In the past decade, the spleen tyrosine kinase (Syk) has shown a high potential for the discovery of new treatments for inflammatory and autoimmune disorders. Pharmacological inhibitors of Syk catalytic site bearing therapeutic potential have been developed, with however limited specificity towards Syk. To address this topic, we opted for the design of drug-like compounds that could impede the interaction of Syk with its cellular partners while maintaining an active kinase protein. To achieve this challenging task, we used the powerful potential of intracellular antibodies for the modulation of cellular functions in vivo, combined to structure-based in silico screening. In our previous studies, we reported the anti-allergic properties of the intracellular antibody G4G11. With the aim of finding functional mimics of G4G11, we developed an Antibody Displacement Assay and we isolated the drug-like compound C-13, with promising in vivo anti-allergic activity. The likely binding cavity of this compound is located at the close vicinity of G4G11 epitope, far away from the catalytic site of Syk. Here we report the virtual screen of a collection of 500,000 molecules against this new cavity, which led to the isolation of 1000 compounds subsequently evaluated for their in vitro inhibitory effects using the Antibody Displacement Assay. Eighty five compounds were selected and evaluated for their ability to inhibit the liberation of allergic mediators from mast cells. Among them, 10 compounds inhibited degranulation with IC50 values ≤10 µM. The most bioactive compounds combine biological activity, significant inhibition of antibody binding and strong affinity for Syk. Moreover, these molecules show a good potential for oral bioavailability and are not kinase catalytic site inhibitors. These bioactive compounds could be used as starting points for the development of new classes of non-enzymatic inhibitors of Syk and for drug discovery endeavour in the field of inflammation related disorders.
In this study we probe and verify the concept of designing unreactive bioactive metal complexes, in which the metal possesses a purely structural function, by investigating the consequences of replacing ruthenium in a bioactive half-sandwich kinase inhibitor scaffold by its heavier congener osmium. The two isostructural complexes are compared with respect to their anticancer properties in 1205Lu melanoma cells, activation of the wnt signaling pathway, IC50 values against the protein kinases GSK-3β and Pim-1, and binding modes to the protein kinase Pim-1 by protein crystallography. It was found that the two congeners display almost indistinguishable biological activities which can be explained by their nearly identical three-dimensional structures and their identical mode of action as protein kinase inhibitors. This is a unique example in which the replacement of a metal in an anticancer scaffold by its heavier homolog does not alter the biological activity.
Bioorganometallic chemistry; kinase inhibitors; anticancer; ruthenium; osmium
Protein tyrosine phosphatases (PTPs) are a diverse family of enzymes encoded by 107 genes in the human genome. Together with protein tyrosine kinases (PTKs), PTPs regulate various cellular activities essential for the initiation and maintenance of malignant phenotypes. While PTK inhibitors are now used routinely for cancer treatment, the PTP inhibitor development field is still in the discovery phase. In this article, the suitability of targeting PTPs for novel anticancer drug discovery is discussed. Examples are presented for PTPs that have been targeted for anticancer drug discovery as well as potential new PTP targets for novel anticancer drug discovery.
Protein tyrosine phosphatase inhibitor; Shp2; PTP1B; Cdc14; PRL-3; LMW-PTP; Cdc25; Eya
Protein kinases are key signaling enzymes that catalyze the transfer of γ-phosphate from an ATP molecule to a phospho-accepting residue in the substrate. Unraveling the molecular features that govern the preference of kinases for particular residues flanking the phosphoacceptor is important for understanding kinase specificities toward their substrates and for designing substrate-like peptidic inhibitors. We applied ANCHORSmap, a new fragment-based computational approach for mapping amino acid side chains on protein surfaces, to predict and characterize the preference of kinases toward Arginine binding. We focus on positions P−2 and P−5, commonly occupied by Arginine (Arg) in substrates of basophilic Ser/Thr kinases. The method accurately identified all the P−2/P−5 Arg binding sites previously determined by X-ray crystallography and produced Arg preferences that corresponded to those experimentally found by peptide arrays. The predicted Arg-binding positions and their associated pockets were analyzed in terms of shape, physicochemical properties, amino acid composition, and in-silico mutagenesis, providing structural rationalization for previously unexplained trends in kinase preferences toward Arg moieties. This methodology sheds light on several kinases that were described in the literature as having non-trivial preferences for Arg, and provides some surprising departures from the prevailing views regarding residues that determine kinase specificity toward Arg. In particular, we found that the preference for a P−5 Arg is not necessarily governed by the 170/230 acidic pair, as was previously assumed, but by several different pairs of acidic residues, selected from positions 133, 169, and 230 (PKA numbering). The acidic residue at position 230 serves as a pivotal element in recognizing Arg from both the P−2 and P−5 positions.
