Discovery of N-[4-(1H-Pyrazolo[3,4-b]pyrazin-6-yl)-phenyl]-sulfonamides as Highly Active and Selective SGK1 Inhibitors

Abstract

From a virtual screening starting point, inhibitors of the serum and glucocorticoid regulated kinase 1 were developed through a combination of classical medicinal chemistry and library approaches. This resulted in highly active small molecules with nanomolar activity and a good overall in vitro and ADME profile. Furthermore, the compounds exhibited unusually high kinase and off-target selectivity due to their rigid structure. KEYWORDS: Serum glucocorticoid regulated kinase, WNT signaling, AGC kinase, virtual screening T he serum and glucocorticoid regulated kinase 1 (SGK1) belongs to the serine/threonine kinase family (AGC kinases) and is an important downstream effector in the phosphatidylinositol-3-kinase pathway. SGK1 regulates transport, hormone release, cell proliferation, and apoptosis.1,2 There is a strong body of evidence that dysfunction or dysregulation of SGK1 is involved in many pathological conditions ranging from cancer, hypertension, diabetes, and thrombotic events to neurodegeneration.3−6 Albeit ubiquitously expressed, the transcription is highly regulated and stimulated by physiological events like hyperglycaemia, cell shrinkage, ischemia, glucocorticoids, mineralocorticoids, and insulin as well as by inflammatory mediators including TGFβ. SGK1 regulates several ion channels such as ENaC, KCNE1/KCNQ1, carriers like NCC, NHE3, SGLT1, Na(+)/K(+)-ATPase, and transcription factors including FOXO3a, NF-κβ, and β-catenin.7−11 Recently, it was shown that β-catenin phosphorylation by SGK1 mediates the crosstalk between the corticoid-and WNT-signaling pathways. 7,12,13 Surprisingly, despite the highly relevant, validated biological function of SGK1 only a few inhibitors with appropriate selectivity and potency for the selective interference with SGK1 have been described so far.14−17 Here we report the identification and optimization of highly active and selective SGK1 inhibitors as chemical tools for the further elucidation and validation of the biological role of SGK1. 18Computational screening, particularly 3D ligand-based virtual screening technologies, have emerged as efficient methods for the discovery of novel drug candidates.19−21 Ligand-based virtual screening uses known active molecules to identify new ligands sharing a set of relevant molecular properties such as molecular shape and electrostatics. A limited number of inhibitors of SGK1 have been described in the literature so far including the azaindoles 1 and 2, the hydrazides 3 and 4, and their 3-aminoindazole isosteres 5 and 6 as shown in Figure 1. 22Cocrystal structures of ligands 1 and 2 in the SGK1 enzyme supported a bidentate interaction of the ligand scaffold with the kinase hinge region.14 Using a docking model 23 a bidentate hinge interaction of the para-phenolic substituent was also assumed for 3 and 4 as well as a tridentate interaction for compounds 5 and 6

mTORC2 Regulates Amino Acid Metabolism in Cancer by Phosphorylation of the Cystine-Glutamate Antiporter xCT

“…Surprisingly, we did not detect physical interaction between any AGC kinases including PKCα, Akt or SGK1 and xCT in either the SILAC or Co-IP experiments across different cell lines (Table S1 and Figures S2C and S2D). Furthermore, neither siRNA-mediated genetic knockdown, nor pharmacological inhibition of PKCα, Akt and SGK1 (Halland et al, 2015) suppressed xCT phosphorylation upon EGF stimulation (Figures S2E and S2F), suggesting that downstream effector AGC kinases are not required for mTORC2-mediated xCT phosphorylation.…”

A Concise Review on the Synthesis and Reactions of Pyrazolopyrazine Heterocycles

“…Cyclization of N ‐[4‐(5‐chloro‐6‐cyano/formylpyrazin‐2‐yl)phenyl]‐4‐sulfonamide derivatives 193a,b into 3‐amino‐pyrazolo[3,4‐ b ] pyrazine 194a and pyrazolo[3,4‐ b ]pyrazine derivative 194b was achieved by hydrazine hydrate in isopropanol under microwave irradiation (Scheme ) .…”

“…2‐Acetyl‐3,5‐dichloropyrazine (195) underwent Suzuki coupling reaction with Boc‐protected 4‐(4,4,5,5‐tetramethyl‐1,3,2‐dioxaborolan‐2‐yl) aniline to afford compound 196 that was cyclized into 3‐methylpyrazolo[3,4‐ b ]pyrazine 197 upon treatment with hydrazine under microwave conditions followed by deprotection reaction upon treatment with arylsulfonyl chlorides to afford 3‐methyl‐ 1H ‐pyrazolo[3,4‐ b ] pyrazine derivative 198 (Scheme ) .…”

Sgk1

“…The most recently described inhibitor, SGK-inh (Castel et al, 2016; Halland et al, 2015), has an IC 50 of 4.8 nM for SGK1. Interestingly, the only other kinase inhibited with selectivity lower than 10-fold is p70S6K.…”