Radiosensitization by gold nanoparticles: effective at megavoltage energies and potential role of oxidative stress

The multidisciplinary field of nanotechnology has the potential to deliver many novel applications in the biomedical field including improved strategies for the detection, diagnosis and treatment of cancer. In the radiation research arena, gold nanoparticles (GNPs) have demonstrated strong potential as diagnostic imaging agents, drug delivery platforms and radiation sensitizers due to their attractive physico-chemical characteristics. In the pursuit of dose modifiers to improve the therapeutic index of radiotherapy, GNPs have attracted much research interest due to the high atomic number (Z) of gold which results in significantly improved contrast compared to soft tissue. In this review, we consider the physical properties of GNPs which make them widely utilizable in the field of radiation research as image contrast agents, drug delivery vehicles and radiation sensitizers. In particular, we focus on the growing amount of preclinical evidence which demonstrates GNPs as radiation sensitizers and highlight the disparity between observed experimental findings and predictions based on mass attenuation, GNP concentration and beam energy. Considering the large amount of studies performed using a wide range of GNPs, emerging evidence suggests oxidative stress as a central mechanism of radiobiological response.