The Ups and Downs of STAT Inhibition in Acute Myeloid Leukemia

Signaling pathways governing the behaviors of leukemia stem cells

Leukemia is a malignancy in the blood that develops from the lymphatic system and bone marrow. Although various treatment options have been used for different types of leukemia, understanding the molecular pathways involved in the development and progression of leukemia is necessary. Recent studies showed that leukemia stem cells (LSCs) play essential roles in the pathogenesis of leukemia by targeting several signaling pathways, including Notch, Wnt, Hedgehog, and STAT3. LSCs are highly proliferative cells that stimulate tumor initiation, migration, EMT, and drug resistance. This review summarizes cellular pathways that stimulate and prevent LSCs' self-renewal, metastasis, and tumorigenesis.

JAK/STAT in leukemia: a clinical update

Over the past three decades, considerable efforts have been expended on understanding the Janus kinase/signal transducer and activator of transcription (JAK/STAT) signaling pathway in leukemia, following the identification of the JAK2V617F mutation in myeloproliferative neoplasms (MPNs). The aim of this review is to summarize the latest progress in our understanding of the involvement of the JAK/STAT signaling pathway in the development of leukemia. We also attempt to provide insights into the current use of JAK/STAT inhibitors in leukemia therapy and explore pertinent clinical trials in this field.

Artesunate reverses cytarabine resistance in acute myeloid leukemia by blocking the JAK/STAT3 signaling

OBJECTIVES

Although cytarabine (AraC) has greatly contributed to improving the prognosis of patients with acute myeloid leukemia (AML), many patients developed drug resistance and eventually succumbed to AML. Thus, resistance to AraC is a major obstacle to improve the efficacy of chemotherapy in AML. Hence, this study aimed to demonstrate that artesunate (ART) can reliably induce cell death in vitro and block AraC resistance.

METHODS

AML cell lines resistant to AraC were first constructed by repeated dosing for 5 months. Further, we analyzed whether ART intervention affected the sensitivity of AraC-resistant cells to AraC by cell function experiments, mainly including CCK-8 to assess cell viability, flow cytometry to examine apoptosis, and Western blotting to measure the Janus kinase (JAK)/signal transducers and activators of transcription 3 (STAT3) pathway protein expression. Furthermore, whether JAK/STAT3 pathway knockdown has a blocking effect on the efficacy of ART was also assessed.

RESULTS

Co-treatment of ART and AraC increased the sensitivity of AML cells to AraC. Also, it effectively reversed the resistance of AML cells to AraC that is shown by the significantly reduced proliferation and increased apoptosis rates. ART intervention suppressed the activation of the JAK/STAT3 signaling pathway in AraC-resistant AML cells, suggesting that the function of ART in reversing AraC resistance is indeed dependent on the JAK/STAT3 signaling pathway.

CONCLUSIONS

In summary, ART enhanced the sensitivity of AML/AraC-resistant cells to AraC by modulating the JAK/STAT3 pathway.

2022 Cannon lecture: an ode to signal transduction: how the growth hormone pathway revealed insight into height, malignancy, and obesity

Walter Cannon was a highly regarded American neurologist and physiologist with extremely broad interests. In the tradition of Cannon and his broad interests, we discuss our laboratory's multifaceted work in signal transduction over the past 40+ years. We show how our questioning of how growth hormone (GH) in the blood communicates with cells throughout the body to promote body growth and regulate body metabolism led to insight into not only body height but also important regulators of malignancy and body weight. Highlights include finding that 1) A critical initiating step in GH signal transduction is GH activating the GH receptor-associated tyrosine kinase JAK2; 2) GH activation of JAK2 leads to activation of a number of signaling proteins, including STAT transcription factors; 3) JAK2 is autophosphorylated on multiple tyrosines that regulate the activity of JAK2 and recruit signaling proteins to GH/GH receptor/JAK2 complexes; 4) Constitutively activated STAT proteins are associated with cancer; 5) GH activation of JAK2 recruits the adapter protein SH2B1 to GH/GH receptor/JAK2 complexes where it facilitates GH regulation of the actin cytoskeleton and motility; and 6) SH2B1 is recruited to other receptors in the brain, where it enhances satiety, most likely in part by regulating leptin action and neuronal connections of appetite-regulating neurons. These findings have led to increased understanding of how GH functions, as well as therapeutic interventions for certain cancer and obese individuals, thereby reinforcing the great importance of supporting basic research since one never knows ahead of time what important insight it can provide.

RNA N6-methyladenosine reader IGF2BP3 promotes acute myeloid leukemia progression by controlling stabilization of EPOR mRNA

Background

N6-methyladenosine (m6A) methylation epigenetically regulates normal hematopoiesis and plays a role in the pathogenesis of acute myeloid leukemia (AML). However, its potential value for prognosis remains elusive.

Methods

Analysis of the datasets downloaded from The Cancer Genome Atlas and Genotype Tissue Expression databases revealed that the expression level of 20 regulators related to m6A RNA methylation differ between patients with AML and normal individuals. A prognostic risk model with three genes (YTHDF3, IGF2BP3, and HNRNPA2B1) was developed using univariate Cox regression and the least absolute shrinkage and selection operator Cox regression methods.

