Endothelial cell derived angiocrine support of acute myeloid leukemia targeted by receptor tyrosine kinase inhibition

Harnessing upregulated E-selectin while enhancing SDF-1α sensing redirects infused NK cells to the AML-perturbed bone marrow

Increased bone marrow (BM) homing of NK cells is associated with positive outcome in patients with acute myeloid leukemia (AML) treated within adoptive NK cell transfer trials. While most efforts to further improve the efficacy focus on augmenting NK cell persistence and cytotoxicity, few address their ability to home to the tumor. Here, we decipher how AML growth alters the BM niche to impair NK cell infiltration and how insights can be utilized to resolve this issue. We show that AML development gradually impairs the BM homing capacity of infused NK cells, which was tightly linked to loss of SDF-1α in this environment. AML development also triggered up-regulation of E-selectin on BM endothelial cells. Given the poor E-selectin-binding capacity of NK cells, introduction of fucosyltransferase-7 (FUT7) to the NK cells per mRNA transfection resulted in potent E-selectin binding and stronger adhesion to E-selectin+ endothelial cells. Co-introduction of FUT7 and gain-of-function CXCR4 (CXCR4R334X) redirected NK cell homing to the BM of AML-bearing mice nearly to the levels in AML-free mice. This work shows how impaired NK cell homing caused by AML-induced microenvironmental changes can be overcome by genetic engineering. We speculate our insights can help further advance future NK cell immunotherapies.

Conversation before crossing: dissecting metastatic tumor-vascular interactions in microphysiological systems

Tumor metastasis via the circulation requires crossing the vascular barrier twice: first, during intravasation when tumor cells disseminate from the primary site through proximal vasculature, and second, during extravasation, when tumor cells exit the circulation to form distant metastatic seeds. During these key metastatic events, chemomechanical signaling between tumor cells and endothelial cells elicits reciprocal changes in cell morphology and behavior that are necessary to breach the vessel wall. Existing experimental systems have provided a limited understanding of the diverse mechanisms underlying tumor-endothelial interactions during intravasation and extravasation. Recent advances in microphysiological systems have revolutionized the ability to generate miniaturized human tissues with tailored three-dimensional architectures, physiological cell interfaces, and precise chemical and physical microenvironments. By doing so, microphysiological systems enable experimental access to complex morphogenic processes associated with human tumor progression with unprecedented resolution and biological control. Here, we discuss recent examples in which microphysiological systems have been leveraged to reveal new mechanistic insight into cellular and molecular control systems operating at the tumor-endothelial interface during intravasation and extravasation.

Modelling acute myeloid leukemia (AML): What's new? A transition from the classical to the modern

Acute myeloid leukemia (AML) is a heterogeneous malignancy affecting myeloid cells in the bone marrow (BM) but can spread giving rise to impaired hematopoiesis. AML incidence increases with age and is associated with poor prognostic outcomes. There has been a disconnect between the success of novel drug compounds observed in preclinical studies of hematological malignancy and less than exceptional therapeutic responses in clinical trials. This review aims to provide a state-of-the-art overview on the different preclinical models of AML available to expand insights into disease pathology and as preclinical screening tools. Deciphering the complex physiological and pathological processes and developing predictive preclinical models are key to understanding disease progression and fundamental in the development and testing of new effective drug treatments. Standard scaffold-free suspension models fail to recapitulate the complex environment where AML occurs. To this end, we review advances in scaffold/matrix-based 3D models and outline the most recent advances in on-chip technology. We also provide an overview of clinically relevant animal models and review the expanding use of patient-derived samples, which offer the prospect to create more "patient specific" screening tools either in the guise of 3D matrix models, microphysiological "organ-on-chip" tools or xenograft models and discuss representative examples.

Fundamentals of bone vasculature: Specialization, interactions and functions

Angiogenesis, hematopoiesis and osteogenesis are fundamental processes mediating complex and essential biological functions. In the bone marrow, endothelial cells (ECs) are a principal mediator of regulatory signals that govern hematopoietic and mesenchymal stem cells. EC and osteoblast interactions and niche functions of ECs are fundamental in maintaining bone health and coordinating repair and regeneration following injury. These cellular interactions are subject to dysregulation and deterioration under stress, aging, chronic disease states and malignancy. Thus, the prospect of manipulating the bone vasculature has tremendous potential to advance therapeutic interventions for the management of bone diseases. This review discusses the current state of vascular-skeletal tissue interactions focusing on osteoblast and hematopoietic stem cells interaction with ECs.

