c-Myc plays part in drug resistance mediated by bone marrow stromal cells in acute myeloid leukemia

LncRNA SNHG5 induces CAFs-like phenotype and autophagy of AML-MSCs via PTBP1/ATG5 axis to confer chemoresistance of AML cells

BACKGROUND

Acute myeloid leukemia (AML) is still a threaten to human health due to its high occurrence and poor prognosis. Mesenchymal stem cells (MSCs) in bone marrow microenvironment (BMM) play a critical role in the development of AML. This study elucidated the interaction between MSCs and AML cells and its underlying mechanism.

METHOD

MSCs were isolated, identified, and co-cultured with AML cells. qRT-PCR, Western blotting and immunofluorescence were used to determine molecule expression. Cell viability and apoptosis were determined by CCK-8 and flow cytometry. Exosomes were isolated and characterized, and PKH26 was used for monitoring exosome internalization. RNA-FISH was used to determine the localization of SNHG5. RIP, RNA-pull down and ChIP assays were used to evaluate the molecular interaction.

RESULTS

SNHG5 expression was up-regulated and positively correlated with cancer-associated fibroblasts (CAFs)-related biomarkers in AML-MSCs. AML cells-derived exosomes delivered SNHG5 to enhance its expression in MSCs. SNHG5 overexpression induced CAFs-like phenotype and autophagy in HD-MSCs that led to daunorubicin resistance of AML cells. Mechanistically, SNHG5 stabilized autophagy related 5 (ATG5) mRNA by interaction with polypyrimidine tract-binding protein 1 (PTBP1).

CONCLUSION

AML cells-derived exosomal lncRNA SNHG5 triggered CAFs-like phenotype and autophagy of AML-MSCs via interaction with PTBP1 to increase ATG5 mRNA stability, thereby leading to chemoresistance of AML cells.

BRD4 degraders may effectively counteract therapeutic resistance of leukemic stem cells in AML and ALL

Acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL) are life-threatening hematopoietic malignancies characterized by clonal expansion of leukemic blasts in the bone marrow and peripheral blood. The epigenetic reader BRD4 and its downstream effector MYC have recently been identified as potential drug targets in human AML and ALL. We compared anti-leukemic efficacies of the small-molecule BET inhibitor JQ1 and the recently developed BRD4 degraders dBET1 and dBET6 in AML and ALL cells. JQ1, dBET1, and dBET6 were found to suppress growth and viability in all AML and ALL cell lines examined as well as in primary patient-derived AML and ALL cells, including CD34+/CD38- and CD34+/CD38+ leukemic stem and progenitor cells, independent of the type (variant) of leukemia or molecular driver expressed in leukemic cells. Moreover, we found that dBET6 overcomes osteoblast-induced drug resistance in AML and ALL cells, regardless of the type of leukemia or the drug applied. Most promising cooperative or even synergistic drug combination effects were seen with dBET6 and the FLT3 ITD blocker gilteritinib in FLT3 ITD-mutated AML cells, and with dBET6 and the multi-kinase blocker ponatinib in BCR::ABL1+ ALL cells. Finally, all BRD4-targeting drugs suppressed interferon-gamma- and tumor necrosis factor-alpha-induced expression of the resistance-related checkpoint antigen PD-L1 in AML and ALL cells, including LSC. In all assays examined, the BRD4 degrader dBET6 was a superior anti-leukemic drug compared with dBET1 and JQ1. Together, BRD4 degraders may provide enhanced inhibition of multiple mechanisms of therapy resistance in AML and ALL.

Hematopoietic and leukemic stem cells homeostasis: the role of bone marrow niche

The bone marrow microenvironment (BMM) has highly specialized anatomical characteristics that provide a sanctuary place for hematopoietic stem cells (HSCs) that allow appropriate proliferation, maintenance, and self-renewal capacity. Several cell types contribute to the constitution and function of the bone marrow niche. Interestingly, uncovering the secrets of BMM and its interaction with HSCs in health paved the road for research aiming at better understanding the concept of leukemic stem cells (LSCs) and their altered niche. In fact, they share many signals that are responsible for interactions between LSCs and the bone marrow niche, due to several biological similarities between LSCs and HSCs. On the other hand, LSCs differ from HSCs in their abnormal activation of important signaling pathways that regulate survival, proliferation, drug resistance, invasion, and spread. Targeting these altered niches can help in better treatment choices for hematological malignancies and bone marrow disorders in general and acute myeloid leukemia (AML) in particular. Moreover, targeting those niches may help in decreasing the emergence of drug resistance and lower the relapse rate. In this article, the authors reviewed the most recent literature on bone marrow niches and their relations with either normal HSCs and AML cells/LSC, by focusing on pathogenetic and therapeutic implications.

Mesenchymal Stem Cells in Myelodysplastic Syndromes and Leukaemia

Mesenchymal stem cells (MSCs) are one of the main residents in the bone marrow (BM) and have an essential role in the regulation of haematopoietic stem cell (HSC) differentiation and proliferation. Myelodysplastic syndromes (MDSs) are a group of myeloid disorders impacting haematopoietic stem and progenitor cells (HSCPs) that are characterised by BM failure, ineffective haematopoiesis, cytopenia, and a high risk of transformation through the expansion of MDS clones together with additional genetic defects. It has been indicated that MSCs play anti-tumorigenic roles such as in cell cycle arrest and pro-tumorigenic roles including the induction of metastasis in MDS and leukaemia. Growing evidence has shown that MSCs have impaired functions in MDS, such as decreased proliferation capacity, differentiation ability, haematopoiesis support, and immunomodulation function and increased inflammatory alterations within the BM through some intracellular pathways such as Notch and Wnt and extracellular modulators abnormally secreted by MSCs, including increased expression of inflammatory factors and decreased expression of haematopoietic factors, contributing to the development and progression of MDSs. Therefore, MSCs can be targeted for the treatment of MDSs and leukaemia. However, it remains unclear what drives MSCs to behave abnormally. In this review, dysregulations in MSCs and their contributions to myeloid haematological malignancies will be discussed.

Mesenchymal Stem Cells Increase Drug Tolerance of A431 Cells Only in 3D Spheroids, Not in 2D Co-Cultures

Mesenchymal stem cells (MSCs) are an integral part of the tumor microenvironment (TME); however, their role is somewhat controversial: conflicting reports suggest that, depending on the stage of tumor development, MSCs can either support or suppress tumor growth and spread. Additionally, the influence of MSCs on drug resistance is also ambiguous. Previously, we showed that, despite MSCs proliferating significantly more slowly than cancer cells, there are chemotherapeutic drugs which proved to be similarly toxic to both cell types. Here we established 2D co-cultures and 3D co-culture spheroids from different ratios of GFP-expressing, adipose tissue-derived MSCs and A431 epidermoid carcinoma cells tagged with mCherry to investigate the effect of MSCs on cancer cell growth, survival, and drug sensitivity. We examined the cytokine secretion profile of mono- and co-cultures, explored the inner structure of the spheroids, applied MSC-(nutlin-3) and cancer cell-targeting (cisplatin) treatments separately, monitored the response with live-cell imaging and identified a new, double-fluorescent cell type emerging from these cultures. In 2D co-cultures, no effect on proliferation or drug sensitivity was observed, regardless of the changes in cytokine secretion induced by the co-culture. Conversely, 3D spheroids developed a unique internal structure consisting of MSCs, which significantly improved cancer cell survival and resilience to treatment, suggesting that physical proximity and cell-cell connections are required for MSCs to considerably affect nearby cancer cells. Our results shed light on MSC-cancer cell interactions and could help design new, better treatment options for tumors.

