Aurora isoform selectivity: design and synthesis of imidazo[4,5-b]pyridine derivatives as highly selective inhibitors of Aurora-A kinase in cells

QSAR Study, Molecular Docking and Molecular Dynamic Simulation of Aurora Kinase Inhibitors Derived from Imidazo[4,5-b]pyridine Derivatives

Cancer is a serious threat to human life and social development and the use of scientific methods for cancer prevention and control is necessary. In this study, HQSAR, CoMFA, CoMSIA and TopomerCoMFA methods are used to establish models of 65 imidazo[4,5-b]pyridine derivatives to explore the quantitative structure-activity relationship between their anticancer activities and molecular conformations. The results show that the cross-validation coefficients q2 of HQSAR, CoMFA, CoMSIA and TopomerCoMFA are 0.892, 0.866, 0.877 and 0.905, respectively. The non-cross-validation coefficients r2 are 0.948, 0.983, 0.995 and 0.971, respectively. The externally validated complex correlation coefficients r2pred of external validation are 0.814, 0.829, 0.758 and 0.855, respectively. The PLS analysis verifies that the QSAR models have the highest prediction ability and stability. Based on these statistics, virtual screening based on R group is performed using the ZINC database by the Topomer search technology. Finally, 10 new compounds with higher activity are designed with the screened new fragments. In order to explore the binding modes and targets between ligands and protein receptors, these newly designed compounds are conjugated with macromolecular protein (PDB ID: 1MQ4) by molecular docking technology. Furthermore, to study the nature of the newly designed compound in dynamic states and the stability of the protein-ligand complex, molecular dynamics simulation is carried out for N3, N4, N5 and N7 docked with 1MQ4 protease structure for 50 ns. A free energy landscape is computed to search for the most stable conformation. These results prove the efficient and stability of the newly designed compounds. Finally, ADMET is used to predict the pharmacology and toxicity of the 10 designed drug molecules.

Activation of lysosomal iron triggers ferroptosis in cancer

Iron catalyses the oxidation of lipids in biological membranes and promotes a form of cell death referred to as ferroptosis1-3. Identifying where this chemistry takes place in the cell can inform the design of drugs capable of inducing or inhibiting ferroptosis in various disease-relevant settings. Whereas genetic approaches have revealed underlying mechanisms of lipid peroxide detoxification1,4,5, small molecules can provide unparalleled spatiotemporal control of the chemistry at work6. Here, we show that the ferroptosis inhibitor liproxstatin-1 (Lip-1) exerts a protective activity by inactivating iron in lysosomes. Based on this, we designed the bifunctional compound fentomycin that targets phospholipids at the plasma membrane and activates iron in lysosomes upon endocytosis, promoting oxidative degradation of phospholipids and ferroptosis. Fentomycin effectively kills primary sarcoma and pancreatic ductal adenocarcinoma cells. It acts as a lipolysis-targeting chimera (LIPTAC), preferentially targeting iron-rich CD44high cell-subpopulations7,8 associated with the metastatic disease and drug resistance9,10. Furthermore, we demonstrate that fentomycin also depletes CD44high cells in vivo and reduces intranodal tumour growth in an immunocompetent murine model of breast cancer metastasis. These data demonstrate that lysosomal iron triggers ferroptosis and that lysosomal iron redox chemistry can be exploited for therapeutic benefits.

Efficient and metal-free synthesis of 2-aroyl 7-azaindoles via thermally induced denitrogenative intramolecular annulation of 1,2,3,4-tetrazolopyridines

A facile and metal-free intramolecular denitrogenative annulation strategy for the preparation of novel 2-aroyl 7-azaindoles has been developed from 3-(tetrazolo[1,5-a]pyridin-8-yl)prop-2-en-1-one in the presence of the deep eutectic solvent Dowtherm A. The valuable features of the protocol include a short reaction time, absence of any metal catalyst, utilization of a eutectic solvent, easy product isolation, and very good yields of novel 2-aroyl 7-azaindoles.

