Pharmacologic inhibition of STAT5 in acute myeloid leukemia

Novel antileukemic compound with sub-micromolar potency against STAT5 addicted myeloid leukemia cells

Signal Transdcer and Activator of Transcription 5A and 5B (STAT5A/5B) are key effectors of tyrosine kinase oncogenes in myeloid leukemias. It is now clearly evidenced that inhibition of STAT5A/5B not only blocks the growth and survival of myeloid leukemia cells but also overcomes the resistance of leukemic cells to chemotherapy. Previous screening experiments allowed us to identify 17f as a lead compound with promising antileukemic activity that blocks the phosphorylation and transcriptional activity of STAT5A/5B in myeloid leukemia cells addicted to these proteins. In light of these findings, we initiated further pharmacomodulations of 17f to develop new derivatives with enhanced antileukemic activity. Our screening assays identified 14a, an aminopyrimidine derivative of 17f, as a new lead compound that: 1) blocks the growth and survival of myeloid leukemia cells at sub-micromolar concentrations, 2) targets the phosphorylation of STAT5 but also the expression of STAT5B and 3) relieves the resistance of Chronic and Acute Myeloid leukemia cells to conventional chemotherapy.

Inhibition of NLRP3 enhances pro-apoptotic effects of FLT3 inhibition in AML

FLT3 mutations occur in approximately 25% of all acute myeloid leukemia (AML) patients. While several FLT3 inhibitors have received FDA approval, their use is currently limited to combination therapies with chemotherapy, as resistance occurs, and efficacy decreases when the inhibitors are used alone. Given the highly heterogeneous nature of AML, there is an urgent need for novel targeted therapies that address the disease from multiple angles. Recent research has identified the NLRP3 inflammasome as a potential new driver in AML. Here, we investigated the efficacy of different NLRP3 inhibitors in targeting AML cells in vitro. Our findings reveal that NLRP3 inhibition induces cell cycle arrest as well as signs of senescence in multiple AML cell lines. In contrast, NLRP3 inhibition selectively induced apoptosis in FLT3 mutant AML cell lines, but not in FLT3 wild-type AML cells. Moreover, we show that NLRP3 inhibition impairs FLT3 signaling by reducing both FLT3 expression as well as downstream signaling in FLT3 mutant cells. A database analysis revealed a strong positive correlation between FLT3 and NLRP3 in cancer, which was particularly evident in AML patients. Strikingly, the simultaneous inhibition of NLRP3 and FLT3 markedly enhanced apoptosis in FLT3-ITD mutant AML cells, but not in FLT3 wild-type cells. In summary, this study reveals a promising combined therapeutic strategy specifically targeting NLRP3/FLT3-ITD positive AML blasts in vitro, highlighting a potential new avenue for AML treatment.

Acute myeloid leukemia with t(8;21) translocation: Molecular pathogenesis, potential therapeutics and future directions

Acute myeloid leukemia (AML) is a highly heterogeneous and aggressive blood cancer. Genetic abnormalities, such as the t(8;21) rearrangement, play a significant role in AML onset. This rearrangement leads to the formation of the RUNX1/RUNX1T1 fusion protein, disrupting gene regulation and genomic stability, ultimately causing full-blown leukemia. Despite a generally favorable prognosis, t(8;21) patients face relapse and chemotherapy resistance, particularly when harboring cooperating mutations. While advances in cellular genetics and molecular biology have improved AML treatment, there are currently no specific targeted therapies against RUNX1/RUNX1T1. Therefore, investigating targeted therapies for this AML subtype holds promise for patients. This review explores the complex landscape of t(8;21) AML, unravels the molecular mechanisms of RUNX1/RUNX1T1-driven leukemogenesis, and discusses recent advancements in target therapies including small molecule drugs and PROTAC. Our goal is to develop more effective and less toxic strategies for managing t(8;21) AML patients.

Prognostic, biological, and structural implications of FLT3-JMD point mutations in acute myeloid leukemia: an analysis of Alliance studies

The FLT3 gene frequently undergoes mutations in acute myeloid leukemia (AML), with internal tandem duplications (ITD) and tyrosine kinase domain (TKD) point mutations (PMs) being most common. Recently, PMs and deletions in the FLT3 juxtamembrane domain (JMD) have been identified, but their biological and clinical significance remains poorly understood. We analyzed 1660 patients with de novo AML and found FLT3-JMD mutations, mostly PMs, in 2% of the patients. Patients with FLT3-JMD mutations had a higher relapse rate and shorter disease-free survival than those with FLT3-TKD, whereas their relapse rate, disease-free and overall survival were not significantly different from those of FLT3-ITD-positive patients. In vitro experiments showed that FLT3-JMD PMs transformed hematopoietic cells and responded well to type I and II FLT3 inhibitors. Molecular dynamics simulations were used to explore the conformational changes of JMD PMs relative to wild-type FLT3. These mutations exhibited constrained domain motions with wider gate openings, potentially enhancing drug binding. Altered residue interactions and structural changes shed light on their unique functional mechanisms, with increased allosteric pathways suggesting reduced interactions with other residues. We conclude that patients with FLT3-JMD PMs represent uncommon but important subset with distinct molecular and biological features, and may benefit from FLT3 inhibitors.

The AXL inhibitor bemcentinib overcomes microenvironment-mediated resistance to pioglitazone in acute myeloid leukemia

Prognosis of acute myeloid leukemia (AML) remains poor especially in older patients who are ineligible for standard chemotherapy or have refractory disease. Here, we study the potential of Peroxisome Proliferator-Activated Receptor (PPAR)-γ agonist pioglitazone to improve the treatment of AML. We show that pioglitazone exerts an anti-proliferative and anti-clonogenic effect on AML cell lines KG-1a, MOLM-14 and OCI-AML3 and on primary cultures from AML patients. However, co-culture of AML cells with stromal cells mimicking the bone marrow microenvironment counteracts this effect, suggesting the existence of a stroma-mediated resistance mechanism to pioglitazone. We show that pioglitazone treatment upregulates the receptor AXL in AML cells at the mRNA and protein level, allowing AXL to be phosphorylated by its ligand Gas6, which is secreted by the stroma. Addition of exogenous Gas6 or stromal cell conditioned medium also abolishes the anti-proliferative effect of pioglitazone, with an increase in AXL phosphorylation observed in both conditions. Co-incubation with the AXL inhibitor bemcentinib restored the anti-leukemic activity of pioglitazone in the presence of stromal cells by reducing AXL phosphorylation to its baseline level. We also confirm that this resistance mechanism is PPAR-γ-dependent as stromal cells invalidated for PPAR-γ are unable to inhibit the antileukemic effect of pioglitazone. Altogether, we suggest that pioglitazone treatment exerts an anti-leukemic effect but concomitantly triggers a stroma-mediated resistance mechanism involving the Gas6/AXL axis. We demonstrate that a combination of pioglitazone with an AXL inhibitor overcomes this mechanism in primary cultures and AML cell lines and exerts potent anti-leukemic activity requiring further evaluation in vivo through murine xenograft pre-clinical models.

The structural influence of the oncogenic driver mutation N642H in the STAT5B SH2 domain

The point mutation N642H of the signal transducer and activator of transcription 5B (STAT5B) protein is associated with aggressive and drug-resistant forms of leukemia. This mutation is thought to promote cancer due to hyperactivation of STAT5B caused by increased stability of the active, parallel dimer state. However, the molecular mechanism leading to this stabilization is not well understood as there is currently no structure of the parallel dimer. To investigate the mutation's mechanism of action, we conducted extensive all-atom molecular dynamics simulations of multiple oligomeric forms of both STAT5B and STAT5BN642H, including a model for the parallel dimer. The N642H mutation directly affects the hydrogen bonding network within the phosphotyrosine (pY)-binding pocket of the parallel dimer, enhancing the pY-binding interaction. The simulations indicate that apo STAT5B is highly flexible, exploring a diverse conformational space. In contrast, apo STAT5BN642H accesses two distinct conformational states, one of which resembles the conformation of the parallel dimer. The simulation predictions of the effects of the mutation on structure and dynamics are supported by the results of hydrogen-deuterium exchange (HDX) mass spectrometry measurements carried out on STAT5B and STAT5BN642H in which a phosphopeptide was used to mimic the effects of parallel dimerization on the SH2 domain. The molecular-level information uncovered in this work contributes to our understanding of STAT5B hyperactivation by the N642H mutation and could help pave the way for novel therapeutic strategies targeting this mutation.