Biology and Therapeutic Properties of Mesenchymal Stem Cells in Leukemia

This comprehensive review delves into the multifaceted roles of mesenchymal stem cells (MSCs) in leukemia, focusing on their interactions within the bone marrow microenvironment and their impact on leukemia pathogenesis, progression, and treatment resistance. MSCs, characterized by their ability to differentiate into various cell types and modulate the immune system, are integral to the BM niche, influencing hematopoietic stem cell maintenance and functionality. This review extensively explores the intricate relationship between MSCs and leukemic cells in acute myeloid leukemia, acute lymphoblastic leukemia, chronic myeloid leukemia, and chronic lymphocytic leukemia. This review also addresses the potential clinical applications of MSCs in leukemia treatment. MSCs' role in hematopoietic stem cell transplantation, their antitumor effects, and strategies to disrupt chemo-resistance are discussed. Despite their therapeutic potential, the dual nature of MSCs in promoting and inhibiting tumor growth poses significant challenges. Further research is needed to understand MSCs' biological mechanisms in hematologic malignancies and develop targeted therapeutic strategies. This in-depth exploration of MSCs in leukemia provides crucial insights for advancing treatment modalities and improving patient outcomes in hematologic malignancies.

Mesenchymal stromal cells in myeloid malignancies: Immunotherapeutic opportunities

Myeloid malignancies are clonal disorders of the progenitor cells or hematopoietic stem cells, including acute myeloid leukemia, myelodysplastic syndromes, myeloproliferative malignancies, and chronic myelomonocytic leukemia. Myeloid neoplastic cells affect the proliferation and differentiation of other hematopoietic lineages in the bone marrow and peripheral blood, leading to severe and life-threatening complications. Mesenchymal stromal cells (MSCs) residing in the bone marrow exert immunosuppressive functions by suppressing innate and adaptive immune systems, thus creating a supportive and tolerant microenvironment for myeloid malignancy progression. This review summarizes the significant features of MSCs in myeloid malignancies, including their role in regulating cell growth, cell death, and antineoplastic resistance, in addition to their immunosuppressive contributions. Understanding the implications of MSCs in myeloid malignancies could pave the path for potential use in immunotherapy.

Bone Marrow Microenvironment as a Source of New Drug Targets for the Treatment of Acute Myeloid Leukaemia

Acute myeloid leukaemia (AML) is a heterogeneous disease with one of the worst survival rates of all cancers. The bone marrow microenvironment is increasingly being recognised as an important mediator of AML chemoresistance and relapse, supporting leukaemia stem cell survival through interactions among stromal, haematopoietic progenitor and leukaemic cells. Traditional therapies targeting leukaemic cells have failed to improve long term survival rates, and as such, the bone marrow niche has become a promising new source of potential therapeutic targets, particularly for relapsed and refractory AML. This review briefly discusses the role of the bone marrow microenvironment in AML development and progression, and as a source of novel therapeutic targets for AML. The main focus of this review is on drugs that modulate/target this bone marrow microenvironment and have been examined in in vivo models or clinically.

Blockade of FGF2/FGFR2 partially overcomes bone marrow mesenchymal stromal cells mediated progression of T-cell acute lymphoblastic leukaemia

The development of acute lymphoblastic leuakemia (ALL) is partly attributed to the effects of bone marrow (BM) microenvironment, especially mesenchymal stromal cells (MSCs), which interact bilaterally with leukaemia cells, leading to ALL progression. In order to find MSCs-based microenvironment targeted therapeutic strategies, Notch1-induced T-cell ALL (T-ALL) mice models were used and dynamic alterations of BM-MSCs with increased cell viability during T-ALL development was observed. In T-ALL mice derived stroma-based condition, leukaemia cells showed significantly elevated growth capacity indicating that MSCs participated in leukaemic niche formation. RNA sequence results revealed that T-ALL derived MSCs secreted fibroblast growth factor 2 (FGF2), which combined with fibroblast growth factor receptor 2 (FGFR2) on leukaemia cells, resulting in activation of PI3K/AKT/mTOR signalling pathway in leukaemia cells. In vitro blocking the interaction between FGF2 and FGFR2 with BGJ398 (infigratinib), a FGFR1-3 kinase inhibitor, or knockdown FGF2 in MSCs by interference caused deactivation of PI3K/AKT/mTOR pathway and dysregulations of genes associated with cell cycle and apoptosis in ALL cells, leading to decrease of leukaemia cells. In mouse model received BGJ398, overall survival was extended and dissemination of leukaemia cells in BM, spleen, liver and peripheral blood was decreased. After subcutaneous injection of primary human T-ALL cells with MSCs, tumour growth was suppressed when FGF2/FGFR2 was interrupted. Thus, inhibition of FGF2/FGFR2 interaction appears to be a valid strategy to overcome BM-MSCs mediated progression of T-ALL, and BGJ398 could indeed improve outcomes in T-ALL, which provide theoretical basis of BGJ398 as a BM microenvironment based therapeutic strategy to control disease progression.

Mesenchymal stroma/stem cells: Haematologists' friend or foe?

Mesenchymal stromal cells (MSCs) are non-haematopoietic cells found in fetal and adult organs, that play important roles in tissue repair, inflammation and immune modulation. MSCs residing in the bone marrow interact closely with haematopoietic cells and comprise an important component of the microenvironment supporting haematopoiesis, in both health and disease states. Since their identification in 1970, basic scientific and preclinical research efforts have shed light on the role of MSCs in the regulation of haematopoiesis and evoked interest in their clinical application in haematopoietic stem cell transplantation (HSCT) and malignant haematology. Over the last two decades, these research efforts have led to numerous clinical trials, which have established the safety of MSC therapy; however, the optimal mode of administration and the benefit remain inconclusive. In this paper, we will review the clinical experience with use of MSCs in HSCT for enhancement of engraftment, prevention and treatment of graft-versus-host disease and haemorrhagic cystitis. Then, we will discuss the contradictory evidence regarding tumour-promoting versus tumour-suppressing effects of MSCs in haematological malignancies, which may have relevance for future clinical applications.

Mesenchymal Stem/Stromal Cells May Decrease Success of Cancer Treatment by Inducing Resistance to Chemotherapy in Cancer Cells

Simple Summary

Tumours consist of different cell types and an extracellular matrix, all of which together form a complex microenvironment. The tumour microenvironment plays a critical role in various aspects of tumour development and progression. Mesenchymal stem/stromal cells (MSCs) are multipotent stem cells that have a tri-lineage differentiation capacity and are one of the key stromal cells in the tumour microenvironment. Following the interaction with cancer cells, they are transformed from naïve MSCs to tumour-associated MSCs, which substantially affect tumour growth and progression as well as the development of chemoresistance in cancer cells. The aim of this review article is to provide an overview of studies that have investigated how MSCs affect the susceptibility of cancer cells to chemotherapeutics. Their results show that MSCs protect cancer cells from chemotherapeutics by influencing several signalling pathways. This knowledge is crucial for the development of new treatment approaches that will lead to improved treatment outcomes.

Abstract

The tumour microenvironment, which is comprised of various cell types and the extracellular matrix, substantially impacts tumour initiation, progression, and metastasis. Mesenchymal stem/stromal cells (MSCs) are one of the key stromal cells in the tumour microenvironment, and their interaction with cancer cells results in the transformation of naïve MSCs to tumour-associated MSCs. The latter has an important impact on tumour growth and progression. Recently, it has been shown that they can also contribute to the development of chemoresistance in cancer cells. This review provides an overview of 42 studies published between 1 January 2001 and 1 January 2022 that examined the effect of MSCs on the susceptibility of cancer cells to chemotherapeutics. The studies showed that MSCs affect various signalling pathways in cancer cells, leading to protection against chemotherapy-induced damage. Promising results emerged from the use of inhibitors of various signalling pathways that are affected in cancer cells due to interactions with MSCs in the tumour microenvironment. These studies present a good starting point for the investigation of novel treatment approaches and demonstrate the importance of targeting the stroma in the tumour microenvironment to improve treatment outcomes.

