Molecular docking study of compound was performed using the
Molecular docking study of Coumarin was performed using the Schrödinger Small-Molecule Drug Discovery Suite taking advantage of known X-ray crystal structures of activated EPAC2 protein. The model shows that compound occupies the CBD of EPAC2 and forms hydrogen bonds with Arg448 and the cyano-hydrazine substituent (A). The fused tetrahydronaphthalene ring B lays in the same pocket as -butyl isoxazole ring of ESI-09 does and is surrounded by hydrophobic Ala416, Leu406, Val447, Val386, etc. Interestingly, ring A of compound extends to the opposite direction (the solvent region) compared to ESI-09 (B). This docking mode suggests that there exists a large space deep pocket remaining to be explored in the CBD domain of EPAC protein for the discovery of next generation ligands.
We have designed and synthesized a new series of 2-substituted phenyl--phenyl-2-oxoacetohydrazonoyl cyanides as EPAC inhibitors via simple chemistry with inexpensive starting material and synthetic ease suitable for scale up. Among those new molecules, compound (ZL0524) was the most potent EPAC inhibitory activities with IC values of 3.6 µM and 1.2 µM against EPAC1 and EPAC2, respectively. Docking studies of ZL0524 with activated EPAC2 reveal that it occupies the CBD2 hydrophobic pocket, forms hydrogen bonds with Arg448 and extended to the solvent region. The findings provide us inspirations to rationally design larger molecules to reach a deeper binding pocket as next generation EPAC inhibitors. efficacy studies of in infectious disease models (e.g. rickettsiosis) are under way, and the results will be reported in due course.
This work was supported by grants R01 GM106218, R01 AI111464, R01 GM066170 and R35 GM122536 from the National Institutes of Health. We want to thank Drs. Lawrence C. Sowers at the Department of Pharmacology as well as Dr. Tianzhi Wang at the NMR core facility of UTMB for the NMR spectroscopy assistance.
Introduction 3′,5′-Cyclic adenosine monophosphate (cAMP) plays an important role in vascular tone regulation since it exerts a direct, endothelium-independent vasorelaxant effect , ,  and an endothelium-dependent vasorelaxant action , , . This last action is partially mediated by an increase in endothelial NO release due to an enhanced endothelial NO synthase (eNOS) activity through cyclic-AMP protein kinase (PKA) and exchange protein directly activated by cAMP (Epac) activation in endothelial cells . Among the mechanisms that regulate eNOS activity are several post-translational regulatory modifications, including fatty acid acylation, phosphorylation, acetylation, s-nitrosylation and protein interactions, in response to physiological or pathological stimuli , . Those multiple regulatory mechanisms closely control eNOS activation to prevent harmful effects due to both overproduction and insufficient production of NO . Although eNOS can be phosphorylated at multiple sites , the most important residues of phosphorylation, in terms of the regulation of its activity, are serine (Ser) 1177, in the reductase domain, and threonine (Thr) 495, at the calmodulin (CaM)-binding domain. Phosphorylation of eNOS at Ser 1177 increases NO production by 2–3 times compared to basal level and it is initiated by various stimuli, such as shear stress, oestrogens, vascular endothelial growth factor, insulin or bradykinin, and catalysed by different protein kinases, depending on the applied stimulus, including Akt, PKA, 5′adenosine monophosphate-activated protein kinase (AMPK), protein kinase G or Ca2+/calmodulin-dependent protein kinase II (CaMKII) . In addition, the action of numerous phosphatases, such as phosphoprotein phosphatase 1, phosphatase 2A and phosphoprotein phosphate 2B or calcineurin, can activate or inhibit eNOS, depending on the specific region of dephosphorylation . eNOS activity has been considered for many years to be dependent on cytoplasmic Ca2+ ([Ca2+]c) rise and the subsequent binding of the Ca2+/CaM complex to the enzyme . However, eNOS can be activated by different stimuli, the most important being activation of Akt by shear stress, without an increase in [Ca2+]c , , .