Compositions and methods for modulating a DNA repair process in vivo or in vitro are provided. One aspect of the disclosure provides a pharmaceutical composition including a DNA repair modulator. The DNA repair modulator includes, but is not limited to, compositions such as polypeptides, for example antibodies; modified polypeptides; and branched or unbranched aliphatic, cycloaliphatic, substituted aliphatic, aromatic hydrocarbons, or heterocyclic carbon-based compounds that associate with a DNA repair polypeptide, for example, DNA-PKcs.
 Aspects of the work described herein were supported, in part, by grant numbers GM35866 awarded by the National Institutes of Health and DE-FG07-99ER62875 awarded by the U.S. Department of Energy. Therefore, the U.S. government has certain rights in the invention.