Inhibiting PI3K–AKT–mTOR Signaling in Multiple Myeloma-Associated Mesenchymal Stem Cells Impedes the Proliferation of Multiple Myeloma Cells

The microenvironment of cancer cells is receiving increasing attention as an important factor influencing the progression and prognosis of tumor diseases. In multiple myeloma (MM), a hematological cancer of plasma cells, mesenchymal stem cells (MSCs) represent an integral part of the bone marrow niche and tumor microenvironment. It has been described that MM cells alter MSCs in a way that MM-associated MSCs promote the proliferation and survival of MM cells. Yet, our understanding of the molecular mechanisms governing the interaction between MM cells and MSCs and whether this can be targeted for therapeutic interventions is limited. To identify potential molecular targets, we examined MSCs by RNA sequencing and Western blot analysis. We report that MSCs from MM patients with active disease (MM-Act-MSCs) show a distinct gene expression profile as compared with MSCs from patients with other (non-) malignant diseases (CTR-MSCs). Of note, we detected a significant enrichment of the PI3K–AKT–mTOR hallmark gene set in MM-Act-MSCs and further confirmed the increased levels of related proteins in these MSCs. Pictilisib, a pan-PI3K inhibitor, selectively reduced the proliferation of MM-Act-MSCs as compared with CTR-MSCs. Furthermore, pictilisib treatment impaired the MM-promoting function of MM-Act-MSCs. Our data thus provide a deeper insight into the molecular signature and function of MSCs associated with MM and show that targeting PI3K–AKT–mTOR signaling in MSCs may represent an additional therapeutic pathway in the treatment of MM patients.

Bone Marrow Aging and the Leukaemia-Induced Senescence of Mesenchymal Stem/Stromal Cells: Exploring Similarities

Bone marrow aging is associated with multiple cellular dysfunctions, including perturbed haematopoiesis, the propensity to haematological transformation, and the maintenance of leukaemia. It has been shown that instructive signals from different leukemic cells are delivered to stromal cells to remodel the bone marrow into a supportive leukemic niche. In particular, cellular senescence, a physiological program with both beneficial and deleterious effects on the health of the organisms, may be responsible for the increased incidence of haematological malignancies in the elderly and for the survival of diverse leukemic cells. Here, we will review the connection between BM aging and cellular senescence and the role that these processes play in leukaemia progression. Specifically, we discuss the role of mesenchymal stem cells as a central component of the supportive niche. Due to the specificity of the genetic defects present in leukaemia, one would think that bone marrow alterations would also have particular changes, making it difficult to envisage a shared therapeutic use. We have tried to summarize the coincident features present in BM stromal cells during aging and senescence and in two different leukaemias, acute myeloid leukaemia, with high frequency in the elderly, and B-acute lymphoblastic leukaemia, mainly a childhood disease. We propose that mesenchymal stem cells are similarly affected in these different leukaemias, and that the changes that we observed in terms of cellular function, redox balance, genetics and epigenetics, soluble factor repertoire and stemness are equivalent to those occurring during BM aging and cellular senescence. These coincident features may be used to explore strategies useful to treat various haematological malignancies.

SAF-248, a novel PI3Kδ-selective inhibitor, potently suppresses the growth of diffuse large B-cell lymphoma

PI3Kδ is expressed predominately in leukocytes and overexpressed in B-cell-related malignances. PI3Kδ has been validated as a promising target for cancer therapy, and specific PI3Kδ inhibitors were approved for clinical practice. However, the substantial toxicity and relatively low efficacy as a monotherapy in diffuse large B-cell lymphoma (DLBCL) limit their clinical use. In this study, we described a novel PI3Kδ inhibitor SAF-248, which exhibited high selectivity for PI3Kδ (IC₅₀ = 30.6 nM) over other PI3K isoforms at both molecular and cellular levels, while sparing most of the other human protein kinases in the kinome profiling. SAF-248 exhibited superior antiproliferative activity against 27 human lymphoma and leukemia cell lines compared with the approved PI3Kδ inhibitor idelalisib. In particular, SAF-248 potently inhibited the proliferation of a panel of seven DLBCL cell lines (with GI₅₀ values < 1 μM in 5 DLBCL cell lines). We demonstrated that SAF-248 concentration-dependently blocked PI3K signaling followed by inducing G₁ phase arrest and apoptosis in DLBCL KARPAS-422, Pfeiffer and TMD8 cells. Its activity against the DLBCL cells was negatively correlated to the protein level of PI3Kα. Oral administration of SAF-248 dose-dependently inhibited the growth of xenografts derived from Pfeiffer and TMD8 cells. Activation of mTORC1, MYC and JAK/STAT signaling was observed upon prolonged treatment and co-targeting these pathways would potentiate the activity of SAF-248. Taken together, SAF-248 is a promising selective PI3Kδ inhibitor for the treatment of DLBCL and rational drug combination would further improve its efficacy.

Mesenchymal stem/stromal cells in cancer therapy

The multipotent mesenchymal stem/stromal cells (MSCs), initially discovered from bone marrow in 1976, have been identified in nearly all tissues of human body now. The multipotency of MSCs allows them to give rise to osteocytes, chondrocytes, adipocytes, and other lineages. Moreover, armed with the immunomodulation capacity and tumor-homing property, MSCs are of special relevance for cell-based therapies in the treatment of cancer. However, hampered by lack of knowledge about the controversial roles that MSC plays in the crosstalk with tumors, limited progress has been made with regard to translational medicine. Therefore, in this review, we discuss the prospects of MSC-associated anticancer strategies in light of therapeutic mechanisms and signal transduction pathways. In addition, the clinical trials designed to appraise the efficacy and safety of MSC-based anticancer therapies will be assessed according to published data.

Oncogene-Induced Reprogramming in Acute Lymphoblastic Leukemia: Towards Targeted Therapy of Leukemia-Initiating Cells

Simple Summary

Acute lymphoblastic leukemia is a heterogeneous disease characterized by a diversity of genetic alterations, following a sophisticated and controversial organization. In this review, we present and discuss the concepts exploring the cellular, molecular and functional heterogeneity of leukemic cells. We also review the emerging evidence indicating that cell plasticity and oncogene-induced reprogramming should be considered at the biological and clinical levels as critical mechanisms for identifying and targeting leukemia-initiating cells.

Abstract

Our understanding of the hierarchical structure of acute leukemia has yet to be fully translated into therapeutic approaches. Indeed, chemotherapy still has to take into account the possibility that leukemia-initiating cells may have a distinct chemosensitivity profile compared to the bulk of the tumor, and therefore are spared by the current treatment, causing the relapse of the disease. Therefore, the identification of the cell-of-origin of leukemia remains a longstanding question and an exciting challenge in cancer research of the last few decades. With a particular focus on acute lymphoblastic leukemia, we present in this review the previous and current concepts exploring the phenotypic, genetic and functional heterogeneity in patients. We also discuss the benefits of using engineered mouse models to explore the early steps of leukemia development and to identify the biological mechanisms driving the emergence of leukemia-initiating cells. Finally, we describe the major prospects for the discovery of new therapeutic strategies that specifically target their aberrant stem cell-like functions.

