IC86621, also known as DNA-PK Inhibitor III, is primarily used in research to study the role of DNA-dependent protein kinase (DNA-PK) in cellular processes. It is particularly valuable in investigating DNA repair mechanisms, specifically non-homologous end joining (NHEJ), which is crucial for repairing double-strand breaks in DNA. By inhibiting DNA-PK, researchers can better understand how cells respond to DNA damage and explore potential therapeutic strategies for conditions like cancer, where DNA repair pathways are often dysregulated. Additionally, it is used in preclinical studies to evaluate the effects of DNA-PK inhibition in combination with radiotherapy or chemotherapy, as blocking this enzyme can sensitize cancer cells to these treatments.