CLK8 is a potent and specific CLOCK inhibitor which can disrupt the interaction between CLOCK and BMAL1 [1]. CLK8 inhibits the translocation of CLOCK into the nucleus, leading to the stabilization of the negative arm of the transcription/translation feedback loop (TTFL) and enhancing the amplitude of the circadian rhythm [2]. CLK8 has been widely used to increase leukocyte-endothelium interactions [3].
In vitro, CLK8 treatment (20μM) for 12 hours significantly inhibited the entry of herpes simplex virus type 1 (HSV-1) into SH-SY5Y cells, and reduced the expression of NECTIN-1 protein as well as the protein levels of early HSV-1 protein ICP0 and late protein ICP5 [4].
In vivo, CLK8 treatment via intraperitoneal injection at a dose of 20mg/kg every other day for 10 days significantly inhibited tumor progression in AB1-HA tumor-bearing mice and reduced the number of αSMA-positive cancer-associated fibroblasts in the tumor tissue [5].
References:
[1] Doruk Y U, Yarparvar D, Akyel Y K, et al. A CLOCK-binding small molecule disrupts the interaction between CLOCK and BMAL1 and enhances circadian rhythm amplitude[J]. Journal of Biological Chemistry, 2020, 295(11): 3518-3531.
[2] Kavakli I H, Gul S, Turkay M. Identification of novel small molecules targeting core clock proteins to regulate circadian rhythm[J]. Current Opinion in Chemical Engineering, 2022, 35: 100730.
[3] Luna-Marco C, Devos D, Cacace J, et al. Molecular circadian clock disruption in the leukocytes of individuals with type 2 diabetes and overweight, and its relationship with leukocyte–endothelial interactions[J]. Diabetologia, 2024, 67(10): 2316-2328.
[4] Tang J J, Pan M, Liu J, et al. Circadian clock proteins BMAL1 and CLOCK regulate HSV-1 entry into nerve cells through NECTIN-1[J]. Virology Journal, 2025, 22(1): 333.
[5] Mitsuhashi A, Koyama K, Ogino H, et al. Clock pathway inhibitor overcomes tumor immune-exclusion via regulation of fibrocyte differentiation[J]. NPJ Precision Oncology, 2025, 9(1): 274.