Bone marrow mesenchymal stem cell exosomes suppress JAK/STAT signaling pathway in acute myeloid leukemia in vitro

INTRODUCTION

Despite advances in the treatment of acute myeloid leukemia (AML), refractory forms of this malignancy and relapse remain common. Therefore, development of novel, synergistic targeted therapies are needed urgently. Recently, mesenchymal stem cells (MSCs) have been shown to be effective in treating various diseases, with most of their therapeutic outcomes attributed to their exosomes. In the current study, we investigated the effects of bone marrow mesenchymal stem cell (BM-MSC) exosomes on the expression of the Janus kinase/signal transducers and activators of transcription (JAK/STAT) signaling genes involved in AML pathogenesis.

MATERIAL AND METHODS

Exosomes were isolated from BM-MSCs and confirmed using transmission electron microscopy, dynamic light scattering, and flow cytometry. Subsequently, the exosome concentration was estimated using the bicinchoninic acid assay, and HL-60 cells were cocultured with 100 µg/mL of BM-MSC exosomes. Finally, the JAK2, STAT3, and STAT5 expression levels were analyzed using qRT-PCR.

RESULTS

The exosome characterization results confirmed that most isolated nanoparticles exhibited a round morphology, expressed CD9, CD63, and CD81, which are specific protein markers for exosome identification, and ranged between 80 and 100 nm in diameter. Furthermore, qRT-PCR analysis revealed a significant downregulation of JAK2, STAT3, and STAT5 in HL-60 cells treated with 100 μg/mL of BM-MSC exosomes.

CONCLUSION

Since JAK/STAT signaling contributes to AML survival, our findings suggest that the downregulation of JAK/STAT genes by BM-MSC exosomes in leukemic cells may aid in designing a potent therapeutic strategy for AML treatment.

Structure-Guided Drug Design Targeting Abl Kinase: How Structure and Regulation Can Assist in Designing New Drugs

The human protein Abelson kinase (Abl), a tyrosine kinase, plays a pivotal role in developing chronic myeloid leukemia (CML). Abl's involvement in various signaling pathways underscores its significance in regulating fundamental biological processes, including DNA damage responses, actin polymerization, and chromatin structural changes. The discovery of the Bcr-Abl oncoprotein, resulting from a chromosomal translocation in CML patients, revolutionized the understanding and treatment of the disease. The introduction of targeted therapies, starting with interferon-alpha and culminating in the development of tyrosine kinase inhibitors (TKIs) like imatinib, significantly improved patient outcomes. However, challenges such as drug resistance and side effects persist, indicating the necessity of research into novel therapeutic strategies. This review describes advancements in Abl kinase inhibitor development, emphasizing rational compound design from structural and regulatory information. Strategies, including bivalent inhibitors, PROTACs, and compounds targeting regulatory domains, promise to overcome resistance and minimize side effects. Additionally, leveraging the intricate structure and interactions of Bcr-Abl may provide insights into developing inhibitors for other kinases. Overall, this review highlights the importance of continued research into Abl kinase inhibition and its broader implications for therapeutic interventions targeting kinase-driven diseases. It provides valuable insights and strategies that may guide the development of next-generation therapies.

Discovery of novel and potent CDK8 inhibitors for the treatment of acute myeloid leukaemia

It has been reported that CDK8 plays a key role in acute myeloid leukaemia. Here, a total of 40 compounds were rational designed and synthesised based on the previous SAR. Among them, compound 12 (3-(3-(furan-3-yl)-1H-pyrrolo[2,3-b]pyridin-5-yl)benzamide) showed the most potent inhibiting activity against CDK8 with an IC50 value of 39.2 ± 6.3 nM and anti AML cell proliferation activity (molm-13 GC50 = 0.02 ± 0.01 μM, MV4-11 GC50 = 0.03 ± 0.01 μM). Mechanistic studies revealed that this compound 12 could inhibit the phosphorylation of STAT-1 and STAT-5. Importantly, compound 12 showed relative good bioavailability (F = 38.80%) and low toxicity in vivo. This study has great significance for the discovery of more efficient CDK8 inhibitors and the development of drugs for treating AML in the future.

ARID1A is a coactivator of STAT5 that contributes to CD8+ T cell dysfunction and anti-PD-1 resistance in gastric cancer

ARID1A deletion mutation contributes to improved treatment of several malignancies with immune checkpoint inhibitors (ICIs). However, its role in modulating of tumor immune microenvironment (TIME) of gastric cancer (GC) remains unclear. Here, we report an increase of CD8+ T cells infiltration in GC patients with ARID1A-mutation (MUT), which enhances sensitivity to ICIs. Kaplan-Meier survival analysis showed that ARID1A-mutation patients with gastrointestinal malignancies benefit from immunotherapy. Transcriptome analysis implicated that ARID1A regulates STAT5 downstream targets to inhibit T-cell mediated toxicity. Integrated dual luciferase assay and ChIP-qPCR analyses indicated that ARID1A coordinated with STAT5 to facilitate the transcription of the immunosuppressive factors TGF-β1 and NOX4. ARID1A recruited canonical BAF complex (cBAF) subunits, including SMARCB1 and SMARCD1, to sustain DNA accessibility. Downregulation of ARID1A reduced chromatin remodeling into configurations which make GC more sensitive to ICIs. In addition, targeting STAT5 effectively improved anti-PD-1 efficiency in ARID1A-wild type (WT) GC patients. Taken together, ARID1A is a coactivator of STAT5, function as a chromatin organizer in GC ICIs resistance, and targeting STAT5 is an effective strategy to improve the efficiency of ICIs in GC.

Understanding mechanisms of resistance to FLT3 inhibitors in adult FLT3-mutated acute myeloid leukemia to guide treatment strategy

The presence of FLT3 mutations, including the most common FLT3-ITD (internal tandem duplications) and FLT3-TKD (tyrosine kinase domain), is associated with an unfavorable prognosis in patients affected by acute myeloid leukemia (AML). In this setting, in recent years, new FLT3 inhibitors have demonstrated efficacy in improving survival and treatment response. Nevertheless, the development of primary and secondary mechanisms of resistance poses a significant obstacle to their efficacy. Understanding these mechanisms is crucial for developing novel therapeutic approaches to overcome resistance and improve the outcomes of patients. In this context, the use of novel FLT3 inhibitors and the combination of different targeted therapies have been studied. This review provides an update on the molecular alterations involved in the resistance to FLT3 inhibitors, and describes how the molecular monitoring may be used to guide treatment strategy in FLT3-mutated AML.

Design and synthesis of 7-azaindole derivatives as potent CDK8 inhibitors for the treatment of acute myeloid leukemia

It is of great significance to design and synthesize novel structural inhibitors with good antitumor activity. In this study, based on rational design, a total of 42 7-azaindole derivatives as novel CDK8 inhibitors were designed and synthesized. All compounds were screened with antitumor activity and compound 6 (1-(3-((1H-pyrrolo[2,3-b]pyridin-5-yl)oxy)phenyl)-3-(m-tolyl)urea) exhibited the best activity, especially in acute myeloid leukemia (GI50 MV4-11 = 1.97 ± 1.24 μM). This compound also exhibited excellent inhibitory activity against CDK8 (IC50 = 51.3 ± 4.6 nM). Further mechanism studies shown that it could inhibit STAT5 phosphorylation and induce cell cycle arrest in the G1 phase, leading to apoptosis in acute myeloid leukemia cells. In addition, acute toxicity at a dose of 1000 mg kg-1 indicated the low toxicity of this compound.

Targeting the undruggables-the power of protein degraders

Undruggable targets typically refer to a class of therapeutic targets that are difficult to target through conventional methods or have not yet been targeted, but are of great clinical significance. According to statistics, over 80% of disease-related pathogenic proteins cannot be targeted by current conventional treatment methods. In recent years, with the advancement of basic research and new technologies, the development of various new technologies and mechanisms has brought new perspectives to overcome challenging drug targets. Among them, targeted protein degradation technology is a breakthrough drug development strategy for challenging drug targets. This technology can specifically identify target proteins and directly degrade pathogenic target proteins by utilizing the inherent protein degradation pathways within cells. This new form of drug development includes various types such as proteolysis targeting chimera (PROTAC), molecular glue, lysosome-targeting Chimaera (LYTAC), autophagosome-tethering compound (ATTEC), autophagy-targeting chimera (AUTAC), autophagy-targeting chimera (AUTOTAC), degrader-antibody conjugate (DAC). This article systematically summarizes the application of targeted protein degradation technology in the development of degraders for challenging drug targets. Finally, the article looks forward to the future development direction and application prospects of targeted protein degradation technology.

