JAK Family Research Articles

Nonclinical evaluations of deucravacitinib and Janus kinase inhibitors in homeostatic and inflammatory pathways.

Translational medicine provides insight into novel drugs and predicts unwanted effects. In well-characterized pathways (e.g., cytokine-Janus kinase [JAK]-signal transducers and activators of transcription [STAT]), a variety of in vitro assessments were used to estimate selectivity of effects on different potential targets (i.e., JAK1, JAK2, JAK3, and tyrosine kinase 2 [TYK2]). Several approved drugs were characterized as selective for the JAK family. These assessments are challenged by a lack of compounds that only inhibit one JAK family member. Deucravacitinib is a first-in-class, oral, selective, allosteric inhibitor of TYK2, a kinase required for IL-12, IL-23, and Type I interferon signaling. Unlike deucravacitinib, which selectively binds to the TYK2 regulatory domain, JAK1,2,3 inhibitors target the catalytic domain, contributing to nonselective targeting of JAK1,2,3. Cytokines associated with JAK1,2,3 signaling are required for both immune and nonimmune functions. A similar laboratory abnormality profile was observed in clinical trials using JAK1,2,3 inhibitors that has not been observed with deucravacitinib. In vitro testing of JAK1,2,3 inhibitors has relied upon assays of signal transduction, such as those measuring STAT phosphorylation, for estimates of potency and selectivity. These assay systems can be effective in estimating in vivo efficacy; however, they may not provide insight into downstream outcomes of receptor signaling, which may be more relevant for evaluating safety aspects. Assay systems assessing functional outcomes from cells may yield a more useful translational evaluation. Here, deucravacitinib was assessed for potency and selectivity versus three representatives of the JAK inhibitor class (tofacitinib, baricitinib, and upadacitinib) based on functional assays. JAK inhibitors had suppressive activity against JAK2-dependent hematopoietic colony-forming assays modeling thrombopoiesis, erythropoiesis, and myelopoiesis; however, deucravacitinib did not. Deucravacitinib had limited potency against NK cells, cytotoxic T cells, T-helper cells, and regulatory T cells activated by JAK1/JAK3-dependent common gamma chain cytokines. These data are consistent with the biologic role of JAK1,2,3 and pharmacodynamic changes in clinical laboratory abnormalities. Against TYK2-dependent cytokines, deucravacitinib selectively inhibited Type I interferon stimulation of monocytes and dendritic cells and was a more potent inhibitor than JAK inhibitors. IL-12 and IL-23 functional outputs were similarly potently inhibited by deucravacitinib. Results are consistent with deucravacitinib selectively inhibiting TYK2.

Pyrimidine compounds BY4003 and BY4008 inhibit glioblastoma cells growth via modulating JAK3/STAT3 signaling pathway

Glioblastoma (GBM) is a brain tumor characterized by its aggressive and invasive properties. It is found that STAT3 is abnormally activated in GBM, and inhibiting STAT3 signaling can effectively suppress tumor progression. In this study, novel pyrimidine compounds, BY4003 and BY4008, were synthesized to target the JAK3/STAT3 signaling pathway, and their therapeutic efficacy and mechanisms of action were evaluated and compared with Tofacitinib in U251, A172, LN428 and patient-derived glioblastoma cells. The ADP-Glo™ kinase assay was utilized to assessed the inhibitory effects of BY4003 and BY4008 on JAK3, a crucial member of the JAK family. The results showed that both compounds significantly inhibited JAK3 enzyme activity, with IC50 values in the nanomolar range. The antiproliferative effects of BY4003, BY4008, and Tofacitinib on GBM and patient-derived glioblastoma cells were evaluated by MTT and H&E assays. The impact of BY4003 and BY4008 on GBM cell migration and apoptosis induction was assessed through wound healing, transwell, and TUNEL assays. STAT3-regulated protein expression and relative mRNA levels were analyzed by western blotting, immunocytochemistry, immunofluorescence, and qRT-PCR. It was found that BY4003, BY4008 and Tofacitinib could inhibit U251, A172, LN428 and patient-derived glioblastoma cells growth and proliferation. Results showed decreased expression of STAT3-associated proteins, including p-STAT3, CyclinD1, and Bcl-2, and increased expression of Bax, a pro-apoptotic protein, as well as significant down-regulation of STAT3 and STAT3-related genes. These findings suggested that BY4003 and BY4008 could inhibit GBM growth by suppressing the JAK3/STAT3 signaling pathway, providing valuable insights into the therapeutic development of GBM.

