D4476 is a selective inhibitor of casein kinase 1 (CK1), particularly CK1δ and CK1ε. It is widely used in research to study signaling pathways regulated by CK1, such as the Wnt, p53, and circadian rhythm pathways. By inhibiting CK1 activity, D4476 helps modulate key cellular processes including cell cycle progression, DNA damage response, and apoptosis. It has been applied in cancer research to investigate the role of CK1 in tumor growth and survival, showing potential to sensitize certain cancer cells to chemotherapy. Additionally, D4476 is used as a tool compound in neurodegenerative disease studies, where CK1 dysregulation is linked to tau phosphorylation in conditions like Alzheimer’s disease. Its cell permeability and reversible inhibition make it suitable for in vitro and cellular assays.