Betulin, a Newly Characterized Compound in Acacia auriculiformis Bark, Is a Multi-Target Protein Kinase Inhibitor

The purpose of this work is to investigate the protein kinase inhibitory activity of constituents from Acacia auriculiformis stem bark. Column chromatography and NMR spectroscopy were used to purify and characterize betulin from an ethyl acetate soluble fraction of acacia bark. Betulin, a known inducer of apoptosis, was screened against a panel of 16 disease-related protein kinases. Betulin was shown to inhibit Abelson murine leukemia viral oncogene homolog 1 (ABL1) kinase, casein kinase 1ε (CK1ε), glycogen synthase kinase 3α/β (GSK-3 α/β), Janus kinase 3 (JAK3), NIMA Related Kinase 6 (NEK6), and vascular endothelial growth factor receptor 2 kinase (VEGFR2) with activities in the micromolar range for each. The effect of betulin on the cell viability of doxorubicin-resistant K562R chronic myelogenous leukemia cells was then verified to investigate its putative use as an anti-cancer compound. Betulin was shown to modulate the mitogen-activated protein (MAP) kinase pathway, with activity similar to that of imatinib mesylate, a known ABL1 kinase inhibitor. The interaction of betulin and ABL1 was studied by molecular docking, revealing an interaction of the inhibitor with the ABL1 ATP binding pocket. Together, these data demonstrate that betulin is a multi-target inhibitor of protein kinases, an activity that can contribute to the anticancer properties of the natural compound and to potential treatments for leukemia.

Neurymenolide A, a Novel Mitotic Spindle Poison from the New Caledonian Rhodophyta Phacelocarpus neurymenioides

The marine α-pyrone macrolide neurymenolide A was previously isolated from the Fijian red macroalga, Neurymenia fraxinifolia, and characterized as an antibacterial agent against antibiotic-resistant strains that also exhibited moderate cytotoxicity in vitro against cancer cell lines. This compound was also shown to exhibit allelopathic effects on Scleractinian corals. However, to date no mechanism of action has been described in the literature. The present study showed, for the first time, the isolation of neurymenolide A from the New Caledonian Rhodophyta, Phacelocarpus neurymenioides. We confirmed the compound’s moderate cytotoxicity in vitro against several human cell lines, including solid and hematological malignancies. Furthermore, we combined fluorescence microscopy and flow cytometry to demonstrate that treatment of U-2 OS osteosarcoma human cells with neurymenolide A could block cell division in prometaphase by inhibiting the correct formation of the mitotic spindle, which induced a mitotic catastrophe that led to necrosis and apoptosis. Absolute configuration of the stereogenic center C-17 of neurymenolide A was deduced by comparison of the experimental and theoretical circular dichroism spectra. Since the total synthesis of this compound has already been described, our findings open new avenues in cancer treatment for this class of marine molecules, including a new source for the natural product.

Casein kinase 1ε and 1α as novel players in polycystic kidney disease and mechanistic targets for (R)-roscovitine and (S)-CR8

Following the discovery of (R)-roscovitine's beneficial effects in three polycystic kidney disease (PKD) mouse models, cyclin-dependent kinases (CDKs) inhibitors have been investigated as potential treatments. We have used various affinity chromatography approaches to identify the molecular targets of roscovitine and its more potent analog (S)-CR8 in human and murine polycystic kidneys. These methods revealed casein kinases 1 (CK1) as additional targets of the two drugs. CK1ε expression at the mRNA and protein levels is enhanced in polycystic kidneys of 11 different PKD mouse models as well as in human polycystic kidneys. A shift in the pattern of CK1α isoforms is observed in all PKD mouse models. Furthermore, the catalytic activities of both CK1ε and CK1α are increased in mouse polycystic kidneys. Inhibition of CK1ε and CK1α may thus contribute to the long-lasting attenuating effects of roscovitine and (S)-CR8 on cyst development. CDKs and CK1s may constitute a dual therapeutic target to develop kinase inhibitory PKD drug candidates.