Enhancement of vincristine sensitivity in retinoblastoma through Janus kinase inhibition by ruxolitinib.

Chemotherapy remains the main approach conserving vision during the treatment of retinoblastoma, the most prevalent eye cancer in children. Unfortunately, the development of chemoresistance stands as the primary reason for treatment failure. Within this study, we showed that prolonged exposure to vincristine led to heightened expression of JAK1 and JAK2 in retinoblastoma cells, while the other members of the JAK family exhibited no such changes. Employing a genetic intervention, we demonstrated the efficacy of depleting either JAK1 or JAK2 in countering vincristine-resistant retinoblastoma cells. In addition, the dual depletion of both JAK1 and JAK2 produced a more potent inhibitory outcome compared to the depletion of either gene alone. We further demonstrated that ruxolitinib, a small molecular inhibitor of JAK1/2, effectively reduced viability and colony formation in vincristine-resistant retinoblastoma cells. It also acts synergistically with vincristine in retinoblastoma cells regardless of inherent cellular and genetic heterogeneity. The effectiveness of ruxolitinib as standalone treatment against chemoresistant retinoblastoma, as well as its combination with vincristine, was validated in multiple retinoblastoma mouse models. Importantly, mice exhibited favorable tolerance to ruxolitinib administration. We confirmed that the underlying mechanism of ruxolitinib's action in chemoresistant retinoblastoma cells is the inhibition of Janus kinase/signal transducer and activator of transcription (JAK/STAT) signaling. Our study reveals that the underlying mechanism driving ruxolitinib's impact on chemoresistant retinoblastoma cells is the inhibition of JAK/STAT signaling. This study reveals the contribution of JAK1/2 to the development of chemoresistance in retinoblastoma and underscores the effectiveness of targeting JAK1/2 as a strategy to sensitize retinoblastoma to chemotherapy.

Identification of novel covalent JAK3 inhibitors through consensus scoring virtual screening: integration of common feature pharmacophore and covalent docking.

Accumulated research strongly indicates that Janus kinase 3 (JAK3) is intricately involved in the initiation and advancement of a diverse range of human diseases, underscoring JAK3 as a promising target for therapeutic intervention. However, JAK3 shows significant homology with other JAK family isoforms, posing substantial challenges in the development of JAK3 inhibitors. To address these limitations, one strategy is to design selective covalent JAK3 inhibitors. Therefore, this study introduces a virtual screening approach that combines common feature pharmacophore modeling, covalent docking, and consensus scoring to identify novel inhibitors for JAK3. First, common feature pharmacophore models were constructed based on a selection of representative covalent JAK3 inhibitors. The optimal qualitative pharmacophore model proved highly effective in distinguishing active and inactive compounds. Second, 14 crystal structures of the JAK3-covalent inhibitor complex were chosen for the covalent docking studies. Following validation of the screening performance, 5TTU was identified as the most suitable candidate for screening potential JAK3 inhibitors due to its higher predictive accuracy. Finally, a virtual screening protocol based on consensus scoring was conducted, integrating pharmacophore mapping and covalent docking. This approach resulted in the discovery of multiple compounds with notable potential as effective JAK3 inhibitors. We hope that the developed virtual screening strategy will provide valuable guidance in the discovery of novel covalent JAK3 inhibitors.

TYK2 as a novel therapeutic target in Alzheimer's Disease with TDP-43 inclusions.

Neuroinflammation is a pathological feature of many neurodegenerative diseases, including Alzheimer's disease (AD)1,2 and amyotrophic lateral sclerosis (ALS)3, raising the possibility of common therapeutic targets. We previously established that cytoplasmic double-stranded RNA (cdsRNA) is spatially coincident with cytoplasmic pTDP-43 inclusions in neurons of patients with C9ORF72-mediated ALS4. CdsRNA triggers a type-I interferon (IFN-I)-based innate immune response in human neural cells, resulting in their death4. Here, we report that cdsRNA is also spatially coincident with pTDP-43 cytoplasmic inclusions in brain cells of patients with AD pathology and that type-I interferon response genes are significantly upregulated in brain regions affected by AD. We updated our machine-learning pipeline DRIAD-SP (Drug Repurposing In Alzheimer's Disease with Systems Pharmacology) to incorporate cryptic exon (CE) detection as a proxy of pTDP-43 inclusions and demonstrated that the FDA-approved JAK inhibitors baricitinib and ruxolitinib that block interferon signaling show a protective signal only in cortical brain regions expressing multiple CEs. Furthermore, the JAK family member TYK2 was a top hit in a CRISPR screen of cdsRNA-mediated death in differentiated human neural cells. The selective TYK2 inhibitor deucravacitinib, an FDA-approved drug for psoriasis, rescued toxicity elicited by cdsRNA. Finally, we identified CCL2, CXCL10, and IL-6 as candidate predictive biomarkers for cdsRNA-related neurodegenerative diseases. Together, we find parallel neuroinflammatory mechanisms between TDP-43 associated-AD and ALS and nominate TYK2 as a possible disease-modifying target of these incurable neurodegenerative diseases.

