Activity of the Type II JAK2 Inhibitor CHZ868 in B Cell Acute Lymphoblastic Leukemia

Recent advances and future perspectives in small molecule JAK2 inhibitors

The Janus kinase (JAK)/Signal Transducer and Activator of Transcription (STAT) signaling pathway is essential for controlling immune function, blood cell formation, and cell growth. Dysregulation of this pathway is implicated in various diseases, including hematologic malignancies, autoimmune disorders, and chronic inflammatory conditions. This review provides a comprehensive overview of the structural and functional aspects of JAK/STAT signaling, with a particular focus on the role of JAK2. This manuscript explores the primary regulators of the JAK/STAT pathway, such as Suppressors Of Cytokine Signaling (SOCS), Protein Inhibitors of Activated STATs (PIAS), and Protein Tyrosine Phosphatases (PTPs), which play a crucial role in maintaining cellular balance and stability. Additionally, the therapeutic landscape of JAK2 inhibitors is explored, covering both approved and investigational drugs, including their mechanisms of action, efficacy, and safety profiles. Emerging strategies such as drug repositioning using computational approaches and experimental validation are also highlighted. By integrating insights from molecular docking studies, machine learning models, and kinase assays, this review emphasizes the potential of JAK2 inhibitors in disease management.

Nuciferine ameliorates blood-brain barrier disruption post-ischemic stroke via inhibiting the JAK2/STAT3 pathway

BACKGROUND

Ischemic stroke frequently results in the compromise of the blood-brain barrier (BBB), a pathological occurrence strongly linked to the impairment of cerebral microvascular endothelial cells and the disintegration of tight junction (TJ) proteins. Nuciferine, a naturally occurring aporphine alkaloid extracted from the leaves of Nelumbo nucifera, exhibits favorable pharmacokinetic characteristics, including the capacity to traverse the BBB, and has demonstrated neuroprotective potential in IS models. Nevertheless, the specific mechanisms by which nuciferine modulates BBB integrity following ischemia, and the molecular pathways involved, remain inadequately understood.

PURPOSE

This study probed into the protective function of nuciferine against BBB disruption following IS and the molecular pathways involved in its therapeutic action.

METHODS

In vivo, a photothrombotic focal cerebral ischemia mouse model was established and evaluated through neurological scoring, blood flow measurement, and 2,3,5-triphenyltetrazolium chloride staining. BBB disruption was assessed utilizing Evans Blue dye and endogenous immunoglobulin G extravasation. nuciferine (10, 20, 40 mg/kg, intragastric administration, daily for 7 days) was administered post-ischemia. In vitro, oxygen-glucose deprivation (OGD, 2 h)-induced bEnd.3 cell model was employed and treated with nuciferine (10, 20, and 40 μM, 24 h) to uncover the related mechanisms.

RESULTS

Our findings revealed that nuciferine effectively preserved BBB integrity and prevented cerebral edema post-photothrombotic. Mechanistically, nuciferine restored the expression of ZO-1, occludin, and claudin-5, both in photothrombotic and OGD models. Meanwhile, it showed the protective effect on OGD-induced endothelial cells injury by inhibiting apoptosis and mitochondrial dysfunction. Importantly, nuciferine targeted Janus kinase 2 and suppressed p-JAK2 and p-STAT3 in IS model.

CONCLUSIONS

Our findings present novel evidence that nuciferine improves the BBB integrity following IS through blocking the JAK2/STAT3 pathway. Through demonstrating the targeted suppression of JAK2 activation by nuciferine, this work contributes to a more nuanced understanding of how this pathway influences endothelial barrier function in ischemic conditions. Our results offer a conceptual basis for the continued exploration of Nuciferine as a potential therapeutic agent to address BBB dysfunction in the post-stroke setting.

Exploring the therapeutic potential and in vitro validation of baicalin for the treatment of triple-negative breast cancer

Objective

To explore the mechanism of action of baicalin (BA) in the treatment of triple-negative breast cancer (TNBC) based on network pharmacology, molecular docking and molecular dynamics simulations and in vitro validation.

Methods

The inhibitory effects of different concentrations of baicalin on the proliferation of MDA-MB-231, 4T1, MCF-7, and MCF-10A cell lines were evaluated by CCK8 assay with clone formation assay. Three compound target prediction platforms, Swiss Target Prediction, SEA and Pharmmapper, were used to predict baicalin-related targets, and mapped with the triple-negative breast cancer-related targets retrieved from GeneCards and OMMI databases to obtain the potential targets of baicalin for the treatment of triple-negative breast cancer; the STRING database and the STRING database and Cytoscape software were used to construct the protein interaction network and screen the core targets; GO and KEGG enrichment analyses were performed on the core targets; the binding of baicalin to the key targets of triple-negative breast cancer was verified by molecular docking and molecular dynamics simulation; and the expression of the relevant proteins was verified.

Results

Baicalin showed more obvious antiproliferative effects on triple-negative breast cancer cell lines at certain concentrations, and had less effect on the proliferation of normal breast cells. A total of nine core targets of baicalin in the treatment of triple-negative breast cancer, including AKT1, ESR1, TNF-α, SRC, EGFR, MMP9, JAK2, PPARG, and GSK3B, were identified through the construction of the PPI protein interactions network and the 'Traditional Chinese Medicine-Component-Target-Disease' network, and a total of 252 targets related to the intersected targets were identified in the GO analysis. GO analysis enriched a total of 2,526 Biological process, 105 Cellular component and 250 Molecular function related to the intersecting targets; KEGG analysis enriched a total of 128 signaling pathways related to the intersecting targets; molecular docking results and molecular dynamics studies found that baicalin was able to interact with MMP9, TNF-α, JAK2, PPARG, GSK3B, and other core targets of baicalin for the treatment of triple-negative breast, MMP9, TNF-α, and JAK2 target proteins, and had significant changes in the expression levels of the target proteins.

Conclusion

Baicalin inhibits the protein expression of MMP9, TNF-α and JAK2 and their related signaling pathways in the treatment of triple-negative breast cancer.

Co-targeting of the thymic stromal lymphopoietin receptor to decrease immunotherapeutic resistance in CRLF2-rearranged Ph-like and Down syndrome acute lymphoblastic leukemia

CRLF2 rearrangements occur in >50% of Ph-like and Down syndrome (DS)-associated B-acute lymphoblastic leukemia (ALL) and induce constitutive kinase signaling targetable by the JAK1/2 inhibitor ruxolitinib under current clinical investigation. While chimeric antigen receptor T cell (CART) immunotherapies have achieved remarkable remission rates in children with relapsed/refractory B-ALL, ~50% of CD19CART-treated patients relapse again, many with CD19 antigen loss. We previously reported preclinical activity of thymic stromal lymphopoietin receptor-targeted cellular immunotherapy (TSLPRCART) against CRLF2-overexpressing ALL as an alternative approach. In this study, we posited that combinatorial TSLPRCART and ruxolitinib would have superior activity and first validated potent TSLPRCART-induced inhibition of leukemia proliferation in vitro in CRLF2-rearranged ALL cell lines and in vivo in Ph-like and DS-ALL patient-derived xenograft (PDX) models. However, simultaneous TSLPRCART/ruxolitinib or CD19CART/ruxolitinib treatment during initial CART expansion diminished T cell proliferation, blunted cytokine production, and/or facilitated leukemia relapse, which was abrogated by time-sequenced/delayed ruxolitinib co-exposure. Importantly, ruxolitinib co-administration prevented fatal TSLPRCART cytokine-associated toxicity in ALL PDX mice. Upon ruxolitinib withdrawal, TSLPRCART functionality recovered in vivo with clearance of subsequent ALL rechallenge. These translational studies demonstrate an effective two-pronged therapeutic strategy that mitigates acute CART-induced hyperinflammation and provides potential anti-leukemia 'maintenance' relapse prevention for CRLF2-rearranged Ph-like and DS-ALL.

