Design, Synthesis, and Molecular Docking of Novel Miscellaneous Chalcones as p38α Mitogen-Activated Protein Kinase Inhibitors.

New chalcones were synthesized and evaluated to serve as p38-α type of mitogen-activated protein kinase (MAPK) inhibitors. According to the National Cancer Institute, the findings indicated that at a 10 µM dosage, compounds 3a and 6 were the most active among all the compounds examined, with mean growth inhibition% of 94.83 and 58.49, respectively. In 5-dose testing, they showed anticancer activity in the micro-molar range with GI50 in the range of 1.41-46.1 and 2.07-31.3 µM, respectively. Besides, powerful activity, especially against the leukaemia cell lines and good selectivity to cancer cells compared to normal PCS-800-017 with a selectivity index=12.41 and 23.77, respectively. Compounds 3a and 6 inhibited p38α MAPK with IC50 values of 0.1462±0.0063 and 0.4356±0.0189 µM, correspondingly. 3a showed good inhibition for HL-60(TB) cells and induced cell cycle arrest in HL-60(TB) cells at the G2/M phase. Besides, it elevated the total apoptosis by 14.68-fold and increased the caspase-3 level by 3.52-fold compared with doxorubicin, which raised it by 4.30-fold, inducing apoptosis by acting as caspase-dependent inducers. These results suggest that 3a is a promising antiproliferative and p38α MAPK inhibitor, confirmed by molecular docking with high compatibility 3a with the p38α MAPK binding site.

Architecture of the MKK6-p38α complex defines the basis of MAPK specificity and activation.

The mitogen-activated protein kinase (MAPK) p38α is a central component of signaling in inflammation and the immune response and is, therefore, an important drug target. Little is known about the molecular mechanism of its activation by double phosphorylation from MAPK kinases (MAP2Ks), because of the challenge of trapping a transient and dynamic heterokinase complex. We applied a multidisciplinary approach to generate a structural model of p38α in complex with its MAP2K, MKK6, and to understand the activation mechanism. Integrating cryo-electron microscopy with molecular dynamics simulations, hydrogen-deuterium exchange mass spectrometry, and experiments in cells, we demonstrate a dynamic, multistep phosphorylation mechanism, identify catalytically relevant interactions, and show that MAP2K-disordered amino termini determine pathway specificity. Our work captures a fundamental step of cell signaling: a kinase phosphorylating its downstream target kinase.

Machine Learning Assisted Discovery of Novel p38α Inhibitors from Natural Products.

BACKGROUND: P38α, emerging as a hot spot for drug discovery, is a member of the mitogen- activated protein kinase (MAPK) family and plays a crucial role in regulating the production of inflammatory mediators. However, despite a massive number of highly potent molecules being reported and several under clinical trials, no p38α inhibitor has been approved yet. There is still demand to discover novel p38α to deal with the safety issue induced by off-target effects. OBJECTIVE: In this study, we performed a machine learning-based virtual screening to identify p38α inhibitors from a natural products library, expecting to find novel drug lead scaffolds. METHODS: Firstly, the training dataset was processed with similarity screening to fit the chemical space of the natural products library. Then, six classifiers were constructed by combing two sets of molecular features with three different machine learning algorithms. After model evaluation, the three best classifiers were used for virtual screening. RESULTS: Among the 15 compounds selected for experimental validation, picrasidine S was identified as a p38α inhibitor with the IC50 as 34.14 µM. Molecular docking was performed to predict the interaction mode of picrasidine S and p38α, indicating a specific hydrogen bond with Met109. CONCLUSION: This work provides a protocol and example for machine learning-assisted discovery of p38α inhibitor from natural products, as well as a novel lead scaffold represented by picrasidine S for further optimization and investigation.

p38α Kinase Auto-Activation through Its Conformational Transition Induced by Tyr323 Phosphorylation.

p38α is a key serine/threonine kinase that can enable atypical auto-activation through Zap70 phosphorylation and initiate T cell receptor signaling. The auto-activation plays an important role in autoimmune diseases. Although the classical activation mechanism of p38α has been studied in-depth, the atypical activation mechanism of Y323 phosphorylation-induced p38α auto-activation remains largely unexplained, especially the regulatory effects of phosphorylation on different sites (Y323 vs T180). From the X-ray experimental data, we identified the inactive and active states of p38α using principal component analysis. To understand the auto-activation process and the internal driving mechanism, a computational paradigm that couples the targeted molecular dynamics simulations, the String Method, and the umbrella sampling strategy were employed to generate the conformational landscape of p38α, including p38α T180-Y323, p38α T180-pY323, and p38α pT180-pY323 systems (pT180/pY323: phosphorylated T180/Y323). We explored that pY323 could change the conformational distribution and promote the conformational transition of p38α from the inactive state to the active state. Auto-activation of p38α is regulated by pY323 through destabilization of the hydrophobic core structure and aided by R173. This study will further explain the conformational transition of p38α induced by Y323 phosphorylation and provide insights into the universal molecular auto-activation mechanism of the p38 subfamily at the atomic level.

