In order to discover novel ASK1 inhibitors we have performed screening program, using both in silico and in vitro approaches. The virtual screening experiments were carried out targeting the ATP binding site of ASK1 by browsing the Otava Ltd. compound library of 156,000 organic compounds. The best-scored compounds have been selected and taken for the kinase assay study.
We have identified two classes of human ASK1 ATP-competitive inhibitors:
In vitro experiments revealed that ethyl 2,7-dioxo-2,7-dihydro-3H-naphtho[1,2,3-de]quinoline-1-carboxylate (NQDI-1) inhibited ASK1 with a Ki of 500 nM. The competitive character of inhibition is demonstrated in Lineweaver-Burk plots. In our preliminary selectivity study this compound exhibited strong specific inhibitory activity toward ASK1. Structure-activity relationships of 15 tested 3H-naphtho[1,2,3-de]quinoline-2,7-dione derivatives have been studied and binding mode of this chemical class has been predicted.
Residual Activity of Protein Kinases (%) in the Presence of NQDI-1 at 25 μM Concentration
The binding mode of NQDI-1 in the active site of the ASK1 catalytic subunit. Hydrogen bonds are shown by the dotted lines.
Reference: Identification of 3H-naphtho[1,2,3-de]quinoline-2,7-diones as inhibitors of apoptosis signal-regulating kinase 1 (ASK1). Volynets GP, Chekanov MO, Synyugin AR, Golub AG, Kukharenko OP, Bdzhola VG, Yarmoluk SM. J Med Chem. 2011, 54(8):2680-2686.
In vitro tests revealed that seven derivatives of 2-Thioxo-thiazolidin-4-one exhibited inhibitory activity against ASK1. The most active compound was 5-bromo-3-(4-oxo-2-thioxo-thiazolidin-5-ylidene)-1,3-dihydro-indol-2-one (IC50 = 2 μM). Binding mode for inhibitors of this class with ASK1 ATP-binding site was proposed.
The binding mode of inhibitor in the active site of the ASK1 catalytic subunit. Hydrogen bond is shown by the dotted line.
Reference: Volynets GP, Bdzhola VG, Kukharenko OP, Yarmoluk SM. Identification of ASK1 Small-Molecule Inhibitors. Ukr. Biochim. J. 2010; 82 (5): 41-50.