The Novel Oral BET-CBP/p300 Dual Inhibitor NEO2734 Is Highly Effective in Eradicating Acute Myeloid Leukemia Blasts and Stem/Progenitor Cells

Acute myeloid leukemia (AML) is a disease characterized by transcriptional dysregulation that results in a block in differentiation and aberrant self-renewal. Inhibitors directed to epigenetic modifiers, aiming at transcriptional reprogramming of AML cells, are currently in clinical trials for AML patients. Several of these inhibitors target bromodomain and extraterminal domain (BET) proteins, cyclic AMP response binding protein-binding protein (CBP), and the E1A-interacting protein of 300 kDa (p300), affecting histone acetylation. Unfortunately, single epigenetic inhibitors showed limited efficacy due to appearance of resistance and lack of effective eradication of leukemic stem cells. Here, we describe the efficacy of 2 novel, orally available inhibitors targeting both the BET and CBP/p300 proteins, NEO1132 and NEO2734, in primary AML. NEO2734 and NEO1132 efficiently reduced the viability of AML cell lines and primary AML cells by inducing apoptosis. Importantly, both NEO drugs eliminated leukemic stem/progenitor cells from AML patient samples, and NEO2734 increased the effectiveness of combination chemotherapy treatment in an in vivo AML patient-derived mouse model. Thus, dual inhibition of BET and CBP/p300 using NEO2734 is a promising therapeutic strategy for AML patients, making it a focus for clinical translation.

Myeloid-Derived Suppressor Cells and Mesenchymal Stem/Stromal Cells in Myeloid Malignancies

Myeloid malignancies arise from an altered hematopoietic stem cell and mainly comprise acute myeloid leukemia, myelodysplastic syndromes, myeloproliferative malignancies, and chronic myelomonocytic leukemia. Myeloid neoplastic leukemic cells may influence the growth and differentiation of other hematopoietic cell lineages in peripheral blood and bone marrow. Myeloid-derived suppressor cells (MDSCs) and mesenchymal stromal cells (MSCs) display immunoregulatory properties by controlling the innate and adaptive immune systems that may induce a tolerant and supportive microenvironment for neoplasm development. This review analyzes the main features of MDSCs and MSCs in myeloid malignancies. The number of MDSCs is elevated in myeloid malignancies exhibiting high immunosuppressive capacities, whereas MSCs, in addition to their immunosuppression contribution, regulate myeloid leukemia cell proliferation, apoptosis, and chemotherapy resistance. Moreover, MSCs may promote MDSC expansion, which may mutually contribute to the creation of an immuno-tolerant neoplasm microenvironment. Understanding the implication of MDSCs and MSCs in myeloid malignancies may favor their potential use in immunotherapeutic strategies.

Myeloid-Derived Suppressor Cells and Mesenchymal Stem/Stromal Cells in Myeloid Malignancies

Myeloid malignancies arise from an altered hematopoietic stem cell and mainly comprise acute myeloid leukemia, myelodysplastic syndromes, myeloproliferative malignancies, and chronic myelomonocytic leukemia. Myeloid neoplastic leukemic cells may influence the growth and differentiation of other hematopoietic cell lineages in peripheral blood and bone marrow. Myeloid-derived suppressor cells (MDSCs) and mesenchymal stromal cells (MSCs) display immunoregulatory properties by controlling the innate and adaptive immune systems that may induce a tolerant and supportive microenvironment for neoplasm development. This review analyzes the main features of MDSCs and MSCs in myeloid malignancies. The number of MDSCs is elevated in myeloid malignancies exhibiting high immunosuppressive capacities, whereas MSCs, in addition to their immunosuppression contribution, regulate myeloid leukemia cell proliferation, apoptosis, and chemotherapy resistance. Moreover, MSCs may promote MDSC expansion, which may mutually contribute to the creation of an immuno-tolerant neoplasm microenvironment. Understanding the implication of MDSCs and MSCs in myeloid malignancies may favor their potential use in immunotherapeutic strategies.

Crosstalk between hnRNP K and SET in ATRA-induced differentiation in acute promyelocytic leukemia

HnRNP K protein is a heterogeneous nuclear ribonucleoprotein which has been proposed to be involved in the leukemogenesis of acute promyelocytic leukemia (APL), as well as in differentiation induced by all‐trans retinoic acid (ATRA). We previously demonstrated a connection between SET and hnRNP K function in head and neck squamous cell carcinoma (HNSCC) cells related to splicing processing. The objective of this study was to characterize the participation of hnRNP K and SET proteins in ATRA‐induced differentiation in APL. We observed higher (5‐ to 40‐fold) levels of hnRNP K and SET mRNA in APL patients at the diagnosis phase compared with induction and maintenance phases. hnRNP K knockdown using short‐hairpin RNA led to cell death in ATRA‐sensitive NB4 and resistant NB4‐R2 cells by apoptosis with SET cleavage. In addition, hnRNP K knockdown increased granulocytic differentiation in APL cells, mainly in NB4‐R2 with ATRA. hnRNP K knockdown had an effect similar to that of treatment with U0126 (an meiosis‐specific serine/threonine protein kinase/ERK inhibitor), mainly in NB4‐R2 cells. SET knockdown in APL cells revealed that apoptosis induction in cells with hnRNP K knockdown occurred by SET cleavage rather than by reduction in SET protein. Transplantation of NB4‐R2 cells into nude mice confirmed that arsenic trioxide (ATO) combined with U0126 has higher potential against tumor progression when compared to ATO. Therefore, hnRNP K/SET and ERK are potential therapeutic targets for both antineoplastic leukemia therapy and relapsed APL patients with ATRA resistance.

Driving CAR T Stem Cell Targeting in Acute Myeloid Leukemia: The Roads to Success

Current treatment outcome for acute myeloid leukemia (AML) patients is unsatisfactory and characterized by high rates of relapse and poor overall survival. Increasing evidence points to a crucial role of leukemic stem cells (LSC) and the bone marrow (BM) leukemic niche, in which they reside, in AML evolution and chemoresistance. Thus, future strategies aiming at improving AML therapeutic protocols are likely to be directed against LSC and their niche. Chimeric antigen receptor (CAR) T-cells have been extremely successful in the treatment of relapsed/refractory acute lymphoblastic leukemia and B-cell non-Hodgkin lymphoma and comparable results in AML are highly desirable. At present, we are at the dawn of CAR T-cell application in AML, with several preclinical studies and few early phase clinical trials. However, the lack of leukemia-specific targets and the genetic and phenotypic heterogeneity of the disease combined with the leukemia-induced remodeling of the BM microenvironment are limiting CAR T-cell exploitation in AML. Here, we reviewed AML-LSC and AML-BM niche features in the context of their therapeutic targeting using CAR T-cells. We summarized recent progress in CAR T-cell application to the treatment of AML, and we discussed the remaining therapeutic challenges and promising novel strategies to overcome them.

Gene Transactivation and Transrepression in MYC-Driven Cancers

MYC is a proto-oncogene regulating a large number of genes involved in a plethora of cellular functions. Its deregulation results in activation of MYC gene expression and/or an increase in MYC protein stability. MYC overexpression is a hallmark of malignant growth, inducing self-renewal of stem cells and blocking senescence and cell differentiation. This review summarizes the latest advances in our understanding of MYC-mediated molecular mechanisms responsible for its oncogenic activity. Several recent findings indicate that MYC is a regulator of cancer genome and epigenome: MYC modulates expression of target genes in a site-specific manner, by recruiting chromatin remodeling co-factors at promoter regions, and at genome-wide level, by regulating the expression of several epigenetic modifiers that alter the entire chromatin structure. We also discuss novel emerging therapeutic strategies based on both direct modulation of MYC and its epigenetic cofactors.

