Abstract: The present disclosure relates to inhibitors of DNA protein kinase, and compositions and methods of use thereof. In some embodiments, the inhibitors have the structure of Formula I: or a salt thereof, wherein: x1 is C—R3 or N; R1 is C1-C3 alkyl; R2 is cycloalkyl or heterocyclyl, and cycloalkyl and heterocyclyl are optionally substituted with one or more R6; R3 is H or C1-C3 alkyl; R4 is H or C1-C3 alkyl; R5 is C1-C3 alkyl; each R6 is independently selected from hydroxy, halo, alkyl, alkoxy, cycloalkyl, amino, and cyano, or two R6, taken together with the atom or atoms to which they are bonded, form a spirocyclic or fused ring; and R7 is H or C1-C3 alkyl.