Design, synthesis, and biochemical and computational screening of novel oxindole derivatives as inhibitors of Aurora A kinase and SARS-CoV-2 spike/host ACE2 interaction

Isatin (indol-2,3-dione), a secondary metabolite of tryptophan, has been used as the core structure to design several compounds that have been tested and identified as potent inhibitors of apoptosis, potential antitumor agents, anticonvulsants, and antiviral agents. In this work, several analogs of isatin hybrids have been synthesized and characterized, and their activities were established as inhibitors of both Aurora A kinase and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike/host angiotensin-converting enzyme II (ACE2) interactions. Amongst the synthesized isatin hybrids, compounds 6a, 6f, 6g, and 6m exhibited Aurora A kinase inhibitory activities (with IC50 values < 5 μ M), with GScore values of -7.9, -7.6, -8.2 and -7.7 kcal/mol, respectively. Compounds 6g and 6i showed activities in blocking SARS-CoV-2 spike/ACE2 binding (with IC50 values in the range < 30 μ M), with GScore values of -6.4 and -6.6 kcal/mol, respectively. Compounds 6f, 6g, and 6i were both capable of inhibiting spike/ACE2 binding and blocking Aurora A kinase. Pharmacophore profiling indicated that compound 6g tightly fits Aurora A kinase and SARS-CoV-2 pharmacophores, while 6d fits SARS-CoV-2 and 6l fits Aurora A kinase pharmacophore. This work is a proof of concept that some existing cancer drugs may possess antiviral properties. Molecular modeling showed that the active compound for each protein adopted different binding modes, hence interacting with a different set of amino acid residues in the binding site. The weaker activities against spike/ACE2 could be explained by the small sizes of the ligands that fail to address the important interactions for binding to the ACE2 receptor site.

Recent Updates on Oncogenic Signaling of Aurora Kinases in Chemosensitive, Chemoresistant Cancers: Novel Medicinal Chemistry Approaches for Targeting Aurora Kinases

The Aurora Kinase family (AKI) is composed of serine-threonine protein kinases involved in the modulation of the cell cycle and mitosis. These kinases are required for regulating the adherence of hereditary-related data. Members of this family can be categorized into aurora kinase A (Ark-A), aurora kinase B (Ark-B), and aurora kinase C (Ark-C), consisting of highly conserved threonine protein kinases. These kinases can modulate cell processes such as spindle assembly, checkpoint pathway, and cytokinesis during cell division. The main aim of this review is to explore recent updates on the oncogenic signaling of aurora kinases in chemosensitive/chemoresistant cancers and to explore the various medicinal chemistry approaches to target these kinases. We searched Pubmed, Scopus, NLM, Pubchem, and Relemed to obtain information pertinent to the updated signaling role of aurora kinases and medicinal chemistry approaches and discussed the recently updated roles of each aurora kinases and their downstream signaling cascades in the progression of several chemosensitive/chemoresistant cancers; subsequently, we discussed the natural products (scoulerine, Corynoline, Hesperidin Jadomycin-B, fisetin), and synthetic, medicinal chemistry molecules as aurora kinase inhibitors (AKIs). Several natural products' efficacy was explained as AKIs in chemosensitization and chemoresistant cancers. For instance, novel triazole molecules have been used against gastric cancer, whereas cyanopyridines are used against colorectal cancer and trifluoroacetate derivatives could be used for esophageal cancer. Furthermore, quinolone hydrazine derivatives can be used to target breast cancer and cervical cancer. In contrast, the indole derivatives can be preferred to target oral cancer whereas thiosemicarbazone-indole could be used against prostate cancer, as reported in an earlier investigation against cancerous cells. Moreover, these chemical derivatives can be examined as AKIs through preclinical studies. In addition, the synthesis of novel AKIs through these medicinal chemistry substrates in the laboratory using in silico and synthetic routes could be beneficial to develop prospective novel AKIs to target chemoresistant cancers. This study is beneficial to oncologists, chemists, and medicinal chemists to explore novel chemical moiety synthesis to target specifically the peptide sequences of aurora kinases in several chemoresistant cancer cell types.