A lineage-specific STAT5BN642H mouse model to study NK-cell leukemia

ABSTRACT

Patients with T- and natural killer (NK)-cell neoplasms frequently have somatic STAT5B gain-of-function mutations. The most frequent STAT5B mutation is STAT5BN642H, which is known to drive murine T-cell leukemia, although its role in NK-cell malignancies is unclear. Introduction of the STAT5BN642H mutation into human NK-cell lines enhances their potential to induce leukemia in mice. We have generated a mouse model that enables tissue-specific expression of STAT5BN642H and have selectively expressed the mutated STAT5B in hematopoietic cells (N642Hvav/+) or exclusively in NK cells (N642HNK/NK). All N642Hvav/+ mice rapidly develop an aggressive T/NKT-cell leukemia, whereas N642HNK/NK mice display an indolent NK-large granular lymphocytic leukemia (NK-LGLL) that progresses to an aggressive leukemia with age. Samples from patients with NK-cell leukemia have a distinctive transcriptional signature driven by mutant STAT5B, which overlaps with that of murine leukemic N642HNK/NK NK cells. To our knowledge, we have generated the first reliable STAT5BN642H-driven preclinical mouse model that displays an indolent NK-LGLL progressing to aggressive NK-cell leukemia. This novel in vivo tool will enable us to explore the transition from an indolent to an aggressive disease and will thus permit the study of prevention and treatment options for NK-cell malignancies.

Single Cell Profiling Distinguishes Leukemia-Selective Chemotypes

A central challenge in chemical biology is to distinguish molecular families in which small structural changes trigger large changes in cell biology. Such families might be ideal scaffolds for developing cell-selective chemical effectors - for example, molecules that activate DNA damage responses in malignant cells while sparing healthy cells. Across closely related structural variants, subtle structural changes have the potential to result in contrasting bioactivity patterns across different cell types. Here, we tested a 600-compound Diversity Set of screening molecules from the Boston University Center for Molecular Discovery (BU-CMD) in a novel phospho-flow assay that tracked fundamental cell biological processes, including DNA damage response, apoptosis, M-phase cell cycle, and protein synthesis in MV411 leukemia cells. Among the chemotypes screened, synthetic congeners of the rocaglate family were especially bioactive. In follow-up studies, 37 rocaglates were selected and deeply characterized using 12 million additional cellular measurements across MV411 leukemia cells and healthy peripheral blood mononuclear cells. Of the selected rocaglates, 92% displayed significant bioactivity in human cells, and 65% selectively induced DNA damage responses in leukemia and not healthy human blood cells. Furthermore, the signaling and cell-type selectivity were connected to structural features of rocaglate subfamilies. In particular, three rocaglates from the rocaglate pyrimidinone (RP) structural subclass were the only molecules that activated exceptional DNA damage responses in leukemia cells without activating a detectable DNA damage response in healthy cells. These results indicate that the RP subset should be extensively characterized for anticancer therapeutic potential as it relates to the DNA damage response. This single cell profiling approach advances a chemical biology platform to dissect how systematic variations in chemical structure can profoundly and differentially impact basic functions of healthy and diseased cells.

STAT5 is essential for inducing the suppressive subset and attenuate cytotoxicity of Vδ2+ T cells in acute myeloid leukemia

Under the sustained exposure to tumor microenvironment, effector lymphocytes may transform into the suppressive populations. γδ T cells are recognized as a crucial mediator and effector of immune surveillance and thereby a promising candidate for anti-tumor immunotherapy. Emerging clinical studies implicate that some γδ T subsets play an important role in promoting tumor progression. Our previous study identified an abnormal Vδ2+ T cells subset with regulatory features (Reg-Vδ2) in the patients with newly diagnosed acute myeloid leukemia (AML), and demonstrated that Reg-Vδ2 cells significantly suppressed the anti-AML effects of effector Vδ2 cells (Eff-Vδ2). The molecular mechanism underlying the subset transformation of Vδ2 cells remains unclear. Here, we found that the expression and activity of STAT5 were significantly induced in Reg-Vδ2 cells compared with Eff-Vδ2 cells, which was consistent with the differences found in primary Vδ2 cells between AML patients and healthy donors. In-vitro experiments further indicated that STAT5 was required for the induction of Reg-Vδ2 cells. The combined immunophenotypical and functional assays showed that blockage of STAT5 alleviated the immunosuppressive effect of Reg-Vδ2 cells on Eff-Vδ2 cells and enhanced the anti-AML capacity of Vδ2 cells from health donors and AML patients. Collectively, these results suggest that STAT5 acts as a critical regulator in the transformation of effector Vδ2 cells into a subset with immunosuppressive characteristics, providing a potential target for the improvement the efficacy of γδ T cells-based immunotherapy to treat AML and other hematologic malignancies.

Inflammation as a driver of hematological malignancies

Hematopoiesis is a tightly regulated process that produces all adult blood cells and immune cells from multipotent hematopoietic stem cells (HSCs). HSCs usually remain quiescent, and in the presence of external stimuli like infection or inflammation, they undergo division and differentiation as a compensatory mechanism. Normal hematopoiesis is impacted by systemic inflammation, which causes HSCs to transition from quiescence to emergency myelopoiesis. At the molecular level, inflammatory cytokine signaling molecules such as tumor necrosis factor (TNF), interferons, interleukins, and toll-like receptors can all cause HSCs to multiply directly. These cytokines actively encourage HSC activation, proliferation, and differentiation during inflammation, which results in the generation and activation of immune cells required to combat acute injury. The bone marrow niche provides numerous soluble and stromal cell signals, which are essential for maintaining normal homeostasis and output of the bone marrow cells. Inflammatory signals also impact this bone marrow microenvironment called the HSC niche to regulate the inflammatory-induced hematopoiesis. Continuous pro-inflammatory cytokine and chemokine activation can have detrimental effects on the hematopoietic system, which can lead to cancer development, HSC depletion, and bone marrow failure. Reactive oxygen species (ROS), which damage DNA and ultimately lead to the transformation of HSCs into cancerous cells, are produced due to chronic inflammation. The biological elements of the HSC niche produce pro-inflammatory cytokines that cause clonal growth and the development of leukemic stem cells (LSCs) in hematological malignancies. The processes underlying how inflammation affects hematological malignancies are still not fully understood. In this review, we emphasize the effects of inflammation on normal hematopoiesis, the part it plays in the development and progression of hematological malignancies, and potential therapeutic applications for targeting these pathways for therapy in hematological malignancies.

Myeloproliferative Neoplasms: Diseases Mediated by Chronic Activation of Signal Transducer and Activator of Transcription (STAT) Proteins

Myeloproliferative neoplasms (MPNs) are hematopoietic diseases characterized by the clonal expansion of single or multiple lineages of differentiated myeloid cells that accumulate in the blood and bone marrow. MPNs are grouped into distinct categories based on key clinical presentations and distinctive mutational hallmarks. These include chronic myeloid leukemia (CML), which is strongly associated with the signature BCR::ABL1 gene translocation, polycythemia vera (PV), essential thrombocythemia (ET), and primary (idiopathic) myelofibrosis (PMF), typically accompanied by molecular alterations in the JAK2, MPL, or CALR genes. There are also rarer forms such as chronic neutrophilic leukemia (CNL), which involves mutations in the CSF3R gene. However, rather than focusing on the differences between these alternate disease categories, this review aims to present a unifying molecular etiology in which these overlapping diseases are best understood as disruptions of normal hematopoietic signaling: specifically, the chronic activation of signaling pathways, particularly involving signal transducer and activator of transcription (STAT) transcription factors, most notably STAT5B, leading to the sustained stimulation of myelopoiesis, which underpins the various disease sequalae.