Association between ferritin, hemoglobin, and anemia response in jaktinib-treated patients with myelofibrosis: A post-hoc analysis of the ZGJAK006 study.

e18527 Background: Iron metabolism is disrupted in MF through the increased production of hepcidin, contributing to increased ferritin levels and iron-binding capacity, decreased serum iron levels and hemoglobin levels. Hepcidin production is upregulated by JAK/STAT pathway and BMP6/ACVR1/SMAD pathway. Jaktinib showed inhibition effects on JAK family and ACVR1 in preclinical studies. Anemia benefits with jaktinib treatment were observed in several clinical studies in MF pts. To explore the underlying mechanisms, we conducted a post-hoc analysis to investigate the change of ferritin levels during jaktinib treatment in MF pts with and without anemia response from a phase 2 study in pts who were intolerant to ruxolitinib (the ZGJAK006 study). Methods: Pts from the ZGJAK006 study were included if they were RBC transfusion dependent or with hemoglobin level ≤100 g/L at baseline. Transfusion dependence was assigned to pts with an average RBC transfusion of ≥2 U/month within 3 months prior to study drug administration. Pts without baseline ferritin results were excluded. Eligible pts were divided into 2 groups: anemia responders by week 24 and non-responders by week 24. Anemia response was defined as becoming RBC transfusion independent (defined by no transfusion in ≥12 consecutive weeks and hemoglobin ≥85 g/L) for transfusion-dependent pts or a ≥20 g/L increase in hemoglobin for non-transfusion-dependent pts with baseline hemoglobin ≤100 g/L. Results: A total of 39 pts were included in this post-hoc analysis, with 14 anemia responders and 25 non-responders. The baseline hemoglobin was similar in responders (median: 78.5 g/L) and non-responders (median: 78.0 g/L). The baseline levels of ferritin were higher than upper limit of normal in most pts (69.2%) with a median of 784.6 ng/mL in the overall population (697.5 ng/mL in responders and 785.0 ng/mL in non-responders). Ferritin decreased to 583.9 and 531.7 ng/mL at weeks 12 and 24, respectively. Notably, anemia responders had a fast reduction in ferritin and increase in hemoglobin compared to non-responders. In addition, the hemoglobin levels of those non-responders maintained were stable and eight non-responders had a ≥50% decrease in RBC infusion frequency or unit. Six (42.9%) of 14 responders and 10 (40.0%) of 25 non-responders achieved spleen volume reduction of ≥ 35% from baseline at week 24. Conclusions: In this post-hoc analysis of pts with anemic MF, jaktinib treatment led to improvement in iron metabolism and anemia. The results were in consistence with the known activities of jaktinib against JAK family and ACVR1. Moreover, similar spleen responses were observed for anemia responders and non-responders. Nevertheless, ferritin was the only marker of iron metabolism measured in this study, a translational biology study evaluating hepcidin may be needed to further support the clinical findings. Clinical trial information: NCT04217993 .

Targeting TYK2 for Fighting Diseases: Recent Advance of TYK2 Inhibitors.

TYK2 (tyrosine-protein kinase 2) is a non-receptor protein kinase belonging to the JAK family and is closely associated with various diseases, such as psoriasis, inflammatory bowel disease, systemic lupus erythematosus. TYK2 activates the downstream proteins STAT1-5 by participating in the signal transduction of immune factors such as IL-12, IL-23, and IL-10, resulting in immune expression. The activity of the inhibitor TYK2 can effectively block the transduction of excessive immune signals and treat diseases. TYK2 inhibitors are divided into two types of inhibitors according to the different binding sites. One is a TYK2 inhibitor that binds to JH2 and inhibits its activity through an allosteric mechanism. The representative inhibitor is BMS-986165, developed by Bristol-Myers Squibb. The other class binds to the JH1 adenosine triphosphate (ATP) site and prevents the catalytic activity of the kinase by blocking ATP and downstream phosphorylation. This paper mainly introduces the protein structure, signaling pathway, synthesis, structure-activity relationship and clinical research of TYK2 inhibitors.

