Phenylaminopyrimidines as inhibitors of Janus kinases (JAKs)

Nitrogen-containing heterocyclic drug products approved by the FDA in 2023: Synthesis and biological activity

This article profiles 13 newly approved nitrogen-containing heterocyclic drugs by the U.S. Food and Drug Administration (FDA) in 2023. These drugs target a variety of therapeutic areas including proteinuria in patients with IgA nephropathy, migraine in adults, Rett syndrome, PI3Kδ syndrome, vasomotor symptoms, alopecia areata, acute myeloid leukemia, postpartum depression, myelofibrosis, and various cancer and tumor types. The molecular structures of these approved drugs feature common aromatic heterocyclic compounds such as pyrrole, imidazole, pyrazole, isoxazole, pyridine, and pyrimidine, as well as aliphatic heterocyclic compounds like caprolactam, piperazine, and piperidine. Some compounds also contain multiple heteroatoms like 1,2,4-thiadiazole and 1,2,4-triazole. The article provides a comprehensive overview of the bioactivity spectrum, medicinal chemistry discovery, and synthetic methods for each compound.

Discovery of Two Highly Selective Structurally Orthogonal Chemical Probes for Activin Receptor-like Kinases 1 and 2

Activin receptor-like kinases 1-7 (ALK1-7) regulate a complex network of SMAD-independent as well as SMAD-dependent signaling pathways. One of the widely used inhibitors for functional investigations of these processes, in particular for bone morphogenetic protein (BMP) signaling, is LDN-193189. However, LDN-193189 has insufficient kinome-wide selectivity complicating its use in cellular target validation assays. Herein, we report the identification and comprehensive characterization of two chemically distinct highly selective inhibitors of ALK1 and ALK2, M4K2234 and MU1700, along with their negative controls. We show that both MU1700 and M4K2234 efficiently block the BMP pathway via selective in cellulo inhibition of ALK1/2 kinases and exhibit favorable in vivo profiles in mice. MU1700 is highly brain penetrant and shows remarkably high accumulation in the brain. These high-quality orthogonal chemical probes offer the selectivity required to become widely used tools for in vitro and in vivo investigation of BMP signaling.

Next-Generation JAK2 Inhibitors for the Treatment of Myeloproliferative Neoplasms: Lessons from Structure-Based Drug Discovery Approaches

Selective inhibitors of Janus kinase (JAK) 2 have been in demand since the discovery of the JAK2 V617F mutation present in patients with myeloproliferative neoplasms (MPN); however, the structural basis of V617F oncogenicity has only recently been elucidated. New structural studies reveal a role for other JAK2 domains, beyond the kinase domain, that contribute to pathogenic signaling. Here we evaluate the structure-based approaches that led to recently-approved type I JAK2 inhibitors (fedratinib and pacritinib), as well as type II (BBT594 and CHZ868) and pseudokinase inhibitors under development (JNJ7706621). With full-length JAK homodimeric structures now available, superior selective and mutation-specific JAK2 inhibitors are foreseeable.

SIGNIFICANCE

The JAK inhibitors currently used for the treatment of MPNs are effective for symptom management but not for disease eradication, primarily because they are not strongly selective for the mutant clone. The rise of computational and structure-based drug discovery approaches together with the knowledge of full-length JAK dimer complexes provides a unique opportunity to develop better targeted therapies for a range of conditions driven by pathologic JAK2 signaling.

Dual-target Janus kinase (JAK) inhibitors: Comprehensive review on the JAK-based strategies for treating solid or hematological malignancies and immune-related diseases

Janus kinases (JAKs) are the non-receptor tyrosine kinases covering JAK1, JAK2, JAK3, and TYK2 which regulate signal transductions of hematopoietic cytokines and growth factors to play essential roles in cell growth, survival, and development. Dysregulated JAK activity leading to a constitutively activated signal transducers and activators of transcription (STAT) is strongly associated with immune-related diseases and cancers. Targeting JAK to interfere the signaling of JAK/STAT pathway has achieved quite success in the treatment of these diseases. However, inadequate clinical response and serious adverse events come along by the treatment of monotherapy of JAK inhibitors. With better and deeper understanding of JAK/STAT pathway in the pathogenesis of diseases, researchers start to show huge interest in combining inhibition of JAK and other oncogenic targets to realize a broader regulation on pathological processes to block disease development and progression, which has hastened extensive research of dual JAK inhibitors over the past decades. Until now, studies of dual JAK inhibitors have added BTK, SYK, FLT3, HDAC, Src, and Aurora kinases to the overall inhibitory profile and demonstrated significant advantage and superiority over single-target inhibitors. In this review, we elucidated the possible mechanism of synergic effects caused by dual JAK inhibitors and briefly describe the development of these agents.