Distinct roles of hematopoietic cytokines in the regulation of leukemia stem cells in murine MLL-AF9 leukemia

Lymphoid-primed multipotent progenitor (LMPP)-like and granulocyte-monocyte progenitor (GMP)-like leukemia stem cells (LSCs) co-exist in the blood of most patients with acute myeloid leukemia (AML). Complete elimination of both types of LSCs is required to cure AML. Using an MLL-AF9-induced murine AML model, we studied the role of hematopoietic cytokines in the survival of LMPP- and GMP-like LSCs. We found that SCF or FLT3L promotes the survival of LMPP-like LSCs by stimulating Stat5-mediated Mcl1 expression, whereas interleukin-3 (IL-3) or IL-6 induces the survival of GMP-like LSCs by stimulating Stat3/nuclear factor κB (NF-κB)-mediated Bcl2 expression. Functional study demonstrated that, compared to AML cells cultured in IL-3 and IL-6 medium, AML cells in SCF- or Flt3L-only culture are highly clonogenic in in vitro culture and are highly leukemogenic in vivo. Our study suggests that co-inhibition of both STAT5-MCL1 and STAT3/NF-κB-BCL2 signaling might represent an improved treatment strategy against AML, specifically AML cases with a monocytic phenotype and/or FLT3 mutations.

Targeting of STAT5 using the small molecule topotecan hydrochloride suppresses acute myeloid leukemia progression

Acute myeloid leukemia (AML) is a common type of acute leukemia in adults and relapse is one of the main reasons for treatment failure. FLT3‑ITD mutations are associated with poor prognosis, short disease‑free progression survival and high relapse rates in patients with AML. STAT5 is activated by FLT3‑ITD and drives the pathogenesis of AML. STAT5 activation is usually a hallmark of hematologic malignancies and occurs in ~70% of patients with AML. Moreover, STAT5 is a key molecule which regulates hematopoiesis, and its high expression is closely associated with drug resistance, thus direct targeting of STAT5 for AML is of great clinical value. The present study introduces a new small‑molecule inhibitor that targets STAT5, presenting a promising approach for AML therapy. A high throughput fluorescence polarization (FP) screening system for STAT5 was designed and established, and used to screen an existing compound library to obtain the highly active small molecule inhibitor, topotecan hydrochloride. Topotecan hydrochloride was demonstrated to be an effective inhibitor of STAT5 by molecular docking prediction and cellular thermal shift assay. Topotecan hydrochloride bound to STAT5, inhibiting its dimerization, phosphorylation and transcription of specific target genes. The compound exhibits cellular activity at the nanomolar level and significantly inhibits the proliferation of human AML cell lines and FLT3‑ITD+ AML cells. Furthermore, topotecan hydrochloride has the potential to exert an anti‑tumor effect in vivo. Overall, topotecan hydrochloride offers a new opportunity for the treatment of AML and other hematologic malignancies by directly targeting STAT5.

A combinatorial therapeutic approach to enhance FLT3-ITD AML treatment

Internal tandem duplication mutations of the FMS-like tyrosine kinase-3 (FLT3-ITDs) occur in 25%-30% of patients with acute myeloid leukemia (AML) and are associated with dismal prognosis. Although FLT3 inhibitors have demonstrated initial clinical efficacy, the overall outcome of patients with FLT3-ITD AML remains poor, highlighting the urgency to develop more effective treatment strategies. In this study, we reveal that FLT3 inhibitors reduced protein stability of the anti-cancer protein p53, resulting in drug resistance. Blocking p53 degradation with proteasome inhibitors restores intracellular p53 protein levels and, in combination with FLT3-ITD inhibitors, shows superior therapeutic effects against FLT3-ITD AML in cells, mouse models, and patients. These data suggest that this combinatorial therapeutic approach may represent a promising strategy to target FLT3-ITD AML.

NADPH oxidase mediated oxidative stress signaling in FLT3-ITD acute myeloid leukemia

The internal tandem duplication of the juxtamembrane domain of the FMS-like tyrosine kinase 3 (FLT3-ITD) is the most common genetic change in acute myeloid leukemia (AML), and about 30% of all AMLs harbor a FLT3-ITD mutation. Even though FLT3 inhibitors have displayed encouraging effects in FLT3-ITD-mutated AML, the extent of the clinical response to these compounds is cut short due to the rapid development of drug resistance. Evidence has shown that FLT3-ITD triggered activation of oxidative stress signaling may exert a pivotal role in drug resistance. The downstream pathways of FLT3-ITD, including STAT5, PI3K/AKT, and RAS/MAPK, are considered to be major oxidative stress signaling pathways. These downstream pathways can inhibit apoptosis and promote proliferation and survival by regulating apoptosis-related genes and promoting the generation of reactive oxygen species (ROS) through NADPH oxidase (NOX) or other mechanisms. Appropriate levels of ROS may promote proliferation, but high levels of ROS can lead to oxidative damage to the DNA and increase genomic instability. In addition, post-translational modifications of FLT3-ITD and changes in its subcellular localization can affect downstream signaling which may also be one of the mechanisms leading to drug resistance. In this review, we summarized the research progress on NOX mediated oxidative stress signaling and its relationship with drug resistance in FLT3-ITD AML, and discuss the possible new targets in FLT3-ITD signal blocking to reverse drug resistance in FLT3-ITD-mutated AML.

A selective small-molecule STAT5 PROTAC degrader capable of achieving tumor regression in vivo

Signal transducer and activator of transcription 5 (STAT5) is an attractive therapeutic target, but successful targeting of STAT5 has proved to be difficult. Here we report the development of AK-2292 as a first, potent and selective small-molecule degrader of both STAT5A and STAT5B isoforms. AK-2292 induces degradation of STAT5A/B proteins with an outstanding selectivity over all other STAT proteins and more than 6,000 non-STAT proteins, leading to selective inhibition of STAT5 activity in cells. AK-2292 effectively induces STAT5 depletion in normal mouse tissues and human chronic myeloid leukemia (CML) xenograft tissues and achieves tumor regression in two CML xenograft mouse models at well-tolerated dose schedules. AK-2292 is not only a powerful research tool with which to investigate the biology of STAT5 and the therapeutic potential of selective STAT5 protein depletion and inhibition but also a promising lead compound toward ultimate development of a STAT5-targeted therapy.

Prolactin receptor signaling induces acquisition of chemoresistance and reduces clonogenicity in acute myeloid leukemia

BACKGROUND

Development of precision medicine requires the identification of easily detectable and druggable biomarkers. Despite recent targeted drug approvals, prognosis of acute myeloid leukemia (AML) patients needs to be greatly improved, as relapse and refractory disease are still difficult to manage. Thus, new therapeutic approaches are needed. Based on in silico-generated preliminary data and the literature, the role of the prolactin (PRL)-mediated signaling was interrogated in AML.

METHODS

Protein expression and cell viability were determined by flow cytometry. Repopulation capacity was studied in murine xenotransplantation assays. Gene expression was measured by qPCR and luciferase-reporters. SA-β-Gal staining was used as a senescence marker.

RESULTS

The prolactin receptor (PRLR) was upregulated in AML cells, as compared to their healthy counterpart. The genetic and molecular inhibition of this receptor reduced the colony-forming potential. Disruption of the PRLR signaling, either using a mutant PRL or a dominant-negative isoform of PRLR, reduced the leukemia burden in vivo, in xenotransplantation assays. The expression levels of PRLR directly correlated with resistance to cytarabine. Indeed, acquired cytarabine resistance was accompanied with the induction of PRLR surface expression. The signaling associated to PRLR in AML was mainly mediated by Stat5, in contrast to the residual function of Stat3. In concordance, Stat5 mRNA was significantly overexpressed at mRNA levels in relapse AML samples. A senescence-like phenotype, measured by SA-β-gal staining, was induced upon enforced expression of PRLR in AML cells, partially dependent on ATR. Similar to the previously described chemoresistance-induced senescence in AML, no cell cycle arrest was observed. Additionally, the therapeutic potential of PRLR in AML was genetically validated.

CONCLUSIONS

These results support the role of PRLR as a therapeutic target for AML and the further development of drug discovery programs searching for specific PRLR inhibitors.