TAB1 binding induced p38α conformation change: an accelerated molecular dynamics simulation study.

p38α mitogen-activated protein kinase (MAPK) undergoes autophosphorylation induced by the binding of TGFß-activated kinase 1 binding protein 1 (TAB1) in myocardial ischemia. Investigation of the conformational transformations in p38α triggered by TAB1 binding is motivated by the need to find selective p38α activation inhibitors to treat myocardial ischemia. Herein, the conformational transformations of p38α were studied via all-atom accelerated molecular dynamics simulations and principal component analysis. With the binding of TAB1, the conformational changes of p38α auto-activation were characterized by the movement of the activation loop (A-loop) away from the αG helix toward the αF, αE helixes and L16-loop. In addition, a diverse intermediate state with an extensional and phosphorylated A-loop different from the transition intermediate state was explored. The conformational changes, including the A-loop alpha-structure breaking and the stronger hydrogen bond network formation, are accompanied by the extension of the A-loop and more intramolecular interactions in p38α. TAB1 correlates with other regions of p38α that are distal from the TAB1-binding site, including the A-loop, αC helix, and L16-loop, which regulates the intramolecular correlation of p38α. And, the phosphorylation further enhances the correlations between the A-loop and the other regions of p38α. The correlation results imply the regulation process of p38α conformational transformations. These findings will improve our understanding of the autophosphorylation of kinase and facilitate the development of selective inhibitors for the treatment of ischemic injury.

Decisive role of water and protein dynamics in residence time of p38α MAP kinase inhibitors.

Target residence time plays a crucial role in the pharmacological activity of small molecule inhibitors. Little is known, however, about the underlying causes of inhibitor residence time at the molecular level, which complicates drug optimization processes. Here, we employ all-atom molecular dynamics simulations (~400 µs in total) to gain insight into the binding modes of two structurally similar p38α MAPK inhibitors (type I and type I½) with short and long residence times that otherwise show nearly identical inhibitory activities in the low nanomolar IC50 range. Our results highlight the importance of protein conformational stability and solvent exposure, buried surface area of the ligand and binding site resolvation energy for residence time. These findings are further confirmed by simulations with a structurally diverse short residence time inhibitor SB203580. In summary, our data provide guidance in compound design when aiming for inhibitors with improved target residence time.

Enthalpy-Entropy Compensation in the Promiscuous Interaction of an Intrinsically Disordered Protein with Homologous Protein Partners.

Intrinsically disordered proteins (IDPs) can engage in promiscuous interactions with their protein targets; however, it is not clear how this feature is encoded in the primary sequence of the IDPs and to what extent the surface properties and the shape of the binding cavity dictate the binding mode and the final bound conformation. Here we show, using a combination of nuclear magnetic resonance (NMR) spectroscopy and isothermal titration calorimetry (ITC), that the promiscuous interaction of the intrinsically disordered regulatory domain of the mitogen-activated protein kinase kinase MKK4 with p38α and JNK1 is facilitated by folding-upon-binding into two different conformations, despite the high sequence conservation and structural homology between p38α and JNK1. Our results support a model whereby the specific surface properties of JNK1 and p38α dictate the bound conformation of MKK4 and that enthalpy-entropy compensation plays a major role in maintaining comparable binding affinities for MKK4 towards the two kinases.

Screening of DNA-Encoded Small Molecule Libraries inside a Living Cell.

DNA-encoded small molecule libraries (DELs) have facilitated the discovery of novel modulators of many different therapeutic protein targets. We report the first successful screening of a multimillion membered DEL inside a living cell. We demonstrate a novel method using oocytes from the South African clawed frog Xenopus laevis. The large size of the oocytes of 1 µL, or 100 000 times bigger than a normal somatic cell, permits simple injection of DELs, thus resolving the fundamental problem of delivering DELs across cell membranes for in vivo screening. The target protein was expressed in the oocytes fused to a prey protein, to allow specific DNA labeling and hereby discriminate between DEL members binding to the target protein and the endogenous cell proteins. The 194 million member DEL was screened against three pharmaceutically relevant protein targets, p38α, ACSS2, and DOCK5. For all three targets multiple chemical clusters were identified. For p38α, validated hits with single digit nanomolar potencies were obtained. This work demonstrates a powerful new approach to DEL screening, which eliminates the need for highly purified active target protein and which performs the screening under physiological relevant conditions and thus is poised to increase the DEL amenable target space and reduce the attrition rates.

