Gold Nanoparticles Enhance Radiation Therapy at Low Concentrations, and Remain in Tumors for Days

Gold nanoparticles are a potential method for enhancing radiation therapy, causing extra damage to tumors when irradiated through the Auger effect. One of the major obstacles to using gold nanoparticles in human trials is the relatively large amount of gold required. This paper details an experiment where a relatively small amount of gold (200 mu g) was used to significantly reduce tumor volume in mice, as well as the results of an inter-tissue biodistribution experiment. Using a longitudinal analysis, tumor size as a function of time was found to be significantly reduced when mice were given 200 mu g of gold nanoparticles and 20 Gray of radiation, compared to radiation alone. 200 mu g in a 20-gram mouse would be mass equivalent to 750 mg of gold in a 75 kg person. Biodistribution measurements demonstrated that gold nanoparticles stayed in the tumor for at least one week after injection when targeted to tumors using pH-Low Insertion Peptide and intratumoral injections. These results show gold nanoparticles to be effective at one of the smallest amounts of gold ever attempted in a mouse, and showed that tumor targeting has the potential to keep gold nanoparticles available in tumors long enough to be beneficial to fractionated radiation treatments (a key component of radiation therapy in the clinic).