SH2db, an information system for the SH2 domain

SH2 domains are key mediators of phosphotyrosine-based signalling, and therapeutic targets for diverse, mostly oncological, disease indications. They have a highly conserved structure with a central beta sheet that divides the binding surface of the protein into two main pockets, responsible for phosphotyrosine binding (pY pocket) and substrate specificity (pY + 3 pocket). In recent years, structural databases have proven to be invaluable resources for the drug discovery community, as they contain highly relevant and up-to-date information on important protein classes. Here, we present SH2db, a comprehensive structural database and webserver for SH2 domain structures. To organize these protein structures efficiently, we introduce (i) a generic residue numbering scheme to enhance the comparability of different SH2 domains, (ii) a structure-based multiple sequence alignment of all 120 human wild-type SH2 domain sequences and their PDB and AlphaFold structures. The aligned sequences and structures can be searched, browsed and downloaded from the online interface of SH2db (http://sh2db.ttk.hu), with functions to conveniently prepare multiple structures into a Pymol session, and to export simple charts on the contents of the database. Our hope is that SH2db can assist researchers in their day-to-day work by becoming a one-stop shop for SH2 domain related research.

The Role of STATs in Ovarian Cancer: Exploring Their Potential for Therapy

Ovarian cancer (OvCa) is a deadly gynecologic malignancy that presents many clinical challenges due to late-stage diagnoses and the development of acquired resistance to standard-of-care treatment protocols. There is an increasing body of evidence suggesting that STATs may play a critical role in OvCa progression, resistance, and disease recurrence, and thus we sought to compile a comprehensive review to summarize the current state of knowledge on the topic. We have examined peer reviewed literature to delineate the role of STATs in both cancer cells and cells within the tumor microenvironment. In addition to summarizing the current knowledge of STAT biology in OvCa, we have also examined the capacity of small molecule inhibitor development to target specific STATs and progress toward clinical applications. From our research, the best studied and targeted factors are STAT3 and STAT5, which has resulted in the development of several inhibitors that are under current evaluation in clinical trials. There remain gaps in understanding the role of STAT1, STAT2, STAT4, and STAT6, due to limited reports in the current literature; as such, further studies to establish their implications in OvCa are necessitated. Moreover, due to the deficiency in our understanding of these STATs, selective inhibitors also remain elusive, and therefore present opportunities for discovery.

Phosphorylation stabilized TET1 acts as an oncoprotein and therapeutic target in B cell acute lymphoblastic leukemia

Although the overall survival rate of B cell acute lymphoblastic leukemia (B-ALL) in childhood is more than 80%, it is merely 30% in refractory/relapsed and adult patients with B-ALL. This demonstrates a need for improved therapy targeting this subgroup of B-ALL. Here, we show that the ten-eleven translocation 1 (TET1) protein, a dioxygenase involved in DNA demethylation, is overexpressed and plays a crucial oncogenic role independent of its catalytic activity in B-ALL. Consistent with its oncogenic role in B-ALL, overexpression of TET1 alone in normal precursor B cells is sufficient to transform the cells and cause B-ALL in mice within 3 to 4 months. We found that TET1 protein is stabilized and overexpressed because of its phosphorylation mediated by protein kinase C epsilon (PRKCE) and ATM serine/threonine kinase (ATM), which are also overexpressed in B-ALL. Mechanistically, TET1 recruits STAT5B to the promoters of CD72 and JCHAIN and promotes their transcription, which in turn promotes B-ALL development. Destabilization of TET1 protein by treatment with PKC or ATM inhibitors (staurosporine or AZD0156; both tested in clinical trials), or by pharmacological targeting of STAT5B, greatly decreases B-ALL cell viability and inhibits B-ALL progression in vitro and in vivo. The combination of AZD0156 with staurosporine or vincristine exhibits a synergistic effect on inhibition of refractory/relapsed B-ALL cell survival and leukemia progression in PDX models. Collectively, our study reveals an oncogenic role of the phosphorylated TET1 protein in B-ALL independent of its catalytic activity and highlights the therapeutic potential of targeting TET1 signaling for the treatment of refractory/relapsed B-ALL.

Discovery of a novel oral type Ⅰ CDK8 inhibitor against acute myeloid leukemia

CDK8 plays a key role in acute myeloid leukemia, colorectal cancer and other cancers. Here, a total of 54 compounds were designed and synthesized. Among them, the most potent one compound 43 (3-(1H-pyrrolo[2,3-b]pyridin-5-yl)benzamide), a novel CDK8 Ⅰ inhibitor, showed strong inhibitory activity against CDK8 (IC₅₀ = 51.9 nM), good kinase selectivity, good anti AML cell proliferation activity (molm-13 GC₅₀ = 1.57 ± 0.59 μM) and low toxicity in vivo (acute toxicity: 2000 mg/kg). Further mechanistic studies revealed that this compound could target CDK8 and then phosphorylate STAT-1 and STAT-5 thereby inhibiting of AML cell proliferation. In addition, compound 43 showed relatively good bioavailability (F = 28.00%) and could inhibit the growth of AML tumors in a dose-dependent manner in vivo. This study facilitates the further development of more potent CDK8 inhibitors for the treatment of the AML.

Discovery of a Potent and Selective STAT5 PROTAC Degrader with Strong Antitumor Activity In Vivo in Acute Myeloid Leukemia

STAT5 is an attractive therapeutic target for human cancers. We report herein the discovery of a potent and selective STAT5 degrader with strong antitumor activity in vivo. We first obtained small-molecule ligands with sub-micromolar to low micromolar binding affinities to STAT5 and STAT6 SH2 domains and determined co-crystal structures of three such ligands in complex with STAT5A. We successfully transformed these ligands into potent and selective STAT5 degraders using the PROTAC technology with AK-2292 as the best compound. AK-2292 effectively induces degradation of STAT5A, STAT5B, and phosphorylated STAT5 proteins in a concentration- and time-dependent manner in acute myeloid leukemia (AML) cell lines and demonstrates excellent degradation selectivity for STAT5 over all other STAT members. It exerts potent and specific cell growth inhibitory activity in AML cell lines with high levels of phosphorylated STAT5. AK-2292 effectively reduces STAT5 protein in vivo and achieves strong antitumor activity in mice at well-tolerated dose schedules.

Stafiba: A STAT5-Selective Small-Molecule Inhibitor

The transcription factors STAT5a and STAT5b are constitutively active in many human tumors. Combined inhibition of both STAT5 proteins is a valuable approach with promising applications in tumor biology. We recently reported resorcinol bisphosphate as a moderately active inhibitor of the protein-protein interaction domains, the SH2 domains, of both STAT5a and STAT5b. Here, we describe the development of resorcinol bisphosphate to Stafiba, a phosphatase-stable inhibitor of STAT5a and STAT5b with activity in the low micromolar concentration range. Our data provide insights into the structure-activity relationships of resorcinol bisphosphates and the corresponding bisphosphonates for use as inhibitors of both STAT5a and STAT5b.

Inhibition of O-GlcNAcase Inhibits Hematopoietic and Leukemic Stem Cell Self-Renewal and Drives Dendritic Cell Differentiation via STAT3/5 Signaling

Myeloid differentiation blockage at immature and self-renewing stages is a common hallmark across all subtypes of acute myeloid leukemia (AML), despite their genetic heterogeneity. Metabolic state is an important regulator of hematopoietic stem cell (HSC) self-renewal and lineage-specific differentiation as well as several aggressive cancers. However, how O-GlcNAcylation, a nutrient-sensitive posttranslational modification of proteins, contributes to both normal myelopoiesis and AML pathogenesis remains largely unknown. Using small molecule inhibitors and the CRISPR/Cas9 system, we reveal for the first time that inhibition of either OGA or OGT, which subsequently caused an increase or decrease in cellular O-GlcNAcylation, inhibits the self-renewal and maintenance of CD34+ hematopoietic stem/progenitor cells (HSPCs) and leukemic stem/progenitor cells and drives normal and malignant myeloid differentiation. We further unveiled the distinct roles of OGA and OGT inhibition in lineage-specific differentiation. While OGT inhibition induces macrophage differentiation, OGA inhibition promotes the differentiation of both CD34+ HSPCs and AML cells into dendritic cells (DCs), in agreement with an upregulation of a multitude of genes involved in DC development and function and their ability to induce T-cell proliferation, via STAT3/5 signaling. Our novel findings provide significant basic knowledge that could be important in understanding AML pathogenesis and overcoming differentiation blockage-agnostic to the genetic background of AML. Additionally, the parallel findings in normal HSPCs may lay the groundwork for future cellular therapy as a means to improve the ex vivo differentiation of normal DCs and macrophages.