Current status and future prospects of p38α/MAPK14 kinase and its inhibitors.

P38α (which is also named MAPK14) plays a pivotal role in initiating different disease states such as inflammatory disorders, neurodegenerative diseases, cardiovascular cases, and cancer. Inhibitors of p38α can be utilized for treatment of these diseases. In this article, we reviewed the structural and biological characteristics of p38α, its relationship to the fore-mentioned disease states, as well as the recently reported inhibitors and classified them according to their chemical structures. We focused on the articles published in the literature during the last decade (2011-2020).

Conformational selection vs. induced fit: insights into the binding mechanisms of p38α MAP Kinase inhibitors.

The conformational dynamics of a kinase's activation loop have been challenging to assess due to the activation loop's intrinsic flexibility. To directly probe the conformational equilibrium of the activation loop of mitogen-activated protein kinase p38α, we present an approach based on site-directed spin labeling, electron paramagnetic resonance (EPR) distance restraints, and multilateration. We demonstrate that the activation loop of apo p38α resides in a highly flexible equilibrium state and we reveal that binding of small molecules significantly alters this equilibrium and the populated sub-states.

Optimal linker length for small molecule PROTACs that selectively target p38α and p38ß for degradation.

We report the design of hetero-bifunctional small molecules that selectively target p38α and p38ß for degradation. These proteolysis targeted chimeras (PROTACs) are based on an ATP competitive inhibitor of p38α and p38ß, which is linked to thalidomide analogues to recruit the Cereblon E3 ubiquitin ligase complex. Compound synthesis was facilitated by the use of a copper catalyzed "click" reaction. We show that optimization of the linker length and composition is crucial for the degradation-inducing activity of these PROTACs. We provide evidence that these chemical compounds can induce degradation of p38α and p38ß but no other related kinases at nanomolar concentrations in several mammalian cell lines. Accordingly, the PROTACs inhibit stress and cytokine-induced p38α signaling. Our compounds contribute to understanding the development of PROTACs, and provide a useful tool to investigate functions of the p38 MAPK pathway and its involvement in diseases.

MAP Kinase-Mediated Activation of RSK1 and MK2 Substrate Kinases.

Mitogen-activated protein kinases (MAPKs) control essential eukaryotic signaling pathways. While much has been learned about MAPK activation, much less is known about substrate recruitment and specificity. MAPK substrates may be other kinases that are crucial to promote a further diversification of the signaling outcomes. Here, we used a variety of molecular and cellular tools to investigate the recruitment of two substrate kinases, RSK1 and MK2, to three MAPKs (ERK2, p38α, and ERK5). Unexpectedly, we identified that kinase heterodimers form structurally and functionally distinct complexes depending on the activation state of the MAPK. These may be incompatible with downstream signaling, but naturally they may also form structures that are compatible with the phosphorylation of the downstream kinase at the activation loop, or alternatively at other allosteric sites. Furthermore, we show that small-molecule inhibitors may affect the quaternary arrangement of kinase heterodimers and thus influence downstream signaling in a specific manner.

Proline Hydroxylation Primes Protein Kinases for Autophosphorylation and Activation.

Activation of dual-specificity tyrosine-phosphorylation-regulated kinases 1A and 1B (DYRK1A and DYRK1B) requires prolyl hydroxylation by PHD1 prolyl hydroxylase. Prolyl hydroxylation of DYRK1 initiates a cascade of events leading to the release of molecular constraints on von Hippel-Lindau (VHL) ubiquitin ligase tumor suppressor function. However, the proline residue of DYRK1 targeted by hydroxylation and the role of prolyl hydroxylation in tyrosine autophosphorylation of DYRK1 are unknown. We found that a highly conserved proline in the CMGC insert of the DYRK1 kinase domain is hydroxylated by PHD1, and this event precedes tyrosine autophosphorylation. Mutation of the hydroxylation acceptor proline precludes tyrosine autophosphorylation and folding of DYRK1, resulting in a kinase unable to preserve VHL function and lacking glioma suppression activity. The consensus proline sequence is shared by most CMGC kinases, and prolyl hydroxylation is essential for catalytic activation. Thus, formation of prolyl-hydroxylated intermediates is a novel mechanism of kinase maturation and likely a general mechanism of regulation of CMGC kinases in eukaryotes.