Abstract 7209: Overcoming platinum resistance of high-grade serous ovarian cancer targeting the activated JAK/STAT pathways via extracellular vesicles

Abstract High-grade serous ovarian cancer (HGSOC) is the most common subtype of ovarian cancer. While HGSOC usually responds to initial treatment, most cases eventually relapse and develop platinum-resistant ovarian cancer (PROC). The molecular definition of PROC is still unclear, and overcoming PROC has been the biggest challenges. Extracellular vesicles (EVs) have an essential role in cell-to-cell communication within both the primary and distant microenvironments. In this study. we aimed to identify molecular mechanisms of PROC via EVs to suggest novel therapeutic strategies. Platinum responses were categorized by primary treatment-free interval of platinum less than 6 months as PROC, and more than 36 months as platinum good response. Ascites and tumor tissues have been collected prior to initial chemotherapy in patients with HGSOC for analysis according to platinum response. mRNA sequencing in tumor tissues identified significantly upregulated JAK/STAT pathways in PROC. The JAK/STAT family was highly expressed in PROC than the good response group, and also increased than adjusted normal ovaries and fallopian tubes. In addition, PROC cell lines and PROC patient-derived xenograft model tumor tissues showed high JAK expression. Small RNA sequencing for HGSOC tissues and ascites-EVs revealed that miR-135a-5p and miR-221-5p were highly expressed in both PROC tissues and ascites, and the expression of the two miRNAs had a positive correlation between tissues and ascites. Overexpression of the two miRNAs in HGSOC cell lines resulted in higher JAK family expression and resistance to cisplatin. JAK inhibitors (JAKi) had equivalent efficacy for platinum-sensitive/resistant HGSOC cell lines and JAKi highly suppress tumor growth in the PROC mouse model. In addition, suppression of JAK family expression in PROC cell lines significantly increased sensitivity to cisplatin. JAKi also had a synergistic effect with cisplatin for PROC cell lines. IPA analyses in mRNA sequencing in tumor tissues, TGF-β was highly expressed in upstream regulators in PROC, and TGF-β stimulation resulted in the upregulation of the two miRNAs in mesothelial cells, but not in HGSOC cell lines and fibroblasts. In summary, we here demonstrate novel molecular mechanisms of PROC via EVs and provided the rationale for JAK-targeted therapy for PROC. EV-miRNAs can regulate the PROC activated JAK/STAT pathway and can be diagnostic and therapeutic biomarkers for PROC definition or JAKi indications, suggesting that patient stratification in precision medicine for initial treatment of HGSOC. Citation Format: Kazuhiro Suzuki, Akira Yokoi, Kousuke Yoshida, Yusuke Yamamoto, Hiroaki Kajiyama. Overcoming platinum resistance of high-grade serous ovarian cancer targeting the activated JAK/STAT pathways via extracellular vesicles [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 7209.

Selective JAK-Inhibitors in Spondyloarthritis.

As our research interest and knowledge increases in the field of Spondyloarthritis, new aspects also emerge as regards to their therapeutic approach. JAK inhibitors (JAKi) are a relatively new treatment option, aiming molecules in the JAK-STAT pathway, which has a leading role in the pathophysiology of both Psoriatic Arthritis and Axial Spondyloarthritis. JAKi exhibit different selectivity towards the four different members of the JAK family (namely JAK1, JAK2, JAK3, and TYK2), possibly reflecting different efficacy and safety profile. Although knowledge is more consolidated for rheumatoid arthritis in which JAKi are being used for more than 10 years, data are still accumulating for PsA/SpA. In this review we aim to present and assess current knowledge about the efficacy of JAKi (with a focus on selective JAKi) in the treatment of patients with SpA and evaluate their safety profile as some concerns may arise around this therapeutic option.