Selective JAK2 pathway inhibition enhances anti-leukemic functionality in CD19 CAR-T cells

The integration of molecular targeted therapeutics with chimeric antigen receptor T (CAR-T) cell therapy represents a novel strategy to amplify the anti-tumor efficacy of immunotherapy. While CD19-targeted CAR-T cells and Janus kinase (JAK) inhibitors have independently shown efficacy against certain B-cell leukemias, such as Philadelphia chromosome-like acute lymphoblastic leukemia, the concurrent use of JAK1/2 inhibitors, such as ruxolitinib, has been implicated in reducing CAR-T cell potency by inhibiting the JAK1-dependent T cell activation pathway. This study explores the combinatorial use of a selective type II JAK2 inhibitor, CHZ868, with CD19 CAR-T cells, revealing a synergistic enhancement of anti-leukemic activity across B-cell tumor models irrespective of JAK2 mutational status. CHZ868-mediated JAK2 inhibition did not induce the exhaustion of CAR-T cells, maintaining efficacy over repeated tumor challenges and significantly extending survival in mouse models engrafted with JAK2 inhibitor-resistant leukemia cells (median survival, CD19 CAR-T + CHZ868 vs. CD19 CAR-T + DMSO: 32 days vs. 26 days, p = 0.0303). Transcriptomic analyses suggest that CHZ868 impedes CAR-T cell differentiation while preserving their proliferative capacity, a crucial factor in maintaining CAR-T cell functionality. Therefore, the selective inhibition of the JAK2 pathway may potentiate CAR-T cell therapy and offer a viable treatment strategy for patients with resistant B-cell leukemias.

How I treat Philadelphia chromosome-like acute lymphoblastic leukemia in children, adolescents, and young adults

ABSTRACT

Philadelphia chromosome-like acute lymphoblastic leukemia (Ph-like ALL) represents a high-risk B-lineage ALL subtype characterized by adverse clinical features and poor relapse-free survival despite risk-adapted multiagent chemotherapy regimens. The advent of next-generation sequencing has unraveled the diversity of kinase-activating genetic drivers in Ph-like ALL that are potentially amenable to personalized molecularly-targeted therapies. Based upon robust preclinical data and promising case series of clinical activity of tyrosine kinase inhibitor (TKI)-based treatment in adults and children with relevant genetic Ph-like ALL subtypes, several clinical trials have investigated the efficacy of JAK- or ABL-directed TKIs in cytokine receptor-like factor 2 (CRLF2)/JAK pathway-mutant or ABL-class Ph-like ALL, respectively. The final results of these trials are pending, and standard-of-care therapeutic approaches for patients with Ph-like ALL have yet to be defined. In this How I Treat perspective, we review recent literature to guide current evidence-based treatment recommendations via illustrative clinical vignettes of children, adolescents, and young adults with newly diagnosed or relapsed/refractory Ph-like ALL, and we further highlight open and soon-to-open trials investigating immunotherapy and TKIs specifically for this high-risk patient population.

SOHO State of the Art Updates and Next Questions | Approach to BCR::ABL1-Like Acute Lymphoblastic Leukemia

Philadelphia-like (Ph-like) or BCR::ABL1-like acute lymphoblastic leukemia (ALL) is a common high-risk subtype of B-cell precursor ALL (B-ALL) characterized by a diverse range of genetic alterations that challenge diagnose and converge on distinct kinase and cytokine receptor-activated gene expression profiles, resembling those from BCR::ABL1-positive ALL from which its nomenclature. The presence of kinase-activating genetic drivers has prompted the investigation in preclinical models and clinical settings of the efficacy of tyrosine kinase inhibitor (TKI)-based treatments. This was further supported by an inadequate response to conventional chemotherapy, high rates of induction failure and persistent measurable residual disease (MRD) positivity, which translate in lower survival rates compared to other B-ALL subtypes. Therefore, innovative approaches are underway, including the integration of TKIs with frontline regimens and the early introduction of immunotherapy strategies (monoclonal antibodies, T-cell engagers, drug-conjugates, and CAR-T cells). Allogeneic hematopoietic cell transplantation (HSCT) is currently recommended for adult BCR::ABL1-like ALL patients in first complete remission. However, the incorporation of novel therapies, a more accurate diagnosis and a more sensitive MRD assessment may modify the risk stratification and the indication for transplant in these patients.

Selective metabolic regulations by p53 mutant variants in pancreatic cancer

BACKGROUND

Approximately half of all human cancers harbour mutations in the p53 gene, leading to the generation of neomorphic p53 mutant proteins. These mutants can exert gain-of-function (GOF) effects, potentially promoting tumour progression. However, the clinical significance of p53 GOF mutations, as well as the selectivity of individual variants, remains controversial and unclear.

METHODS

To elucidate the metabolic regulations and molecular underpinnings associated with the specific p53R270H and p53R172H mutant variants (the mouse equivalents of human p53R273H and p53R175H, respectively), we employed a comprehensive approach. This included integrating global metabolomic analysis with epigenomic and transcriptomic profiling in mouse pancreatic cancer cells. Additionally, we assessed metabolic parameters such as oxygen consumption rate and conducted analyses of proliferation and cell-cell competition to validate the biological impact of metabolic changes on pancreatic ductal adenocarcinoma (PDAC) phenotype. Our findings were further corroborated through analysis of clinical datasets from human cancer cohorts.

RESULTS

Our investigation revealed that the p53R270H variant, but not p53R172H, sustains mitochondrial function and energy production while also influencing cellular antioxidant capacity. Conversely, p53R172H, while not affecting mitochondrial metabolism, attenuates the activation of pro-tumorigenic metabolic pathways such as the urea cycle. Thus, the two variants selectively control different metabolic pathways in pancreatic cancer cells. Mechanistically, p53R270H induces alterations in the expression of genes associated with oxidative stress and reduction in mitochondrial respiration. In contrast, p53R172H specifically impacts the expression levels of enzymes involved in the urea metabolism. However, our analysis of cell proliferation and cell competition suggested that the expression of either p53R270H or p53R172H does not influence confer any selective advantage to this cellular model in vitro. Furthermore, assessment of mitochondrial priming indicated that the p53R270H-driven mitochondrial effect does not alter cytochrome c release or the apoptotic propensity of pancreatic cancer cells.

CONCLUSIONS

Our study elucidates the mutant-specific impact of p53R270H and p53R172H on metabolism of PDAC cancer cells, highlighting the need to shift from viewing p53 mutant variants as a homogeneous group of entities to a systematic assessment of each specific p53 mutant protein. Moreover, our finding underscores the importance of further exploring the significance of p53 mutant proteins using models that more accurately reflect tumor ecology.

Therapeutic potential of anticancer activity of nitrogen-containing heterocyclic scaffolds as Janus kinase (JAK) inhibitor: Biological activity, selectivity, and structure-activity relationship

The JAK-STAT signalling pathway is primarily involved in cytokine signalling and induces various factors namely, erythropoietin, thrombopoietin, interferons, interleukins, and granulocyte colony-stimulating factors. These factors tremendously influenced understanding human health and illness, specifically cancer. Inhibiting the JAK/STAT pathway offers enormous therapeutic promises against cancer. Many JAK inhibitors are now being studied due to their efficacy in various cancer treatments. Further, the Nitrogen-heterocyclic (N-heterocyclic) scaffold has always shown to be a powerful tool for designing and discovering synthetic compounds with diverse pharmacological characteristics. The review focuses on several FDA-approved JAK inhibitors and their systematic categorization. The medicinal chemistry perspective is highlighted and classified review on the basis of N-heterocyclic molecules. Several examples of designing strategies of N-heterocyclic rings including pyrrolo-azepine, purine, 1H-pyrazolo[3,4-d]pyrimidine, 1H-pyrrolo[2,3-b]pyridine, pyrazole, thieno[3,2-d] pyrimidine, and, pyrimidine-based derivatives and their structure-activity relationships (SAR) are discussed. Among the various N-heterocyclic-based JAK inhibitors pyrimidine-containing compound 1 exhibited excellent inhibition activity against JAK2WT and mutated-JAK2V617F with IC50 of 2.01 and 18.84 nM respectively. Amino pyrimidine-containing compound 6 and thiopheno[3,2-d]pyrimidine-containing compound 13 expressed admirable JAK3 inhibition activity with IC50 of 1.7 nM and 1.38 nM respectively. Our review will support the medicinal chemists in refining and directing the development of novel N-heterocyclic-based JAK inhibitors.

The roles of patient-derived xenograft models and artificial intelligence toward precision medicine

Patient-derived xenografts (PDX) involve transplanting patient cells or tissues into immunodeficient mice, offering superior disease models compared with cell line xenografts and genetically engineered mice. In contrast to traditional cell-line xenografts and genetically engineered mice, PDX models harbor the molecular and biologic features from the original patient tumor and are generationally stable. This high fidelity makes PDX models particularly suitable for preclinical and coclinical drug testing, therefore better predicting therapeutic efficacy. Although PDX models are becoming more useful, the several factors influencing their reliability and predictive power are not well understood. Several existing studies have looked into the possibility that PDX models could be important in enhancing our knowledge with regard to tumor genetics, biomarker discovery, and personalized medicine; however, a number of problems still need to be addressed, such as the high cost and time-consuming processes involved, together with the variability in tumor take rates. This review addresses these gaps by detailing the methodologies to generate PDX models, their application in cancer research, and their advantages over other models. Further, it elaborates on how artificial intelligence and machine learning were incorporated into PDX studies to fast-track therapeutic evaluation. This review is an overview of the progress that has been done so far in using PDX models for cancer research and shows their potential to be further improved in improving our understanding of oncogenesis.