A novel class of pyrazole analogues as aurora kinase A inhibitor: design, synthesis, and anticancer evaluation

Pyrazole, as a small molecule, was discovered for higher cytotoxicity and affinity towards Aurora-A kinase. Based on these facts, a novel pyrazole substituted at the 4th position was designed, synthesized, and evaluated against MCF-7, MDA-MB-23, and Vero (non-cancerous kidney cell) cell lines. Compounds5hand5eexhibited greater cytotoxicity in the series against MCF-7 and MDA-MB-231, with GI50 values of 0.12 µM and 0.63 µM, respectively, as compared to Imatinib (GI50 values of 16.08 µM and 10.36 µM). All of the compounds displayed selective cytotoxicity against cancer cells but not on normal Vero cells, supporting the design strategy to be a selective anticancer agent. Furthermore, compounds 5h and 5e inhibited Aurora-A kinase with IC50 values of 0.78 µM (4.70-fold) and 1.12 µM (2.84-fold), respectively, as compared to alisertib (IC50 = 3.36 µM). In addition, compound 5h significantly arrested the cell cycle at G2/M (34.89 %, 5.56-fold) and the apoptotic phase (25.04 %, 11.81-fold) compared to the control. It also triggered an increase in early (7.43 %) and late (14.89 %) phase apoptosis compared to vehicle (0.235 and 0.36 %, respectively), causing 37.89-fold higher total apoptosis in the annexin-V assay. These data imply that Aurora-A kinase inhibition may be linked to apoptosis induction and cell cycle arrest. Furthermore, their higher docking score in the study confirmed evidence of Aurora-kinase suppression. It was observed that fluorine and imidazole increased the H-bond and lipophilic interactions with the binding residue. Also, the substitution of electron-rich and lipophilic groups increased hydrophobic interactions. Moreover, the three-atom linkage (CH2NHCH2) expanded compound 5h to fill the cavity. Based on current findings, it is concluded that compounds 5h and 5e with strong Aurora-A kinase suppression may be promising anticancer agents.

α-Aminophosphonate inhibitors of metallo-β-lactamases NDM-1 and VIM-2

The upswing of antibiotic resistance is an escalating threat to human health. Resistance mediated by bacterial metallo-β-lactamases is of particular concern as these enzymes degrade β-lactams, our most frequently prescribed class of antibiotics. Inhibition of metallo-β-lactamases could allow the continued use of existing β-lactam antibiotics, such as penicillins, cephalosporins and carbapenems, whose applicability is becoming ever more limited. The design, synthesis, and NDM-1, VIM-2, and GIM-1 inhibitory activities (IC50 4.1-506 μM) of a series of novel non-cytotoxic α-aminophosphonate-based inhibitor candidates are presented herein. We disclose the solution NMR spectroscopic and computational investigation of their NDM-1 and VIM-2 binding sites and binding modes. Whereas the binding modes of the inhibitors are similar, VIM-2 showed a somewhat higher conformational flexibility, and complexed a larger number of inhibitor candidates in more varying binding modes than NDM-1. Phosphonate-type inhibitors may be potential candidates for development into therapeutics to combat metallo-β-lactamase resistant bacteria.

Imidazopyridine-based kinase inhibitors as potential anticancer agents: A review

Considering the fundamental role of protein kinases in the mechanism of protein phosphorylation in critical cellular processes, their dysregulation, especially in cancers, has underscored their therapeutic relevance. Imidazopyridines represent versatile scaffolds found in abundant bioactive compounds. Given their structural features, imidazopyridines have possessed pivotal potency to interact with different protein kinases, inspiring researchers to carry out numerous structural variations. In this comprehensive review, we encompass an extensive survey of the design and biological evaluations of imidazopyridine-based small molecules as potential agents targeting diverse kinases for anticancer applications. We describe the structural elements critical to inhibitory potency, elucidating their key structure-activity relationships (SAR) and mode of actions, where available. We classify these compounds into two groups: Serine/threonine and Tyrosine inhibitors. By highlighting the promising role of imidazopyridines in kinase inhibition, we aim to facilitate the design and development of more effective, targeted compounds for cancer treatment.

Imidazopyridine, a promising scaffold with potential medicinal applications and structural activity relationship (SAR): recent advances

Imidazopyridine scaffold has gained tremendous importance over the past few decades. Imidazopyridines have been expeditiously used for the rationale design and development of novel synthetic analogs for various therapeutic disorders. A wide variety of imidazopyridine derivatives have been developed as potential anti-cancer, anti-diabetic, anti-tubercular, anti-microbial, anti-viral, anti-inflammatory, central nervous system (CNS) agents besides other chemotherapeutic agents. Imidazopyridine heterocyclic system acts as a key pharmacophore motif for the identification and optimization of lead structures to increase medicinal chemistry toolbox. The present review highlights the medicinal significances of imidazopyridines for their rationale development as lead molecules with improved therapeutic efficacies. This review further emphasis on the structure-activity relationships (SARs) of the various designed imidazopyridines to establish a relationship between the key structural features versus the biological activities.Communicated by Ramaswamy H. Sarma.