6E11, a highly selective inhibitor of Receptor-Interacting Protein Kinase 1, protects cells against cold hypoxia-reoxygenation injury

Necroptosis is a programmed cell death pathway that has been shown to be of central pathophysiological relevance in multiple disorders (hepatitis, brain and cardiac ischemia, pancreatitis, viral infection and inflammatory diseases). Necroptosis is driven by two serine threonine kinases, RIPK1 (Receptor Interacting Protein Kinase 1) and RIPK3, and a pseudo-kinase MLKL (Mixed Lineage Kinase domain-Like) associated in a multi-protein complex called necrosome. In order to find new inhibitors for use in human therapy, a chemical library containing highly diverse chemical structures was screened using a cell-based assay. The compound 6E11, a natural product derivative, was characterized as a positive hit. Interestingly, this flavanone compound: inhibits necroptosis induced by death receptors ligands TNF-α (Tumor Necrosis Factor) or TRAIL (TNF-Related Apoptosis-Inducing Ligand); is an extremely selective inhibitor, among kinases, of human RIPK1 enzymatic activity with a nM Kd; has a non-ATP competitive mode of action and a novel putative binding site; is weakly cytotoxic towards human primary blood leukocytes or retinal pigment epithelial cells at effective concentrations; protects human aortic endothelial cells (HAEC) from cold hypoxia/reoxygenation injury more effectively than necrostatin-1 (Nec-1) and Nec-1s. Altogether, these data demonstrate that 6E11 is a novel potent small molecular inhibitor of RIPK1-driven necroptosis.

Sibiriline, a new small chemical inhibitor of receptor-interacting protein kinase 1, prevents immune-dependent hepatitis

Necroptosis is a regulated form of cell death involved in several disease models including in particular liver diseases. Receptor-interacting protein kinases, RIPK1 and RIPK3, are the main serine/threonine kinases driving this cell death pathway. We screened a noncommercial, kinase-focused chemical library which allowed us to identify Sibiriline as a new inhibitor of necroptosis induced by tumor necrosis factor (TNF) in Fas-associated protein with death domain (FADD)-deficient Jurkat cells. Moreover, Sib inhibits necroptotic cell death induced by various death ligands in human or mouse cells while not protecting from caspase-dependent apoptosis. By using competition binding assay and recombinant kinase assays, we demonstrated that Sib is a rather specific competitive RIPK1 inhibitor. Molecular docking analysis shows that Sib is trapped closed to human RIPK1 adenosine triphosphate-binding site in a relatively hydrophobic pocket locking RIPK1 in an inactive conformation. In agreement with its RIPK1 inhibitory property, Sib inhibits both TNF-induced RIPK1-dependent necroptosis and RIPK1-dependent apoptosis. Finally, Sib protects mice from concanavalin A-induced hepatitis. These results reveal the small-molecule Sib as a new RIPK1 inhibitor potentially of interest for the treatment of immune-dependent hepatitis.

Synthesis, biological evaluation and molecular modeling studies of imidazo[1,2-a]pyridines derivatives as protein kinase inhibitors

We report here the synthesis, the biological evaluation and the molecular modeling studies of new imidazo[1,2-a]pyridines derivatives designed as potent kinase inhibitors. This collection was obtained from 2-aminopyridines and 2-bromoacetophenone which afforded final compound in only one step. The bioactivity of this family of new compounds was tested using protein kinase and ATP competition assays. The structure-activity relationship (SAR) revealed that six compounds inhibit DYRK1A and CLK1 at a micromolar range. Docking studies provided possible explanations that correlate with the SAR data. The most active compound 4c inhibits CLK1 (IC50 of 0.7 μM) and DYRK1A (IC50 of 2.6 μM).

Development of new highly potent imidazo[1,2-b]pyridazines targeting Toxoplasma gondii calcium-dependent protein kinase 1

Using a structure-based design approach, we have developed a new series of imidazo[1,2-b]pyridazines, targeting the calcium-dependent protein kinase-1 (CDPK1) from Toxoplasma gondii. Twenty derivatives were thus synthesized. Structure-activity relationships and docking studies confirmed the binding mode of these inhibitors within the ATP binding pocket of TgCDPK1. Two lead compounds (16a and 16f) were then identified, which were able to block TgCDPK1 enzymatic activity at low nanomolar concentrations, with a good selectivity profile against a panel of mammalian kinases. The potential of these inhibitors was confirmed in vitro on T. gondii growth, with EC50 values of 100 nM and 70 nM, respectively. These best candidates also displayed low toxicity to mammalian cells and were selected for further in vivo investigations on murine model of acute toxoplasmosis.