Results

This established signature demonstrated good predictive efficacy with an area under the curve of 0.892 and 0.731 in the training cohort and the validation cohort, respectively. Patients with AML and an increased level of Insulin growth factor 2 mRNA binding protein 3 (IGF2BP3) expression exhibited a poor prognosis. IGF2BP3 knockdown significantly induced G0/G1 phase arrest and inhibited cell proliferation, apoptosis, and/or differentiation. Further, the JAK/STAT pathway may be involved in the regulation of EPOR expression by IGF2BP3-mediated m6A RNA methylation.

Conclusion

These findings indicate that IGF2BP3 plays a carcinogenic role in AML, implying that it can predict patient survival and could be an effective strategy for AML therapy.

Cancer Stem Cells: Biology and Therapeutic Implications

It is well recognized that most cancers derive and progress from transformation and clonal expansion of a single cell that possesses stem cell properties, i.e., self-renewal and multilineage differentiation capacities. Such cancer stem cells (CSCs) are usually present at very low frequencies and possess properties that make them key players in tumor development. Indeed, besides having the ability to initiate tumor growth, CSCs drive tumor progression and metastatic dissemination, are resistant to most cancer drugs, and are responsible for cancer relapse. All of these features make CSCs attractive targets for the development of more effective oncologic treatments. In the present review article, we have summarized recent advances in the biology of CSCs, including their identification through their immunophenotype, and their physiology, both in vivo and in vitro. We have also analyzed some molecular markers that might become targets for developing new therapies aiming at hampering CSCs regeneration and cancer relapse.

Advances in molecular characterization of myeloid proliferations associated with Down syndrome

Myeloid leukemia associated with Down syndrome (ML-DS) has a unique molecular landscape that differs from other subtypes of acute myeloid leukemia. ML-DS is often preceded by a myeloproliferative neoplastic condition called transient abnormal myelopoiesis (TAM) that disrupts megakaryocytic and erythroid differentiation. Over the last two decades, many genetic and epigenetic changes in TAM and ML-DS have been elucidated. These include overexpression of molecules and micro-RNAs located on chromosome 21, GATA1 mutations, and a range of other somatic mutations and chromosomal alterations. In this review, we summarize molecular changes reported in TAM and ML-DS and provide a comprehensive discussion of these findings. Recent advances in the development of CRISPR/Cas9-modified induced pluripotent stem cell-based disease models are also highlighted. However, despite significant progress in this area, we still do not fully understand the pathogenesis of ML-DS, and there are no targeted therapies. Initial diagnosis of ML-DS has a favorable prognosis, but refractory and relapsed disease can be difficult to treat; therapeutic options are limited in Down syndrome children by their stronger sensitivity to the toxic effects of chemotherapy. Because of the rarity of TAM and ML-DS, large-scale multi-center studies would be helpful to advance molecular characterization of these diseases at different stages of development and progression.

The Multifaceted Role of STAT3 in NK-Cell Tumor Surveillance

Signal transducer and activator of transcription 3 (STAT3) is a member of the Janus kinase (JAK)-STAT pathway, which is one of the key pathways contributing to cancer. STAT3 regulates transcription downstream of many cytokines including interleukin (IL)-6 and IL-10. In cancer, STAT3 is mainly described as a tumor promoter driving tumor cell proliferation, resistance to apoptosis, angiogenesis and metastasis and aberrant activation of STAT3 is associated with poor prognosis. STAT3 is also an important driver of immune evasion. Among many other immunosuppressive mechanisms, STAT3 aids tumor cells to escape natural killer (NK) cell-mediated immune surveillance. NK cells are innate lymphocytes, which can directly kill malignant cells but also regulate adaptive immune responses and contribute to the composition of the tumor microenvironment. The inborn ability to lyse transformed cells renders NK cells an attractive tool for cancer immunotherapy. Here, we provide an overview of the role of STAT3 in the dynamic interplay between NK cells and tumor cells. On the one hand, we summarize the current knowledge on how tumor cell-intrinsic STAT3 drives the evasion from NK cells. On the other hand, we describe the multiple functions of STAT3 in regulating NK-cell cytotoxicity, cytokine production and their anti-tumor responses in vivo. In light of the ongoing research on STAT3 inhibitors, we also discuss how targeting STAT3 would affect the two arms of STAT3-dependent regulation of NK cell-mediated anti-tumor immunity. Understanding the complexity of this interplay in the tumor microenvironment is crucial for future implementation of NK cell-based immunotherapies.

Mechanisms of Resistance to Targeted Therapies for Relapsed or Refractory Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is an aggressive disease of clonal hematopoiesis with a high rate of relapse and refractory disease despite intensive therapy. Traditionally, relapsed or refractory AML has increased therapeutic resistance and poor long-term survival. In recent years, advancements in the mechanistic understanding of leukemogenesis have allowed for the development of targeted therapies. These therapies offer novel alternatives to intensive chemotherapy and have prolonged survival in relapsed or refractory AML. Unfortunately, a significant portion of patients do not respond to these therapies and relapse occurs in most patients who initially responded. This review focuses on the mechanisms of resistance to targeted therapies in relapsed or refractory AML.