Recent Advancement in Drug Design and Discovery of Pyrazole Biomolecules as Cancer and Inflammation Therapeutics

Pyrazole, an important pharmacophore and a privileged scaffold of immense significance, is a five-membered heterocyclic moiety with an extensive therapeutic profile, viz., anti-inflammatory, anti-microbial, anti-anxiety, anticancer, analgesic, antipyretic, etc. Due to the expansion of pyrazolecent red pharmacological molecules at a quicker pace, there is an urgent need to put emphasis on recent literature with hitherto available information to recognize the status of this scaffold for pharmaceutical research. The reported potential pyrazole-containing compounds are highlighted in the manuscript for the treatment of cancer and inflammation, and the results are mentioned in % inhibition of inflammation, % growth inhibition, IC₅₀, etc. Pyrazole is an important heterocyclic moiety with a strong pharmacological profile, which may act as an important pharmacophore for the drug discovery process. In the struggle to cultivate suitable anti-inflammatory and anticancer agents, chemists have now focused on pyrazole biomolecules. This review conceals the recent expansion of pyrazole biomolecules as anti-inflammatory and anticancer agents with an aim to provide better correlation among different research going around the world.

2-(3-Bromophenyl)-8-fluoroquinazoline-4-carboxylic Acid as a Novel and Selective Aurora A Kinase Inhibitory Lead with Apoptosis Properties: Design, Synthesis, In Vitro and In Silico Biological Evaluation

New quinazoline derivatives were designed based on the structural modification of the reported inhibitors to enhance their selectivity toward Aurora A. The synthesized compounds were tested over Aurora A, and a cytotoxicity assay was performed over NCI cell lines to select the best candidate for further evaluation. Compound 6e (2-(3-bromophenyl)-8-fluoroquinazoline-4-carboxylic acid) was the most potent compound among the tested derivatives. A Kinase panel assay was conducted for compound 6e over 14 kinases to evaluate its selectivity profile. Further cell cycle and apoptosis analysis were evaluated for compound 6e over the MCF-7 cell line at its IC50 of 168.78 µM. It arrested the cell cycle at the G1 phase and induced apoptosis. Molecular docking was performed to explore the possible binding mode of compound 6e into the active site. It showed significant binding into the main pocket in addition to potential binding interactions with the key amino acid residues. Accordingly, compound 6e can be considered a potential lead for further structural and molecular optimization of the quinazoline-based carboxylic acid scaffold for Aurora A kinase selective inhibition with apoptosis properties.

CCT245718, a dual FLT3/Aurora A inhibitor overcomes D835Y-mediated resistance to FLT3 inhibitors in acute myeloid leukaemia cells

BACKGROUND

Activating mutations in the Fms-like tyrosine kinase 3 (FLT3) are among the most prevalent oncogenic mutations in acute myeloid leukaemia. Inhibitors selectively targeting FLT3 kinase have shown promising clinical activity; their success in the clinic, however, has been limited due to the emergence of acquired resistance.

METHODS

CCT245718 was identified and characterised as a dual Aurora A/FLT3 inhibitor through cell-based and biochemical assays. The ability of CCT245718 to overcome TKD-mediated resistance was evaluated in a cell line-based model of drug resistance to FLT3 inhibitors.

RESULTS

CCT245718 exhibits potent antiproliferative activity towards FLT3-ITD + AML cell lines and strongly binds to FLT3-ITD and TKD (D835Y) mutants in vitro. Activities of both FLT3-ITD and Aurora A are also inhibited in cells. Inhibition of FLT3 results in reduced phosphorylation of STAT5, downregulation of survivin and induction of apoptotic cell death. Moreover, CCT245718 overcomes TKD-mediated resistance in a MOLM-13-derived cell line containing FLT3 with both ITD and D835Y mutations. It also inhibits FLT3 signalling in both parental and resistant cell lines compared to FLT3-specific inhibitor MLN518, which is only active in the parental cell line.

