CLK inhibitor C81 (2-desaza-annomontine) is a derivative of the natural β-carboline alkaloid annomontine, exert anti-inflammatory and anti-angiogenic effects on endothelial cells, promotes the recovery of IκBα by inhibiting IκBα ubiquitination, impairs the NF-κB signaling cascade upstream of IκBα by down-regulation of TNFR1, inhibits CDC2-like kinases (CLKs).
C81 attenuates leukocyte-endothelial cell interactions in vitro
C81 binds to different protein kinases (BMP2K, CLK1 and CLK4 as well as AAK1) with a very high affinity, but these kinases are not involved in the actions of C81.
C81 potently binds to the CLK family members CLK4 and CLK1 with IC50 values of 0.8 and 3.5 µM respectively. C81 also bound DYRK2 with an IC50 of 6.1 µM and PIM3 with an IC50 of 6.3 µM, both kinases regulating apoptosis and cell proliferation.
C81 significantly downregulated the expression of cell adhesion molecules (VCAM-1, ICAM-1 and E-selectin) in HUVECs.
C81 attenuates the levels of CAMs by impairment of the NFκB signaling cascade, reduces the TNF-induced levels of VCAM-1, ICAM-1 and E-selectin.
C81 reduces the TNFR1 protein levels by inhibition of the de novo protein synthesis.
C81 also inhibits DYRK1B and attenuates STAT3 phosphorylation, impedes inflammatory processes in leukocytes.
C81 impedes angiogenesis through reduced VEGFR2 expression derived from inhibition of C81 CDC2-like kinases.