Inhibitor of Multi-cyclin-dependent Kinases (AT7519) Reduced Survival of U937 Leukemic Cells and Enhanced Anti-leukemic Effect of Vincristine: A Highlight to CDK Inhibition Efficacy in Acute Leukemia

Background: The conservative character of the cell cycle outlined that any dysregulation in the regulatory components of this process in normal cells opens a gate toward neoplastic transformation. Objectives: Given the critical role of cyclin-dependent kinases (CDKs) in cancer pathogenesis and based on their frequent aberrancy in human leukemia, the present study aimed at evaluating the suppressive effect of a multi-CDK inhibitor AT7519 on acute myeloid leukemia-derived U937 cells. Methods: To assess the anti-leukemic effects of the inhibitor on acute myeloid leukemia (AML) cells, we used MTT and trypan blue assays. Flow cytometric analysis and q-RT-PCR were also applied to evaluate the impact of AT7519 on cell cycle and apoptosis. Results: The results suggested that suppression of CDK in U937 cells hampered the proliferation of leukemic cells through a G2/M arrest mediated by p21 gene. Additionally, the anti-survival impact of AT7519 on these cells was shown to be along with the apoptosis initiation not only through the increment of pro-apoptotic gene expression but also through diminishing the mRNA levels of both Pin1 and Survivin. Notably, the potent anti-leukemic property of this agent has become more prominent when we found that the blockage of CDKs in AML cells could synergize with the cytotoxic effect of vincristine (VCR). To the best of our knowledge, little is known about the molecular mechanisms of resistance to AT7519 and we proposed that the effectiveness of this agent was partially attenuated through either c-Myc or autophagy activation in U937 cells. Conclusions: This study suggests that the pharmacological targeting of CDKs could probably unwind the complexity of therapeutic obstacles on the way of acute leukemia, either in the context of mono- or combined-modal strategy.

Nrf2 overexpression increases risk of high tumor mutation burden in acute myeloid leukemia by inhibiting MSH2

Nuclear factor erythroid 2-related factor 2 (Nrf2, also called NFE2L2) plays an important role in cancer chemoresistance. However, little is known about the role of Nrf2 in tumor mutation burden and the effect of Nrf2 in modulating DNA mismatch repair (MMR) gene in acute myeloid leukemia (AML). Here we show that Nrf2 expression is associated with tumor mutation burden in AML. Patients with Nrf2 overexpression had a higher frequency of gene mutation and drug resistance. Nrf2 overexpression protected the AML cells from apoptosis induced by cytarabine in vitro and increased the risk of drug resistance associated with a gene mutation in vivo. Furthermore, Nrf2 overexpression inhibited MutS Homolog 2 (MSH2) protein expression, which caused DNA MMR deficiency. Mechanistically, the inhibition of MSH2 by Nrf2 was in a ROS-independent manner. Further studies showed that an increased activation of JNK/c-Jun signaling in Nrf2 overexpression cells inhibited the expression of the MSH2 protein. Our findings provide evidence that high Nrf2 expression can induce gene instability-dependent drug resistance in AML. This study demonstrates the reason why the high Nrf2 expression leads to the increase of gene mutation frequency in AML, and provides a new strategy for clinical practice.

Aging of Bone Marrow Mesenchymal Stromal Cells: Hematopoiesis Disturbances and Potential Role in the Development of Hematologic Cancers

Simple Summary

As for many other cancers, the risk of developing hematologic malignancies increases considerably as people age. In recent years, a growing number of studies have highlighted the influence of the aging microenvironment on hematopoiesis and tumor progression. Mesenchymal stromal cells are a major player in intercellular communication inside the bone marrow microenvironment involved in hematopoiesis support. With aging, their functions may be altered, leading to hematopoiesis disturbances which can lead to hematologic cancers. A good understanding of the mechanisms involved in mesenchymal stem cell aging and the consequences on hematopoiesis and tumor progression is therefore necessary for a better comprehension of hematologic malignancies and for the development of therapeutic approaches.

Abstract

Aging of bone marrow is a complex process that is involved in the development of many diseases, including hematologic cancers. The results obtained in this field of research, year after year, underline the important role of cross-talk between hematopoietic stem cells and their close environment. In bone marrow, mesenchymal stromal cells (MSCs) are a major player in cell-to-cell communication, presenting a wide range of functionalities, sometimes opposite, depending on the environmental conditions. Although these cells are actively studied for their therapeutic properties, their role in tumor progression remains unclear. One of the reasons for this is that the aging of MSCs has a direct impact on their behavior and on hematopoiesis. In addition, tumor progression is accompanied by dynamic remodeling of the bone marrow niche that may interfere with MSC functions. The present review presents the main features of MSC senescence in bone marrow and their implications in hematologic cancer progression.

Integrated analysis of microRNA and transcription factors in the bone marrow of patients with acute monocytic leukemia

Acutemonocytic leukemia (AMoL) is a distinct subtype of acute myeloid leukemia (AML) with poor prognosis. However, the molecular mechanisms and key regulators involved in the global regulation of gene expression levels in AMoL are poorly understood. In order to elucidate the role of microRNAs (miRNAs/miRs) and transcription factors (TFs) in AMoL pathogenesis at the network level, miRNA and TF expression level profiles were systematically analyzed by miRNA sequencing and TF array, respectively; this identified 285 differentially expressed miRNAs and 139 differentially expressed TFs in AMoL samples compared with controls. By combining expression level profile data and bioinformatics tools available for predicting TF and miRNA targets, a comprehensive AMoL-specific miRNA-TF-mediated regulatory network was constructed. A total of 26 miRNAs and 23 TFs were identified as hub nodes in the network. Among these hubs, miR-29b-3p, MYC, TP53 and NFKB1 were determined to be potential AMoL regulators, and were subsequently extracted to construct sub-networks. A hypothetical pathway model was also proposed for miR-29b-3p to reveal the potential co-regulatory mechanisms of miR-29b-3p, MYC, TP53 and NFKB1 in AMoL. The present study provided an effective approach to discover critical regulators via a comprehensive regulatory network in AMoL, in addition to enhancing understanding of the pathogenesis of this disease at the molecular level.

Ex vivo cultures and drug testing of primary acute myeloid leukemia samples: Current techniques and implications for experimental design and outcome

New treatment options of acute myeloid leukemia (AML) are rapidly emerging. Pre-clinical models such as ex vivo cultures are extensively used towards the development of novel drugs and to study synergistic drug combinations, as well as to discover biomarkers for both drug response and anti-cancer drug resistance. Although these approaches empower efficient investigation of multiple drugs in a multitude of primary AML samples, their translational value and reproducibility are hampered by the lack of standardized methodologies and by culture system-specific behavior of AML cells and chemotherapeutic drugs. Moreover, distinct research questions require specific methods which rely on specific technical knowledge and skills. To address these aspects, we herein review commonly used culture techniques in light of diverse research questions. In addition, culture-dependent effects on drug resistance towards commonly used drugs in the treatment of AML are summarized including several pitfalls that may arise because of culture technique artifacts. The primary aim of the current review is to provide practical guidelines for ex vivo primary AML culture experimental design.

Deciphering the role of Wnt signaling in acute myeloid leukemia prognosis: how alterations in DNA methylation come into play in patients' prognosis

Acute myeloid leukemia (AML) is a malignant clonal disorder affecting myeloid differentiation through mechanisms that include epigenetic dysregulation. Abnormal changes in DNA methylation and gene expression profiles of pathways involved in hematopoietic development, such as Wnt/β-catenin, contribute to the transformation, development, and maintenance of leukemic cells. This review summarizes the alterations of Wnt signaling-related genes at the epigenetic and transcriptional level and their implications for AML prognosis. Among the implications of epigenetic alterations in AML, methylation of Wnt antagonists is related to poor prognosis, whereas their upregulation has been associated with a better clinical outcome. Furthermore, Wnt target genes c-Myc and LEF-1 present distinct implications. LEF-1 expression positively influences the patient overall survival. c-Myc upregulation has been associated with treatment resistance in AML, although c-Myc expression is not exclusively dependent of Wnt signaling. Understanding the signaling abnormalities could help us to further understand leukemogenesis, improve the current risk stratification for AML patients, and even serve to propose novel therapeutic targets.

