PF-4800567 is a potent and selective inhibitor of casein kinase 1ϵ (CK1ϵ), with an IC₅₀ of 32 nM, which is greater than 20-fold selectivity over CK1δ (IC₅₀, 711 nM). IC50 & Target: IC50: 32 nM (CK1ϵ), 711 nM (CK1δ)^[1] In Vitro: PF-4800567 is a potent and selective inhibitor of casein kinase 1ϵ (CK1ϵ), with an IC₅₀ of 32 nM, which is greater than 20-fold selectivity over CK1δ (IC₅₀, 711 nM). PF-4800567 shows inhibitory activity against CK1ϵ and CK1δ in whole cells, with IC₅₀s of 2.65 and 20.38 μM, respectively. PF-4800567 (0.01-10 μM) blocks CK1ϵ-mediated PER3 nuclear localization mediated by CK1ϵ and suppresses PER2 degradation at 1 μM. In addition, PF-4800567 has little effect on the circadian clock at 32 nM^[1]. In Vivo: PF-4800567 (100 mg/kg, s.c.) is rapidly absorpted and distributed in plasma and brain of mice^[1].