CONCLUSIONS

Our results demonstrate that CCT245718 is a potent dual FLT3/Aurora A inhibitor that can overcome TKD-mediated acquired resistance.

Synthetic Strategies of Pyrimidine-Based Scaffolds as Aurora Kinase and Polo-like Kinase Inhibitors

The past few decades have witnessed significant progress in anticancer drug discovery. Small molecules containing heterocyclic moieties have attracted considerable interest for designing new antitumor agents. Of these, the pyrimidine ring system is found in multitude of drug structures, and being the building unit of DNA and RNA makes it an attractive scaffold for the design and development of anticancer drugs. Currently, 22 pyrimidine-containing entities are approved for clinical use as anticancer drugs by the FDA. An exhaustive literature search indicates several publications and more than 59 patents from the year 2009 onwards on pyrimidine derivatives exhibiting potent antiproliferative activity. These pyrimidine derivatives exert their activity via diverse mechanisms, one of them being inhibition of protein kinases. Aurora kinase (AURK) and polo-like kinase (PLK) are protein kinases involved in the regulation of the cell cycle. Within the numerous pyrimidine-based small molecules developed as anticancer agents, this review focuses on the pyrimidine fused heterocyclic compounds modulating the AURK and PLK proteins in different phases of clinical trials as anticancer agents. This article aims to provide a comprehensive overview of synthetic strategies for the preparation of pyrimidine derivatives and their associated biological activity on AURK/PLK. It will also present an overview of the synthesis of the heterocyclic-2-aminopyrimidine, 4-aminopyrimidine and 2,4-diaminopyrimidine scaffolds, and one of the pharmacophores in AURK/PLK inhibitors is described systematically.

Aurora kinase inhibitors as potential anticancer agents: Recent advances

Aurora kinases are a family of serine/threonine kinases that play a crucial role in cell proliferation through the regulation of mitotic spindles. These kinases are the regulatory proteins localized in the various phases of the cell cycle and are involved in centrosome maturation, chromosome alignment, chromosomal segregation, and cytokinesis. They have emerged as one of the validated drug targets for anticancer drug discovery as their overexpression has been implicated in the pathogenesis of various carcinomas. Inhibitors of Aurora kinases induce growth inhibition and apoptosis in a variety of tumor cells. Hence, the design and development of Aurora kinase inhibitors have been widely explored in recent years by the scientific community as potential anticancer agents. Various Aurora kinase inhibitors have been under preclinical and clinical investigations as antitumor agents. This review summarizes the recent strategies of various researchers for the design and development of Aurora kinase inhibitors belonging to different structural classes. Their bioactivity, SARs, molecular modelling, and mechanistic studies have also been described. The comprehensive compilation of research work carried out in the field will provide inevitable scope for the design and development of novel drug candidates with better selectivity and efficacy. The review is constructed after the exhaustive research in this discipline and includes the papers from 2011 to 2020.

Electrochemical Synthesis of Benzimidazoles via Dehydrogenative Cyclization of Amidines

The development of efficient and sustainable methodologies for the synthesis of N-heterocycles is a constant focus of organic synthesis. Herein an electrochemical method is reported for the synthesis of benzimidazoles through dehydrogenative cyclization of easily available N-aryl amidines. The reactions were conducted under simple constant current conditions in an undivided cell without need for catalysts, chemical oxidants, or additives, and produced H₂ as the only theoretical byproduct.

Overview of recent developments of pyrazole derivatives as an anticancer agent in different cell line

Pyrazole is a five-membered aromatic heterocyclic ring with two adjacent nitrogen atoms C₃H₃N₂H.The presence of this nucleus in pharmacological agents of various therapeutic categories gifts a broad spectrum of biological activities and pharmaceuticals that contain pyrazole like celecoxib (anti-inflammatory), CDPPB (antipsychotic), Rimonabant (anti-obesity), Difenamizole, (Analgesic), Betazole (H2 receptor agonist), Fezolamide (Antidepressant), etc… The pharmacological potential of the pyrazole fraction is proved in many publication where they synthesized and evaluated pyrazoles against several biological agents. The aim of this article review is to survey recent works linking pyrazole structures to anticancer activities corresponding to 9 different type of cancer.