Protein kinases are key signaling enzymes and major drug targets that catalyze the transfer of phosphate group to a phospho-accepting residue in the substrate. Unraveling molecular features that govern the preference of kinases for particular residues flanking the phosphoacceptor (substrate consensus sequence, SCS) is important for understanding kinase-substrates specificities and for designing peptidic inhibitors. Current methods used to predict this set of essential residues usually rely on linking between experimentally determined SCSs to kinase sequences. As such, these methods are less sensitive when specificity is dictated by subtle or kinase-unique sequence/structural features. In this study, we took a different approach for studying kinases specificities, by applying a new fragment-based method for mapping amino acid side chains on protein surfaces. We predicted and characterized the preference of Ser/Thr kinases toward Arginine binding, using the unbound kinase structures. The method produced high quality predictions and was able to provide novel insights and interesting departures from the prevailing views regarding the specificity-determining elements governing specificity toward Arginine. This work paves the way for studying the kinase binding preferences for other amino acids, for predicting protein-peptide structures, for facilitating the design of novel inhibitors, and for re-engineering of kinase specificities.
Carboxylesterases (CEs) are important enzymes that catalyze biological detoxification, hydrolysis of certain pesticides, and metabolism of many esterified drugs. The development of inhibitors for CE has many potential uses, including increasing drug lifetime and altering biodistrubution; reducing or abrogating toxicity of metabolized drugs; and reducing pest resistance to insecticides. In this review, we discuss the major classes of known mammalian CE inhibitors and describe our computational efforts to design new scaffolds for development of novel, selective inhibitors. We discuss several strategies for in silico inhibitor development, including structure docking, database searching, multidimensional quantitative structure activity analysis (QSAR), and a newly-used approach that uses QSAR combined with de novo drug design. While our research is focused on design of specific inhibitors for human intestinal carboxylesterase (hiCE), the methods described are generally applicable to inhibitors of other enzymes, including CE from other tissues and organisms.
irinotecan; CPT-11; molecular dynamics; QSAR; drug design; modeling
Novel classes of antimicrobials are needed to address the challenge of multidrug-resistant bacteria such as methicillin-resistant Staphylococcus aureus (MRSA). Using the architecture of the MRSA interactome, we identified pyruvate kinase (PK) as a potential novel drug target based upon it being a highly connected, essential hub in the MRSA interactome. Structural modeling, including X-ray crystallography, revealed discrete features of PK in MRSA, which appeared suitable for the selective targeting of the bacterial enzyme. In silico library screening combined with functional enzymatic assays identified an acyl hydrazone-based compound (IS-130) as a potent MRSA PK inhibitor (50% inhibitory concentration [IC50] of 0.1 μM) with >1,000-fold selectivity over human PK isoforms. Medicinal chemistry around the IS-130 scaffold identified analogs that more potently and selectively inhibited MRSA PK enzymatic activity and S. aureus growth in vitro (MIC of 1 to 5 μg/ml). These novel anti-PK compounds were found to possess antistaphylococcal activity, including both MRSA and multidrug-resistant S. aureus (MDRSA) strains. These compounds also exhibited exceptional antibacterial activities against other Gram-positive genera, including enterococci and streptococci. PK lead compounds were found to be noncompetitive inhibitors and were bactericidal. In addition, mutants with significant increases in MICs were not isolated after 25 bacterial passages in culture, indicating that resistance may be slow to emerge. These findings validate the principles of network science as a powerful approach to identify novel antibacterial drug targets. They also provide a proof of principle, based upon PK in MRSA, for a research platform aimed at discovering and optimizing selective inhibitors of novel bacterial targets where human orthologs exist, as leads for anti-infective drug development.