Understanding the Immune-Stroma Microenvironment in B Cell Malignancies for Effective Immunotherapy

Cancers, including lymphomas, develop in complex tissue environments where malignant cells actively promote the creation of a pro-tumoral niche that suppresses effective anti-tumor effector T cell responses. Research is revealing that the tumor microenvironment (TME) differs between different types of lymphoma, covering inflamed environments, as exemplified by Hodgkin lymphoma, to non-inflamed TMEs as seen in chronic lymphocytic leukemia (CLL) or diffuse-large B-cell lymphoma (DLBCL). In this review we consider how T cells and interferon-driven inflammatory signaling contribute to the regulation of anti-tumor immune responses, as well as sensitivity to anti-PD-1 immune checkpoint blockade immunotherapy. We discuss tumor intrinsic and extrinsic mechanisms critical to anti-tumor immune responses, as well as sensitivity to immunotherapies, before adding an additional layer of complexity within the TME: the immunoregulatory role of non-hematopoietic stromal cells that co-evolve with tumors. Studying the intricate interactions between the immune-stroma lymphoma TME should help to design next-generation immunotherapies and combination treatment strategies to overcome complex TME-driven immune suppression.

Bone Vasculature and Bone Marrow Vascular Niches in Health and Disease

Bone vasculature and bone marrow vascular niches supply oxygen, nutrients, and secrete angiocrine factors required for the survival, maintenance, and self-renewal of stem and progenitor cells. In the skeletal system, vasculature creates nurturing niches for bone and blood-forming stem cells. Blood vessels regulate hematopoiesis and drive bone formation during development, repair, and regeneration. Dysfunctional vascular niches induce skeletal aging, bone diseases, and hematological disorders. Recent cellular and molecular characterization of the bone marrow microenvironment has provided unprecedented insights into the complexity, heterogeneity, and functions of the bone vasculature and vascular niches. The bone vasculature is composed of distinct vessel subtypes that differentially regulate osteogenesis, hematopoiesis, and disease conditions in bones. Further, bone marrow vascular niches supporting stem cells are often complex microenvironments involving multiple different cell populations and vessel subtypes. This review provides an overview of the emerging vascular cell heterogeneity in bone and the new roles of the bone vasculature and associated vascular niches in health and disease. © 2020 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Endothelial cells produce angiocrine factors to regulate bone and cartilage via versatile mechanisms

Blood vessels are conduits distributed throughout the body, supporting tissue growth and homeostasis by the transport of cells, oxygen and nutrients. Endothelial cells (ECs) form the linings of the blood vessels, and together with pericytes, are essential for organ development and tissue homeostasis through producing paracrine signalling molecules, called angiocrine factors. In the skeletal system, ECs - derived angiocrine factors, combined with bone cells-released angiogenic factors, orchestrate intercellular crosstalk of the bone microenvironment, and the coupling of angiogenesis-to-osteogenesis. Whilst the involvement of angiogenic factors and the blood vessels of the skeleton is relatively well established, the impact of ECs -derived angiocrine factors on bone and cartilage homeostasis is gradually emerging. In this review, we survey ECs - derived angiocrine factors, which are released by endothelial cells of the local microenvironment and by distal organs, and act specifically as regulators of skeletal growth and homeostasis. These may potentially include angiocrine factors with osteogenic property, such as Hedgehog, Notch, WNT, bone morphogenetic protein (BMP), fibroblast growth factor (FGF), insulin-like growth factor (IGF), and platelet-derived growth factor (PDGF). Understanding the versatile mechanisms by which ECs-derived angiocrine factors orchestrate bone and cartilage homeostasis, and pathogenesis, is an important step towards the development of therapeutic potential for skeletal diseases.

7‑Difluoromethyl‑5,4'‑dimethoxygenistein exerts anti‑angiogenic effects on acute promyelocytic leukemia HL‑60 cells by inhibiting the TLR4/NF‑κB signaling pathway

Angiogenesis plays an important role in the development and metastasis of tumors, and anti-angiogenesis agents are used to treat tumors. For example, the acute promyelocytic leukemia (APL) may be treated with arsenic trioxide. Angiogenesis in APL is a multi-step dynamic equilibrium process coordinated by various angiogenic stimulators and inhibitors, which play key roles in the occurrence, progression and chemosensitivity of this disease. Our research group previously synthesized 7-difluoromethyl-5,4′-dimethoxygenistein (DFMG), and found that it inhibits angiogenesis during atherosclerotic plaque formation. In the present study, the effect and mechanism of DFMG in angiogenesis induced by APL HL-60 cells was investigated using a chick embryo chorioallantoic membrane model and Matrigel tubule formation assays. The results obtained revealed an anti-angiogenesis effect of DFMG towards HL-60 cells. When the Toll-like receptor 4/nuclear factor-κB (TLR4/NF-κB) signaling pathway was inhibited, the anti-angiogenic effect of DFMG was further enhanced. However, when the TLR4/NF-κB signaling pathway was activated, the anti-angiogenic effect of DFMG was attenuated. These results demonstrated that DFMG inhibits angiogenesis induced by APL HL-60 cells, and provides insights into the mechanism by which DFMG inhibits the TLR4/NF-κB signaling pathway. In conclusion, in the present study, the anti-angiogenesis effect of DFMG on APL has been reported, and the mechanism by which DFMG induced the anti-angiogenesis effect was explored. These findings have provided a potential new drug candidate for the treatment of patients with APL.