Blocking STAT3/5 through direct or upstream kinase targeting in leukemic cutaneous T-cell lymphoma

Leukemic cutaneous T-cell lymphomas (L-CTCL) are lymphoproliferative disorders of skin-homing mature T-cells causing severe symptoms and high mortality through chronic inflammation, tissue destruction, and serious infections. Despite numerous genomic sequencing efforts, recurrent driver mutations have not been identified, but chromosomal losses and gains are frequent and dominant. We integrated genomic landscape analyses with innovative pharmacologic interference studies to identify key vulnerable nodes in L-CTCL. We detected copy number gains of loci containing the STAT3/5 oncogenes in 74% (n = 17/23) of L-CTCL, which correlated with the increased clonal T-cell count in the blood. Dual inhibition of STAT3/5 using small-molecule degraders and multi-kinase blockers abolished L-CTCL cell growth in vitro and ex vivo, whereby PAK kinase inhibition was specifically selective for L-CTCL patient cells carrying STAT3/5 gains. Importantly, the PAK inhibitor FRAx597 demonstrated encouraging anti-leukemic activity in vivo by inhibiting tumor growth and disease dissemination in intradermally xenografted mice. We conclude that STAT3/5 and PAK kinase interaction represents a new therapeutic node to be further explored in L-CTCL.

Targeting STAT5 Signaling Overcomes Resistance to IDH Inhibitors in Acute Myeloid Leukemia through Suppression of Stemness

Mutant isocitrate dehydrogenase 1 (IDH1) and IDH2 block the differentiation of acute myeloid leukemia (AML) cells through production of R-2-hydroxyglutarate (R-2-HG). IDH inhibitors can induce differentiation of AML cells by lowering R-2-HG but have limited clinical efficacy as single agents. Here, we performed a genome-wide CRISPR knockout screen in an Idh1-mutated hematopoietic progenitor cell line to identify genes that increased the differentiation response to ivosidenib, an IDH1 inhibitor. The screen identified C-type lectin member 5a (Clec5a), which encodes a spleen tyrosine kinase (SYK)-coupled surface receptor, as one of the top hits. Knockout of Clec5a and Syk rendered cells more sensitive to ivosidenib-induced differentiation through a reduction in STAT5-dependent expression of stemness-related genes, including genes in the homeobox (HOX) family. Importantly, direct inhibition of STAT5 activity was sufficient to increase the differentiation response to IDH inhibitors in primary human IDH1- and IDH2-mutated AML cells, including those harboring mutations in receptor tyrosine kinase (RTK) and MAPK genes that have been linked to drug resistance. In patient-derived xenograft models of IDH1-mutated AML, combination treatment with ivosidenib and the STAT5 inhibitor pimozide was superior to each agent alone in inducing differentiation in leukemic cells without compromising normal hematopoiesis. These findings demonstrate that STAT5 is a critical mediator of resistance to IDH inhibitors and provide the rationale for combining STAT5 and IDH inhibitors in the treatment of IDH-mutated AML.

SIGNIFICANCE

A CRISPR knockout screen identifies a mechanism of resistance to IDH inhibitors in AML involving activated STAT5 signaling, suggesting a potential strategy to improve the clinical efficacy of IDH inhibitors.

Targeting integrated stress response with ISRIB combined with imatinib treatment attenuates RAS/RAF/MAPK and STAT5 signaling and eradicates chronic myeloid leukemia cells

The integrated stress response (ISR) facilitates cellular adaptation to unfavorable conditions by reprogramming the cellular response. ISR activation was reported in neurological disorders and solid tumors; however, the function of ISR and its role as a possible therapeutic target in hematological malignancies still remain largely unexplored. Previously, we showed that the ISR is activated in chronic myeloid leukemia (CML) cells and correlates with blastic transformation and tyrosine kinase inhibitor (TKI) resistance. Moreover, the ISR was additionally activated in response to imatinib as a type of protective internal signaling. Here, we show that ISR inhibition combined with imatinib treatment sensitized and more effectively eradicated leukemic cells both in vitro and in vivo compared to treatment with single agents. The combined treatment specifically inhibited the STAT5 and RAS/RAF/MEK/ERK pathways, which are recognized as drivers of resistance. Mechanistically, this drug combination attenuated both interacting signaling networks, leading to BCR-ABL1- and ISR-dependent STAT5 activation. Consequently, leukemia engraftment in patient-derived xenograft mice bearing CD34+ TKI-resistant CML blasts carrying PTPN11 mutation responsible for hyperactivation of the RAS/RAF/MAPK and JAK/STAT5 pathways was decreased upon double treatment. This correlated with the downregulation of genes related to the RAS/RAF/MAPK, JAK/STAT5 and stress response pathways and was associated with lower expression of STAT5-target genes regulating proliferation, viability and the stress response. Collectively, these findings highlight the effect of imatinib plus ISRIB in the eradication of leukemic cells resistant to TKIs and suggest potential clinical benefits for leukemia patients with TKI resistance related to RAS/RAF/MAPK or STAT5 signaling. We propose that personalized treatment based on the genetic selection of patients carrying mutations that cause overactivation of the targeted pathways and therefore make their sensitivity to such treatment probable should be considered as a possible future direction in leukemia treatment.

Dissection of the MEF2D-IRF8 transcriptional circuit dependency in acute myeloid leukemia

Transcriptional dysregulation is a prominent feature in leukemia. Here, we systematically surveyed transcription factor (TF) vulnerabilities in leukemia and uncovered TF clusters that exhibit context-specific vulnerabilities within and between different subtypes of leukemia. Among these TF clusters, we demonstrated that acute myeloid leukemia (AML) with high IRF8 expression was addicted to MEF2D. MEF2D and IRF8 form an autoregulatory loop via direct binding to mutual enhancer elements. One important function of this circuit in AML is to sustain PU.1/MEIS1 co-regulated transcriptional outputs via stabilizing PU.1’s chromatin occupancy. We illustrated that AML could acquire dependency on this circuit through various oncogenic mechanisms that results in the activation of their enhancers. In addition to forming a circuit, MEF2D and IRF8 can also separately regulate gene expression, and dual perturbation of these two TFs leads to a more robust inhibition of AML proliferation. Collectively, our results revealed a TF circuit essential for AML survival.

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MEF2D is a context-specific vulnerability in IRF8^hi AML

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MEF2D and IRF8 form a transcriptional circuit via binding to each other’s enhancers

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MEF2D-IRF8 circuit supports PU.1’s chromatin occupancy and transcriptional output

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MEF2D and IRF8 can regulate separate gene expression programs alongside the circuit

Genomic Mutations of the STAT5 Transcription Factor Are Associated with Human Cancer and Immune Diseases

Signal transducer and activation of transcription 5 (STAT5) is a key transcription factor that regulates various biological processes in mammalian development. Aberrant regulation of STAT5 has also been causally linked to many diseases, including cancers and immune-related diseases. Although persistent activation of STAT5 due to dysregulation of the signaling cascade has been reported to be associated with the progression of solid tumors and leukemia, various genomic mutations of STAT5 have also been found to cause a wide range of diseases. The present review comprehensively summarizes results of recent studies evaluating the intrinsic function of STAT5 and the link between STAT5 mutations and human diseases. This review also describes the types of disease models useful for investigating the mechanism underlying STAT5-driven disease progression. These findings provide basic knowledge for understanding the regulatory mechanisms of STAT5 and the progression of various diseases resulting from aberrant regulation of STAT5. Moreover, this review may provide insights needed to create optimal disease models that reflect human disease associated STAT5 mutations and to design gene therapies to correct STAT5 mutations.

PDGFRβ promotes oncogenic progression via STAT3/STAT5 hyperactivation in anaplastic large cell lymphoma

BACKGROUND

Anaplastic large cell lymphoma (ALCL) is an aggressive non-Hodgkin T cell lymphoma commonly driven by NPM-ALK. AP-1 transcription factors, cJUN and JUNb, act as downstream effectors of NPM-ALK and transcriptionally regulate PDGFRβ. Blocking PDGFRβ kinase activity with imatinib effectively reduces tumor burden and prolongs survival, although the downstream molecular mechanisms remain elusive.

METHODS AND RESULTS

In a transgenic mouse model that mimics PDGFRβ-driven human ALCL in vivo, we identify PDGFRβ as a driver of aggressive tumor growth. Mechanistically, PDGFRβ induces the pro-survival factor Bcl-xL and the growth-enhancing cytokine IL-10 via STAT5 activation. CRISPR/Cas9 deletion of both STAT5 gene products, STAT5A and STAT5B, results in the significant impairment of cell viability compared to deletion of STAT5A, STAT5B or STAT3 alone. Moreover, combined blockade of STAT3/5 activity with a selective SH2 domain inhibitor, AC-4-130, effectively obstructs tumor development in vivo.

