The present disclosure provides compounds and methods for inhibiting DNA-dependent protein kinase (DNA-PK). Aspects of the present disclosure also include methods of using the compounds to treat diseases, including, but not limited to, cancer. In certain embodiments, the compounds inhibit DNA-PK and thus sensitize cancers to therapies such as chemotherapy and radiotherapy. Certain compounds of the present disclosure are in the form of prodrugs that release the DNA-PK inhibitor in hypoxic tissue such as is known to occur in cancers. Aspects of the present disclosure also include methods of using the compounds for repairing a DNA break in a target genomic region or for modifying expression of one or more genes or proteins. Compounds provided are of formula: (II)