An orally available inhibitor of DNA-dependent protein kinase (DNA-PK), with potential antineoplastic and chemo/radiosensitizing activities. Upon oral administration, the DNA-PK inhibitor MSC2490484A binds to and inhibits the activity of DNA-PK. This inhibits the ability of tumor cells to repair damaged DNA, which may lead to a reduction in cellular proliferation of cancer cells expressing DNA-PK. DNA-PK, a serine/threonine kinase and a member of the PI3K-related kinase subfamily of protein kinases, is activated upon DNA damage and plays a key role in repairing DNA double-strand breaks (DSBs) via the DNA nonhomologous end joining (NHEJ) pathway. The enhanced ability of tumor cells to repair DSBs plays a major role in the resistance of tumor cells to chemo- and radiotherapy.