Optimisation of momelotinib with improved potency and efficacy as pan-JAK inhibitor

Dysregulated JAK-STAT signaling has been proven to be involved in several immune-mediated diseases. Several janus kinase (JAK) inhibitors have been approved for the treatment of various inflammatory and autoimmune diseases such as rheumatoid arthritis (RA), plaque psoriasis, psoriatic arthritis, inflammatory bowel disease (IBD). Here, we report the design, optimisation, synthesis and biological evaluation of momelotinib analogues (a pyrimidine based JAK inhibitor), to get pan-JAK inhibitors. Systematic structure activity relationship studies led to the discovery of compound 32, which potently inhibited JAK1, JAK2 and JAK3. The in vivo investigation indicated that compound 32 possessed favourable pharmacokinetic properties and displayed superior anti-inflammatory efficacy than momelotinib 1. Accordingly, compound 32 was advanced into preclinical development.

The Emerging Role of Janus Kinase Inhibitors in the Treatment of Cancer

Cancer is a leading cause of death worldwide. The Janus kinase (JAK) signal transducer and activator of transcription (STAT) signalling pathway is activated abnormally, which promotes carcinogenesis. Several cytokines are important cancer drivers. These proteins bind to receptors and use the Janus kinase (JAK) and STAT pathways to communicate their responses. Cancer risks are linked to genetic differences in the JAK-STAT system. JAK inhibitors have shown to reduce STAT initiation, tissue propagation, and cell existence in preclinical investigations in solid tumour cell line models. JAK inhibitors, notably ruxolitinib, a, JAK1 or 2 blockers, make cell lines and mouse models more susceptible to radiotherapy, biological response modifier therapy, and oncolytic viral treatment. Numerous JAK antagonists have been or are now being evaluated in cancerous patients as monotherapy or by combining with other drugs in clinical studies. In preclinical investigations, certain JAK inhibitors showed promise anticancer effects; however, clinical trials explicitly evaluating their effectiveness against the JAK/STAT system in solid tumours have yet to be completed. JAK inhibition is a promising strategy to target the JAK/STAT system in solid tumours, and it deserves to be tested further in clinical studies. The function of directing Janus kinases (JAKs), an upstream accelerator of STATs, as a technique for lowering STAT activity in various malignant circumstances is summarized in this article, which will help scientists to generate more specific drug molecules in future.

Shifting the paradigm in treating multi-factorial diseases: polypharmacological co-inhibitors of HDAC6

Multi-factorial diseases are illnesses that exploit multiple cellular processes, or stages within one process, and thus highly targeted therapies often succumb to the disease, losing efficacy as resistance sets in. Combination therapies have become a mainstay to battle these diseases, however these regimens are plagued with caveats. An emerging avenue to treat multi-factorial diseases is polypharmacology, wherein a single drug is rationally designed to bind multiple targets, and is widely touted to be superior to combination therapy by inherently addressing the latter's shortcomings, which include poor patient compliance, narrow therapeutic windows and spiraling healthcare costs. Through its roles in intracellular trafficking, cell motility, mitosis, protein folding and as a back-up to the proteasome pathway, HDAC6 has rapidly become an exciting new target for therapeutics, particularly in the discovery of new drugs to treat Alzheimer's disease and cancer. Herein, we describe recent efforts to marry together HDAC pharmacophores, with a particular emphasis on HDAC6 selectivity, with those of other targets towards the discovery of potent therapeutics to treat these evasive diseases. Such polypharmacological agents may supercede combination therapies through inherent synergism, permitting reduced dosing, wider therapeutic windows and improved compliance.

Hydrogen Peroxide Inducible JAK3 Covalent Inhibitor: Prodrug for the Treatment of RA with Enhanced Safety Profile

Selective inhibition of Janus kinases (JAKs) is an arising strategy in drug discovery. Covalent inhibitors targeting a unique cysteine in JAK3 exhibit ultraselectivity among JAK family members. However, safety and tissue specific concerns still remain. A prodrug of a known JAK3 covalent inhibitor sensitive to H₂O₂ was designed and synthesized and its therapeutic effect was evaluated in the CIA (collagen-induced arthritis) mice model of RA (rheumatoid arthritis). The prodrug strategy relied on the introduction of a hydrogen peroxide-sensitive borate trigger group to avoid random covalent binding to thiol functionalities in biomacromolecules. The results show that the prodrug can be activated and released under pathophysiological concentration of H₂O₂. In addition, the prodrug demonstrated stability to the physiological environment. In comparison to the parent compound, the prodrug showed a similar therapeutic effect in the CIA model but notably exhibited lower toxicity and a larger therapeutic window.