The receptor tyrosine kinase AXL has emerged in recent years as an potential oncology target due to its over expression in several types of cancers coupled with its ability to promote tumor growth and metastasis. In order to identify small molecule inhibitors of AXL, we built a homology model of its catalytic domain to virtually screen and identify scaffolds displaying an affinity for AXL. Further computational and structure-based design resulted in the synthesis of a series of 2,4,5-trisubstitued pyrimidines which demonstrated potent inhibition of AXL in vitro (IC50 19 nM) and strongly inhibited the growth of several pancreatic cell lines.
AXL kinase inhibitors; anticancer; structure-activity relationship
The clinical success of multitargeted kinase inhibitors has stimulated efforts to identify promiscuous drugs with optimal selectivity profiles. It remains unclear to what extent such drugs can be rationally designed, particularly for combinations of targets that are structurally divergent. Here we report the systematic discovery of molecules that potently inhibit both tyrosine kinases and PI3-Ks, two protein families that are among the most intensely pursued cancer drug targets. Through iterative chemical synthesis, X-ray crystallography, and kinome-level biochemical profiling, we identify compounds that inhibit a spectrum of novel target combinations in these two families. Crystal structures reveal that the dual selectivity of these molecules is controlled by a hydrophobic pocket conserved in both enzyme classes and accessible through a rotatable bond in the drug skeleton. We show that one compound, PP121, blocks the proliferation of tumor cells by direct inhibition of oncogenic tyrosine kinases and PI3-Ks. These molecules demonstrate the feasibility of accessing a chemical space that intersects two families of oncogenes.
Drug discovery in the field of oncology has been advanced mainly through the targeting of receptor tyrosine kinases. Both antibodies and small molecule inhibitors have been found to have successful applications in blocking the proliferative functions of these cell surface receptors. Based on these early successes, additional kinases within the cytoplasm have been found to promote cancer and, as such, have been recognized as feasible targets for additional modes of therapies. Unlike these oncogene targets, most tumor suppressors are irreversibly altered during cancer progression and therefore are not feasible targets for therapy. However, a subset of these genes is reversibly epigenetically suppressed. One such gene is BRM, and when it is re-expressed in cancer cells, this gene halts their growth. Moreover, as the key catalytic subunit of the SWI/SNF complex, BRM is centrally important to a host of anticancer pathways and cellular mechanisms, and its status may serve as a biomarker. Restoring its expression will both reconnect a number of growth-controlling pathways and affect cellular adhesion, DNA repair, and immune functions. For these reasons, restoring BRM expression is not only feasible, but potentially a potent form of anticancer therapy. To identify BRM-restoring compounds, we developed a cell-based luciferase assay. In this review, we discuss some of the challenges we encountered, issues related to this type of drug discovery, and our future ambitions. We hope this review will provide insight to this type of endeavor and lead to more investigations pursuing this type of drug research.
Brahma; Anticancer; Tumor suppressor; Epigenetic suppression; SWI/SNF; High throughput screening
Imatinib mesylate (IM) is a potent tyrosine kinase inhibitor used as front-line therapy in chronic myeloid leukemia, a disease caused by the oncogenic kinase Bcr-Abl. Although the clinical success of IM set a new paradigm in molecular-targeted therapy, the emergence of IM resistance is a clinically significant problem. In an effort to obtain new insights into the mechanisms of adaptation and tolerance to IM, as well as the signaling pathways potentially affected by this drug, we performed a two-dimensional electrophoresis-based quantitative- and phospho-proteomic analysis in the eukaryotic model Saccharomyces cerevisiae. We singled out proteins that were either differentially expressed or differentially phosphorylated in response to IM, using the phosphoselective dye Pro-Q® Diamond, and identified 18 proteins in total. Ten were altered only at the content level (mostly decreased), while the remaining 8 possessed IM-repressed phosphorylation. These 18 proteins are mainly involved in cellular carbohydrate processes (glycolysis/gluconeogenesis), translation, protein folding, ion homeostasis, and nucleotide and amino acid metabolism. Remarkably, all 18 proteins have human functional homologs. A role for HSP70 proteins in the response to IM, as well as decreased glycolysis as a metabolic marker of IM action are suggested, consistent with findings from studies in human cell lines. The previously-proposed effect of IM as an inhibitor of vacuolar H+-ATPase function was supported by the identification of an underexpressed protein subunit of this complex. Taken together, these findings reinforce the role of yeast as a valuable eukaryotic model for pharmacological studies and identification of new drug targets, with potential clinical implications in drug reassignment or line extension under a personalized medicine perspective.