TYK2 signaling promotes the development of autoreactive CD8+ cytotoxic T lymphocytes and type 1 diabetes

Tyrosine kinase 2 (TYK2), a member of the JAK family, has attracted attention as a potential therapeutic target for autoimmune diseases. However, the role of TYK2 in CD8+ T cells and autoimmune type 1 diabetes (T1D) is poorly understood. In this study, we generate Tyk2 gene knockout non-obese diabetes (NOD) mice and demonstrate that the loss of Tyk2 inhibits the development of autoreactive CD8+ T-BET+ cytotoxic T lymphocytes (CTLs) by impairing IL-12 signaling in CD8+ T cells and the CD8+ resident dendritic cell-driven cross-priming of CTLs in the pancreatic lymph node (PLN). Tyk2-deficient CTLs display reduced cytotoxicity. Increased inflammatory responses in β-cells with aging are dampened by Tyk2 deficiency. Furthermore, treatment with BMS-986165, a selective TYK2 inhibitor, inhibits the expansion of T-BET+ CTLs, inflammation in β-cells and the onset of autoimmune T1D in NOD mice. Thus, our study reveals the diverse roles of TYK2 in driving the pathogenesis of T1D.

High-Resolution Structure of RNA G-Quadruplex Containing Unique Structural Motifs Originating from the 5'-UTR of Human Tyrosine Kinase 2 (TYK2).

Tyrosine kinase 2 (TYK2) is a member of the JAK family of nonreceptor-associated tyrosine kinases together with highly homologous JAK1, JAK2, and JAK3 paralogues. Overexpression of TYK2 is associated with several inflammatory diseases, including severe complications during the COVID-19 infection. Since the downregulation of JAK paralogues could lead to serious health consequences or even death, it is critical to avoid it when designing drugs to suppress TYK2. To achieve the required specificity only for TYK2, researchers have recently selectively targeted TYK2 mRNA by developing antisense oligonucleotides. In this work, we expand the target space of TYK2 mRNA by showing that the mRNA adopts tetra-helical noncanonical structures called G-quadruplexes. We identified a TYKwt RNA oligonucleotide from the 5'-UTR of TYK2 mRNA, which adopts multiple different parallel G-quadruplexes that exist at equilibrium. Using NMR spectroscopy, we showed that some of the G-quadruplexes adopt unique structural motifs, mainly due to the formation of a stable GA bulge. Using guanine to uridine substitutions, we prepared the oligonucleotide TYK3_U6, which serves as an excellent model for the bulged G-quadruplexes formed by the TYKwt oligonucleotide. NMR structural analysis, including data on the residual coupling constants (RDC) of the loop regions, unveiled that the studied three-quartet parallel G-quadruplex contains many unusual structural features such as a G(U)A bulge, a guanine residue in the syn conformation, A and U residues stacked on the top G-quartet, and a well-defined adenine from a three-residue long propeller loop oriented in the groove, all of which could be valuable targets for future drug design.

P718 Observational real-world evidence on the efficacy and safety of Janus Kinase inhibitors (JAKi) in the treatment of moderate to severe Active Ulcerative Colitis (UC)

Abstract Background Janus kinase inhibitors (JAKi) are the first orally administered treatment for Ulcerative Colitis (UC). The JAK family comprises of four intracellular tyrosine kinases inhibitors (JAK1, JAK2, JAK3 and Tyrosine Kinase 2). Inhibition of the JAK kinases lead to dampening of the inflammatory cytokines which drive Inflammatory Bowel Disease (IBD). Tofacitinib was the first generation pan-JAKi. This was followed by second generation JAKi: Filgotinib and Upadacinib which preferentially inhibit JAK1. We report on the real-world evidence on the efficacy and safety of JAKi in the treatment of UC in a tertiary IBD treatment centre. Methods Patients attending the IBD clinic at weeks 8-12 of initiation of therapy were included. Baseline demographics, disease activity and previous therapies were recorded. Clinical response was measured using the SCCAI and biochemical response was measured using calprotectin and CRP. We defined clinical response as ≥3 points reduction from baseline SCCAI, and clinical remission as SCCAI Score of <2.5, and / or biochemical remission as a CRP of less than 5 mg/L and a calprotectin level of < 250 mg/g. We also assessed treatment persistence, and the reasons for treatment cessation. Results The UC populations are shown in Table 1. 52 patients were included and an additional 24 patients who discontinued therapy early on were assessed to review secondary outcomes. Table 1 summarises the comparative outcomes of the JAKi. 81% and 63% of patients achieved clinical and biochemical remission respectively. Overall, 31% discontinued treatment due to lack of efficacy or adverse events. 60% of patients reported adverse events (AEs), 25 % of patients discontinued treatment due to AEs and 84% of patients continued treatment despite reporting AEs. The most common AEs were hypercholesteremia and cold and flu like symptoms and the most common AEs related with treatment discontinuation were recurrent infection or persistent deranged liver functions contributed to patients’ history of primary sclerosing cholangitis. No Serious Adverse Events were reported. 60% of patients on tofacitinib developed side effects and persisted with therapy, which included hypercholesteremia (67%), shingles (11%), flu like symptom (11%) and hair loss (11%). 53% had side effects with Filgotinib; hypercholesteremia (25%), cold like symptoms (25%), chest infection (13%), shingles (13%), acne (13%). 68% developed side effects with Upadacitinib; reports of acne (20%), cold and flu (33%), shingles and mood swings (7%) and high cholesterol (67%). Conclusion In this real-world cohort of UC patients, JAKi was effective in inducing remission and had an acceptable safety profile. The observed safety profile was as expected compared to clinical data results.