Type II mode of JAK2 inhibition and destabilization are potential therapeutic approaches against the ruxolitinib resistance driven myeloproliferative neoplasms

Background

Ruxolitinib has been approved by the US FDA for the treatment of myeloproliferative neoplasms such as polycythemia vera and primary myelofibrosis. Ruxolitinib will remain a main stay in the treatment of MPN patients due to its effective therapeutic benefits. However, there have been instances of ruxolitinib resistance in MPN patients. As JAK2 is a direct target of ruxolitinib, we generated ruxolitinib-resistant clones to find out the mechanism of resistance.

Methods

Cell-based screening strategy was used to detect the ruxolitinib-resistant mutations in JAK2. The Sanger sequencing method was used to detect the point mutations in JAK2. Mutations were re-introduced using the site-directed mutagenesis method and stably expressed in Ba/F3 cells. Drug sensitivities against the JAK2 inhibitors were measured using an MTS-based assay. JAK2 and STAT5 activation levels and total proteins were measured using immunoblotting. Computational docking studies were performed using the Glide module of Schrodinger Maestro software.

Results

In this study, we have recovered seven residues in the kinase domain of JAK2 that affect ruxolitinib sensitivity. All these mutations confer cross-resistance across the panel of JAK2 kinase inhibitors except JAK2-L983F. JAK2-L983F reduces the sensitivity towards ruxolitinib. However, it is sensitive towards fedratinib indicating that our screen identifies the drug-specific resistance profiles. All the ruxolitinib-resistant JAK2 variants displayed sensitivity towards type II JAK2 inhibitor CHZ-868. In this study, we also found that JAK1-L1010F (homologous JAK2-L983F) is highly resistant towards ruxolitinib suggesting the possibility of JAK1 escape mutations in JAK2-driven MPNs and JAK1 mutated ALL. Finally, our study also shows that HSP90 inhibitors are potent against ruxolitinib-resistant variants through the JAK2 degradation and provides the rationale for clinical evaluation of potent HSP90 inhibitors in genetic resistance driven by JAK2 inhibitors.

Conclusion

Our study identifies JAK1 and JAK2 resistance variants against the type I JAK2 inhibitors ruxolitinib, fedratinib, and lestaurtinib. The sensitivity of these resistant variants towards the type II JAK2 inhibitor CHZ-868 indicates that this mode of type II JAK2 inhibition is a potential therapeutic approach against ruxolitinib refractory leukemia. This also proposes the development of potent and specific type II JAK2 inhibitors using ruxolitinib-resistance variants as a prototype.

JAK inhibition enhances checkpoint blockade immunotherapy in patients with Hodgkin lymphoma

Unleashing antitumor T cell activity by checkpoint inhibitor immunotherapy is effective in cancer patients, but clinical responses are limited. Cytokine signaling through the Janus kinase (JAK)-signal transducer and activator of transcription (STAT) pathway correlates with checkpoint immunotherapy resistance. We report a phase I clinical trial of the JAK inhibitor ruxolitinib with anti-PD-1 antibody nivolumab in Hodgkin lymphoma patients relapsed or refractory following checkpoint inhibitor immunotherapy. The combination yielded a best overall response rate of 53% (10/19). Ruxolitinib significantly reduced neutrophil-to-lymphocyte ratios and percentages of myeloid suppressor cells but increased numbers of cytokine-producing T cells. Ruxolitinib rescued the function of exhausted T cells and enhanced the efficacy of immune checkpoint blockade in preclinical solid tumor and lymphoma models. This synergy was characterized by a switch from suppressive to immunostimulatory myeloid cells, which enhanced T cell division.

Jak2V617F Reversible Activation Shows Its Essential Requirement in Myeloproliferative Neoplasms

Gain-of-function mutations activating JAK/STAT signaling are seen in the majority of patients with myeloproliferative neoplasms (MPN), most commonly JAK2V617F. Although clinically approved JAK inhibitors improve symptoms and outcomes in MPNs, remissions are rare, and mutant allele burden does not substantively change with chronic therapy. We hypothesized this is due to limitations of current JAK inhibitors to potently and specifically abrogate mutant JAK2 signaling. We therefore developed a conditionally inducible mouse model allowing for sequential activation, and then inactivation, of Jak2V617F from its endogenous locus using a combined Dre-rox/Cre-lox dual-recombinase system. Jak2V617F deletion abrogates MPN features, induces depletion of mutant-specific hematopoietic stem/progenitor cells, and extends overall survival to an extent not observed with pharmacologic JAK inhibition, including when cooccurring with somatic Tet2 loss. Our data suggest JAK2V617F represents the best therapeutic target in MPNs and demonstrate the therapeutic relevance of a dual-recombinase system to assess mutant-specific oncogenic dependencies in vivo.

SIGNIFICANCE

Current JAK inhibitors to treat myeloproliferative neoplasms are ineffective at eradicating mutant cells. We developed an endogenously expressed Jak2V617F dual-recombinase knock-in/knock-out model to investigate Jak2V617F oncogenic reversion in vivo. Jak2V617F deletion abrogates MPN features and depletes disease-sustaining MPN stem cells, suggesting improved Jak2V617F targeting offers the potential for greater therapeutic efficacy. See related commentary by Celik and Challen, p. 701. This article is featured in Selected Articles from This Issue, p. 695.

Development of Resistance to Type II JAK2 Inhibitors in MPN Depends on AXL Kinase and Is Targetable

PURPOSE

Myeloproliferative neoplasms (MPN) dysregulate JAK2 signaling. Because clinical JAK2 inhibitors have limited disease-modifying effects, type II JAK2 inhibitors such as CHZ868 stabilizing inactive JAK2 and reducing MPN clones, gain interest. We studied whether MPN cells escape from type ll inhibition.

EXPERIMENTAL DESIGN

MPN cells were continuously exposed to CHZ868. We used phosphoproteomic analyses and ATAC/RNA sequencing to characterize acquired resistance to type II JAK2 inhibition, and targeted candidate mediators in MPN cells and mice.

RESULTS

MPN cells showed increased IC50 and reduced apoptosis upon CHZ868 reflecting acquired resistance to JAK2 inhibition. Among >2,500 differential phospho-sites, MAPK pathway activation was most prominent, while JAK2-STAT3/5 remained suppressed. Altered histone occupancy promoting AP-1/GATA binding motif exposure associated with upregulated AXL kinase and enriched RAS target gene profiles. AXL knockdown resensitized MPN cells and combined JAK2/AXL inhibition using bemcentinib or gilteritinib reduced IC50 to levels of sensitive cells. While resistant cells induced tumor growth in NOD/SCID gamma mice despite JAK2 inhibition, JAK2/AXL inhibition largely prevented tumor progression. Because inhibitors of MAPK pathway kinases such as MEK are clinically used in other malignancies, we evaluated JAK2/MAPK inhibition with trametinib to interfere with AXL/MAPK-induced resistance. Tumor growth was halted similarly to JAK2/AXL inhibition and in a systemic cell line-derived mouse model, marrow infiltration was decreased supporting dependency on AXL/MAPK.

CONCLUSIONS

We report on a novel mechanism of AXL/MAPK-driven escape from type II JAK2 inhibition, which is targetable at different nodes. This highlights AXL as mediator of acquired resistance warranting inhibition to enhance sustainability of JAK2 inhibition in MPN.

The relapsed acute lymphoblastic leukemia network (ReALLNet): a multidisciplinary project from the spanish society of pediatric hematology and oncology (SEHOP)

Acute lymphoblastic leukemia (ALL) is the most common pediatric cancer, with survival rates exceeding 85%. However, 15% of patients will relapse; consequently, their survival rates decrease to below 50%. Therefore, several research and innovation studies are focusing on pediatric relapsed or refractory ALL (R/R ALL). Driven by this context and following the European strategic plan to implement precision medicine equitably, the Relapsed ALL Network (ReALLNet) was launched under the umbrella of SEHOP in 2021, aiming to connect bedside patient care with expert groups in R/R ALL in an interdisciplinary and multicentric network. To achieve this objective, a board consisting of experts in diagnosis, management, preclinical research, and clinical trials has been established. The requirements of treatment centers have been evaluated, and the available oncogenomic and functional study resources have been assessed and organized. A shipping platform has been developed to process samples requiring study derivation, and an integrated diagnostic committee has been established to report results. These biological data, as well as patient outcomes, are collected in a national registry. Additionally, samples from all patients are stored in a biobank. This comprehensive repository of data and samples is expected to foster an environment where preclinical researchers and data scientists can seek to meet the complex needs of this challenging population. This proof of concept aims to demonstrate that a network-based organization, such as that embodied by ReALLNet, provides the ideal niche for the equitable and efficient implementation of "what's next" in the management of children with R/R ALL.

