Measurement of H2AX Phosphorylation as a Marker of Ionizing Radiation Induced Cell Damage

Cancer therapy often involves drugs or radiation, which induce DNA double-strand breaks (DSBs) and cause death of tumor cells. A dilemma with radiation and chemotherapy is the narrow therapeutic window and the fact that the sensitivity to DNA damage varies greatly in the human population, resulting in severe side effects and therapy-related deaths. Radiation and chemotherapy are usually planned during 1-3 weeks and delivered over a period of weeks to months. DNA damage testing of the patient could therefore be performed as part of the therapy planning. The level of DNA damage and DNA repair capacity could be measured after the first dose of chemotherapy or radiation, to allow personalized dosing during the following weeks of treatment. Induction of DSBs is followed by rapid formation of gamma-H2AX foci, with thousands of H2AX molecules being phosphorylated in the chromatin flanking the DSB site. Gamma-H2AX foci, each representing one radiation-induced DSB, can be measured by flow cytometry or counted in cell nuclei by fluorescence microscopy. In this chapter we will focus on radiation-induced DNA damage and its biological effects. We will also describe available methods for gammaH2AX detection and discuss its possible use in clinical practice.