Identification of para-Substituted Benzoic Acid Derivatives as Potent Inhibitors of the Protein Phosphatase Slingshot

Discovery of benzofuran-2-carboxylic acid derivatives as lymphoid tyrosine phosphatase (LYP) inhibitors for cancer immunotherapy

Lymphoid-tyrosine phosphatase (LYP) is mainly expressed in the immune system and plays an important role in the T-cell receptor (TCR) signaling pathway and tumor immunity. Herein, we identify benzofuran-2-carboxylic acid as a potent pTyr mimic and design a new series of new LYP inhibitors. The most active compound, D34 and D14, reversibly inhibits LYP (K_i = 0.93 μM and 1.34 μM) and possess a certain degree of selectivity toward other phosphatases. Meanwhile, D34 and D14 regulate the TCR signaling by specifically inhibiting LYP. In particular, D34 and D14 significantly suppress tumor growth in an MC38 syngeneic mouse model by boosting antitumor immunity, including activation of T-cell and inhibition of M2 macrophage polarization. Moreover, treatment of D34 or D14 upregulate PD-1/PD-L1 expression, which can be leveraged with PD-1/PD-L1 inhibition to augment immunotherapy. In summary, our study demonstrates the feasibility of targeting LYP for cancer immunotherapy and provides new lead compounds for further drug development.

Cofilin activation in pancreatic acinar cells plays a pivotal convergent role for mediating CCK-stimulated enzyme secretion and growth

Introduction: The actin regulatory protein, cofilin plays a key signaling role in many cells for numerous cellular responses including in proliferation, development, motility, migration, secretion and growth. In the pancreas it is important in islet insulin secretion, growth of pancreatic cancer cells and in pancreatitis. However, there are no studies on its role or activation in pancreatic acinar cells. Methods: To address this question, we studied the ability of CCK to activate cofilin in pancreatic acinar cells, AR42J cells and CCK₁-R transfected Panc-1 cells, the signaling cascades involved and its effect on enzyme secretion and MAPK activation, a key mediator of pancreatic growth. Results: CCK (0.3 and 100 nM), TPA, carbachol, Bombesin, secretin and VIP decreased phospho-cofilin (i.e., activate cofilin) and both phospho-kinetic and inhibitor studies of cofilin, LIM kinase (LIMK) and Slingshot Protein Phosphatase (SSH1) demonstrated these conventional activators of cofilin were not involved. Serine phosphatases inhibitors (calyculin A and okadaic acid), however inhibited CCK/TPA-cofilin activation. Studies of various CCK-activated signaling cascades showed activation of PKC/PKD, Src, PAK4, JNK, ROCK mediated cofilin activation, but not PI3K, p38, or MEK. Furthermore, using both siRNA and cofilin inhibitors, cofilin activation was shown to be essential for CCK-mediated enzyme secretion and MAPK activation. Conclusion: These results support the conclusion that cofilin activation plays a pivotal convergent role for various cell signaling cascades in CCK mediated growth/enzyme secretion in pancreatic acini.

Identification of HN252 as a potent inhibitor of protein phosphatase PPM1B

Protein phosphatase 1B (PPM1B), a member of metal-dependent protein serine/threonine phosphatase family, is involved in the regulation of several signalling pathways. However, our understanding of its substrate interaction and physiological functions is still largely limited. There is no reported PPM1B inhibitor to date. In this study, we identified HN252, a p-terphenyl derivative, as a potent PPM1B inhibitor (K_i  = 0.52 ± 0.06 µM). HN252 binding to PPM1B displayed remarkable and specific inhibition of PPM1B in both in vitro and ex vivo. With the aid of this small molecular inhibitor, we identified 30 proteins' serine/threonine phosphorylation as potential substrates of PPM1B, 5 of which were demonstrated by immunoprecipitation, including one known (CDK2) and 4 novel ones (AKT1, HSP90B, β-catenin and BRCA1). Furthermore, GO and KEGG analysis of dramatically phosphorylated proteins by PPM1B inhibition indicated that PPM1B plays roles in the regulation of multiple cellular processes and signalling pathways, such as gene transcription, inflammatory regulation, ageing and tumorigenesis. Our work provides novel insights into further investigation of molecular mechanisms of PPM1B.