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.

New scaffolds for type II JAK2 inhibitors overcome the acquired G993A resistance mutation

Recurrent JAK2 alterations are observed in myeloproliferative neoplasms, B-cell acute lymphoblastic leukemia, and other hematologic malignancies. Currently available type I JAK2 inhibitors have limited activity in these diseases. Preclinical data support the improved efficacy of type II JAK2 inhibitors, which lock the kinase in the inactive conformation. By screening small molecule libraries, we identified a lead compound with JAK2 selectivity. We highlight analogs with on-target biochemical and cellular activity and demonstrate in vivo activity using a mouse model of polycythemia vera. We present a co-crystal structure that confirms the type II binding mode of our compounds with the "DFG-out" conformation of the JAK2 activation loop. Finally, we identify a JAK2 G993A mutation that confers resistance to the type II JAK2 inhibitor CHZ868 but not to our analogs. These data provide a template for identifying novel type II kinase inhibitors and inform further development of agents targeting JAK2 that overcome resistance.

Philadelphia-like acute lymphoblastic leukemia: the journey from molecular background to the role of bone marrow transplant-review article

Philadelphia chromosome-like (Ph-like) ALL is a recent subtype of acute lymphoblastic leukemia. Although it does not express the BCR-ABL fusion gene, it has a behavior like true BCR/ABL1-positive cases. This subtype harbors different molecular alterations most commonly CRLF2 rearrangements. Most cases of Ph-like ALL are associated with high white blood cell count, high minimal residual disease level after induction therapy, and high relapse rate. Efforts should be encouraged for early recognition of Ph-like ALL to enhance therapeutic strategies. Recently, many trials are investigating the possibility of adding the tyrosine kinase inhibitor (TKI) to chemotherapy to improve clinical outcomes. The role and best timing of allogeneic bone marrow transplant in those cases are still unclear. Precision medicine should be implemented in the treatment of such cases. Here in this review, we summarize the available data on Ph-like ALL.

Molecular basis of JAK2 H608Y and H608N mutations in the pathology of acute myeloid leukemia

Risk-stratification of acute myeloid leukemia (AML) based on (cyto)genetic aberrations, including hotspot mutations, deletions and point mutations have evolved substantially in recent years. With the development of next-generation sequence technology, more and more novel mutations in the AML were identified. Thus, to unravel roles and mechanism of novel mutations would improve prognostic and predictive abilities. In this study, two novel germline JAK2 His608Tyr (H608Y) and His608Asn (H608N) mutations were identified and the molecular basis of these mutations in the leukemiagenesis of AML was elucidated. Our results indicated that JAK2 H608Y and H608N mutations disrupted the hydrogen bond between Q656 and H608 which reduced the JH2 domain's activity and abolished interactions between JH1 and JH2 domains, forced JAK2 into the active conformation, facilitated the entrance of substrates and thus caused JAK2 hyperactivation. Further studies suggested that JAK2 H608Y and H608N mutations enhanced the cell proliferation and inhibited the differentiation of Ba/F3 and MV4-11 cells via activating the JAK2-STAT5 signaling pathway. Moreover, rescue experiments demonstrated that mutations repaired the hydrogen bond between Q656 and H608 displayed opposite results. Thus, this study revealed the molecular basis of JAK2 H608Y and H608N mutations in the pathology of AML.

Pharmacological Modulation of the Crosstalk between Aberrant Janus Kinase Signaling and Epigenetic Modifiers of the Histone Deacetylase Family to Treat Cancer

Hyperactivated Janus kinase (JAK) signaling is an appreciated drug target in human cancers. Numerous mutant JAK molecules as well as inherent and acquired drug resistance mechanisms limit the efficacy of JAK inhibitors (JAKi). There is accumulating evidence that epigenetic mechanisms control JAK-dependent signaling cascades. Like JAKs, epigenetic modifiers of the histone deacetylase (HDAC) family regulate the growth and development of cells and are often dysregulated in cancer cells. The notion that inhibitors of histone deacetylases (HDACi) abrogate oncogenic JAK-dependent signaling cascades illustrates an intricate crosstalk between JAKs and HDACs. Here, we summarize how structurally divergent, broad-acting as well as isoenzyme-specific HDACi, hybrid fusion pharmacophores containing JAKi and HDACi, and proteolysis targeting chimeras for JAKs inactivate the four JAK proteins JAK1, JAK2, JAK3, and tyrosine kinase-2. These agents suppress aberrant JAK activity through specific transcription-dependent processes and mechanisms that alter the phosphorylation and stability of JAKs. Pharmacological inhibition of HDACs abrogates allosteric activation of JAKs, overcomes limitations of ATP-competitive type 1 and type 2 JAKi, and interacts favorably with JAKi. Since such findings were collected in cultured cells, experimental animals, and cancer patients, we condense preclinical and translational relevance. We also discuss how future research on acetylation-dependent mechanisms that regulate JAKs might allow the rational design of improved treatments for cancer patients. SIGNIFICANCE STATEMENT: Reversible lysine-ɛ-N acetylation and deacetylation cycles control phosphorylation-dependent Janus kinase-signal transducer and activator of transcription signaling. The intricate crosstalk between these fundamental molecular mechanisms provides opportunities for pharmacological intervention strategies with modern small molecule inhibitors. This could help patients suffering from cancer.

BCL6 inhibition ameliorates resistance to ruxolitinib in CRLF2-rearranged acute lymphoblastic leukemia

Philadelphia chromosome-like acute lymphoblastic leukemia (Ph-like ALL) is an intractable disease and most cases harbor genetic alterations that activate JAK or ABL signaling. The commonest subtype of Ph-like ALL exhibits a CRLF2 gene rearrangement that brings about JAK1/2-STAT5 pathway activation. However, JAK1/2 inhibition alone is insufficient as a treatment, so combinatorial therapies targeting multiple signals are needed. To better understand the mechanisms underlying the insufficient efficacy of JAK inhibition, we explored gene expression changes upon treatment with a JAK1/2 inhibitor (ruxolitinib) and found that elevated BCL6 expression was one such mechanism. Upregulated BCL6 suppressed the expression of TP53 along with its downstream cell cycle inhibitor p21 (CDKN2A) and pro-apoptotic molecules, such as FAS, TNFRSF10B, BID, BAX, BAK, PUMA, and NOXA, conferring cells some degree of resistance to therapy. BCL6 inhibition (with FX1) alone was able to upregulate TP53 and restore the TP53 expression that ruxolitinib had diminished. In addition, ruxolitinib and FX1 concertedly downregulated MYC. As a result, FX1 treatment alone had growth-inhibitory and apoptosis- sensitizing effects, but the combination of ruxolitinib and FX1 more potently inhibited leukemia cell growth, enhanced apoptosis sensitivity, and prolonged the survival of xenografted mice. These findings provide one mechanism for the insufficiency of JAK inhibition for the treatment of CRLF2-rearranged ALL and indicate BCL6 inhibition as a potentially helpful adjunctive therapy combined with JAK inhibition.

Efficacy of ruxolitinib in acute lymphoblastic leukemia: A systematic review

Philadelphia-like acute lymphoblastic leukemia (Ph-like ALL) is a high-risk molecular subtype with a gene expression profile similar to Philadelphia-positive ALL, but not harboring the BCR-ABL1 gene fusion. We aimed to investigate the efficacy of target therapy with the Janus kinase inhibitor, ruxolitinib, in patients with Ph-like ALL and molecular signature of JAK-STAT signaling pathway. A systematic search of the literature was performed to identify reports concerning administration of ruxolitinib in Ph-like ALL patients. Additionally, Polish Pediatric ALL registries were searched for patients with Ph-like ALL treated with ruxolitinib. Extracted information included epidemiological background, somatic aberrations, treatment response, and patient outcome. After PubMed database search, twelve patients were identified, and one was identified in the Polish Pediatric ALL registry. In nine patients gene fusions affecting JAK2 (n = 7) and EPOR (n = 2) were detected. Surface overexpression of CRLF2 and IKZF1 deletions were observed in two and three patients, respectively. Induction failure occurred in all the patients. Therapy with ruxolitinib led to complete (n = 7) and partial (n = 2) remission, in three individuals no information was found. Based on the limited number of studies describing the efficacy of ruxolitinib as an additional compound administrated with standard ALL therapy, we conclude that this approach can be considered in patients with aberrations activating JAK-STAT pathway.