Checkpoint kinase 2 (CHK2) is an important serine/threonine kinase in the cellular response to DNA damage. A fragment-based screening campaign using a combination of a high-concentration AlphaScreen™ kinase assay and a biophysical thermal shift assay, followed by X-ray crystallography, identified a number of chemically different ligand-efficient CHK2 hinge-binding scaffolds that have not been exploited in known CHK2 inhibitors. In addition, it showed that the use of these orthogonal techniques allowed efficient discrimination between genuine hit matter and false positives from each individual assay technology. Furthermore, the CHK2 crystal structures with a quinoxaline-based fragment and its follow-up compound highlight a hydrophobic area above the hinge region not previously explored in rational CHK2 inhibitor design, but which might be exploited to enhance both potency and selectivity of CHK2 inhibitors.
The inhibition of tyrosine kinases is a successful approach for the treatment of cancers and the discovery of kinase inhibitor drugs is the focus of numerous academic and pharmaceutical laboratories. With this goal in mind, several strategies have been developed to measure kinase activity and to screen novel tyrosine kinase inhibitors. Nevertheless, a general non-radioactive and inexpensive approach, easy to implement and adapt to a range of applications, is still missing. Herein, using Bcr-Abl tyrosine kinase, an oncogenic target and a model protein for cancer studies, we describe a novel cost-effective high-throughput screening kinase assay. In this approach, named the BacKin assay, substrates displayed on a Bacterial cell surface are incubated with Kinase and their phosphorylation is examined and quantified by flow cytometry. This approach has several advantages over existing approaches, as using bacteria (i.e. Escherichia coli) to display peptide substrates provides a self renewing solid support that does not require laborious chemical strategies. Here we show that the BacKin approach can be used for kinetic and mechanistic studies, as well as a platform to characterize and identify small-molecule or peptide-based kinase inhibitors with potential applications in drug development.
Since in most tumors multiple signaling pathways are involved, many of the inhibitors in clinical development are designed to affect a wide range of targeted kinases. The most important tyrosine kinase families in the development of tyrosine kinase inhibitors are the ABL, SCR, platelet derived growth factor, vascular endothelial growth factor receptor and epidermal growth factor receptor families. Both multi-kinase inhibitors and single-kinase inhibitors have advantages and disadvantages, which are related to potential resistance mechanisms, pharmacokinetics, selectivity and tumor environment. In different malignancies various tyrosine kinases are mutated or overexpressed and several resistance mechanisms exist. Pharmacokinetics is influenced by interindividual differences and differs for two single targeted inhibitors or between patients treated by the same tyrosine kinase inhibitor. Different tyrosine kinase inhibitors have various mechanisms to achieve selectivity, while differences in gene expression exist between tumor and stromal cells. Considering these aspects, one type of inhibitor can generally not be preferred above the other, but will depend on the specific genetic constitution of the patient and the tumor, allowing personalized therapy. The most effective way of cancer treatment by using tyrosine kinase inhibitors is to consider each patient/tumor individually and to determine the strategy that specifically targets the consequences of altered (epi)genetics of the tumor. This strategy might result in treatment by a single multi kinase inhibitor for one patient, but in treatment by a couple of single kinase inhibitors for other patients.
Tyrosine kinase inhibitors; Targeted therapy; Epidermal growth factor receptor; Vascular endothelial growth factor receptor; Platelet derived growth factor; Breakpoint cluster region-Abelson murine leukemia oncogene homolog 1; Janus kinase
Type-II kinase inhibitors represent a class of chemicals that trap their target kinases in an inactive, so-called DFG-out, state, occupying a hydrophobic pocket adjacent to the ATP binding site. These compounds are often more specific than those targeting active, DFG-in, kinase conformations. Unfortunately, the discovery of novel type-II scaffolds presents a considerable challenge, partly because the lack of compatible kinase structures makes structure-based methods inapplicable. We present a computational protocol for converting multiple available DFG-in structures of various kinases (∼70% of mammalian structural kinome) into accurate and specific models of their type-II-bound state. The models, described as Deletion-Of-Loop asp-PHe-gly-IN (DOLPHIN) kinase models, demonstrate exceptional performance in various inhibitor discovery applications, including compound pose prediction, screening, and in silico activity profiling. Given the abundance of the DFG-in structures, the presented approach opens possibilities for kinome-wide discovery of specific molecules targeting inactive kinase states.