Effectiveness of tofacitinib monotherapy for patients with IgG4-RD or idiopathic retroperitoneal fibrosis.

To explore the effectiveness of tofacitinib for immunoglobulin G4-related disease (IgG4-RD) and idiopathic retroperitoneal fibrosis (IRF), and investigate the expression of JAKs in the lesion of these diseases. Clinical data of patients with IgG4-RD or IRF who were administered with tofacitinib monotherapy were collected. IgG4-RD responder index (IgG4-RD RI) was assessed. The expression of JAK1, JAK2, JAK3, and TYK2 were analysed with immunohistochemistry staining in three salivary glands specimens of IgG4-RD and one retroperitoneal tissue of IRF. Two patients with IRF and two patients with IgG4-RD used tofacitinib monotherapy. Two patients with IRF achieved complete remission with diminished retroperitoneal mass and decreased CRP, as IgG4-RD RI decreased from 6 to 1 in both of them. One with IgG4-RD achieved complete remission with alleviated enlargement of pancreas and IgG4 level decreased from 13.7 g/L to 2.4 g/L, as IgG4-RD RI decreased from 12 to 1. One with IgG4-RD achieved partial response with IgG4 level decreased from 77.1g/L to 25.8g/L as IgG4-RD RI from 18 to 6. JAK1, JAK2, JAK3, and TYK2 expression were detected in biopsy tissues. The staining intensity of the JAK family on the lesion from one IRF patient was similar to those from IgG4-RD patients. Tofacitinib is a potentially effective treatment for IgG4-RD and IRF and it is reasonable to conduct clinical trial to validate its efficacy. The JAKs were expressed in the inflammatory lesions of IgG4-RD and IRF and they may share a common pathogenesis pathway that is independent of IgG4 production.

Comparison of the Enzymatic and Cellular Profiles of Clinical JAK2 Inhibitors for the Treatment of Myelofibrosis