Mining the PDB for Tractable Cases Where X-ray Crystallography Combined with Fragment Screens Can Be Used to Systematically Design Protein-Protein Inhibitors: Two Test Cases Illustrated by IL1ß-IL1R and p38α-TAB1 Complexes.

Nowadays, it is possible to combine X-ray crystallography and fragment screening in a medium throughput fashion to chemically probe the surfaces used by proteins to interact and use the outcome of the screens to systematically design protein-protein inhibitors. To prove it, we first performed a bioinformatics analysis of the Protein Data Bank protein complexes, which revealed over 400 cases where the crystal lattice of the target in the free form is such that large portions of the interacting surfaces are free from lattice contacts and therefore accessible to fragments during soaks. Among the tractable complexes identified, we then performed single fragment crystal screens on two particular interesting cases: the Il1ß-ILR and p38α-TAB1 complexes. The result of the screens showed that fragments tend to bind in clusters, highlighting the small-molecule hotspots on the surface of the target protein. In most of the cases, the hotspots overlapped with the binding sites of the interacting proteins.

Bioisosteric Replacement of Arylamide-Linked Spine Residues with N-Acylhydrazones and Selenophenes as a Design Strategy to Novel Dibenzosuberone Derivatives as Type I 1/2 p38α MAP Kinase Inhibitors.

The recent disclosure of type I 1/2 inhibitors for p38α MAPK demonstrated how the stabilization of the R-spine can be used as a strategy to greatly increase the target residence time (TRT) of inhibitors. Herein, for the first time, we describe N-acylhydrazone and selenophene residues as spine motifs, yielding metabolically stable inhibitors with high potency on enzymatic, NanoBRET, and whole blood assays, improved metabolic stability, and prolonged TRT.

Dibenzepinones, dibenzoxepines and benzosuberones based p38α MAP kinase inhibitors: Their pharmacophore modelling, 3D-QSAR and docking studies.

In the present study, a series of dibenzepinones, dibenzoxepines, and benzosuberones targeting p38α MAP kinase were subjected to pharmacophore modelling, 3D-QSAR and molecular docking studies. The IC50 values for these 67 compounds ranged between 0.003 and 6.80 µM. A five-point model (DDHHR.8) was generated using these compounds. This model was found to be statistically significant and was found to have high correlation (R2 = 0.98), cross-validation coefficient (Q2 = 0.95) and F (330) values at six component PLS factor. Tests were performed to ascertain the efficacy of the generated model. These tests included external validation, Tropsha's test for predictive ability, Y-randomisation test and domain of applicability (APD). In order to check the restrictivity of the model, enrichment studies were performed with inactive compounds by using decoy set molecules. To evaluate the effectiveness of the docking protocol, the co-crystallised ligand was extracted from the ligand-binding domain of the protein and was re-docked into the same position. Both the conformers were then superimposed, suggesting satisfactory docking parameters with an RMSD value of less than 1.0 Š(0.853 Å). A 10 ns molecular dynamics simulation confirmed the docking results of the 3UVP-ligand complex and the presumed active conformation. The outcome of the present study provides insight into the molecular features that promote bioactivity and can be exploited for the prediction of novel potent p38α MAP kinase inhibitors before carrying out their synthesis and anticancer evaluation.

A temperature-dependent conformational shift in p38α MAPK substrate-binding region associated with changes in substrate phosphorylation profile.

Febrile-range hyperthermia worsens and hypothermia mitigates lung injury, and temperature dependence of lung injury is blunted by inhibitors of p38 mitogen-activated protein kinase (MAPK). Of the two predominant p38 isoforms, p38α is proinflammatory and p38ß is cytoprotective. Here, we analyzed the temperature dependence of p38 MAPK activation, substrate interaction, and tertiary structure. Incubating HeLa cells at 39.5 °C stimulated modest p38 activation, but did not alter tumor necrosis factor-α (TNFα)-induced p38 activation. In in vitro kinase assays containing activated p38α and MAPK-activated kinase-2 (MK2), MK2 phosphorylation was 14.5-fold greater at 39.5 °C than at 33 °C. By comparison, we observed only 3.1- and 1.9-fold differences for activating transcription factor-2 (ATF2) and signal transducer and activator of transcription-1α (STAT1α) and a 7.7-fold difference for p38ß phosphorylation of MK2. The temperature dependence of p38α:substrate binding affinity, as measured by surface plasmon resonance, paralleled substrate phosphorylation. Hydrogen-deuterium exchange MS (HDX-MS) of p38α performed at 33, 37, and 39.5 °C indicated temperature-dependent conformational changes in an α helix near the common docking and glutamate:aspartate substrate-binding domains at the known binding site for MK2. In contrast, HDX-MS analysis of p38ß did not detect significant temperature-dependent conformational changes in this region. We observed no conformational changes in the catalytic domain of either isoform and no corresponding temperature dependence in the C-terminal p38α-interacting region of MK2. Because MK2 participates in the pathogenesis of lung injury, the observed changes in the structure and function of proinflammatory p38α may contribute to the temperature dependence of acute lung injury.

