VE821

VE821 is a potent, selective, and ATP-competitive small-molecule inhibitor of the **Ataxia telangiectasia mutated and Rad3-related (ATR)** kinase, with an IC50 of approximately 26 nM. Developed by **Vertex Pharmaceuticals**, it serves as a critical research tool for investigating the DNA damage response (DDR). ATR is a key signaling protein that orchestrates the cellular response to replication stress and DNA double-strand breaks. By inhibiting ATR, VE821 prevents the phosphorylation of downstream targets like Chk1, thereby abrogating cell cycle checkpoints and impairing DNA repair. This mechanism sensitizes cancer cells to various DNA-damaging agents, including ionizing radiation and chemotherapeutic drugs like cisplatin and topoisomerase inhibitors. Preclinical studies have demonstrated its efficacy in enhancing apoptosis in multiple malignancies, such as Ewing's sarcoma, osteosarcoma, and hepatocellular carcinoma, particularly in cells with deficiencies in other DDR components like ATM or p53.