LH 846 is a benzothiazole analog that selectively inhibits casein kinase (CK) 1δ (IC50 = 290 nM). It inhibits CK1ε and CK1α at much higher concentrations (IC50s = 1.3 and 2.5 μM, respectively) but does not inhibit CK2. LH 846 has been shown to inhibit CK1δ-dependent phosphorylation and degradation of PER1 protein and to lengthen the circadian period in U2OS cells.