Design, synthesis and biological evaluation of imidazolidine-2,4-dione and 2-thioxothiazolidin-4-one derivatives as lymphoid-specific tyrosine phosphatase inhibitors

Lymphoid-specific tyrosine phosphatase (LYP), which exclusively exists in immune cells and down-regulates T cell receptor signaling (TCR), has becoming a potent target for various autoimmune diseases. Herein, we designed and synthesized imidazolidine-2,4-dione and 2-thioxothiazolidin-4-one derivatives as new LYP inhibitors. Among them, the cinnamic acids-based inhibitors (9p and 9r) displayed good LYP inhibitory activities (IC₅₀ = 2.85-6.95 μM). Especially, the most potent inhibitor 9r was identified as competitive inhibitor (K_i = 1.09 μM) and bind LYP reversibly. Meanwhile, 9r exhibited better selectivity over other phosphatases than known LYP inhibitor A15. Furthermore, compound 9r could regulate TCR associated signaling pathway in Jurkat T cell.

Strategy to design a smart photocleavable and pH sensitive chitosan based hydrogel through a novel crosslinker: a potential vehicle for controlled drug delivery

We report herein the synthesis of a novel photocleavable crosslinker, 4-formylphenyl 4-((4-formylphenoxy)methyl)-3-nitrobenzoate (CHO-ONB-CHO) and its joining with amine-based polysaccharides, viz. chitosan, resulting in the formation of a dual stimuli-responsive (ONB-chitosan) hydrogel having UV- and pH-responsive sites. The detailed mechanism for the formation of CHO-ONB-CHO and ONB-chitosan hydrogel is proposed. The (CHO-ONB-CHO) crosslinker was characterized using 1H-NMR, LCMS and UV-visible spectroscopy. The dual responsive hydrogel is characterized by FTIR, SEM, XRD, DSC and TGA. The crosslinked hydrogel displayed mechanical robustness with a storage modulus of about 1741 pa. The pH-responsiveness of the hydrogel was studied via equilibrium swelling studies in various pH media at 37 °C. The photocleavable behavior of the crosslinker was observed in the UV-absorption range of 310-340 nm and the hydrogel exhibited maximum swelling at pH 5.7. The higher swelling of the hydrogel in acidic conditions and its photo-responsiveness can be exploited for the controlled, temporal and spatial release of therapeutic drugs at any inflammatory areas with acidic environments. It was observed that the hydrogel exhibited higher drug release at pH 5.7 than at pH 7.4.

Group II p21-activated kinase, PAK4, is needed for activation of focal adhesion kinases, MAPK, GSK3, and β-catenin in rat pancreatic acinar cells