A Phase 1B Clinical Study of Combretastatin A1 Diphosphate (OXi4503) and Cytarabine (ARA-C) in Combination (OXA) for Patients with Relapsed or Refractory Acute Myeloid Leukemia

Combretastatin A1 (OXi4503) is a dual-function drug with vascular disrupting and cytotoxic properties that has exhibited single-agent anti-leukemia activity in murine xenograft models of acute myeloid leukemia (AML) and in a prior Phase 1A clinical study for relapsed/refractory (R/R) AML. The purpose of the present multicenter Phase 1B study was to define the maximum tolerated dose (MTD) and safety profile of OXi4503 and cytarabine (ARA-C) administered in combination (OXA). At four centers, 29 patients with R/R AML or myelodysplastic syndrome (MDS) were treated with OXA. The most common grade 3/4 treatment-emergent adverse events (AEs) were febrile neutropenia (28%), hypertension (17%), thrombocytopenia (17%), and anemia (14%). There were no treatment-emergent grade 5 AEs. Drug-related serious adverse events (SAEs) developed in 4/29 patients (14%) and included febrile neutropenia (N = 2), pneumonia/acute respiratory failure (N = 1), and hypotension (N = 1). 9.76 mg/m² was defined as the MTD of OXi4503 when administered in combination with 1 g/m² ARA-C. In 26 evaluable AML patients, there were 2 complete remissions (CR), 2 complete remissions with incomplete count recovery (CRi) and one partial response (PR), for an overall response rate (ORR) of 19%. The median overall survival (OS) time for the four patients who achieved a CR/CRi was 528 days (95% CI: 434-NA), which was significantly longer than the median OS time of 113 days (95% CI: 77-172) for the remaining 22 patients who did not achieve a CR/CRi (Log Rank Chi Square = 11.8, p-value = 0.0006). The safety and early evidence of efficacy of the OXA regimen in R/R AML patients warrant further investigation in a Phase 2 clinical study.

The phenotype of vascular smooth muscle cells co-cultured with endothelial cells is modulated by PDGFR-β/IQGAP1 signaling in LPS-induced intravascular injury

Background Sepsis, a leading cause of death in intensive care units, is generally associated with vascular dysfunction. However, its pathophysiological process has not been fully clarified, lacking in-depth knowledge of its pathophysiological process may hinder the improvement of diagnosis and therapy for sepsis. Hence, as the key parts of the vascular wall, the interaction between endothelial cells (ECs) and smooth muscle cells (SMCs) under septic situation need to be further studied. Methods ECs and SMCs were co-cultured using Transwell plates. Lipopolysaccharide (LPS) was used to induce sepsis. A scratch-wound assay was used to assess cell migration, and western blotting was used to assess the level of redifferentiation of SMCs as well as the expression of PDGFR-β and IQGAP1. Results Co-culture with ECs reduced the redifferentiation of SMCs induced by LPS (10 μg/ml), which was characterized by increased migration ability and decreased expression of contractile proteins (e.g., SM22 and α-SMA). The production of TNF-α could decrease the level of PDGFR-β in SMCs. Treatment of SMCs with the PDGFR-β inhibitor imatinib (5 μM) was able to counteract LPS-induced SMC redifferentiation and reduce IQGAP1 protein expression, especially when SMCs were co-cultured with ECs. Conclusion The phenotype of vascular SMCs co-cultured with ECs was modulated by IQGAP1 through the PDGFR-β pathway, which may lead to vascular remodeling and homeostasis in LPS-induced intravascular injury. This pathway could be a novel target for the treatment of vascular damage.

Roles of the bone marrow niche in hematopoiesis, leukemogenesis, and chemotherapy resistance in acute myeloid leukemia

OBJECTIVES

To summarize the effects of the bone marrow niche on hematopoiesis and leukemogenesis and discuss the chemotherapy resistance that can arise from interactions between the niche and leukemia stem cells.