Molecular mechanisms involved in drug-induced liver injury caused by urate-lowering Chinese herbs: A network pharmacology study and biology experiments.

As an important part of the comprehensive treatment methods, the urate-lowering Chinese herbs could provide favorable clinical effects on hyperuricemia in its ability to invigorate spleen and remove dampness. Owing to the long-term duration, it brought up the potential adverse reactions (ADRs) and concerns about the drug-induced liver injury from these herbs. To address this problem, the bioinformatics approaches which combined the network pharmacology, computer simulation and molecular biology experiments were undertaken to elucidate the underlying drug-induced liver injury molecular mechanisms of urate-lowering Chinese herbs. Several electronic databases were searched to identify the potential liver injury compounds in published research. Then, the putative target profile of liver injury was predicted, and the interaction network was constructed based on the links between the compounds, corresponding targets and core pathways. Accordingly, the molecular docking simulation was performed to recognize the representative compounds with hepatotoxicity. Finally, the cell experiments were conducted to investigate the biochemical indicators and expression of the crucial protein that were closely associated with liver injury. In conclusion, the current research revealed that the compounds with potential liver injury including diosgenin, baicalin, saikosaponin D, tetrandrine, rutaecarpine and evodiamine from urate-lowering Chinese herbs, could lead to decline the survival rate of L-02 cell, increase the activities of aspartate aminotransferase (AST), alanine aminotransferase (ALT), lactate dehydrogenase (LDH) and alkaline phosphatase (ALP) in cell-culture medium, enhance the expression of p-p38/p38, while the p38 inhibitor could achieve the trend of regulating and controlling liver injury. These research findings bring further support to the growing evidence that the mechanism of the liver injury induced by the compounds from urate-lowering Chinese herbs may be associated with the activation of p38α.

Co-crystal structure determination and cellular evaluation of 1,4-dihydropyrazolo[4,3-c] [1,2] benzothiazine 5,5-dioxide p38α MAPK inhibitors.

p38α mitogen-activated protein kinase (MAPK) is an attracting pharmacological target in inflammatory diseases and cancer. Searching for new and more efficient p38-MAPK inhibitors, two recently developed pyrazolobenzothiazine-based (COXP4M12 and COXH11) compounds were investigated in this study using a cellular model of p38 activation. This consisted of HT29 human colorectal adenocarcinoma cells exposed to H2O2 or lipopolysaccharide (LPS). Immunoblot data confirmed the inhibitory effect of COXP4M12 and COXH11 on p38 substrate phosphorylation (MAPK-APK2 and ATF2 transcription factor). Compound cytotoxicity was very low and apparent efficacy of these inhibitors was comparable with that of SB203580, a commercially available type I inhibitor of p38. All these compounds also inhibit upstream kinases that promote p38-MAPK phosphorylation and co-activate the stress-activated protein kinase JNK, while ERK1/2 MAPK phosphorylation was unaffected. Compound-target kinase interaction was investigated by means of co-crystallization experiments that provided further structural and molecular insight on the inhibitory mechanism and optimization strategy of this new class of p38-MAPK inhibitors.

Fragment-Based Structural Optimization of a Natural Product Itampolin A as a p38α Inhibitor for Lung Cancer.

Marine animals and plants provide abundant secondary metabolites with antitumor activity. Itampolin A is a brominated natural tyrosine secondary metabolite that is isolated from the sponge Iotrochota purpurea. Recently, we have achieved the first total synthesis of this brominated tyrosine secondary metabolite, which was found to be a potent p38α inhibitor exhibiting anticancer effects. A fragment-based drug design (FBDD) was carried out to optimize itampolin A. Forty-five brominated tyrosine derivatives were synthesized with interesting biological activities. Then, a QSAR study was carried out to explore the structural determinants responsible for the activity of brominated tyrosine skeleton p38α inhibitors. The lead compound was optimized by a FBDD method, then three series of brominated tyrosine derivatives were synthesized and evaluated for their inhibitory activities against p38α and tumor cells. Compound 6o (IC50 = 0.66 µM) exhibited significant antitumor activity against non-small cell lung A549 cells (A549). This also demonstrated the feasibility of the FBDD method of structural optimization.