Understanding the structural features of JAK2 inhibitors: a combined 3D-QSAR, DFT and molecular dynamics study

JAK2 plays a critical role in JAK/STAT signaling pathway and in patho-mechanism of myeloproliferative disorders and autoimmune diseases. Thus, effective JAK2 inhibitors provide a promising opportunity for the pharmaceutical intervention of many diseases. In this work, 3D-QSAR study was performed on a series of 1-amino-5H-pyrido-indole-4-carboxamide derivatives as JAK2 inhibitors to obtain reliable comparative molecular field analysis (CoMFA) and comparative molecular similarity analysis (CoMSIA) models with three different alignment methods. Among the different alignment methods, ligand-based (CoMFA: q² = 0.676, r² = 0.979; CoMSIA: q² = 0.700, r² = 0.953) and pharmacophore-based alignment (CoMFA: q² = 0.710, r² = 0.982; CoMSIA: q² = 0.686, r² = 0.960) has produced better statistical results when compared to receptor-based alignment (CoMFA: q² = 0.507, r² = 0.979; CoMSIA: q² = 0.544, r² = 0.917). Statistical parameters indicated that data are well fitted and have high predictive ability. The presence of electrostatic and hydrophobic field is highly desirable for potent inhibitory activity, and the steric field plays a minor role in modulating the activity. The contour analysis indicates ARG980, ASN981, ASP939 and LEU937 have more possibility of interacting with bulky, hydrophobic groups in pyrido and positive and negative groups in pyrazole ring. Based on our findings, we have designed sixteen molecules and predicted its activity and drug-like properties. Subsequently, molecular docking, molecular dynamics and DFT calculations were performed to evaluate its potency.

Discovery of Janus Kinase 2 (JAK2) and Histone Deacetylase (HDAC) Dual Inhibitors as a Novel Strategy for the Combinational Treatment of Leukemia and Invasive Fungal Infections

Clinically, leukemia patients often suffer from the limited efficacy of chemotherapy and high risks of infection by invasive fungal pathogens. Herein, a novel therapeutic strategy was developed in which a small molecule can simultaneously treat leukemia and invasive fungal infections (IFIs). Novel Janus kinase 2 (JAK2) and histone deacetylase (HDAC) dual inhibitors were identified to possess potent anti-proliferative activity toward hematological cell lines and excellent synergistic effects with fluconazole to treat resistant Candida albicans infections. In particular, compound 20a, a highly active and selective JAK2/HDAC6 dual inhibitor, showed excellent in vivo antitumor efficacy in several acute myeloid leukemia (AML) models and synergized with fluconazole for the treatment of resistant C. albicans infections. This study highlights the therapeutic potential of JAK2/HDAC dual inhibitors in treating AML and IFIs and provides an efficient strategy for multitargeting drug discovery.

Putative dual inhibitors of Janus kinase 1 and 3 (JAK1/3): Pharmacophore based hierarchical virtual screening

Janus kinase 1 and 3 are non-receptor protein tyrosine kinases, involved in the regulation of various cytokines implicated in the pathogenesis of autoimmune and inflammatory disease conditions. Thus, they serve as therapeutic targets for the designing of multi-targeted agents for the treatment of inflammatory-mediated pathological conditions. In the present study, diverse inhibitors of JAK1 and JAK3 were considered for the development of ligand-based pharmacophore models, followed by docking analysis to design putative dual inhibitors. The pharmacophore models were generated in PHASE 3.4, and top five models for each target were selected on the basis of survival minus inactive score. The best model for JAK1 (AAADH.25) and JAK3 (ADDRR.142) were selected corresponding to the highest value of Q²_test. Both models were employed for the screening of a PHASE database, and subsequently, the retrieved hits were filtered employing molecular docking in JAK1 and JAK3 proteins. The stable interactions between retrieved hits and proteins were confirmed using molecular dynamics simulations. Finally, ADME properties of screened dual inhibitors displaying essential interactions with both proteins were calculated. Thus, the new leads obtained in this way may be prioritized for experimental validation as potential novel therapeutic agents in the treatment of various autoimmune and inflammatory disorders related to JAK1 and JAK3.

