Clonogenic assay to measure bystander cytotoxicity of targeted alpha-particle therapy

Radiation therapy induces targeted effects in the cells that are irradiated and also non-targeted effects (i.e. bystander effects) in non-irradiated cells that are close to or at short distance (< similar to 1 mm) from irradiated cells. Bystander effects are mediated by intercellular communications and may result in cytotoxic and genotoxic modifications. Their occurrence and relative contribution to the irradiation outcome are influenced by several parameters among which the particle linear energy transfer seems to be prominent. Bystander effects were first observed after external radiation therapy, but have been described also following targeted radionuclide therapy. Therefore, we propose a method to investigate their occurrence in experimental conditions where cells are exposed to radiopharmaceuticals. In this approach, clonogenic cell death is the biological endpoint of the bystander effects caused by irradiation with alpha particles (a potent inducer of the bystander response).