kinase; DFG-in; DFG-out; type-II inhibitor; imatinib; structure-based inhibitor discovery; compound screening; compound profiling; phosphorylation; cancer therapeutics
The role of mutational analysis in the selection of a second-generation tyrosine kinase inhibitor for the treatment of patients with chronic myeloid leukemia is examined.
Significant advances in treatment and monitoring for patients with chronic myeloid leukemia have occurred over the last decade. With the introduction of the tyrosine kinase inhibitor imatinib, long-term outcomes have improved and new challenges, such as resistance, including mutations, have emerged. Research efforts into mutational analysis have intensified, with emphasis on the potential of using this technique to guide second-generation tyrosine kinase inhibitor selection. Although some data suggest that a small number of mutations may be associated with a less favorable response to treatment with one second-generation tyrosine kinase inhibitor versus another, these data need to be interpreted cautiously because they are derived primarily retrospectively from single-institution studies and a small number of patients. More research and clinical experience and a better understanding of the implications of in vitro data are needed before these data can be routinely incorporated into therapeutic decisions. Currently, there is no consensus on when to screen patients for mutations, what technique should be used, or how values should be reported. Selection of a second-generation tyrosine kinase inhibitor should therefore be based upon its toxicity profile in conjunction with the patient's comorbidities and the practitioner's experience.
Chronic myeloid leukemia; Mutation; Tyrosine kinase; Imatinib; Dasatinib; Nilotinib
High-throughput screening (HTS) of ~50,000 chemical compounds against phosphorylated and unphosphorylated c-Met, a tyrosine kinase receptor for hepatocyte growth factor (HGF), was carried out in order to compare hit rates, hit potencies and also to explore scaffolds that might serve as potential leads targeting only the unphosphorylated form of the enzyme. The hit rate and potency for the confirmed hit molecules were higher for the unphosphoryalted form of c-Met. While the target of small molecule inhibitor discovery efforts has traditionally been the phosphorylated form, there are now examples of small molecules that target unphosphorylated kinases. Screening for inhibitors of unphosphorylated kinases may represent a complementary approach for prioritizing chemical scaffolds for hit-to-lead follow ups.
Kinase; phosphorylation; high throughput screening; HTRF; c-Met; cancer.
Development of both potent and selective kinase inhibitors
challenging task in modern drug discovery. The innate promiscuity
of kinase inhibitors largely results from ATP-mimetic binding to the
kinase hinge region. We present a novel class of substituted 7,8-dichloro-1-oxo-β-carbolines
based on the distinct structural features of the alkaloid bauerine
C whose kinase inhibitory activity does not rely on canonical ATP-mimetic hinge interactions. Intriguingly, cocrystal structures revealed
an unexpected inverted binding mode and the presence of halogen bonds
with kinase backbone residues. The compounds exhibit excellent selectivity
over a comprehensive panel of human protein kinases while inhibiting
selected kinases such as the oncogenic PIM1 at low nanomolar concentrations.
Together, our biochemical and structural data suggest that this scaffold
may serve as a valuable template for the design and development of
specific inhibitors of various kinases including the PIM family of
kinases, CLKs, DAPK3 (ZIPK), BMP2K (BIKE), and others.
Expression of the receptor tyrosine kinase c-MET in many cancers, and its participation in multiple signal transduction pathways involved in malignant tumor growth, suggest a wide therapeutic potential for MET inhibition in human cancer. Here we describe the discovery and early clinical development of ARQ 197, a novel, selective, non–ATP-competitive inhibitor of MET. Data from ARQ 197 clinical trials in hepatocellular, germ-cell, pancreatic (in combination with gemcitabine), and colorectal (in combination with cetuximab and irinotecan) cancers further highlight the potential role of ARQ 197 in existing and emerging anticancer therapeutic regimens.