Differential Sensitivity of Human Hepatocellular Carcinoma Xenografts to an IGF-II Neutralizing Antibody May Involve Activated STAT3

Hepatocellular carcinoma (HCC) is highly refractory to current therapeutics used in the clinic. DX-2647, a recombinant human antibody, potently neutralizes the action of insulin-like growth factor-II (IGF-II), a ligand for three cell-surface receptors (IGF-IR, insulin receptor A and B isoforms, and the cation-independent mannose-6-phosphate receptor) which is overexpressed in primary human HCC. DX-2647 impaired the growth of tumor xenografts of the HCC cell line, Hep3B; however, xenografts of the HCC cell line, HepG2, were largely unresponsive to DX-2647 treatment. Analysis of a number of aspects of the IGF signaling axis in both cell lines did not reveal any significant differences between the two. However, while DX-2647 abolished phospho (p)-IGF-IR, p-IR and p-AKT signaling in both cell lines, HepG2 showed high levels of p-STAT3, which was unaffected by DX-2647 treatment and was absent from the Hep3B cell line. The driver of p-STAT3 was found to be a secreted cytokine, and treatment of HepG2 cells with a pan- JAK kinase inhibitor resulted in a loss of p-STAT3. These findings implicate the activation of STAT3 as one pathway that may mediate resistance to IGF-II-targeted therapy in HCC.

Pharmacokinetics and Safety of Momelotinib in Subjects With Hepatic or Renal Impairment

Momelotinib is a Janus kinase 1/2 inhibitor in clinical development for the treatment of myelofibrosis. Two phase 1 open-label, parallel-group, adaptive studies were conducted to evaluate the pharmacokinetics of a single 200-mg oral dose of momelotinib in subjects with hepatic or renal impairment compared with healthy matched control subjects with normal hepatic or renal function. Plasma pharmacokinetics of momelotinib and its major active metabolite, M21, were evaluated, and geometric least-squares mean ratios (GMRs) and associated 90% confidence intervals (CIs) for impaired versus each control group were calculated for plasma exposures (area under concentration-time curve from time 0 to ∞ [AUC_∞ ] and maximum concentration) of momelotinib and M21. There was no clinically significant difference in plasma exposures of momelotinib and M21 between subjects with moderate or severe renal impairment or moderate hepatic impairment and healthy control subjects. Compared with healthy control subjects, momelotinib AUC_∞ was increased (GMR, 197%; 90%CI, 129%-301%), and M21 AUC_∞ was decreased (GMR, 52%; 90%CI, 34%-79%) in subjects with severe hepatic impairment. The safety profile following a single dose of momelotinib was similar between subjects with hepatic or renal dysfunction and healthy control subjects. These pharmacokinetic and safety results indicate that dose adjustment is not necessary for momelotinib in patients with renal impairment or mild to moderate hepatic impairment. In patients with severe hepatic impairment, however, the dose of momelotinib should be reduced.

eTOX ALLIES: an automated pipeLine for linear interaction energy-based simulations

BACKGROUND

Computational methods to predict binding affinities of small ligands toward relevant biological (off-)targets are helpful in prioritizing the screening and synthesis of new drug candidates, thereby speeding up the drug discovery process. However, use of ligand-based approaches can lead to erroneous predictions when structural and dynamic features of the target substantially affect ligand binding. Free energy methods for affinity computation can include steric and electrostatic protein-ligand interactions, solvent effects, and thermal fluctuations, but often they are computationally demanding and require a high level of supervision. As a result their application is typically limited to the screening of small sets of compounds by experts in molecular modeling.

RESULTS

We have developed eTOX ALLIES, an open source framework that allows the automated prediction of ligand-binding free energies requiring the ligand structure as only input. eTOX ALLIES is based on the linear interaction energy approach, an efficient end-point free energy method derived from Free Energy Perturbation theory. Upon submission of a ligand or dataset of compounds, the tool performs the multiple steps required for binding free-energy prediction (docking, ligand topology creation, molecular dynamics simulations, data analysis), making use of external open source software where necessary. Moreover, functionalities are also available to enable and assist the creation and calibration of new models. In addition, a web graphical user interface has been developed to allow use of free-energy based models to users that are not an expert in molecular modeling.

CONCLUSIONS

Because of the user-friendliness, efficiency and free-software licensing, eTOX ALLIES represents a novel extension of the toolbox for computational chemists, pharmaceutical scientists and toxicologists, who are interested in fast affinity predictions of small molecules toward biological (off-)targets for which protein flexibility, solvent and binding site interactions directly affect the strength of ligand-protein binding.

Molecular dynamics and integrated pharmacophore-based identification of dual [Formula: see text] inhibitors

Despite increase in the understanding of the pathogenesis of rheumatoid arthritis (RA), it remains a tough challenge. The advent of kinases involved in key intracellular pathways in pathogenesis of RA may provide a new phase of drug discovery for RA. The present study is aimed to identify dual JAK3/[Formula: see text] inhibitors by developing an optimum pharmacophore model integrating the information revealed by ligand-based pharmacophore models and structure-based pharmacophore models (SBPMs). For JAK3 inhibitors, the addition of an aromatic ring feature and for [Formula: see text] the addition of a hydrophobic feature proposed by SBPMs lead to five-point pharmacophore (i.e., AADHR.54 (JAK3)) and six-point pharmacophore (i.e., AAAHRR.45 ([Formula: see text])). The obtained pharmacophores were validated and used for virtual screening and then for docking-based screening. Molecules were further evaluated for ADME properties, and their docked protein complexes were subjected to MM-GBSA energy calculations and molecular dynamic simulations. The top two hit compounds with novel scaffolds 2-oxo-1,2-dihydroquinoline and benzo[d]oxazole showed inhibitory activity for JAK3 and [Formula: see text].

