AZD1390 is a selective inhibitor of the ataxia telangiectasia and Rad3-related (ATR) kinase, primarily investigated for its potential in cancer therapy. It targets the DNA damage response pathway, particularly in tumors with defects in DNA repair mechanisms, such as those associated with BRCA mutations or other homologous recombination deficiencies. By inhibiting ATR, AZD1390 prevents cancer cells from repairing DNA damage, leading to replication stress and cell death, especially in combination with DNA-damaging agents like PARP inhibitors or radiation. It is being studied for efficacy in various cancers, including brain tumors (e.g., gliomas), ATM-deficient cancers, and those resistant to standard therapies. Ongoing clinical trials evaluate its safety, tolerability, dosing, and effectiveness, often in combination regimens to enhance outcomes and overcome resistance.