CDK Blockade Using AT7519 Suppresses Acute Myeloid Leukemia Cell Survival through the Inhibition of Autophagy and Intensifies the Anti-leukemic Effect of Arsenic Trioxide

The strong storyline behind the critical role of cyclin-dependent kinase (CDK) inhibitor proteins in natural defense against malignant transformation not only represents a heroic perspective for these proteins, but also provides a bright future for the application of small molecule inhibitors of CDKs in the novel cancer treatment strategies. The results of the present study revealed that the inhibition of CDKs using pan-CDK inhibitor AT7519, as revealed by the induction of G1 cell cycle arrest as well as the reduction of cyclins expression, resulted in decreased survival in acute myeloid leukemia (AML)-derived KG-1 cells, either in the context of single agent or in combination with arsenic trioxide (ATO). Apart from alterations in the expression of proliferation and apoptotic genes, the anti-survival property of AT7519 was coupled with the inhibition of autophagy-related genes. Notably, we found that the blockage of autophagy system in KG-1 cells resulted in a superior cytotoxic effect, introducing autophagy as a probable suppressor of cell death. As far as we are aware, to date, no study has reported the contributory mechanisms correlated with the less sensitivity of acute leukemia cells to AT7519 and our study suggested for the first time that the activation of both PI3K and c-Myc signaling pathways could overshadow, at least partly, the efficacy of this agent in KG-1 cells. Overall, due to the pharmacologic safety of AT7519, our study proposed this inhibitor as a promising agent for the treatment of AML either as a single agent or in a combined-modal strategy.

Novel c-Myc-Targeting Compound N, N-Bis (5-Ethyl-2-Hydroxybenzyl) Methylamine for Mediated c-Myc Ubiquitin-Proteasomal Degradation in Lung Cancer Cells

Aberrant cellular Myc (c-Myc) is a common feature in the majority of human cancers and has been linked to oncogenic malignancies. Here, we developed a novel c-Myc-targeting compound, N, N-bis (5-ethyl-2-hydroxybenzyl) methylamine (EMD), and present evidence demonstrating its effectiveness in targeting c-Myc for degradation in human lung carcinoma. EMD exhibited strong cytotoxicity toward various human lung cancer cell lines, as well as chemotherapeutic-resistant patient-derived lung cancer cells, through apoptosis induction in comparison with chemotherapeutic drugs. The IC50 of EMD against lung cancer cells was approximately 60 µM. Mechanistically, EMD eliminated c-Myc in the cells and initiated caspase-dependent apoptosis cascade. Cycloheximide chase assay revealed that EMD tended to shorten the half-life of c-Myc by approximately half. The cotreatment of EMD with the proteasome inhibitor MG132 reversed its c-Myc-targeting effect, suggesting the involvement of ubiquitin-mediated proteasomal degradation in the process. We further verified that EMD strongly induced the ubiquitination of c-Myc and promoted protein degradation. c-Myc inhibition and apoptosis induction were additionally shown in hematologic malignant K562 cells, indicating the generality of the observed EMD effects. Altogether, we identified EMD as a novel potent compound targeting oncogenic c-Myc that may offer new opportunities for lung cancer treatment. SIGNIFICANCE STATEMENT: The deregulation of c-Myc is frequently associated with cancer progression. This study examined the effect of a new compound, N, N-bis (5-ethyl-2-hydroxybenzyl) methylamine (EMD), in targeting c-Myc in several lung cancer cell lines and drug-resistant primary lung cancer cells. EMD induced dramatic c-Myc degradation through a ubiquitin-proteasomal mechanism. The promising anticancer and c-Myc-targeted activities of EMD support its use in potential new approaches to treat c-Myc-driven cancer.

A Bird's-Eye View of Cell Sources for Cell-Based Therapies in Blood Cancers

: Hematological malignancies comprise over a hundred different types of cancers and account for around 6.5% of all cancers. Despite the significant improvements in diagnosis and treatment, many of those cancers remain incurable. In recent years, cancer cell-based therapy has become a promising approach to treat those incurable hematological malignancies with striking results in different clinical trials. The most investigated, and the one that has advanced the most, is the cell-based therapy with T lymphocytes modified with chimeric antigen receptors. Those promising initial results prepared the ground to explore other cell-based therapies to treat patients with blood cancer. In this review, we want to provide an overview of the different types of cell-based therapies in blood cancer, describing them according to the cell source.

Ibrutinib Resistance Mechanisms and Treatment Strategies for B-Cell lymphomas

Chronic activation of B-cell receptor (BCR) signaling via Bruton tyrosine kinase (BTK) is largely considered to be one of the primary mechanisms driving disease progression in B-Cell lymphomas. Although the BTK-targeting agent ibrutinib has shown promising clinical responses, the presence of primary or acquired resistance is common and often leads to dismal clinical outcomes. Resistance to ibrutinib therapy can be mediated through genetic mutations, up-regulation of alternative survival pathways, or other unknown factors that are not targeted by ibrutinib therapy. Understanding the key determinants, including tumor heterogeneity and rewiring of the molecular networks during disease progression and therapy, will assist exploration of alternative therapeutic strategies. Towards the goal of overcoming ibrutinib resistance, multiple alternative therapeutic agents, including second- and third-generation BTK inhibitors and immunomodulatory drugs, have been discovered and tested in both pre-clinical and clinical settings. Although these agents have shown high response rates alone or in combination with ibrutinib in ibrutinib-treated relapsed/refractory(R/R) lymphoma patients, overall clinical outcomes have not been satisfactory due to drug-associated toxicities and incomplete remission. In this review, we discuss the mechanisms of ibrutinib resistance development in B-cell lymphoma including complexities associated with genomic alterations, non-genetic acquired resistance, cancer stem cells, and the tumor microenvironment. Furthermore, we focus our discussion on more comprehensive views of recent developments in therapeutic strategies to overcome ibrutinib resistance, including novel BTK inhibitors, clinical therapeutic agents, proteolysis-targeting chimeras and immunotherapy regimens.

Genetic biomarkers of drug resistance: A compass of prognosis and targeted therapy in acute myeloid leukemia

Acute myeloid leukemia (AML) is a highly aggressive hematological malignancy with complex heterogenous genetic and biological nature. Thus, prognostic prediction and targeted therapies might contribute to better chemotherapeutic response. However, the emergence of multidrug resistance (MDR) markedly impedes chemotherapeutic efficacy and dictates poor prognosis. Therefore, prior evaluation of chemoresistance is of great importance in therapeutic decision making and prognosis. In recent years, preclinical studies on chemoresistance have unveiled a compendium of underlying molecular basis, which facilitated the development of targetable small molecules. Furthermore, routing genomic sequencing has identified various genomic aberrations driving cellular response during the course of therapeutic treatment through adaptive mechanisms of drug resistance, some of which serve as prognostic biomarkers in risk stratification. However, the underlying mechanisms of MDR have challenged the certainty of the prognostic significance of some mutations. This review aims to provide a comprehensive understanding of the role of MDR in therapeutic decision making and prognostic prediction in AML. We present an updated genetic landscape of the predominant mechanisms of drug resistance with novel targeted therapies and potential prognostic biomarkers from preclinical and clinical chemoresistance studies in AML. We particularly highlight the unfolded protein response (UPR) that has emerged as a critical regulatory pathway in chemoresistance of AML with promising therapeutic horizon. Futhermore, we outline the most prevalent mutations associated with mechanisms of chemoresistance and delineate the future directions to improve the current prognostic tools. The molecular analysis of chemoresistance integrated with genetic profiling will facilitate decision making towards personalized prognostic prediction and enhanced therapeutic efficacy.