JAK1/STAT3 Activation through a Proinflammatory Cytokine Pathway Leads to Resistance to Molecularly Targeted Therapy in Non-Small Cell Lung Cancer

Molecularly targeted drugs have yielded significant therapeutic advances in oncogene-driven non-small cell lung cancer (NSCLC), but a majority of patients eventually develop acquired resistance. Recently, the relation between proinflammatory cytokine IL6 and resistance to targeted drugs has been reported. We investigated the functional contribution of IL6 and the other members of IL6 family proinflammatory cytokine pathway to resistance to targeted drugs in NSCLC cells. In addition, we examined the production of these cytokines by cancer cells and cancer-associated fibroblasts (CAF). We also analyzed the prognostic significance of these molecule expressions in clinical NSCLC samples. In NSCLC cells with acquired resistance to targeted drugs, we observed activation of the IL6-cytokine pathway and STAT3 along with epithelial-to-mesenchymal transition (EMT) features. In particular, IL6 family cytokine oncostatin-M (OSM) induced a switch to the EMT phenotype and protected cells from targeted drug-induced apoptosis in OSM receptors (OSMRs)/JAK1/STAT3-dependent manner. The cross-talk between NSCLC cells and CAFs also preferentially activated the OSM/STAT3 pathway via a paracrine mechanism and decreased sensitivity to targeted drugs. The selective JAK1 inhibitor filgotinib effectively suppressed STAT3 activation and OSMR expression, and cotargeting inhibition of the oncogenic pathway and JAK1 reversed resistance to targeted drugs. In the analysis of clinical samples, OSMR gene expression appeared to be associated with worse prognosis in patients with surgically resected lung adenocarcinoma. Our data suggest that the OSMRs/JAK1/STAT3 axis contributes to resistance to targeted drugs in oncogene-driven NSCLC cells, implying that this pathway could be a therapeutic target. Mol Cancer Ther; 16(10); 2234-45. ©2017 AACR.

Integration of pharmacophore mapping and molecular docking in sequential virtual screening: towards the discovery of novel JAK2 inhibitors

An integrated sequential virtual screening protocol by combining molecular docking and pharmacophore mapping was successfully constructed to identify novel small-molecule inhibitors of JAK2.

Ligand-based and e-pharmacophore modeling, 3D-QSAR and hierarchical virtual screening to identify dual inhibitors of spleen tyrosine kinase (Syk) and janus kinase 3 (JAK3)

The clinical efficacy of multiple kinase inhibitors has caught the interest of Pharmaceutical and Biotech researchers to develop potential drugs with multi-kinase inhibitory activity for complex diseases. In the present work, we attempted to identify dual inhibitors of spleen tyrosine kinase (Syk) and janus kinase 3 (JAK3), keys players in immune signaling, by developing ideal pharmacophores integrating Ligand-based pharmacophore models (LBPMs) and Structure-based pharmacophore models (SBPMs), thereby projecting the optimum pharmacophoric required for inhibition of both the kinases. The four point LBPM; ADPR.14 suggested the presence of one hydrogen bond acceptor, one hydrogen bond donor, one positive ionizable, and one ring aromatic feature for Syk inhibitory activity and AADH.54 proposed the necessity of two hydrogen bond acceptor, one hydrogen bond donor, and one hydrophobic feature for JAK3 inhibitory activity. To our interest, SBPMs identified additional ring aromatic features required for inhibition of both the kinases. For Syk inhibitory activity, the hydrogen bond acceptor feature indicated by LBPM was devoid of forming hydrogen bonding interaction with the hinge region amino acid residue (Ala451). Thus merging the information revealed by both LBPMs and SBPMs, ideal pharmacophore models i.e. ADPRR.14 (Syk) and AADHR.54 (JAK3) were generated. These models after rigorous statistical validation were used for screening of Asinex database. The systematic virtual screening protocol, including pharmacophore and docking-based screening, ADME property, and MM-GBSA energy calculations, retrieved final 10 hits as dual inhibitors of Syk and JAK3. Final 10 hits thus obtained can aid in the development of potential therapeutic agents for autoimmune disorders. Also the top two hits were evaluated against both the enzymes.