PAK4 is the only member of the Group II p21-activated kinases (PAKs) present in rat pancreatic acinar cells and is activated by gastrointestinal hormones/neurotransmitters stimulating PLC/cAMP and by various pancreatic growth factors. However, little is known of the role of PAK4 activation in cellular signaling cascades in pancreatic acinar cells. In the present study, we examined the role of PAK4's participation in five different cholecystokinin-8 (CCK-8)-stimulated signaling pathways (PI3K/Akt, MAPK, focal adhesion kinase, GSK3, and β-catenin), which mediate many of its physiological acinar-cell effects, as well as effects in pathophysiological conditions. To define PAK4's role, the effect of two different PAK4 inhibitors, PF-3758309 and LCH-7749944, was examined under experimental conditions that only inhibited PAK4 activation and not activation of the other pancreatic PAK, Group I PAK2. The inhibitors' effects on activation of these five signaling cascades by both physiological and pathophysiological concentrations of CCK, as well as by 12-O-tetradecanoylphobol-13-acetate (TPA), a PKC-activator, were examined. CCK/TPA activation of focal adhesion kinases(PYK2/p125^FAK) and the accompanying adapter proteins (paxillin/p130^CAS), Mek1/2, and p44/42, but not c-Raf or other MAPKs (JNK/p38), were mediated by PAK4. Activation of PI3K/Akt/p70s6K was independent of PAK4, whereas GSK3 and β-catenin stimulation was PAK4-dependent. These results, coupled with recent studies showing PAK4 is important in pancreatic fluid/electrolyte/enzyme secretion and acinar cell growth, show that PAK4 plays an important role in different cellular signaling cascades, which have been shown to mediate numerous physiological and pathophysiological processes in pancreatic acinar cells.NEW & NOTEWORTHY In pancreatic acinar cells, cholecystokinin (CCK) or 12-O-tetradecanoylphobol-13-acetate (TPA) activation of focal adhesion kinases (p125^FAK,PYK2) and its accompanying adapter proteins, p130CAS/paxillin; Mek1/2, p44/42, GSK3, and β-catenin are mediated by PAK4. PI3K/Akt/p70s6K, c-Raf, JNK, or p38 pathways are independent of PAK4 activation.

Identification and structure-function analyses of an allosteric inhibitor of the tyrosine phosphatase PTPN22

Protein-tyrosine phosphatase nonreceptor type 22 (PTPN22) is a lymphoid-specific tyrosine phosphatase (LYP), and mutations in the PTPN22 gene are highly correlated with a spectrum of autoimmune diseases. However, compounds and mechanisms that specifically inhibit LYP enzymes to address therapeutic needs to manage these diseases remain to be discovered. Here, we conducted a similarity search of a commercial database for PTPN22 inhibitors and identified several LYP inhibitor scaffolds, which helped identify one highly active inhibitor, NC1. Using noncompetitive inhibition curve and phosphatase assays, we determined NC1's inhibition mode toward PTPN22 and its selectivity toward a panel of phosphatases. We found that NC1 is a noncompetitive LYP inhibitor and observed that it exhibits selectivity against other protein phosphatases and effectively inhibits LYP activity in lymphoid T cells and modulates T-cell receptor signaling. Results from site-directed mutagenesis, fragment-centric topographic mapping, and molecular dynamics simulation experiments suggested that NC1, unlike other known LYP inhibitors, concurrently binds to a "WPD" pocket and a second pocket surrounded by an LYP-specific insert, which contributes to its selectivity against other phosphatases. Moreover, using a newly developed method to incorporate the unnatural amino acid 2-fluorine-tyrosine and ¹⁹F NMR spectroscopy, we provide direct evidence that NC1 allosterically regulates LYP activity by restricting WPD-loop movement. In conclusion, our approach has identified a new allosteric binding site in LYP useful for selective LYP inhibitor development; we propose that the ¹⁹F NMR probe developed here may also be useful for characterizing allosteric inhibitors of other tyrosine phosphatases.

Critical Roles of Dual-Specificity Phosphatases in Neuronal Proteostasis and Neurological Diseases

Protein homeostasis or proteostasis is a fundamental cellular property that encompasses the dynamic balancing of processes in the proteostasis network (PN). Such processes include protein synthesis, folding, and degradation in both non-stressed and stressful conditions. The role of the PN in neurodegenerative disease is well-documented, where it is known to respond to changes in protein folding states or toxic gain-of-function protein aggregation. Dual-specificity phosphatases have recently emerged as important participants in maintaining balance within the PN, acting through modulation of cellular signaling pathways that are involved in neurodegeneration. In this review, we will summarize recent findings describing the roles of dual-specificity phosphatases in neurodegeneration and offer perspectives on future therapeutic directions.