Donated Chemical Probes

Target	CLK1 CLK2 CLK3 CLK4
Targeted domain	Kinase domain (active site)
Mode of action	Inhibitor (type 1, ATP competitive)
Control	T3-CLK-N
Recommended cellular usage concentration	< 100 nM
In vivo use	No
Synonyms	T3, CLK-IN-T3, CLK Inhibitor T3, VC-5561
Donated by	Takeda

Inhibitor/agonist potency: goal is < 100 nM (IC₅₀, K_d)	Surpasses criterion: panCLK probe: CLK1 (IC₅₀ = 0.67 nM), CLK2 (IC₅₀ = 15 nM), CLK3 (IC₅₀ = 110 nM)
Selectivity within target family: > 30-fold	Surpasses criterion: 200 to 300 times selective against dual specificity kinases such as DYRK1A (IC₅₀ = 260 nM) and DYRK1B (IC₅₀ = 230 nM) in vitro; NanoBRET assay results: IC₅₀ DYRK1A 32 nM and DYRK1B 67 nM Closest off targets (kinase family, NanoBRET assay): IC₅₀ values: SIK2 (125 nM) and FLT D835V Mutant (138 nM), FLT3 (668 nM), AAK1, MAP3K19, DYRK2, LRRK2, KIT, PDGFRA, PDGFRB, CDK7, SRPK1, MAP3K5 (waiting for new experiment), MAP2K5, LATS2, RIOK2
Selectivity outside target family	Clean PDSP scan except for weak activity on HRH1 (K_i = 2154.79 nM)
On target cell activity for cell-based targets: goal is < 1 µM IC₅₀/EC₅₀	Surpasses criterion:Potent on target activity: CLK1 (Kiapp = 0.7 nM, IC₅₀ = 3.49 nM), CLK2 (Kiapp = 4 nM, IC₅₀ = 16.6 nM) and CLK4 (Kiapp = 0.2 nM, IC₅₀ = 1.98 nM) (NanoBRET results from SGC Frankfurt).; Potent inhibition of endogenous CLK in two different cellular systems.
Control compound (100 times less potent than the probe)	Control clean and not active Closest off-targets in the PDSP scan are TMEM97 (Ki = 411.9 nM), SIGMAR1 (Ki = 798.34 nM), OPRK1 (Ki =990.27 nM) and HTR2C (Ki = 1066.46 nM).