Momelotinib in myelofibrosis: JAK1/2 inhibitor with a role in treating and understanding the anemia

Myelofibrosis (MF) is a chronic malignancy of the blood-forming system caused by hyperactivation of JAK2/STAT signaling pathway. Small-molecule inhibitors of JAK2 can variably ameliorate MF-related symptoms caused by chronic inflammation and hepatosplenomegaly. Anemia is a significant problem and adverse prognostic factor in over a third of MF patients and is often worsened by JAK2 inhibitors. The JAK1/2 inhibitor momelotinib unexpectedly resulted in reduction of anemia in MF patients during Phase I/II trials. Current Phase III trials will be the basis for seeking regulatory approval of momelotinib during 2017. Studies to determine how momelotinib improves anemia are underway, potentially leading to expanded momelotinib use and/or development of other targeted therapies for treating anemia in MF and related diseases.

CIS is a potent checkpoint in NK cell-mediated tumor immunity

The detection of aberrant cells by natural killer (NK) cells is controlled by the integration of signals from activating and inhibitory ligands and from cytokines such as IL-15. We identified cytokine-inducible SH2-containing protein (CIS, encoded by Cish) as a critical negative regulator of IL-15 signaling in NK cells. Cish was rapidly induced in response to IL-15, and deletion of Cish rendered NK cells hypersensitive to IL-15, as evidenced by enhanced proliferation, survival, IFN-γ production and cytotoxicity toward tumors. This was associated with increased JAK-STAT signaling in NK cells in which Cish was deleted. Correspondingly, CIS interacted with the tyrosine kinase JAK1, inhibiting its enzymatic activity and targeting JAK for proteasomal degradation. Cish(-/-) mice were resistant to melanoma, prostate and breast cancer metastasis in vivo, and this was intrinsic to NK cell activity. Our data uncover a potent intracellular checkpoint in NK cell-mediated tumor immunity and suggest possibilities for new cancer immunotherapies directed at blocking CIS function.

Toward selective TYK2 inhibitors as therapeutic agents for the treatment of inflammatory diseases

The family of JAK comprises four members and has received significant attention in recent years from the pharmaceutical industry as a therapeutic target. The role of JAK is central to cytokine signaling pathways. It is believed that selective modulation of one specific JAK can lead to the inhibition of a restricted set of cytokines, which should avoid undesired side effects and get closer to the profile of biologic therapies. Consequently, selective JAK inhibition has become a major focus area of drug discovery research. A review of the TYK2 patents indicates that industry attention has recently turned toward the development of specific inhibitors. Importantly, despite the increasing number of published patents, none of these drugs have yet made it to the clinical trials.

Inhibitor-based affinity probes for the investigation of JAK signaling pathways

The Janus Kinase (JAK) signaling pathway plays a key role for many cellular processes and has recently been correlated with neuronal disorders. In order to understand new links of JAK family members with other signaling pathways, chemical proteomics tools with broad kinase coverage are desirable. A probe that shows outstanding kinase selectivity and allows for the enrichment of up to 133 kinases including many mitogen activated kinase (MAPK) members and JAK kinases has been developed. Furthermore, this probe was applied to establish the selectivity profile of the JAK1/2 inhibitor momelotinib that is currently evaluated in clinical phase 3 studies. These results render this probe a valuable tool for the investigation of JAK and JAK related signaling pathways and the selectivity profiling of kinase inhibitors.

Pharmacophore and docking-based virtual screening approach for the design of new dual inhibitors of Janus kinase 1 and Janus kinase 2

Janus kinase 1 and 2, non-receptor protein tyrosine kinases, are implicated in various cancerous diseases. Involvement of these two enzymes in the pathways that stimulate cell proliferation in cancerous conditions makes them potential therapeutic targets for designing new dual-targeted agents for the treatment of cancer. In the present study, two separate pharmacophore models were developed and the best models for JAK1 (AAADH.25) and JAK2 (ADRR.92) were selected on the basis of their external predictive ability. Both models were subjected to a systematic virtual screening (VS) protocol using a PHASE database of 1.5 million molecules. The hits retrieved in VS were investigated for ADME properties to avoid selection of molecules with a poor pharmacokinetic profile. The molecules considered to be within the range of acceptable limits of ADME properties were further employed for docking simulations with JAK1 and JAK2 proteins to explore the final hits that possess structural features of both pharmacophore models as well as display essential interactions with both of them. Thus, the new molecules obtained in this way should show inhibitory activity against JAK1 and JAK2 and may serve as novel therapeutic agents for the treatment of cancerous disease conditions.