Molecular Transformer unifies reaction prediction and retrosynthesis across pharma chemical space

Predicting how a complex molecule reacts with different reagents, and how to synthesise complex molecules from simpler starting materials, are fundamental to organic chemistry. We show that an attention-based machine translation model - Molecular Transformer - tackles both reaction prediction and retrosynthesis by learning from the same dataset. Reagents, reactants and products are represented as SMILES text strings. For reaction prediction, the model "translates" the SMILES of reactants and reagents to product SMILES, and the converse for retrosynthesis. Moreover, a model trained on publicly available data is able to make accurate predictions on proprietary molecules extracted from pharma electronic lab notebooks, demonstrating generalisability across chemical space. We expect our versatile framework to be broadly applicable to problems such as reaction condition prediction, reagent prediction and yield prediction.

Discovery of Inhibitors of Aurora/PLK Targets as Anticancer Agents

Aurora and polo-like kinases control the G2/M phase in cell mitosis, which are both considered as crucial targets for cancer cell proliferations. Here, naphthalene-based Aurora/PLK coinhibitors as leading compounds were designed through in silico approach, and a total of 36 derivatives were synthesized. One candidate (AAPK-25) was selected under in vitro cell based high throughput screening with an IC50 value = 0.4 μM to human colon cancer cell HCT-116. A kinome scan assay showed that AAPK-25 was remarkably selective to both Aurora and PLK families. The relevant genome pathways were also depicted by microarray based gene expression analysis. Furthermore, validated from a set of in vitro and in vivo studies, AAPK-25 significantly inhibited the development of the colon cancer growth and prolonged the median survival time at the end of the administration (p < 0.05). To sum up, AAPK-25 has a great potential to be developed for a chemotherapeutic agent in clinical use.

Synthesis and Pharmacological Activities of Pyrazole Derivatives: A Review

Pyrazole and its derivatives are considered a pharmacologically important active scaffold that possesses almost all types of pharmacological activities. The presence of this nucleus in pharmacological agents of diverse therapeutic categories such as celecoxib, a potent anti-inflammatory, the antipsychotic CDPPB, the anti-obesity drug rimonabant, difenamizole, an analgesic, betazole, a H2-receptor agonist and the antidepressant agent fezolamide have proved the pharmacological potential of the pyrazole moiety. Owing to this diversity in the biological field, this nucleus has attracted the attention of many researchers to study its skeleton chemically and biologically. This review highlights the different synthesis methods and the pharmacological properties of pyrazole derivatives. Studies on the synthesis and biological activity of pyrazole derivatives developed by many scientists around the globe are reported.

Synthesis and Pharmacological Activities of Pyrazole Derivatives: A Review

Pyrazole and its derivatives are considered a pharmacologically important active scaffold that possesses almost all types of pharmacological activities. The presence of this nucleus in pharmacological agents of diverse therapeutic categories such as celecoxib, a potent anti-inflammatory, the antipsychotic CDPPB, the anti-obesity drug rimonabant, difenamizole, an analgesic, betazole, a H2-receptor agonist and the antidepressant agent fezolamide have proved the pharmacological potential of the pyrazole moiety. Owing to this diversity in the biological field, this nucleus has attracted the attention of many researchers to study its skeleton chemically and biologically. This review highlights the different synthesis methods and the pharmacological properties of pyrazole derivatives. Studies on the synthesis and biological activity of pyrazole derivatives developed by many scientists around the globe are reported.

Design, synthesis and biological activity of N4-phenylsubstituted-7H-pyrrolo[2,3-d]pyrimidin-4-amines as dual inhibitors of aurora kinase A and epidermal growth factor receptor kinase

Simultaneous inhibition of multiple kinases has been suggested to provide synergistic effects on inhibition of tumour growth and resistance. This study describes the design, synthesis and evaluation of 18 compounds incorporating a pyrrolo[2,3-d]pyrimidine scaffold for dual inhibition of epidermal growth factor receptor kinase (EGFR) and aurora kinase A (AURKA). Compounds 1-18 of this study demonstrate nanomolar inhibition of EGFR and micromolar inhibition of AURKA. Compounds 1-18 allow for a structure-activity relationships (SAR) analysis of the 4-anilino moiety for dual EGFR and AURKA inhibition. Compound 6, a 4-methoxyphenylpyrrolo[2,3-d]pyrimidin-4-amine, demonstrates single-digit micromolar inhibition of both AURKA and EGFR and provides evidence of a single molecule with dual activity against EGFR and AURKA. Compound 2, the most potent inhibitor of EGFR and AURKA from this series, has been further evaluated in four different squamous cell head and neck cancer cell lines for downstream effects resulting from AURKA and EGFR inhibition.