Expression of the receptor tyrosine kinase c-MET (MET, mesenchymal-epithelial transition factor) in many cancers, and its participation in multiple signal transduction pathways involved in malignant tumor growth, suggest a wide therapeutic potential for MET inhibition in human cancer. Here we describe the discovery and early clinical development of ARQ 197, a novel, selective, non–ATP-competitive inhibitor of MET. Phase I studies demonstrate that ARQ 197 has a predictable pharmacokinetics and favorable safety profile, making it a potentially ideal partner for combination with cytotoxic chemotherapies and targeted anticancer agents. Results from phase I and phase II trials demonstrate preliminary evidence of anticancer activity. New data from a global phase II randomized trial comparing a combination of ARQ 197 plus erlotinib with erlotinib/placebo, in endothelial growth factor receptor inhibitor-naïve patients with locally advanced/metastatic non–small cell lung cancer, demonstrate improvement in progression-free and overall survival with combined therapy. Results were especially pronounced for patients with non–squamous lung cancer histologies, and in particular molecularly defined subgroups including KRAS mutations. These and other data from ARQ 197 clinical trials in hepatocellular, germ-cell, pancreatic (in combination with gemcitabine), and colorectal (in combination with cetuximab and irinotecan) cancers further highlight the potential role of ARQ 197 in existing and emerging anticancer therapeutic regimens.
c-MET; EGFR; Epithelial growth factor inhibitor; Kinase receptor inhibitor; Hepatocyte growth factor
Predicting off-targets by computational methods is getting increasing importance in early drug discovery stages. We herewith present a computational method based on binding site three-dimensional comparisons, which prompted us to investigate the cross-reaction of protein kinase inhibitors with synapsin I, an ATP-binding protein regulating neurotransmitter release in the synapse. Systematic pair-wise comparison of the staurosporine-binding site of the proto-oncogene Pim-1 kinase with 6,412 druggable protein-ligand binding sites suggested that the ATP-binding site of synapsin I may recognize the pan-kinase inhibitor staurosporine. Biochemical validation of this hypothesis was realized by competition experiments of staurosporine with ATP-γ35S for binding to synapsin I. Staurosporine, as well as three other inhibitors of protein kinases (cdk2, Pim-1 and casein kinase type 2), effectively bound to synapsin I with nanomolar affinities and promoted synapsin-induced F-actin bundling. The selective Pim-1 kinase inhibitor quercetagetin was shown to be the most potent synapsin I binder (IC50 = 0.15 µM), in agreement with the predicted binding site similarities between synapsin I and various protein kinases. Other protein kinase inhibitors (protein kinase A and chk1 inhibitor), kinase inhibitors (diacylglycerolkinase inhibitor) and various other ATP-competitors (DNA topoisomerase II and HSP-90α inhibitors) did not bind to synapsin I, as predicted from a lower similarity of their respective ATP-binding sites to that of synapsin I. The present data suggest that the observed downregulation of neurotransmitter release by some but not all protein kinase inhibitors may also be contributed by a direct binding to synapsin I and phosphorylation-independent perturbation of synapsin I function. More generally, the data also demonstrate that cross-reactivity with various targets may be detected by systematic pair-wise similarity measurement of ligand-annotated binding sites.
The Eph family of receptor tyrosine kinases has drawn growing attention due to their role in regulating diverse biological phenomena. However, pharmacological interrogation of Eph kinase function has been hampered by a lack of potent and selective Eph kinase inhibitors. Here we report the discovery of compounds 6 and 9 using a rationally designed kinase-directed library which potently inhibit Eph receptor tyrosine kinases, particularly EphB2 with cellular EC50s of 40 nM. Crystallographic data of EphA3 and EphA7 in complex with the inhibitors show that they bind to the “DFG-out” inactive kinase conformation and provide valuable information for structure-based design of second generation inhibitors.
The asymmetric unit of the title compound, C20H16N2O4·CH3OH, contains two Schiff base zwitterions and two methanol solvent molecules. The dihedral angles between the central benzene ring and the two outer benzene rings of the Schiff base are 2.57 (7) and 52.30 (7)° in one molecule and 5.83 (7) and 49.82 (7)° in the other molecule. Intramolecular O—H⋯N and N—H⋯O hydrogen bonds generate S(6) ring motifs, whereas intramolecular N—H⋯N hydrogen bonds generate S(5) ring motifs. In the crystal structure, O—H⋯O, hydrogen bonds and weak C—H⋯O interactions link the molecules into one-dimensional chains along the b-axis direction and are further connected by O—H⋯O and weak C—H⋯O interactions into a three-dimensional network. C—H⋯π and π–π interactions [centroid–centroid distances = 3.6228 (9) and 3.6881 (9) Å] are also observed in the crystal structure.
