparticles without X-rays (figure 1).

The technique works because gold, which strongly absorbs X-rays, selectively accumulates in tumours. This increases the amount of energy that is deposited in the tumour compared with nearby normal tissue. The team now plans to improve targeting of the nanoparticles to tumours and to work towards applications for humans.

"Since the gold also shows up on CT and planar X-rays, it can be useful for early imaging and detection of tumours," Hainfeld told PhysicsWeb. "A major X-ray manufacturer is considering a modification that would optimize our gold nanoparticle radiotherapy for patients."