Characterization of Three Druggable Hot-Spots in the Aurora-A/TPX2 Interaction Using Biochemical, Biophysical, and Fragment-Based Approaches

The mitotic kinase Aurora-A and its partner protein TPX2 (Targeting Protein for Xenopus kinesin-like protein 2) are overexpressed in cancers, and it has been proposed that they work together as an oncogenic holoenzyme. TPX2 is responsible for activating Aurora-A during mitosis, ensuring proper cell division. Disruption of the interface with TPX2 is therefore a potential target for novel anticancer drugs that exploit the increased sensitivity of cancer cells to mitotic stress. Here, we investigate the interface using coprecipitation assays and isothermal titration calorimetry to quantify the energetic contribution of individual residues of TPX2. Residues Tyr8, Tyr10, Phe16, and Trp34 of TPX2 are shown to be crucial for robust complex formation, suggesting that the interaction could be abrogated through blocking any of the three pockets on Aurora-A that complement these residues. Phosphorylation of Aurora-A on Thr288 is also necessary for high-affinity binding, and here we identify arginine residues that communicate the phosphorylation of Thr288 to the TPX2 binding site. With these findings in mind, we conducted a high-throughput X-ray crystallography-based screen of 1255 fragments against Aurora-A and identified 59 hits. Over three-quarters of these hits bound to the pockets described above, both validating our identification of hotspots and demonstrating the druggability of this protein-protein interaction. Our study exemplifies the potential of high-throughput crystallography facilities such as XChem to aid drug discovery. These results will accelerate the development of chemical inhibitors of the Aurora-A/TPX2 interaction.

Dynamic Equilibrium of the Aurora A Kinase Activation Loop Revealed by Single-Molecule Spectroscopy

The conformation of the activation loop (T-loop) of protein kinases underlies enzymatic activity and influences the binding of small-molecule inhibitors. By using single-molecule fluorescence spectroscopy, we have determined that phosphorylated Aurora A kinase is in dynamic equilibrium between a DFG-in-like active T-loop conformation and a DFG-out-like inactive conformation, and have measured the rate constants of interconversion. Addition of the Aurora A activating protein TPX2 shifts the equilibrium towards an active T-loop conformation whereas addition of the inhibitors MLN8054 and CD532 favors an inactive T-loop. We show that Aurora A binds TPX2 and MLN8054 simultaneously and provide a new model for kinase conformational behavior. Our approach will enable conformation-specific effects to be integrated into inhibitor discovery across the kinome, and we outline some immediate consequences for structure-based drug discovery.

High-dimensional QSAR modelling using penalized linear regression model with L1/2-norm

In high-dimensional quantitative structure-activity relationship (QSAR) modelling, penalization methods have been a popular choice to simultaneously address molecular descriptor selection and QSAR model estimation. In this study, a penalized linear regression model with L1/2-norm is proposed. Furthermore, the local linear approximation algorithm is utilized to avoid the non-convexity of the proposed method. The potential applicability of the proposed method is tested on several benchmark data sets. Compared with other commonly used penalized methods, the proposed method can not only obtain the best predictive ability, but also provide an easily interpretable QSAR model. In addition, it is noteworthy that the results obtained in terms of applicability domain and Y-randomization test provide an efficient and a robust QSAR model. It is evident from the results that the proposed method may possibly be a promising penalized method in the field of computational chemistry research, especially when the number of molecular descriptors exceeds the number of compounds.

Azaindole synthesis through dual activation catalysis with N-heterocyclic carbenes

A convergent, transition-metal-free synthesis of 2-aryl-azaindoles has been developed. The interception of a reactive aza-ortho-azaquinone methide intermediate by an acyl anion equivalent generated through carbene catalysis provides high yields, a wide substrate scope, and the synthesis of previously inaccessible azaindoles.