The asymmetric unit of the title Schiff base compound, C21H18N2O4, consists of four independent zwitterions (A, B, C and D) with similar conformations. In each independent molecule, the methyl group is disordered over two positions; the occupancies of the two positions are 0.819 (5) and 0.181 (5) in molecule A, 0.912 (5) and 0.088 (5) in B, 0.734 (5) and 0.266 (5) in C, and 0.940 (6) and 0.060 (6) in D. The dihydroxyphenyl and the hydroxyphenolate rings in molecule A form dihedral angles of 17.36 (12) and 13.30 (12)°, respectively, with the central benzene ring, whereas the respective angles for molecules B, C and D are 30.22 (11)/7.46 (11), 35.26 (12)/11.01 (12) and 39.89 (12)/4.29 (12)°. In all independent molecules, intramolecular N—H⋯O and O—H⋯N hydrogen bonds generate S(6) ring motifs. The four independent molecules are linked into two pairs, viz. A–B and C–D, by intermolecular O—H⋯O hydrogen bonds. These pairs are linked into a two-dimensional network parallel to the ab plane by C—H⋯O hydrogen bonds. In addition, C—H⋯π and π–π [centroid–centroid distance = 3.5153 (14)–3.7810 (15) Å] interactions stabilize the crystal structure.
A new series of 3-ethynyl-1H–indazoles has been synthesized and evaluated in both biochemical and cell-based assays as potential kinase inhibitors. Interestingly, a selected group of compounds identified from this series exhibited low micromolar inhibition against critical components of the PI3K pathway, targeting PI3K, PDK1 and mTOR kinases. Combination of computational modeling and structure-activity relationships studies reveal a possible novel mode for PI3K inhibition, resulting in a PI3Kα isoform specific compound. Hence, by targeting the most oncogenic mutant isoform of PI3K, the compound displays anti-proliferative activity both in monolayer human cancer cell cultures and in three-dimensional tumor models. Because of its favorable physicochemical, in vitro ADME and drug-like properties, we propose that this novel ATP mimetic scaffold could result useful in deriving novel selecting and multi-kinase inhibitors for clinical use.
This essay reviews the experimental treatments and new imaging modalities that are currently being explored by investigators to help treat patients with age-related macular degeneration (AMD).
Literature review and interpretation.
Experimental treatments to preserve vision in patients with exudative AMD include blocking vascular endothelial growth factor (VEGF), binding VEGF, and modulating the VEGF receptors. Investigators are also attempting to block signal transduction with receptor tyrosine kinase inhibitors. Experimental treatments for non-exudative AMD include agents that target inflammation, oxidative stress, and implement immune-modulation. The effectiveness of these newer pharmacologic agents has the potential to grow exponentially when used in combination with new and improved imaging modalities that can help identify disease earlier and follow treatment response more precisely.
With a better understanding, at the genetic and molecular level, of AMD and the development of superior imaging modalities, investigators are able to offer treatment options that may offer unprecedented visual gains while reducing the need for repetitive treatments.
age-related macular degeneration; VEGF; SiRNA; PEDF
In this issue of the JCI, Nissen et al. report that a reciprocal interaction exists between the growth factors FGF2 and PDGF-BB, causing tumors to exhibit increased angiogenesis and metastatic potential (see the related article beginning on page 2766). Both FGF2 and PDGF-BB signal through tyrosine kinase receptors, which have been the target of tyrosine kinase inhibitors for cancer therapies. These inhibitors are usually small molecules that inhibit the kinase activity of a receptor or nonreceptor tyrosine kinase, preventing downstream signaling. The results of this study shed light on why tyrosine kinase inhibitors have been useful for the treatment of only a small number of advanced cancers. Currently, a major focus of pharmaceutical companies is to develop ever more potent and specific tyrosine kinases. The results presented here suggest that this approach may not be successful.