Myc is a prognostic biomarker and potential therapeutic target in osteosarcoma

Background

Over the past four decades, outcomes for osteosarcoma patients have plateaued as there have been few emerging therapies showing clinical results. Thus, the identification of novel biomarkers and therapeutic strategies are urgently needed to address these primary obstacles in patient care. Although the Myc-oncogene has known roles in oncogenesis and cancer cell growth, its expression and function in osteosarcoma are largely unknown.

Methods

Expression of Myc was determined by Western blotting of osteosarcoma cell lines and patient tissues, and by immunohistochemistry of a unique osteosarcoma tissue microarray (TMA) constructed from 70 patient samples with extensive follow-up data. Myc specific siRNA and inhibitor 10058-F4 were applied to examine the effect of Myc inhibition on osteosarcoma cell proliferation. The clonogenicity and migration activity was determined by clonogenic and wound-healing assays. A mimic in vivo assay, three-dimensional (3D) cell culture model, was performed to further validate the effect of Myc inhibition on osteosarcoma cell tumorigenic markers.

Results

Myc was significantly overexpressed in human osteosarcoma cell lines compared with normal human osteoblasts, and also highly expressed in fresh osteosarcoma tissues. Higher Myc expression correlated significantly with metastasis and poor prognosis. Through the addition of Myc specific siRNA and inhibitor, we significantly reduced Myc protein expression, resulting in decreased osteosarcoma cell proliferation. Inhibition of Myc also suppressed the migration, clonogenicity, and spheroid growth of osteosarcoma cells.

Conclusion

Our results support Myc as an emerging prognostic biomarker and therapeutic target in osteosarcoma therapy.

Using antagonistic pleiotropy to design a chemotherapy-induced evolutionary trap to target drug resistance in cancer

Local adaptation directs populations towards environment-specific fitness maxima through acquisition of positively selected traits. However, rapid environmental changes can identify hidden fitness trade-offs that turn adaptation into maladaptation, resulting in evolutionary traps. Cancer, a disease that is prone to drug resistance, is in principle susceptible to such traps. We therefore performed pooled CRISPR-Cas9 knockout screens in acute myeloid leukemia (AML) cells treated with various chemotherapies to map the drug-dependent genetic basis of fitness trade-offs, a concept known as antagonistic pleiotropy (AP). We identified a PRC2-NSD2/3-mediated MYC regulatory axis as a drug-induced AP pathway whose ability to confer resistance to bromodomain inhibition and sensitivity to BCL-2 inhibition templates an evolutionary trap. Across diverse AML cell-line and patient-derived xenograft models, we find that acquisition of resistance to bromodomain inhibition through this pathway exposes coincident hypersensitivity to BCL-2 inhibition. Thus, drug-induced AP can be leveraged to design evolutionary traps that selectively target drug resistance in cancer.

Acute Myeloid Leukaemia in Its Niche: the Bone Marrow Microenvironment in Acute Myeloid Leukaemia

Purpose of Review

Acute myeloid leukaemia (AML) is a heterogeneous malignancy for which treatment options remain suboptimal. It is clear that a greater understanding of the biology of the AML niche will enable new therapeutic strategies to be developed in order to improve treatment outcomes for patients.

Recent Findings

Recent evidence has highlighted the importance of the bone marrow microenvironment in protecting leukaemia cells, and in particular leukaemic stem cells from chemotherapy-induced cell death. This includes mesenchymal stem cells supporting growth and preventing apoptosis, and altered action and secretion profiles of other niche components including adipocytes, endothelial cells and T cells.

Summary

Here, we provide a detailed overview of the current understanding of the AML bone marrow microenvironment. Clinical trials of agents that mobilise leukaemic stem cells from the bone marrow are currently ongoing and show early promise. Future challenges will involve combining these novel therapies targeted at the AML niche with conventional chemotherapy treatment.

Profile of Quizartinib for the Treatment of Adult Patients with Relapsed/Refractory FLT3-ITD-Positive Acute Myeloid Leukemia: Evidence to Date

Acute myeloid leukemia (AML) is a clonal hematologic neoplasm characterized by rapid, uncontrolled cell growth of immature myeloid cells (blasts). There are numerous genetic abnormalities in AML, many of which are prognostic, but an increasing number are targets for drug therapy. One of the most common genetic abnormalities in AML are activating mutations in the FMS-like tyrosine kinase 3 receptor (FLT3). As a receptor tyrosine kinase, FLT3 was the first targetable genetic abnormality in AML. The first generation of FLT3 inhibitors were broad-spectrum kinase inhibitors that inhibited FLT3 among other proteins. Although clinically active, first-generation FLT3 inhibitors had limited success as single agents. This led to the development of a second generation of more selective FLT3 inhibitors. This review focuses on quizartinib, a potent second-generation FLT3 inhibitor. We discuss the clinical trial development, mechanisms of resistance, and the recent FDA decision to deny approval for quizartinib as a single agent in relapsed/refractory AML.

Down-regulation of RAC2 by small interfering RNA restrains the progression of osteosarcoma by suppressing the Wnt signaling pathway

Osteosarcoma (OS) is the most common primary malignancy of bone and is characterized by a high malignant and metastatic potential. Microarray-based differentially expressed gene screening determined RAC2 as the candidate gene related to OS. Highly expressed RAC2 and activated Wnt signaling pathway were determined in OS tissues using reverse transcription quantitative polymerase chain reaction (RT-qPCR) and Western blot analysis. The OS cells were transfected with siRNA-RAC2 or treated with BIO (activator of Wnt pathway), whereby the effects of siRNA-RAC2 on cell proliferation, invasion, cycle and apoptosis were analyzed by CCK-8, Transwell assay and flow cytometry. The mRNA and protein levels of RAC2 and the Wnt signaling pathway-, proliferation- and apoptosis-related genes in OS cells were determined by RT-qPCR and Western blot assay. Importantly, siRNA-mediated RAC2 silencing inhibited the activation of the Wnt signaling pathway in OS. siRNA-RAC2 inhibited the proliferation and invasion, while impeded OS cell cycle progression and facilitated cell apoptosis. However, activation of Wnt signaling pathway reversed the effects of siRNA-RAC2. Finally, orthotopic xenograft OS mouse model confirmed the in vivo anti-tumor effects by silencing RAC2. Taken together, RAC2 gene silencing could suppress OS progression. The mechanism was obtained by inhibiting the activation of the Wnt signaling pathway.

Iron and leukemia: new insights for future treatments

Iron, an indispensable element for life, is involved in all kinds of important physiological activities. Iron promotes cell growth and proliferation, but it also causes oxidative stress damage. The body has a strict regulation mechanism of iron metabolism due to its potential toxicity. As a cancer of the bone marrow and blood cells, leukemia threatens human health seriously. Current studies suggest that dysregulation of iron metabolism and subsequent accumulation of excess iron are closely associated with the occurrence and progress of leukemia. Specifically, excess iron promotes the development of leukemia due to the pro-oxidative nature of iron and its damaging effects on DNA. On the other hand, leukemia cells acquire large amounts of iron to maintain rapid growth and proliferation. Therefore, targeting iron metabolism may provide new insights for approaches to the treatment of leukemia. This review summarizes physiologic iron metabolism, alternations of iron metabolism in leukemia and therapeutic opportunities of targeting the altered iron metabolism in leukemia, with a focus on acute leukemia.

Integrating resistance functions to predict response to induction chemotherapy in de novo acute myeloid leukemia

OBJECTIVES

This study explored resistance functions and their interactions in de novo AML treated with the "7 + 3" induction regimen.

METHODS

We analyzed RNA-sequencing profiles of whole bone marrow samples from 52 de novo AML patients who completed the "7 + 3" regimen and stratified patients into CR (n = 35) and non-CR (n = 17) groups.