JAK2 Alterations in Acute Lymphoblastic Leukemia: Molecular Insights for Superior Precision Medicine Strategies

Acute lymphoblastic leukemia (ALL) is the most common pediatric cancer, arising from immature lymphocytes that show uncontrolled proliferation and arrested differentiation. Genomic alterations affecting Janus kinase 2 (JAK2) correlate with some of the poorest outcomes within the Philadelphia-like subtype of ALL. Given the success of kinase inhibitors in the treatment of chronic myeloid leukemia, the discovery of activating JAK2 point mutations and JAK2 fusion genes in ALL, was a breakthrough for potential targeted therapies. However, the molecular mechanisms by which these alterations activate JAK2 and promote downstream signaling is poorly understood. Furthermore, as clinical data regarding the limitations of approved JAK inhibitors in myeloproliferative disorders matures, there is a growing awareness of the need for alternative precision medicine approaches for specific JAK2 lesions. This review focuses on the molecular mechanisms behind ALL-associated JAK2 mutations and JAK2 fusion genes, known and potential causes of JAK-inhibitor resistance, and how JAK2 alterations could be targeted using alternative and novel rationally designed therapies to guide precision medicine approaches for these high-risk subtypes of ALL.

A Comprehensive Overview of Globally Approved JAK Inhibitors

Janus kinase (JAK) is a family of cytoplasmic non-receptor tyrosine kinases that includes four members, namely JAK1, JAK2, JAK3, and TYK2. The JAKs transduce cytokine signaling through the JAK-STAT pathway, which regulates the transcription of several genes involved in inflammatory, immune, and cancer conditions. Targeting the JAK family kinases with small-molecule inhibitors has proved to be effective in the treatment of different types of diseases. In the current review, eleven of the JAK inhibitors that received approval for clinical use have been discussed. These drugs are abrocitinib, baricitinib, delgocitinib, fedratinib, filgotinib, oclacitinib, pacritinib, peficitinib, ruxolitinib, tofacitinib, and upadacitinib. The aim of the current review was to provide an integrated overview of the chemical and pharmacological data of the globally approved JAK inhibitors. The synthetic routes of the eleven drugs were described. In addition, their inhibitory activities against different kinases and their pharmacological uses have also been explained. Moreover, their crystal structures with different kinases were summarized, with a primary focus on their binding modes and interactions. The proposed metabolic pathways and metabolites of these drugs were also illustrated. To sum up, the data in the current review could help in the design of new JAK inhibitors with potential therapeutic benefits in inflammatory and autoimmune diseases.

Adapted to Survive: Targeting Cancer Cells with BH3 Mimetics

A hallmark of cancer is cell death evasion, underlying suboptimal responses to chemotherapy, targeted agents, and immunotherapies. The approval of the antiapoptotic BCL2 antagonist venetoclax has finally validated the potential of targeting apoptotic pathways in patients with cancer. Nevertheless, pharmacologic modulators of cell death have shown markedly varied responses in preclinical and clinical studies. Here, we review emerging concepts in the use of this class of therapies. Building on these observations, we propose that treatment-induced changes in apoptotic dependency, rather than pretreatment dependencies, will need to be recognized and targeted to realize the precise deployment of these new pharmacologic agents.

SIGNIFICANCE

Targeting antiapoptotic family members has proven efficacious and tolerable in some cancers, but responses are infrequent, particularly for patients with solid tumors. Biomarkers to aid patient selection have been lacking. Precision functional approaches that overcome adaptive resistance to these compounds could drive durable responses to chemotherapy, targeted therapy, and immunotherapies.

MEK and MCL-1 sequential inhibition synergize to enhance rhabdomyosarcoma treatment

Targeted agents have emerged as promising molecules for cancer treatment, but most of them fail to achieve complete tumor regression or attain durable remissions due to tumor adaptations. We used dynamic BH3 profiling to identify targeted agents effectiveness and anti-apoptotic adaptations upon targeted treatment in rhabdomyosarcoma. We focused on studying the use of BH3 mimetics to specifically inhibit pro-survival BCL-2 family proteins, overwhelm resistance to therapy and prevent relapse. We observed that the MEK1/2 inhibitor trametinib rapidly depleted the pro-apoptotic protein NOXA, thus increasing MCL-1 availability. Indeed, we found that the MCL-1 inhibitor S63845 synergistically enhanced trametinib cytotoxicity in rhabdomyosarcoma cells in vitro and in vivo. In conclusion, our findings indicate that the combination of a BH3 mimetic targeting MCL-1 with trametinib improves efficiency on rhabdomyosarcoma by blocking tumor adaptation to treatment.

Transient Inhibition of the JAK/STAT Pathway Prevents B-ALL Development in Genetically Predisposed Mice

Preventing development of childhood B-cell acute lymphoblastic leukemia (B-ALL), a disease with devastating effects, is a longstanding and unsolved challenge. Heterozygous germline alterations in the PAX5 gene can lead to B-ALL upon accumulation of secondary mutations affecting the JAK/STAT signaling pathway. Preclinical studies have shown that this malignant transformation occurs only under immune stress such as exposure to infectious pathogens. Here we show in Pax5+/- mice that transient, early-life administration of clinically relevant doses of ruxolitinib, a JAK1/2 inhibitor, significantly mitigates the risk of B-ALL following exposure to infection; 1 of 29 animals treated with ruxolitinib developed B-ALL versus 8 of 34 untreated mice. Ruxolitinib treatment preferentially targeted Pax5+/- versus wild-type B-cell progenitors and exerted unique effects on the Pax5+/- B-cell progenitor transcriptional program. These findings provide the first in vivo evidence for a potential strategy to prevent B-ALL development.

SIGNIFICANCE

JAK/STAT inhibition suppresses tumorigenesis in a B-ALL-susceptible mouse model, presenting a novel approach to prevent B-ALL onset.

Genome-wide CRISPR-Cas9 screen identifies rationally designed combination therapies for CRLF2-rearranged Ph-like ALL

Acute lymphoblastic leukemia (ALL) harboring the IgH-CRLF2 rearrangement (IgH-CRLF2-r) exhibits poor clinical outcomes and is the most common subtype of Philadelphia chromosome-like acute lymphoblastic leukemia (Ph-like ALL). While multiple chemotherapeutic regimens, including ruxolitinib monotherapy and/or its combination with chemotherapy, are being tested, their efficacy is reportedly limited. To identify molecules/pathways relevant for IgH-CRLF2-r ALL pathogenesis, we performed genome-wide CRISPR-Cas9 dropout screens in the presence or absence of ruxolitinib using 2 IgH-CRLF2-r ALL lines that differ in RAS mutational status. To do so, we employed a baboon envelope pseudotyped lentiviral vector system, which enabled, for the first time, highly efficient transduction of human B cells. While single-guide RNAs (sgRNAs) targeting CRLF2, IL7RA, or JAK1/2 significantly affected cell fitness in both lines, those targeting STAT5A, STAT5B, or STAT3 did not, suggesting that STAT signaling is largely dispensable for IgH-CRLF2-r ALL cell survival. We show that regulators of RAS signaling are critical for cell fitness and ruxolitinib sensitivity and that CRKL depletion enhances ruxolitinib sensitivity in RAS wild-type (WT) cells. Gilteritinib, a pan-tyrosine kinase inhibitor that blocks CRKL phosphorylation, effectively killed RAS WT IgH-CRLF2-r ALL cells in vitro and in vivo, either alone or combined with ruxolitinib. We further show that combining gilteritinib with trametinib, a MEK1/2 inhibitor, is an effective means to target IgH-CRLF2-r ALL cells regardless of RAS mutational status. Our study delineates molecules/pathways relevant for CRLF2-r ALL pathogenesis and could suggest rationally designed combination therapies appropriate for disease subtypes.

JAK2 in Myeloproliferative Neoplasms: Still a Protagonist

The discovery of the activating V617F mutation in Janus kinase 2 (JAK2) has been decisive for the understanding of myeloproliferative neoplasms (MPN). Activated JAK2 signaling by JAK2, CALR, and MPL mutations has become a focus for the development of targeted therapies for patients with MPN. JAK2 inhibitors now represent a standard of clinical care for certain forms of MPN and offer important benefits for MPN patients. However, several key aspects remain unsolved regarding the targeted therapy of MPN with JAK2 inhibitors, such as reducing the MPN clone and how to avoid or overcome a loss of response. Here, we summarize the current knowledge on the structure and signaling of JAK2 as central elements of MPN pathogenesis and feature benefits and limitations of therapeutic JAK2 targeting in MPN.