CONCLUSIONS

We therefore propose PDGFRβ as a novel biomarker and introduce PDGFRβ-STAT3/5 signaling as an important axis in aggressive ALCL. Furthermore, we suggest that inhibition of PDGFRβ or STAT3/5 improve existing therapies for both previously untreated and relapsed/refractory ALK+ ALCL patients.

Mesenchymal stromal cells-derived extracellular vesicles reprogramme macrophages in ARDS models through the miR-181a-5p-PTEN-pSTAT5-SOCS1 axis

RATIONALE

A better understanding of the mechanism of action of mesenchymal stromal cells (MSCs) and their extracellular vesicles (EVs) is needed to support their use as novel therapies for acute respiratory distress syndrome (ARDS). Macrophages are important mediators of ARDS inflammatory response. Suppressor of cytokine signalling (SOCS) proteins are key regulators of the macrophage phenotype switch. We therefore investigated whether SOCS proteins are involved in mediation of the MSC effect on human macrophage reprogramming.

METHODS

Human monocyte-derived macrophages (MDMs) were stimulated with lipopolysaccharide (LPS) or plasma samples from patients with ARDS (these samples were previously classified into hypo-inflammatory and hyper-inflammatory phenotype) and treated with MSC conditioned medium (CM) or EVs. Protein expression was measured by Western blot. EV micro RNA (miRNA) content was determined by miRNA sequencing. In vivo: LPS-injured C57BL/6 mice were given EVs isolated from MSCs in which miR-181a had been silenced by miRNA inhibitor or overexpressed using miRNA mimic.

RESULTS

EVs were the key component of MSC CM responsible for anti-inflammatory modulation of human macrophages. EVs significantly reduced secretion of tumour necrosis factor-α and interleukin-8 by LPS-stimulated or ARDS plasma-stimulated MDMs and this was dependent on SOCS1. Transfer of miR-181a in EVs downregulated phosphatase and tensin homolog (PTEN) and subsequently activated phosphorylated signal transducer and activator of transcription 5 (pSTAT5) leading to upregulation of SOCS1 in macrophages. In vivo, EVs alleviated lung injury and upregulated pSTAT5 and SOCS1 expression in alveolar macrophages in a miR181-dependent manner. Overexpression of miR-181a in MSCs significantly enhanced therapeutic efficacy of EVs in this model.

CONCLUSION

miR-181a-PTEN-pSTAT5-SOCS1 axis is a novel pathway responsible for immunomodulatory effect of MSC EVs in ARDS.

Molecular Dynamics Simulations and Diversity Selection by Extended Continuous Similarity Indices

Molecular dynamics (MD) is a core methodology of molecular modeling and computational design for the study of the dynamics and temporal evolution of molecular systems. MD simulations have particularly benefited from the rapid increase of computational power that has characterized the past decades of computational chemical research, being the first method to be successfully migrated to the GPU infrastructure. While new-generation MD software is capable of delivering simulations on an ever-increasing scale, relatively less effort is invested in developing postprocessing methods that can keep up with the quickly expanding volumes of data that are being generated. Here, we introduce a new idea for sampling frames from large MD trajectories, based on the recently introduced framework of extended similarity indices. Our approach presents a new, linearly scaling alternative to the traditional approach of applying a clustering algorithm that usually scales as a quadratic function of the number of frames. When showcasing its usage on case studies with different system sizes and simulation lengths, we have registered speedups of up to 2 orders of magnitude, as compared to traditional clustering algorithms. The conformational diversity of the selected frames is also noticeably higher, which is a further advantage for certain applications, such as the selection of structural ensembles for ligand docking. The method is available open-source at https://github.com/ramirandaq/MultipleComparisons.

Maximizing the integration of virtual and experimental screening in hit discovery

INTRODUCTION

Experimental and virtual screening contributes to the discovery of more than 50% of clinical candidates. Considering the similar concept and goals, early-phase drug discovery would benefit from the effective integration of these approaches.

AREAS COVERED

After reviewing the recent trends in both experimental and virtual screening, the authors discuss different integration strategies from parallel, focused, sequential, and iterative screening. Strategic considerations are demonstrated in a number of real-life case studies.

EXPERT OPINION

Experimental and virtual screening are complementary approaches that should be integrated in lead discovery settings. Virtual screening can access extremely large synthetically feasible chemical space that can be effectively searched on GPU clusters or cloud architectures. Experimental screening provides reliable datasets by quantitative HTS applications, and DNA-encoded libraries (DEL) have enlarged the chemical space covered by these technologies. These developments, together with the use of artificial intelligence methods, represent new options for their efficient integration. The case studies discussed here demonstrate the benefits of complementary strategies, such as focused and iterative screening.

Resistance to targeted therapies: delving into FLT3 and IDH

Recent advances in FLT3 and IDH targeted inhibition have improved response rates and overall survival in patients with mutations affecting these respective proteins. Despite this success, resistance mechanisms have arisen including mutations that disrupt inhibitor-target interaction, mutations impacting alternate pathways, and changes in the microenvironment. Here we review the role of these proteins in leukemogenesis, their respective inhibitors, mechanisms of resistance, and briefly ongoing studies aimed at overcoming resistance.

Diagnosis and Management of Atypical Chronic Myeloid Leukemia with a t(2;13)(q33;q12) Translocation

Atypical chronic myeloid leukemia (aCML) is a rare myeloproliferative disorder that shares clinical features with chronic myeloid leukemia but lacks the classic t(9;22) BCR-ABL1 translocation and features prominent dysgranulopoiesis and granulocytic dysplasia. Challenges of this diagnosis include clinical and biologic heterogeneity, the high risk of transformation to acute myeloid leukemia, and the lack of standard treatment options. Allogeneic hematopoietic stem cell transplant is likely the preferred treatment, but this can be limited by patient psychosocial support, age, concomitant medical conditions, and availability of an appropriate donor. We report the case of a 61-year-old male with no significant past medical history diagnosed with aCML with a rare t(2;13)(q33;q12). He presented with weight loss, night sweats, splenomegaly, hyperleukocytosis, a leukoerythroblastic differential with a predominant neutrophilia, anemia, and thrombocytopenia. Subsequent peripheral blood and bone marrow studies lead to the diagnosis of aCML. He was recommended to undergo an allogeneic stem cell transplant evaluation and declined. He was initially treated with hydroxyurea and imatinib to which he responded for approximately three years. After clinical progression, he was treated with sorafenib, a multiprotein kinase inhibitor more commonly used in the treatment of hepatocellular and renal cell carcinoma due to its off target FLT3 inhibition. The patient achieved complete hematologic response which has been sustained for 7 years with tolerable side effects.

HIV-1 Vpr drives a tissue residency-like phenotype during selective infection of resting memory T cells

HIV-1 replicates in CD4+ T cells, leading to AIDS. Determining how HIV-1 shapes its niche to create a permissive environment is central to informing efforts to limit pathogenesis, disturb reservoirs, and achieve a cure. A key roadblock in understanding HIV-T cell interactions is the requirement to activate T cells in vitro to make them permissive to infection. This dramatically alters T cell biology and virus-host interactions. Here we show that HIV-1 cell-to-cell spread permits efficient, productive infection of resting memory T cells without prior activation. Strikingly, we find that HIV-1 infection primes resting T cells to gain characteristics of tissue-resident memory T cells (TRM), including upregulating key surface markers and the transcription factor Blimp-1 and inducing a transcriptional program overlapping the core TRM transcriptional signature. This reprogramming is driven by Vpr and requires Vpr packaging into virions and manipulation of STAT5. Thus, HIV-1 reprograms resting T cells, with implications for viral replication and persistence.