Introduction: Three Janus kinase 2 (JAK2) inhibitors (JAKinibs) have been approved by the FDA for the treatment of myelofibrosis (MF): ruxolitinib, fedratinib, and pacritinib; a fourth one, momelotinib, is currently under FDA review. In addition to JAK2, these drugs also inhibit other kinases with distinct profiles with potential implications in their observed pharmacology. Published data on kinase inhibitory profiles of the four JAKinibs are limited and were determined under differing assay conditions (Wernig G et al. Cancer Cell 2008; Pardanani A et al. Leukemia 2009; Quintás-Cardama A et al. Blood 2010; Singer J et al. J Exp Pharm 2016), which limits head-to-head comparisons and understanding of their JAK2 inhibition unrelated effects. Here, we present full kinome profiling data for these four JAKinibs. Additionally, we have compared their effects on signaling and proliferation in myeloid cells and other human cells. Methods and Results: Enzymatic assays performed in the presence of 1 mM ATP showed that ruxolitinib is the most potent JAK2 inhibitor (IC 50 4 nM) followed by fedratinib (14 nM), momelotinib (51 nM), and pacritinib (53 nM). Inhibition of other JAK family proteins such as JAK1 and TYK2 were also observed to varying degrees with each drug, and these enzymatic activities were consistent with inhibition of STAT signaling in response to different cytokines in secreted embryonic alkaline phosphatase (SEAP) cellular reporter assays (HEK-Blue Detection, InvivoGen, San Diego, CA). Full kinome analyses (372 activity assays of 356 unique wild-type protein kinases) were conducted (Reaction Biology, Malvern, PA) with determination of percentage inhibition at 100 nM of each drug with 10 μM ATP. Kinases exhibiting >50% inhibition with any of the drugs were then evaluated for dose-response to each drug with 100 μM ATP. The results shown in the Figure demonstrate that fedratinib, momelotinib, and pacritinib inhibited additional kinases outside of the JAK family with similar potency to JAK2 inhibition, whereas ruxolitinib was relatively selective for JAK2 inhibition. In contrast to published reports on the inhibitory activities of pacritinib and momelotinib against ALK2 ( ACVR1), the inhibition of ALK2 observed here was 5-10 times weaker than JAK2 inhibition. Furthermore, pacritinib and momelotinib were both weaker inhibitors of ALK2 activity when compared with their potency towards more than 30 other kinases screened. Fedratinib, pacritinib, and momelotinib, but not ruxolitinib, exhibited high inhibitory potencies against FLT3 and/or KIT kinases, both of which are critical for the self-renewal and differentiation of normal hematopoietic stem cells. In cellular assays monitoring JAK2 signaling (pSTAT5 level in SET2 cells), ruxolitinib was the most potent agent (IC 50 14 nM), followed by momelotinib (205 nM), pacritinib (429 nM), and fedratinib (672 nM). Similar trends were observed in other cellular assays assessing antiproliferative effects in JAK2-dependent myeloid cell lines. In cells not dependent on JAK pathway signaling for growth in culture, such as primary human fibroblasts and endothelial cells, ruxolitinib showed weak or no inhibition at 5 μM, while fedratinib, pacritinib and momelotinib showed anti-proliferative effects with low micromolar IC 50s. Similar trends were observed in human HEK293 and HepG2 cell lines, which are commonly used to assess drug effects on general cell health. We analyzed the effects of the JAKinibs on the differentiation of CD34 + hematopoietic stem and progenitor cells (HSPCs) derived from healthy donors at concentrations observed in the plasma of MF patients enrolled in clinical trials. Consistent with their activity on multiple kinases, including FLT3 and KIT, fedratinib and pacritinib elicited the most pronounced decrease in overall viability, affecting HSPCs and megakaryocytes. In contrast, ruxolitinib as a more selective JAK2 inhibitor, showed the least effect on the differentiation of normal CD34 + HSPCs. Conclusion: JAKinibs clinically evaluated for treatment of MF exhibit distinct kinase inhibition profiles and cellular activities. Amongst the agents tested in this study, ruxolitinib was the most potent and selective JAK2 inhibitor. At concentrations several fold above clinically relevant concentrations, ruxolitinib had no observable effects on the health of cells not reliant on JAK/STAT mediated signaling.

Ritlecitinib (Litfulo) for severe alopecia areata.

The FDA has approved ritlecitinib (Litfulo – Pfizer), an oral JAK and TEC kinase family inhibitor, for treatment of severe alopecia areata in patients ≥12 years old. Ritlecitinib is the second oral drug to be approved in the US for treatment of severe alopecia areata; baricitinib (Olumiant), a JAK inhibitor, is approved only for use in adults.

HDAC specificity and kinase off-targeting by purine-benzohydroxamate anti-hematological tumor agents

A series of hybrid inhibitors, combining pharmacophores of known kinase inhibitors bearing anilino-purines (ruxolitinib, ibrutinib) and benzohydroxamate HDAC inhibitors (nexturastat A), were generated in the present study. The compounds have been synthesized and tested against solid and hematological tumor cell lines. Compounds 4d-f were the most promising in cytotoxicity assays (IC50 ≤ 50 nM) vs. hematological cells and displayed moderate activity in solid tumor models (EC50 = 9.3–21.7 μM). Compound 4d potently inhibited multiple kinase targets of interest for anticancer effects, including JAK2, JAK3, HDAC1, and HDAC6. Molecular dynamics simulations showed that 4d has stable interactions with HDAC and members of the JAK family, with differences in the hinge binding energy conferring selectivity for JAK3 and JAK2 over JAK1. The kinase inhibition profile of compounds 4d-f allows selective cytotoxicity, with minimal effects on non-tumorigenic cells. Moreover, these compounds have favorable pharmacokinetic profiles, with high stability in human liver microsomes (e.g., see t1/2: >120 min for 4f), low intrinsic clearance, and lack of significant inhibition of four major CYP450 isoforms.