Degradation of Janus kinases in CRLF2-rearranged acute lymphoblastic leukemia

CRLF2-rearranged (CRLF2r) acute lymphoblastic leukemia (ALL) accounts for more than half of Philadelphia chromosome-like (Ph-like) ALL and is associated with a poor outcome in children and adults. Overexpression of CRLF2 results in activation of Janus kinase (JAK)-STAT and parallel signaling pathways in experimental models, but existing small molecule inhibitors of JAKs show variable and limited efficacy. Here, we evaluated the efficacy of proteolysis-targeting chimeras (PROTACs) directed against JAKs. Solving the structure of type I JAK inhibitors ruxolitinib and baricitinib bound to the JAK2 tyrosine kinase domain enabled the rational design and optimization of a series of cereblon (CRBN)-directed JAK PROTACs utilizing derivatives of JAK inhibitors, linkers, and CRBN-specific molecular glues. The resulting JAK PROTACs were evaluated for target degradation, and activity was tested in a panel of leukemia/lymphoma cell lines and xenograft models of kinase-driven ALL. Multiple PROTACs were developed that degraded JAKs and potently killed CRLF2r cell lines, the most active of which also degraded the known CRBN neosubstrate GSPT1 and suppressed proliferation of CRLF2r ALL in vivo, e.g. compound 7 (SJ988497). Although dual JAK/GSPT1-degrading PROTACs were the most potent, the development and evaluation of multiple PROTACs in an extended panel of xenografts identified a potent JAK2-degrading, GSPT1-sparing PROTAC that demonstrated efficacy in the majority of kinase-driven xenografts that were otherwise unresponsive to type I JAK inhibitors, e.g. compound 8 (SJ1008030). Together, these data show the potential of JAK-directed protein degradation as a therapeutic approach in JAK-STAT-driven ALL and highlight the interplay of JAK and GSPT1 degradation activity in this context.

Has Ph-like ALL Superseded Ph+ ALL as the Least Favorable Subtype?

Philadelphia chromosome-like acute lymphoblastic leukemia (Ph-like ALL) is a subset of high-risk B-ALL associated with high relapse risk and inferior clinical outcomes across the pediatric-to-adult age spectrum. Ph-like ALL is characterized by frequent IKZF1 alterations and a kinase-activated gene expression profile similar to that of Philadelphia chromosome-positive (Ph+) ALL, yet lacks the canonical BCR-ABL1 rearrangement. Advances in high-throughput sequencing technologies during the past decade have unraveled the genomic landscape of Ph-like ALL, revealing a diverse array of kinase-activating translocations and mutations that may be amenable to targeted therapies that have set a remarkable precision medicine paradigm for patients with Ph + ALL. Collaborative scientific efforts to identify and characterise Ph-like ALL during the past decade has directly informed current precision medicine trials investigating the therapeutic potential of tyrosine kinase inhibitor-based therapies for children, adolescents, and adults with Ph-like ALL, although the most optimal treatment paradigm for this high-risk group of patients has yet to be established. Herein, we describe the epidemiology, clinical features, and biology of Ph-like ALL, highlight challenges in implementing pragmatic and cost-effective diagnostic algorithms in the clinic, and describe the milieu of treatment strategies under active investigation that strive to decrease relapse risk and improve long-term survival for patients with Ph-like ALL as has been successfully achieved for those with Ph + ALL.

Troxerutin regulates HIF-1α by activating JAK2/STAT3 signaling to inhibit oxidative stress, inflammation, and apoptosis of cardiomyocytes induced by H2 O2

Heart failure (HF) is greatly threatening human health and affecting morbidity and mortality worldwide. Troxerutin can alleviate myocardial injury induced by ischemia and hypoxia. The present study aimed to investigate the protective effect of troxerutin on H₂ O₂ -induced cardiomyocytes and the underlying molecular mechanism. Primary mouse cardiomyocytes morphology induced by H₂ O₂ in a different duration time was observed by a microscope. After indicated treatment, the viability and apoptosis of cardiomyocytes were detected by CCK-8 assay and flow cytometry analysis. The expression of inflammatory factors and oxidative stress biomarkers was detected by Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and assay kits. Hypoxia inducible factor-1a (HIF-1α) expression was determined by western blot analysis, RT-qPCR analysis and immunofluorescence staining. The apoptosis-related protein expression and the phosphorylation level of janus-activated kinase 2 (JAK2)/signal transducer and activator of transcription 3 (STAT3) were detected by the western blot analysis. As a result, after the H₂ O₂ treatment in a different duration time, the primary mouse cardiomyocytes gradually stopped beating and the morphology of cardiomyocytes treated with H₂ O₂ was changed significantly from fusiform shape to round shape. The viability of cardiomyocytes was decreased after H₂ O₂ induction. The HIF-1α expression was increased after the H₂ O₂ treatment within 30 min while decreased over 30 min. In addition, troxerutin improved viability and suppressed apoptosis, inflammation and oxidative stress of H₂ O₂ -induced cardiomyocytes, which was reversed by KC7F2 (a HIF-1α inhibitor) or CHZ868 (a JAK inhibitor). To sum up, troxerutin could regulate HIF-1α by activating JAK2/STAT3 signaling to inhibit oxidative stress, inflammation, and apoptosis of cardiomyocytes induced by H₂ O₂ .

MCL-1 Inhibition Overcomes Anti-apoptotic Adaptation to Targeted Therapies in B-Cell Precursor Acute Lymphoblastic Leukemia

Multiple targeted therapies are currently explored for pediatric and young adult B-cell precursor acute lymphoblastic leukemia (BCP-ALL) treatment. However, this new armamentarium of therapies faces an old problem: choosing the right treatment for each patient. The lack of predictive biomarkers is particularly worrying for pediatric patients since it impairs the implementation of new treatments in the clinic. In this study, we used the functional assay dynamic BH3 profiling (DBP) to evaluate two new treatments for BCP-ALL that could improve clinical outcome, especially for relapsed patients. We found that the MEK inhibitor trametinib and the multi-target tyrosine kinase inhibitor sunitinib exquisitely increased apoptotic priming in an NRAS-mutant and in a KMT2A-rearranged cell line presenting a high expression of FLT3, respectively. Following these observations, we sought to study potential adaptations to these treatments. Indeed, we identified with DBP anti-apoptotic changes in the BCL-2 family after treatment, particularly involving MCL-1 - a pro-survival strategy previously observed in adult cancers. To overcome this adaptation, we employed the BH3 mimetic S63845, a specific MCL-1 inhibitor, and evaluated its sequential addition to both kinase inhibitors to overcome resistance. We observed that the metronomic combination of both drugs with S63845 was synergistic and showed an increased efficacy compared to single agents. Similar observations were made in BCP-ALL KMT2A-rearranged PDX cells in response to sunitinib, showing an analogous DBP profile to the SEM cell line. These findings demonstrate that rational sequences of targeted agents with BH3 mimetics, now extensively explored in clinical trials, may improve treatment effectiveness by overcoming anti-apoptotic adaptations in BCP-ALL.

Acquired JAK2 mutations confer resistance to JAK inhibitors in cell models of acute lymphoblastic leukemia

Ruxolitinib (rux) Phase II clinical trials are underway for the treatment of high-risk JAK2-rearranged (JAK2r) B-cell acute lymphoblastic leukemia (B-ALL). Treatment resistance to targeted inhibitors in other settings is common; elucidating potential mechanisms of rux resistance in JAK2r B-ALL will enable development of therapeutic strategies to overcome or avert resistance. We generated a murine pro-B cell model of ATF7IP-JAK2 with acquired resistance to multiple type-I JAK inhibitors. Resistance was associated with mutations within the JAK2 ATP/rux binding site, including a JAK2 p.G993A mutation. Using in vitro models of JAK2r B-ALL, JAK2 p.G993A conferred resistance to six type-I JAK inhibitors and the type-II JAK inhibitor, CHZ-868. Using computational modeling, we postulate that JAK2 p.G993A enabled JAK2 activation in the presence of drug binding through a unique resistance mechanism that modulates the mobility of the conserved JAK2 activation loop. This study highlights the importance of monitoring mutation emergence and may inform future drug design and the development of therapeutic strategies for this high-risk patient cohort.