A Prognostic Model for Acute Myeloid Leukemia Based on IL-2/STAT5 Pathway-Related Genes

Accurate prognostic stratification of patients can provide guidance for personalized therapy. Many prognostic models for acute myeloid leukemia (AML) have been reported, but most have considerable inaccuracies due to contained variables with insufficient capacity of predicting survival and lack of adequate verification. Here, 235 genes strongly related to survival in AML were systematically identified through univariate Cox regression analysis of eight independent AML datasets. Pathway enrichment analysis of these 235 genes revealed that the IL-2/STAT5 signaling pathway was the most highly enriched. Through Cox proportional-hazards regression model and stepwise algorithm, we constructed a six-gene STAT5-associated signature based on the most robustly survival-related genes related to the IL-2/STAT5 signaling pathway. Good prognostic performance was observed in the training cohort (GSE37642-GPL96), and the signature was validated in seven other validation cohorts. As an independent prognostic factor, the STAT5-associated signature was positively correlated with patient age and ELN2017 risk levels. An integrated score based on these three prognostic factors had higher prognostic accuracy than the ELN2017 risk category. Characterization of immune cell infiltration indicated that impaired B-cell adaptive immunity, immunosuppressive effects, serious infection, and weakened anti-inflammatory function tended to accompany high-risk patients. Analysis of in-house clinical samples revealed that the STAT5-assocaited signature risk scores of AML patients were significantly higher than those of healthy people. Five chemotherapeutic drugs that were effective in these high-risk patients were screened in silico. Among the five drugs, MS.275, a known HDAC inhibitor, selectively suppressed the proliferation of cancer cells with high STAT5 phosphorylation levels in vitro. Taken together, the data indicate that the STAT5-associated signature is a reliable prognostic model that can be used to optimize prognostic stratification and guide personalized AML treatments.

Identification of the Benzoimidazole Compound as a Selective FLT3 Inhibitor by Cell-Based High-Throughput Screening of a Diversity Library

Internal tandem duplication in the FLT3 receptor tyrosine kinase (FLT3/ITD mutation) occurs in approximately 25% of acute myeloid leukemia (AML) patients. To specifically target this driver mutation in AML, we assessed and compared the cell-based cytotoxicity of a diversity library (10,000 compounds) against the normal cell line BaF3 and the isogenic leukemic cell line BaF3/ITD. A benzoimidazole scaffold-based compound (HP1142) was identified as the most selective compound against a series of murine and human leukemia cells with FLT3/ITD. Novel benzoimidazole compounds were further designed to improve the aqueous solubility of HP1142. The most potent compound, HP1328, demonstrated desirable pharmaceutical and pharmacokinetic properties. Treatment with HP1328 significantly reduced the leukemia burden and prolonged the survival of mice with FLT3/ITD leukemia. Our findings establish the specific activity of the benzoimidazole compound against FLT3/ITD leukemia and warrant further investigation in this subset of leukemia patients with poor prognosis.

The STAT3-MYC axis promotes survival of leukemia stem cells by regulating SLC1A5 and oxidative phosphorylation

Acute myeloid leukemia (AML) is characterized by the presence of leukemia stem cells (LSCs), and failure to fully eradicate this population contributes to disease persistence/relapse. Prior studies have characterized metabolic vulnerabilities of LSCs, which demonstrate preferential reliance on oxidative phosphorylation (OXPHOS) for energy metabolism and survival. In the present study, using both genetic and pharmacologic strategies in primary human AML specimens, we show that signal transducer and activator of transcription 3 (STAT3) mediates OXPHOS in LSCs. STAT3 regulates AML-specific expression of MYC, which in turn controls transcription of the neutral amino acid transporter gene SLC1A5. We show that genetic inhibition of MYC or SLC1A5 acts to phenocopy the impairment of OXPHOS observed with STAT3 inhibition, thereby establishing this axis as a regulatory mechanism linking STAT3 to energy metabolism. Inhibition of SLC1A5 reduces intracellular levels of glutamine, glutathione, and multiple tricarboxylic acid (TCA) cycle metabolites, leading to reduced TCA cycle activity and inhibition of OXPHOS. Based on these findings, we used a novel small molecule STAT3 inhibitor, which binds STAT3 and disrupts STAT3-DNA, to evaluate the biological role of STAT3. We show that STAT3 inhibition selectively leads to cell death in AML stem and progenitor cells derived from newly diagnosed patients and patients who have experienced relapse while sparing normal hematopoietic cells. Together, these findings establish a STAT3-mediated mechanism that controls energy metabolism and survival in primitive AML cells.

Discovery of Sulforaphane as an Inducer of Ferroptosis in U-937 Leukemia Cells: Expanding Its Anticancer Potential

In recent years, natural compounds have emerged as inducers of non-canonical cell death. The isothiocyanate sulforaphane (SFN) is a well-known natural anticancer compound with remarkable pro-apoptotic activity. Its ability to promote non-apoptotic cell-death mechanisms remains poorly investigated. This work aimed to explore the capacity of SFN to induce non-apoptotic cell death modalities. SFN was tested on different acute myeloid leukemia cell lines. The mechanism of cell death was investigated using a multi-parametric approach including fluorescence microscopy, western blotting, and flow cytometry. SFN triggered different cell-death modalities in a dose-dependent manner. At 25 μM, SFN induced caspase-dependent apoptosis and at 50 μM ferroptosis was induced through depletion of glutathione (GSH), decreased GSH peroxidase 4 protein expression, and lipid peroxidation. In contrast, necroptosis was not involved in SFN-induced cell death, as demonstrated by the non-significant increase in phosphorylation of receptor-interacting protein kinase 3 and phosphorylation of the necroptotic effector mixed lineage kinase domain-like pseudokinase. Taken together, our results suggest that the antileukemic activity of SFN can be mediated via both ferroptotic and apoptotic cell death modalities.

Efficacy and Synergy of Small Molecule Inhibitors Targeting FLT3-ITD+ Acute Myeloid Leukemia

Constitutive activation of FLT3 by ITD mutations is one of the most common genetic aberrations in AML, present in ~1/3 of cases. Patients harboring FLT3-ITD display worse clinical outcomes. The integration and advancement of FLT3 TKI in AML treatment provided significant therapeutic improvement. However, due to the emergence of resistance mechanisms, FLT3-ITD+ AML remains a clinical challenge. We performed an unbiased drug screen to identify 18 compounds as particularly efficacious against FLT3-ITD+ AML. Among these, we characterized two investigational compounds, WS6 and ispinesib, and two approved drugs, ponatinib and cabozantinib, in depth. We found that WS6, although not yet investigated in oncology, shows a similar mechanism and potency as ponatinib and cabozantinib. Interestingly, ispinesib and cabozantinib prevent activation of AXL, a key driver and mechanism of drug resistance in FLT3-ITD+ AML patients. We further investigated synergies between the selected compounds and found that combination treatment with ispinesib and cabozantinib or ponatinib shows high synergy in FLT3-ITD+ AML cell lines and patient samples. Together, we suggest WS6, ispinesib, ponatinib and cabozantinib as novel options for targeting FLT3-ITD+ AML. Whether combinatorial tyrosine kinase and kinesin spindle blockade is effective in eradicating neoplastic (stem) cells in FLT3-ITD+ AML remains to be determined in clinical trials.

Phenotypic characterization of leukemia-initiating stem cells in chronic myelomonocytic leukemia

Chronic myelomonocytic leukemia (CMML) is a stem cell-derived neoplasm characterized by dysplasia, uncontrolled expansion of monocytes, and substantial risk to transform to secondary acute myeloid leukemia (sAML). So far, little is known about CMML-initiating cells. We found that leukemic stem cells (LSC) in CMML reside in a CD34+/CD38- fraction of the malignant clone. Whereas CD34+/CD38- cells engrafted NSGS mice with overt CMML, no CMML was produced by CD34+/CD38+ progenitors or the bulk of CD34- monocytes. CMML LSC invariably expressed CD33, CD117, CD123 and CD133. In a subset of patients, CMML LSC also displayed CD52, IL-1RAP and/or CLL-1. CMML LSC did not express CD25 or CD26. However, in sAML following CMML, the LSC also expressed CD25 and high levels of CD114, CD123 and IL-1RAP. No correlations between LSC phenotypes, CMML-variant, mutation-profiles, or clinical course were identified. Pre-incubation of CMML LSC with gemtuzumab-ozogamicin or venetoclax resulted in decreased growth and impaired engraftment in NSGS mice. Together, CMML LSC are CD34+/CD38- cells that express a distinct profile of surface markers and target-antigens. During progression to sAML, LSC acquire or upregulate certain cytokine receptors, including CD25, CD114 and CD123. Characterization of CMML LSC should facilitate their enrichment and the development of LSC-eradicating therapies.