Pharmacophore and Virtual Screening of JAK3 inhibitors

Janus kinase 3 (JAK3) is a non-receptor tyrosine kinases family of protein which is comprised of JAK1, JAK2, JAK3 and TYK2. It plays an important role in immune function and lymphoid development and it only resides in the hematopoietic system. Therefore, selective targeting JAK3 is a rational approach in developing new therapeutic molecule. In this study, about 116 JAK3 inhibitors were collected from the literature and were used to build four-point pharmacophore model using Phase (Schrodinger module). The statistically significant pharmacophore hypothesis of AAHR.92 with r2 value of 0.942 was used as 3D query to search against 3D database namely Zincpharmer. A total of 2, 27,483 compounds obtained as hit were subjected to high throughput virtual screening (HTVS module of Schrodinger). Among the hits, ten compounds with good G-score ranging from -12.96 to -11.18 with good binding energy to JAK3 were identified.

The discovery of reverse tricyclic pyridone JAK2 inhibitors. Part 2: lead optimization

This communication discusses the discovery of novel reverse tricyclic pyridones as inhibitors of Janus kinase 2 (JAK2). By using a kinase cross screening approach coupled with molecular modeling, a unique inhibitor-water interaction was discovered to impart excellent broad kinase selectivity. Improvements in intrinsic potency were achieved by utilizing a rapid library approach, while targeted structural changes to lower lipophilicity led to improved rat pharmacokinetics. This multi-pronged approach led to the identification of 31, which demonstrated encouraging rat pharmacokinetics, in vivo potency, and excellent off-target kinase selectivity.

Dual inhibitors of Janus kinase 2 and 3 (JAK2/3): designing by pharmacophore- and docking-based virtual screening approach

JAK2 and JAK3 are non-receptor protein tyrosine kinases implicated in B-cell- and T-cell-mediated diseases. Both enzymes work via different pathways but are involved in the pathogenesis of common lymphoid-derived diseases. Hence, targeting both Janus kinases together can be a potential strategy for the treatment of these diseases. In the present study, two separate pharmacophore-based 3D-QSAR models ADRR.92 (Q(2)(test)0.663, R(2)(train) 0.849, F value 219.3) for JAK2 and ADDRR.142 (Q(2)(test)0.655, R(2)(train) 0.869, F value 206.9) for JAK3 were developed. These models were employed for the screening of a PHASE database of approximately 1.5 million compounds; subsequently, the retrieved hits were screened employing docking simulations with JAK2 and JAK3 proteins. Finally, ADME properties of screened dual inhibitors displaying essential interactions with both proteins were calculated to filter candidates with poor pharmacokinetic profiles. These candidates could serve as novel therapeutic agents in the treatment of lymphoid-related diseases.

P-glycoprotein (MDR1/ABCB1) and breast cancer resistance protein (BCRP/ABCG2) restrict brain accumulation of the JAK1/2 inhibitor, CYT387

CYT387 is an orally bioavailable, small molecule inhibitor of Janus family of tyrosine kinases (JAK) 1 and 2. It is currently undergoing Phase I/II clinical trials for the treatment of myelofibrosis and myeloproliferative neoplasms. We aimed to establish whether the multidrug efflux transporters P-glycoprotein (P-gp; MDR1; ABCB1) and breast cancer resistance protein (BCRP;ABCG2) restrict oral availability and brain penetration of CYT387. In vitro, CYT387 was efficiently transported by both human MDR1 and BCRP, and very efficiently by mouse Bcrp1 and its transport could be inhibited by specific MDR1 inhibitor, zosuquidar and/or specific BCRP inhibitor, Ko143. CYT387 (10 mg/kg) was orally administered to wild-type (WT), Bcrp1(-/-), Mdr1a/1b(-/-) and Bcrp1;Mdr1a/1b(-/-) mice and plasma and brain concentrations were analyzed. Over 8h, systemic exposure of CYT387 was similar between all the strains, indicating that these transporters do not substantially limit oral availability of CYT387. Despite the similar systemic exposure, brain accumulation of CYT387 was increased 10.5- and 56-fold in the Bcrp1;Mdr1a/1b(-/-) mice compared to the WT strain at 2 and 8h after CYT387 administration, respectively. In single Bcrp1(-/-) mice, brain accumulation of CYT387 was more substantially increased than in Mdr1a/1b(-/-) mice, suggesting that CYT387 is a slightly better substrate of Bcrp1 than of Mdr1a at the blood-brain barrier. These results indicate a marked and additive role of Bcrp1 and Mdr1a/1b in restricting brain penetration of CYT387, potentially limiting efficacy of this compound against brain (micro) metastases positioned behind a functional blood-brain barrier.