Genomic landscape of B-other acute lymphoblastic leukemia in an adult retrospective cohort with a focus on BCR-ABL1-like subtype

INTRODUCTION

BCR-ABL1-like acute lymphoblastic leukemia (ALL) is a high-risk disease with a complex genomic background. Though extensively studied, data on the frequency and mutual associations of present mutations are still incomplete in adult patients. This retrospective study aims to map the genomic landscape of B-other ALL in a cohort of adult patients with a focus on the BCR-ABL1-like ALL subtype.

METHODS

We analyzed bone marrow and peripheral blood samples of adult B-other ALL patients treated consecutively at three major Czech teaching hospitals. Samples were analyzed by cytogenetic methods, gene expression profiling, multiplex ligation-dependent probe amplification (MLPA), and next-generation sequencing (NGS).

RESULTS

Fifty-eight B-other ALL patients (not BCR-ABL1, KMT2A-rearranged, ETV6-RUNX1, TCF3-PBX1, or iAMP21) were included in the study. Median follow-up was 23.8 months. Samples from 33 patients were available for a gene expression analysis, 48.9% identified as BCR-ABL1-like ALL. Of the BCR-ABL1-like ALL cases, 18.8% harbored IGH-CRLF2 and 12.5% P2RY8-CRLF2 fusion gene. We observed a higher MRD failure rate in BCR-ABL1-like than in non-BCR-ABL1-like ALL patients after the induction treatment (50.0 vs. 13.3%, p=.05). There was a trend to worse progression-free and overall survival in the BCR-ABL1-like group, though not statistically significant. Deletions in IKZF1 gene were found in 31.3% of BCR-ABL1-like cases. Patients with concurrent IKZF1 and CDKN2A/B, PAX5 or PAR1 region deletions (IKZF1^plus profile) had significantly worse progression-free survival than those with sole IKZF1 deletion or IKZF1 wild-type (p=.02). NGS analysis was performed in 54 patients and identified 99 short variants in TP53, JAK2, NRAS, PAX5, CREBBP, NF1, FLT3, ATM, KRAS, RUNX1, and other genes. Seventy-five of these gene variants have not yet been described in B-cell precursor ALL to date.

CONCLUSION

This study widens existing knowledge of the BCR-ABL1-like and B-other ALL genomic landscape in the adult population, supports previous findings, and identifies a number of novel gene variants.

Constitutive JAK/STAT signaling is the primary mechanism of resistance to JAKi in TYK2-rearranged acute lymphoblastic leukemia

Activating TYK2-rearrangements have recently been identified and implicated in the leukemogenesis of high-risk acute lymphoblastic leukemia (HR-ALL) cases. Pre-clinical studies indicated the JAK/TYK2 inhibitor (JAKi), cerdulatinib, as a promising therapeutic against TYK2-rearranged ALL, attenuating the constitutive JAK/STAT signaling resulting from the TYK2 fusion protein. However, following a period of clinical efficacy, JAKi resistance often occurs resulting in relapse. In this study, we modeled potential mechanisms of JAKi resistance in TYK2-rearranged ALL cells in vitro in order to recapitulate possible clinical scenarios and provide a rationale for alternative therapies. Cerdulatinib resistant B-cells, driven by the MYB-TYK2 fusion oncogene, were generated by long-term exposure to the drug. Sustained treatment of MYB-TYK2-rearranged ALL cells with cerdulatinib led to enhanced and persistent JAK/STAT signaling, co-occurring with JAK1 overexpression. Hyperactivation of JAK/STAT signaling and JAK1 overexpression was reversible as cerdulatinib withdrawal resulted in re-sensitization to the drug. Importantly, histone deacetylase inhibitor (HDACi) therapies were efficacious against cerdulatinib-resistant cells demonstrating a potential alternative therapy for use in TYK2-rearranged B-ALL patients who have lost response to JAKi treatment regimens.

Combination efficacy of ruxolitinib with standard-of-care drugs in CRLF2-rearranged Ph-like acute lymphoblastic leukemia

Philadelphia chromosome-like acute lymphoblastic leukemia (Ph-like ALL) is a high-risk ALL subtype with high rates of relapse and poor patient outcome. Activating mutations affecting components of the JAK-STAT signaling pathway occur in the majority of Ph-like ALL cases. The use of JAK inhibitors represents a potential treatment option for Ph-like ALL, although we and others have shown that CRLF2-rearranged Ph-like ALL responds poorly to single-agent JAK inhibitors in the preclinical setting. Therefore, the aim of this study was to identify effective combination treatments against CRLF2-rearranged Ph-like ALL, and to elucidate the underlying mechanisms of synergy. We carried out a series of high-throughput combination drug screenings and found that ruxolitinib exerted synergy with standard-of-care drugs used in the treatment of ALL. In addition, we investigated the molecular effects of ruxolitinib on Ph-like ALL by combining mass spectrometry phosphoproteomics with gene expression analysis. Based on these findings, we conducted preclinical in vivo drug testing and demonstrated that ruxolitinib enhanced the in vivo efficacy of an induction-type regimen consisting of vincristine, dexamethasone, and L-asparaginase in 2/3 CRLF2-rearranged Ph-like ALL xenografts. Overall, our findings support evaluating the addition of ruxolitinib to conventional induction regimens for the treatment of CRLF2-rearranged Ph-like ALL.

Janus Kinases in Leukemia

Janus kinases (JAKs) transduce signals from dozens of extracellular cytokines and function as critical regulators of cell growth, differentiation, gene expression, and immune responses. Deregulation of JAK/STAT signaling is a central component in several human diseases including various types of leukemia and other malignancies and autoimmune diseases. Different types of leukemia harbor genomic aberrations in all four JAKs (JAK1, JAK2, JAK3, and TYK2), most of which are activating somatic mutations and less frequently translocations resulting in constitutively active JAK fusion proteins. JAKs have become important therapeutic targets and currently, six JAK inhibitors have been approved by the FDA for the treatment of both autoimmune diseases and hematological malignancies. However, the efficacy of the current drugs is not optimal and the full potential of JAK modulators in leukemia is yet to be harnessed. This review discusses the deregulation of JAK-STAT signaling that underlie the pathogenesis of leukemia, i.e., mutations and other mechanisms causing hyperactive cytokine signaling, as well as JAK inhibitors used in clinic and under clinical development.

Philadelphia-Like Acute Lymphoblastic Leukemia: A Systematic Review

Philadelphia-like (Ph-like) acute lymphoblastic leukemia (ALL) is a subgroup of B-cell precursor ALL (BCP-ALL) with a gene expression profile analogous to Philadelphia-positive ALL and recurrent IKAROS Family Zinc Finger 1 (IKZF1) gene deletion despite lacking BCR-ABL1 (Breakpoint cluster region-ABL protooncogene) translocation. Although recognized to occur at all ages, the proportion of cases among BCP-ALL varies (< 10% in children and up to 30% in adolescents). In all age groups, males are more commonly affected. Generally, Ph-like ALL is associated with adverse clinical features and an increased risk of treatment failure with conventional approaches. Genetic alterations such as aberrant expression, point mutations, or fusion translocations lead to activation of cytokine receptors and signaling kinases, which affect the ABL1 (ABL class fusion) or Janus Kinase (JAK) signaling pathways. Several clinical trials are being conducted to understand whether specific tyrosine kinase inhibitor therapy can improve cure rates. This review summarizes the current literature available about this entity.

Challenges and Perspectives for Therapeutic Targeting of Myeloproliferative Neoplasms

Myeloproliferative neoplasms (MPNs) are hematopoietic stem cell disorders with dysregulated myeloid blood cell production and propensity for transformation to acute myeloid leukemia, thrombosis, and bleeding. Acquired mutations in JAK2, MPL, and CALR converge on hyperactivation of Janus kinase 2 (JAK2) signaling as a central feature of MPN. Accordingly, JAK2 inhibitors have held promise for therapeutic targeting. After the JAK1/2 inhibitor ruxolitinib, similar JAK2 inhibitors as fedratinib are entering clinical use. While patients benefit with reduced splenomegaly and symptoms, disease-modifying effects on MPN clone size and clonal evolution are modest. Importantly, response to ruxolitinib may be lost upon treatment suggesting the MPN clone acquires resistance. Resistance mutations, as seen with other tyrosine kinase inhibitors, have not been described in MPN patients suggesting that functional processes reactivate JAK2 signaling. Compensatory signaling, which bypasses JAK2 inhibition, and other processes contribute to intrinsic resistance of MPN cells restricting efficacy of JAK2 inhibition overall. Combinations of JAK2 inhibition with pegylated interferon-α, a well-established therapy of MPN, B-cell lymphoma 2 inhibition, and others are in clinical development with the potential to enhance therapeutic efficacy. Novel single-agent approaches targeting other molecules than JAK2 are being investigated clinically. Special focus should be placed on myelofibrosis patients with anemia and thrombocytopenia, a delicate patient population at high need for options. The extending range of new treatment approaches will increase the therapeutic options for MPN patients. This calls for concomitant improvement of our insight into MPN biology to inform tailored therapeutic strategies for individual MPN patients.