Molecular Characteristics of TYK2 Gene Expressions in Patients with Colorectal Cancer.

TYK2 is a member of the JAK family and is known to mediate signals of multiple cytokines that play a crucial role in immune and inflammatory signaling. Activation of TYK2 in tumor cells has been linked to promote cell survival, growth, and invasion. This study aimed to investigate the expression of tyrosine kinase 2 (TYK2) in colorectal cancer (CRC) and adjacent control tissues. Quantitative Real-Time PCR (qRT-PCR) method was elaborated to examine the expression levels of TYK2 in 100 colorectal tumor tissues and adjacent tissues as a control. Furthermore, we analyzed the diagnostic power of the mentioned TYK2 by plotting the receiver operating characteristic (ROC) curve. Our results revealed that the expression level of TYK2 was significantly up-regulated in CRC patients sample compared to the adjacent sample of the control group. Analysis of patient's clinic pathological features shows that expressions TYK2 were differently associated with lymph vascular invasion and TMN stage (P < 0.0001, P < 0.0006). These results indicated that TYK2 levels potential biomarkers for diagnosing colorectal cancer may be identified.

In silico computational drug discovery: a Monte Carlo approach for developing a novel JAK3 inhibitors

Inhibition of Janus kinase 3 (JAK3), a member of the JAK family of tyrosine kinases, remains an essential area of research for developing treatments for autoimmune diseases, particularly cancer and rheumatoid arthritis. The recent discovery of a new JAK3 protein, PDB ID: 4Z16, offers exciting possibilities for developing inhibitors capable of forming a covalent bond with the Cys909 residue, thereby contributing to JAK3 inhibition. A powerful prediction model was constructed and validated using Monte Carlo methods, employing various internal and external techniques. This approach resulted in the prediction of eleven new molecules, which were subsequently filtered to identify six compounds exhibiting potent pIC50 values. These candidates were then subjected to ADMET analysis, molecular docking (including reversible-reversible docking with tofacitinib, an FDA-approved drug, and reversible-irreversible docking for the newly designed compounds), molecular dynamics (MD) analysis for 300 ns, and calculation of free binding energy. The results suggested that these compounds hold promise as JAK3 inhibitors. In summary, the new compounds have exhibited favorable outcomes compared to other compounds across various modeling approaches. The collective findings from these investigations provide valuable insights into the potential therapeutic applications of covalent JAK3 inhibitors, offering a promising direction for the development of novel treatments for autoimmune disorders. Communicated by Ramaswamy H. Sarma

Targeting the Tyrosine Kinase 2 (TYK2) Pseudokinase Domain: Discovery of the Selective TYK2 Inhibitor ABBV-712.

Tyrosine kinase 2 (TYK2) is a nonreceptor tyrosine kinase that belongs to the JAK family also comprising JAK1, JAK2, and JAK3. TYK2 is an attractive target for various autoimmune diseases as it regulates signal transduction downstream of IL-23 and IL-12 receptors. Selective TYK2 inhibition offers a differentiated clinical profile compared to currently approved JAK inhibitors. However, selectivity for TYK2 versus other JAK family members has been difficult to achieve with small molecules that inhibit the catalytically active kinase domain. Successful targeting of the TYK2 pseudokinase domain as a strategy to achieve isoform selectivity was recently exemplified with deucravacitinib. Described herein is the optimization of selective TYK2 inhibitors targeting the pseudokinase domain, resulting in the discovery of the clinical candidate ABBV-712 (21).

Discovery of the Potent and Selective Inhaled Janus Kinase 1 Inhibitor AZD4604 and Its Preclinical Characterization.

JAK-STAT cytokines are critical in regulating immunity. Persistent activation of JAK-STAT signaling pathways by cytokines drives chronic inflammatory diseases such as asthma. Herein, we report on the discovery of a highly JAK1-selective, ATP-competitive series of inhibitors having a 1000-fold selectivity over other JAK family members and the approach used to identify compounds suitable for inhaled administration. Ultimately, compound 16 was selected as the clinical candidate, and upon dry powder inhalation, we could demonstrate a high local concentration in the lung as well as low plasma concentrations, suggesting no systemic JAK1 target engagement. Compound 16 has progressed into clinical trials. Using 16, we found JAK1 inhibition to be more efficacious than JAK3 inhibition in IL-4-driven Th2 asthma.