The hunt for antimitotic agents: an overview of structure-based design strategies

INTRODUCTION

Structure-based drug discovery offers a rational approach for the design and development of novel anti-mitotic agents which target specific proteins involved in mitosis. This strategy has paved the way for development of a new generation of chemotypes which selectively interfere with the target proteins. The interference of these anti-mitotic targets implicated in diverse stages of mitotic cell cycle progression culminates in cancer cell apoptosis.

AREAS COVERED

This review covers the various mitotic inhibitors developed against validated mitotic checkpoint protein targets using structure-based design and optimization strategies. The protein-ligand interactions and the insights gained from these studies, culminating in the development of more potent and selective inhibitors, have been presented.

EXPERT OPINION

The advent of structure-based drug design coupled with advances in X-ray crystallography has revolutionized the discovery of candidate lead molecules. The structural insights gleaned from the co-complex protein-drug interactions have provided a new dimension in the design of anti-mitotic molecules to develop drugs with a higher selectivity and specificity profile. Targeting non-catalytic domains has provided an alternate approach to address cross-reactivity and broad selectivity among kinase inhibitors. The elucidation of structures of emerging mitotic drug targets has opened avenues for the design of inhibitors that target cancer.

A Cell Biologist's Field Guide to Aurora Kinase Inhibitors

Aurora kinases are essential for cell division and are frequently misregulated in human cancers. Based on their potential as cancer therapeutics, a plethora of small molecule Aurora kinase inhibitors have been developed, with a subset having been adopted as tools in cell biology. Here, we fill a gap in the characterization of Aurora kinase inhibitors by using biochemical and cell-based assays to systematically profile a panel of 10 commercially available compounds with reported selectivity for Aurora A (MLN8054, MLN8237, MK-5108, MK-8745, Genentech Aurora Inhibitor 1), Aurora B (Hesperadin, ZM447439, AZD1152-HQPA, GSK1070916), or Aurora A/B (VX-680). We quantify the in vitro effect of each inhibitor on the activity of Aurora A alone, as well as Aurora A and Aurora B bound to fragments of their activators, TPX2 and INCENP, respectively. We also report kinome profiling results for a subset of these compounds to highlight potential off-target effects. In a cellular context, we demonstrate that immunofluorescence-based detection of LATS2 and histone H3 phospho-epitopes provides a facile and reliable means to assess potency and specificity of Aurora A versus Aurora B inhibition, and that G2 duration measured in a live imaging assay is a specific readout of Aurora A activity. Our analysis also highlights variation between HeLa, U2OS, and hTERT-RPE1 cells that impacts selective Aurora A inhibition. For Aurora B, all four tested compounds exhibit excellent selectivity and do not significantly inhibit Aurora A at effective doses. For Aurora A, MK-5108 and MK-8745 are significantly more selective than the commonly used inhibitors MLN8054 and MLN8237. A crystal structure of an Aurora A/MK-5108 complex that we determined suggests the chemical basis for this higher specificity. Taken together, our quantitative biochemical and cell-based analyses indicate that AZD1152-HQPA and MK-8745 are the best current tools for selectively inhibiting Aurora B and Aurora A, respectively. However, MK-8745 is not nearly as ideal as AZD1152-HQPA in that it requires high concentrations to achieve full inhibition in a cellular context, indicating a need for more potent Aurora A-selective inhibitors. We conclude with a set of “good practice” guidelines for the use of Aurora inhibitors in cell biology experiments.

7-(Pyrazol-4-yl)-3H-imidazo[4,5-b]pyridine-based derivatives for kinase inhibition: Co-crystallisation studies with Aurora-A reveal distinct differences in the orientation of the pyrazole N1-substituent

Introduction of a 1-benzyl-1H-pyrazol-4-yl moiety at C7 of the imidazo[4,5-b]pyridine scaffold provided 7a which inhibited a range of kinases including Aurora-A. Modification of the benzyl group in 7a, and subsequent co-crystallisation of the resulting analogues with Aurora-A indicated distinct differences in binding mode dependent upon the pyrazole N-substituent. Compounds 7a and 14d interact with the P-loop whereas 14a and 14b engage with Thr217 in the post-hinge region. These crystallographic insights provide options for the design of compounds interacting with the DFG motif or with Thr217.