B cell signalling pathways-New targets for precision medicine in chronic lymphocytic leukaemia

The B cell receptor (BCR) is a master regulator of B cells, controlling cellular processes such as proliferation, migration and survival. Cell signalling downstream of the BCR is aberrantly activated in the B cell malignancy chronic lymphocytic leukaemia (CLL), supporting the pathophysiology of the disease. This insight has led to development and approval of small molecule inhibitors that target components of the BCR pathway. These advances have greatly improved the management of CLL, but the disease remains incurable. This may partly be explained by the inter-patient heterogeneity of the disease, also when it comes to treatment responses. Precision medicine is therefore required to optimize treatment and move towards a cure. Here, we discuss how the introduction of BCR signalling inhibitors has facilitated the development of functional in vitro assays to guide clinical treatment decisions on use of the same therapeutic agents in individual patients. The cellular responses to these agents can be analysed in high-throughput assays such as dynamic BH3 profiling, phospho flow experiments and drug sensitivity screens to identify predictive biomarkers. This progress exemplifies the positive synergy between basal and translational research needed to optimize patient care.

Sequential combinations of chemotherapeutic agents with BH3 mimetics to treat rhabdomyosarcoma and avoid resistance

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in childhood and adolescence. Refractory/relapsed RMS patients present a bad prognosis that combined with the lack of specific biomarkers impairs the development of new therapies. Here, we utilize dynamic BH3 profiling (DBP), a functional predictive biomarker that measures net changes in mitochondrial apoptotic signaling, to identify anti-apoptotic adaptations upon treatment. We employ this information to guide the use of BH3 mimetics to specifically inhibit BCL-2 pro-survival proteins, defeat resistance and avoid relapse. Indeed, we found that BH3 mimetics that selectively target anti-apoptotic BCL-xL and MCL-1, synergistically enhance the effect of clinically used chemotherapeutic agents vincristine and doxorubicin in RMS cells. We validated this strategy in vivo using a RMS patient-derived xenograft model and observed a reduction in tumor growth with a tendency to stabilization with the sequential combination of vincristine and the MCL-1 inhibitor S63845. We identified the molecular mechanism by which RMS cells acquire resistance to vincristine: an enhanced binding of BID and BAK to MCL-1 after drug exposure, which is suppressed by subsequently adding S63845. Our findings validate the use of DBP as a functional assay to predict treatment effectiveness in RMS and provide a rationale for combining BH3 mimetics with chemotherapeutic agents to avoid tumor resistance, improve treatment efficiency, and decrease undesired secondary effects.

Oncogene-independent BCR-like signaling adaptation confers drug resistance in Ph-like ALL

Children and adults with Philadelphia chromosome-like B cell acute lymphoblastic leukemia (Ph-like B-ALL) experience high relapse rates despite best-available conventional chemotherapy. Ph-like ALL is driven by genetic alterations that activate constitutive cytokine receptor and kinase signaling, and early-phase trials are investigating the potential of the addition of tyrosine kinase inhibitors (TKIs) to chemotherapy to improve clinical outcomes. However, preclinical studies have shown that JAK or PI3K pathway inhibition is insufficient to eradicate the most common cytokine receptor-like factor 2-rearranged (CRLF2-rearranged) Ph-like ALL subset. We thus sought to define additional essential signaling pathways required in Ph-like leukemogenesis for improved therapeutic targeting. Herein, we describe an adaptive signaling plasticity of CRLF2-rearranged Ph-like ALL following selective TKI pressure, which occurs in the absence of genetic mutations. Interestingly, we observed that Ph-like ALL cells have activated SRC, ERK, and PI3K signaling consistent with activated B cell receptor (BCR) signaling, although they do not express cell surface μ-heavy chain (μHC). Combinatorial targeting of JAK/STAT, PI3K, and "BCR-like" signaling with multiple TKIs and/or dexamethasone prevented this signaling plasticity and induced complete cell death, demonstrating a more optimal and clinically pragmatic therapeutic strategy for CRLF2-rearranged Ph-like ALL.

Evidence-based review of genomic aberrations in B-lymphoblastic leukemia/lymphoma: Report from the cancer genomics consortium working group for lymphoblastic leukemia

Clinical management and risk stratification of B-lymphoblastic leukemia/ lymphoma (B-ALL/LBL) depend largely on identification of chromosomal abnormalities obtained using conventional cytogenetics and Fluorescence In Situ Hybridization (FISH) testing. In the last few decades, testing algorithms have been implemented to support an optimal risk-oriented therapy, leading to a large improvement in overall survival. In addition, large scale genomic studies have identified multiple aberrations of prognostic significance that are not routinely tested by existing modalities. However, as chromosomal microarray analysis (CMA) and next-generation sequencing (NGS) technologies are increasingly used in clinical management of hematologic malignancies, these abnormalities may be more readily detected. In this article, we have compiled a comprehensive, evidence-based review of the current B-ALL literature, focusing on known and published subtypes described to date. More specifically, we describe the role of various testing modalities in the diagnosis, prognosis, and therapeutic relevance. In addition, we propose a testing algorithm aimed at assisting laboratories in the most effective detection of the underlying genomic abnormalities.

MYC's Fine Line Between B Cell Development and Malignancy

The transcription factor MYC is transiently expressed during B lymphocyte development, and its correct modulation is essential in defined developmental transitions. Although temporary downregulation of MYC is essential at specific points, basal levels of expression are maintained, and its protein levels are not completely silenced until the B cell becomes fully differentiated into a plasma cell or a memory B cell. MYC has been described as a proto-oncogene that is closely involved in many cancers, including leukemia and lymphoma. Aberrant expression of MYC protein in these hematological malignancies results in an uncontrolled rate of proliferation and, thereby, a blockade of the differentiation process. MYC is not activated by mutations in the coding sequence, and, as reviewed here, its overexpression in leukemia and lymphoma is mainly caused by gene amplification, chromosomal translocations, and aberrant regulation of its transcription. This review provides a thorough overview of the role of MYC in the developmental steps of B cells, and of how it performs its essential function in an oncogenic context, highlighting the importance of appropriate MYC regulation circuitry.

Pharmacological Inhibition of Oncogenic STAT3 and STAT5 Signaling in Hematopoietic Cancers

Signal Transducer and Activator of Transcription (STAT) 3 and 5 are important effectors of cellular transformation, and aberrant STAT3 and STAT5 signaling have been demonstrated in hematopoietic cancers. STAT3 and STAT5 are common targets for different tyrosine kinase oncogenes (TKOs). In addition, STAT3 and STAT5 proteins were shown to contain activating mutations in some rare but aggressive leukemias/lymphomas. Both proteins also contribute to drug resistance in hematopoietic malignancies and are now well recognized as major targets in cancer treatment. The development of inhibitors targeting STAT3 and STAT5 has been the subject of intense investigations during the last decade. This review summarizes the current knowledge of oncogenic STAT3 and STAT5 functions in hematopoietic cancers as well as advances in preclinical and clinical development of pharmacological inhibitors.

Clinical diagnostics and treatment strategies for Philadelphia chromosome-like acute lymphoblastic leukemia

Philadelphia chromosome-like B-cell acute lymphoblastic leukemia (Ph-like ALL) accounts for 15% to 30% of B-cell acute lymphoblastic leukemia in older children, adolescents, and adults and is associated with high rates of conventional treatment failure and relapse. Current clinical trials are assessing the efficacy of the addition of tyrosine kinase inhibitors (TKIs) to chemotherapy for children and adults with Ph-like ALL harboring ABL class translocations or CRLF2 rearrangements and other JAK pathway alterations. However, real-time diagnosis of patients can be quite challenging given the genetic heterogeneity of this disease and the often cytogenetically cryptic nature of Ph-like ALL-associated alterations. In this review, we discuss the complex biologic and clinical features of Ph-like ALL across the age spectrum, available diagnostic testing modalities, and current clinical treatment strategies for these high-risk patients. We further propose a practical and step-wise approach to Ph-like ALL genetic testing to facilitate the identification and allocation of patients to appropriate clinical trials of TKI-based therapies or commercially available drugs. Although the majority of patients with Ph-like ALL can be successfully identified via current clinical assays by the end of induction chemotherapy, increasing diagnostic efficiency and sensitivity and decreasing time to test resulting will facilitate earlier therapeutic intervention and may improve clinical outcomes for these high-risk patients.