  Gold nanoparticles have been conceived as a radiosensitizer in cancer
radiation therapy, but one of the important questions for primary drug
screening is what size of gold nanoparticles can optimally enhance radiation
effects. Herein, we perform in vitro and in vivo radiosensitization studies of
4.8, 12.1, 27.3, and 46.6 nm PEG-coated gold nanoparticles. In vitro results
show that all sizes of the PEG-coated gold nanoparticles can cause a
significant decrease in cancer cell survival after gamma radiation. 12.1 and
27.3 nm PEG-coated gold nanoparticles have dispersive distributions in the
cells and have stronger sensitization effects than 4.8 and 46.6 nm particles by
both cell apoptosis and necrosis. Further, in vivo results also show all sizes
of the PEG-coated gold nanoparticles can decrease tumor volume and weight after
5 Gy radiations, and 12.1 and 27.3 nm PEG-coated gold nanoparticles have
greater sensitization effects than 4.8 and 46.6 nm particles, which can lead to
almost complete disappearance of the tumor. In vivo biodistribution confirms
that 12.1 and 27.3 nm PEG-coated gold nanoparticles are accumulated in the
tumor with high concentrations. The pathology, immune response, and blood
biochemistry indicate that the PEG-coated gold nanoparticles do not cause
spleen and kidney damages, but give rise to liver damage and gold accumulation.
It can be concluded that 12.1 and 27.3 nm PEG-coated gold nanoparticles show
high radiosensitivity, and these results have an important indication for
possible radiotherapy and drug delivery.