Advances in the discovery of selective JAK inhibitors

In this review, we describe the current knowledge of the biology of the JAKs. The JAK family comprises the four nonreceptor tyrosine kinases JAK1, JAK2, JAK3, and Tyk2, all key players in the signal transduction from cytokine receptors to transcription factor activation. We also review the progresses made towards the optimization of JAK inhibitors and the importance of their selectivity profile. Indeed, the full array of many medicinal chemistry enabling tools (HTS, X-ray crystallography, scaffold morphing, etc.) has been deployed to successfully design molecules that discriminate among JAK family and other kinases. While the first JAK inhibitor was launched in 2011, this review also summarizes the status of several other small-molecule JAK inhibitors currently in development to treat arthritis, psoriasis, organ rejection, and multiple cancer types.

Liquid chromatography-tandem mass spectrometric assay for the JAK2 inhibitor CYT387 in plasma

A quantitative bioanalytical liquid chromatography-tandem mass spectrometric (LC-MS/MS) assay for the JAK2 inhibitor CYT387 was developed and validated. Plasma samples were pre-treated using protein precipitation with acetonitrile containing cediranib as internal standard. The extract was directly injected into the chromatographic system after dilution with water. This system consisted of a sub-2 μm particle, trifunctional bonded octadecyl silica column with a gradient using 0.005% (v/v) of formic acid in a mixture of water and methanol. The eluate was transferred into the electrospray interface with positive ionization and the analyte was detected in the selected reaction monitoring mode of a triple quadrupole mass spectrometer. The assay was validated in a 0.25-1000 ng/ml calibration range. Within day precisions were 3.0-13.5%, between day precisions 5.7% and 14.5%. Accuracies were between 96% and 113% for the whole calibration range. The drug was stable under all relevant analytical conditions. Finally, the assay was successfully used to assess drug levels in mice.

Discovery of potent and highly selective thienopyridine Janus kinase 2 inhibitors

Developing Janus kinase 2 (Jak2) inhibitors has become a significant focus for small molecule drug discovery programs in recent years due to the identification of a Jak2 gain-of-function mutation in the majority of patients with myeloproliferative disorders (MPD). Here, we describe the discovery of a thienopyridine series of Jak2 inhibitors that culminates with compounds showing 100- to >500-fold selectivity over the related Jak family kinases in enzyme assays. Selectivity for Jak2 was also observed in TEL-Jak cellular assays, as well as in cytokine-stimulated peripheral blood mononuclear cell (PBMC) and whole blood assays. X-ray cocrystal structures of 8 and 19 bound to the Jak2 kinase domain aided structure-activity relationship efforts and, along with a previously reported small molecule X-ray cocrystal structure of the Jak1 kinase domain, provided structural rationale for the observed high levels of Jak2 selectivity.

Signal transducer and activator of transcription 3 (STAT3): a promising target for anticancer therapy

Signal transducer and activator of transcription 3 (STAT3) is an oncogenic protein whose inhibition is sought for the prevention and treatment of cancer. In this review, the validated therapeutic strategy to block aberrant activity of STAT3 in many tumor cell lines is evaluated by presenting the most promising inhibitors to date. The compounds are discussed in classes based on their different mechanisms of action, which are critically explained. In addition, their future clinical development as anticancer agents is considered. Furthermore, the efforts devoted to the comprehension of the structure-activity relationships and to the identification of the biological effects are brought to attention. The synthetic and technological approaches recently developed to overcome the difficulties in the obtainment of clinically suitable drugs are also presented.

The novel JAK inhibitor CYT387 suppresses multiple signalling pathways, prevents proliferation and induces apoptosis in phenotypically diverse myeloma cells

Janus kinases (JAKs) are involved in various signalling pathways exploited by malignant cells. In multiple myeloma (MM), the interleukin-6/JAK/signal transducers and activators of transcription (IL-6/JAK/STAT) pathway has been the focus of research for a number of years and IL-6 has an established role in MM drug resistance. JAKs therefore make a rational drug target for anti-MM therapy. CYT387 is a novel, orally bioavailable JAK1/2 inhibitor, which has recently been described. This preclinical evaluation of CYT387 for treatment of MM demonstrated that CYT387 was able to prevent IL-6-induced phosphorylation of STAT3 and greatly decrease IL-6- and insulin-like growth factor-1-induced phosphorylation of AKT and extracellular signal-regulated kinase in human myeloma cell lines (HMCL). CYT387 inhibited MM proliferation in a time- and dose-dependent manner in 6/8 HMCL, and this was not abrogated by the addition of exogenous IL-6 (3/3 HMCL). Cell cycling was inhibited with a G(2)/M accumulation of cells, and apoptosis was induced by CYT387 in all HMCL tested (3/3). CYT387 synergised in killing HMCL when used in combination with the conventional anti-MM therapies melphalan and bortezomib. Importantly, apoptosis was also induced in primary patient MM cells (n=6) with CYT387 as a single agent, and again synergy was seen when combined with conventional therapies.