RESULTS

A systematic gene set analysis revealed significant associations between chemoresistance and mTOR (P < .001), myc (P < .001), mitochondrial oxidative phosphorylation (P < .001), and stemness (P = .002). These functions were independent with regard to gene contents and activity scores. An integration of these four functions showed a prediction of chemoresistance (area under the receiver operating characteristic curve = 0.815) superior to that of each function alone. Moreover, our proposed seven-gene scoring system significantly correlated with the four-function model (r = .97; P < .001) to predict chemoresistance to the "7 + 3" regimen. On multivariate analysis, a seven-gene score of ≥-0.027 (hazard ratio: 11.18; 95% confidence interval: 2.06-60.65; P = .005) was an independent risk factor for induction failure.

CONCLUSIONS

Myc, OXPHOS, mTOR, and stemness were responsive for chemoresistance in AML. Treatments other than the "7 + 3" regimen need to be considered for de novo AML patients predicted to be refractory to the "7 + 3" regimen.

Promoter methylation and expression of SOCS3 affect the clinical outcome of pediatric acute lymphoblastic leukemia by JAK/STAT pathway

Suppressor of cytokine signaling 3 (SOCS3) has been characterized as one of the most crucial negative regulator in the JAK2/STAT3 signaling pathway. However, there are few studies on the relationship between SOCS3 and pediatric acute lymphoblastic leukemia (ALL). This study analyzes the influence of SOCS3 expression on the risk and the progression of pediatric ALL and the underlying mechanism. The levels of SOCS3, p-JAK2, p-STAT3, SOCS3 methylation, CD4+CD25+CD127lowTreg were detected by PCR, laser confocal microscopy, western blot, bisulfite sequencing and flow cytometry at different progression of ALL. We found that the SOCS3 expression level at initial diagnosis (DG) of ALL patients was significantly lower than that of healthy controls (HC), while the expression of SOCS3 methylation was opposite. The expression of SOCS3 and SOCS3 methylation were returned to normal in the complete remission (CR) stage, and there were no difference between resistance, relapse and initial diagnosis. The expression of SOCS3 decreased and weakened the inhibition of pSTAT3 expression in DG, resistance and relapse groups. The levels of Treg cells in ALL children were significantly higher than those in the HC children. There was a positive correlation between the expression level of STAT3 and the expression level of Treg cells in children with ALL, while that was negatively correlated with the expression levels of Treg cells. Compared with high-level of SOCS3, the low-level of SOCS3 patients had more high risk factors, as higher WBC counts, LDH level and much more poor prognostic genes. SOCS3 methylation leads to low-expression of SOCS3, which can lead to continuous activation of JAK/STAT3 and increased expression of Treg cells, which in turn affects the anti-tumor immunological effect of the body. Taken together, our data show that monitoring the level of SOCS3 can contribute to the understanding of the state of illness and evaluate the risk of progression of ALL.

Mesenchymal stem cells in suppression or progression of hematologic malignancy: current status and challenges

Mesenchymal stem cells (MSCs) are known for being multi-potent. However, they also possess anticancer properties, which has prompted efforts to adapt MSCs for anticancer therapies. However, MSCs have also been widely implicated in pathways that contribute to tumor growth. Numerous studies have been conducted to adapt MSCs for further clinical use; however, the results have been inconclusive, possibly due to the heterogeneity of MSC populations. Moreover, the conflicting roles of MSCs in tumor inhibition and tumor growth impede their adaptation for anticancer therapies. Antitumorigenic and protumorigenic properties of MSCs in hematologic malignancies are not as well established as they are for solid malignancies, and data comparing them are still limited. Herein the effect of MSCs on hematologic malignancies, such as leukemia and lymphoma, their mechanisms, sources of MSCs, and their effects on different types of cancer, have been discussed. This review describes how MSCs preserve both antitumorigenic and protumorigenic effects, as they tend to not only inhibit tumor growth by suppressing tumor cell proliferation but also promote tumor growth by suppressing tumor cell apoptosis. Thus clinical studies trying to adapt MSCs for anticancer therapies should consider that MSCs could actually promote hematologic cancer progression. It is necessary to take extreme care while developing MSC-based cell therapies in order to boost anticancer properties while eliminating tumor-favoring effects. This review emphasizes that research on the therapeutic applications of MSCs must consider that they exert both antitumorigenic and protumorigenic effects on hematologic malignancies.

Moving Myeloid Leukemia Drug Discovery Into the Third Dimension

The development of therapies aimed at leukemia has progressed substantially in the past years but childhood acute myeloid leukemia (AML) remains one of the most challenging cancers to treat. Genomic profiling of AML has greatly enhanced our understanding of the genetic and epigenetic landscape of this high-risk leukemia. With it comes the opportunity to develop targeted therapies that are expected to be more effective and less toxic than current treatment regimens. Nevertheless, often overlooked in leukemia drug discovery are the dynamic interactions between leukemic cells and the bone marrow environment. The interplay between leukemic cells, stromal cells and the extracellular matrix plays critical roles in the development, progression and relapse of AML as well as in drug response and the development of resistance. Here we will review pediatric leukemia with a special focus on acute myeloid disease in children, and discuss the tumor microenvironment in the context of drug resistance and leukemia stem cell survival. We will emphasize how three-dimensional (3D) cell-based drug discovery may offer hope for both the identification and advancement of more effective treatment options for patients suffering from this devastating disease.

MYC protein expression is an important prognostic factor in acute myeloid leukemia

As new drugs targeting MYC show clinical activity in acute myeloid leukemia (AML), understanding MYC expression in AML is of critical importance. We assessed MYC protein expression by immunohistochemistry in bone marrow of patients with untreated AML (n = 265). Overall, 90% of patients demonstrated MYC overexpression and MYC immunopositivity ≤6% was associated with superior complete remission (CR) duration of 23 months versus 12 months for MYC immunopositivity >6% (p = .028). Among 241 patients at higher risk for relapse, including those ≥55 years of age and patients with intermediate- and high-risk AML, MYC immunopositivity ≤6% conferred significantly superior median overall survival (OS) (24 versus 13 months; p = .042), event-free survival (EFS) (14 versus 6 months; p = .048), and relapse-free survival (RFS) (25 versus 12 months; p = .024). The prognostic impact of MYC-immunopositivity was retained on multivariate analysis of OS, EFS, and RFS. We conclude that MYC immunopositivity is an important prognostic factor in patients with untreated AML, particularly those at higher risk for relapse.

PARP inhibitor re‑sensitizes Adriamycin resistant leukemia cells through DNA damage and apoptosis

Resistance to Adriamycin (ADR) is an increasing problem in the treatment of leukemia and the development of novel therapeutic strategies is becoming increasingly important. Olaparib is a poly (adenosine diphosphate-ribose) polymerase (PARP) 1 inhibitor, which has promising antitumor activity in patients with metastatic breast cancer and germline BRCA mutations. Previously published studies have indicated that Olaparib is able to overcome drug resistance in cancer; however, its underlying mechanism of action is yet to be elucidated. The aim of the present study was to explore the mechanism underlying re-sensitization. Annexin V-propidium iodide staining indicated that the percentage of apoptotic ADR resistant cells was markedly increased and the cell cycle was blocked at the G2/M-phase following treatment with ADR combined with Olaparib, when compared with the control group. The alkaline comet assay demonstrated that ADR combined with Olaparib significantly upregulated the induction of the DNA damage response in ADR-resistant cells. Western blot analysis revealed that the protein expression of γ-H2A histone family member X, cleaved PARP, caspase 3 and cleaved caspase 3 was markedly enhanced, while the cell cycle-associated protein cyclin B1 was downregulated in K562/ADR cells following treatment with a combination of ADR and Olaparib. Similar synergistic cytotoxicity was observed in blood mononuclear cells, which were isolated from patients with chemotherapy-resistant leukemia. As Olaparib is available for clinical use, the results of the present study provide a rationale for the development of Olaparib combinational therapies for cases of ADR resistant leukemia.