METHODS

We review the major roles of the bone marrow niche in cell proliferation, adhesion and drug resistance. The signaling pathways and major molecular participants in the niche are discussed. We also address potential niche-targeting strategies for the treatment of acute myeloid leukemia (AML).

RESULTS

The bone marrow niche supports normal hematopoiesis and affects acute myeloid leukemia (AML) initiation, progression and chemotherapy resistance.

DISCUSSION

AML is a group of heterogeneous malignant diseases characterized by the excessive proliferation of hematopoietic stem and/or progenitor cells. Even with intensive chemotherapy regimens and stem cell transplantation, the overall survival rate for AML is poor. The bone marrow niches of malignant cells are remodeled into a leukemia-permissive environment, and these reformed niches protect AML cells from chemotherapy-induced cell death. Inhibiting the cellular and molecular interactions between the niche and leukemia cells is a promising direction for targeted therapies for AML treatment.

CONCLUSIONS

Interactions between leukemia cells and the bone marrow niche influence hematopoiesis, leukemogenesis, and chemotherapy resistance in AML and require ongoing study. Understanding the mechanisms that underlie these interactions will help identify rational niche-targeting therapies to improve treatment outcomes in AML patients.

Targeting tumour microenvironment by tyrosine kinase inhibitor

Tumour microenvironment (TME) is a key determinant of tumour growth and metastasis. TME could be very different for each type and location of tumour and TME may change constantly during tumour growth. Multiple counterparts in surrounding microenvironment including mesenchymal-, hematopoietic-originated cells as well as non-cellular components affect TME. Thus, therapeutics that can disrupt the tumour-favouring microenvironment should be further explored for cancer therapy. Previous efforts in unravelling the dysregulated mechanisms of TME components has identified numerous protein tyrosine kinases, while its corresponding inhibitors have demonstrated potent modulatory effect on TME. Recent works have demonstrated that beyond the direct action on cancer cells, tyrosine kinase inhibitors (TKIs) have been implicated in inactivation or normalization of dysregulated TME components leading to cancer regression. Either through re-sensitizing the tumour cells or reversing the immunological tolerance microenvironment, the emergence of these TME modulatory mechanism of TKIs supports the combinatory use of TKIs with current chemotherapy or immunotherapy for cancer therapy. Therefore, an appropriate understanding on TME modulation by TKIs may offer another mode of action of TKIs for cancer treatment. This review highlights mode of kinase activation or paracrine ligand production from TME components and summarises the findings on the potential use of various TKIs on regulating TME components. At last, the combination use of current TKIs with immunotherapy in the perspectives of efficacy and safety are discussed.

Antileukemic effects of midostaurin in acute myeloid leukemia - the possible importance of multikinase inhibition in leukemic as well as nonleukemic stromal cells

INTRODUCTION

Midostaurin is a multikinase inhibitor that inhibits receptor tyrosine kinases (Flt3, CD117/c-kit, platelet-derived growth factor receptor, vascular endothelial growth factor receptor 2) as well as non-receptor tyrosine kinases (Frg, Src, Syk, Protein kinase C). Combination of midostaurin with conventional intensive chemotherapy followed by one year maintenance monotherapy was recently reported to improve the survival of acute myeloid leukemia (AML) patients with Flt3 mutations. Areas covered: Relevant publications were identified through literature searches in the PubMed database. We searched for (i) original articles describing the results from clinical studies; (ii) published articles describing the importance of midostaurin-inhibited kinases for leukemogenesis and chemosensitivity. Expert opinion: Midostaurin monotherapy is well tolerated, combined with conventional chemotherapy gastrointestinal toxicity increases significantly. Midostaurin alters anthracycline pharmacokinetics. Furthermore, its antileukemic effects may not only be mediated through Flt3 inhibition alone; the inhibition of other kinases may also be important for the overall antileukemic effect. Midostaurin may then have direct effects on the leukemic cells but also indirect antileukemic effects through inhibition of the AML-supporting effects of neighboring stromal cells in the bone marrow microenvironment. Midostaurin may thus be used in combination with intensive chemotherapy, as maintenance treatment or as disease-stabilizing treatment for elderly unfit patients.

Myeloid malignancies and the microenvironment

Research in the last few years has revealed a sophisticated interaction network between multiple bone marrow cells that regulate different hematopoietic stem cell (HSC) properties such as proliferation, differentiation, localization, and self-renewal during homeostasis. These mechanisms are essential to keep the physiological HSC numbers in check and interfere with malignant progression. In addition to the identification of multiple mutations and chromosomal aberrations driving the progression of myeloid malignancies, alterations in the niche compartment recently gained attention for contributing to disease progression. Leukemic cells can remodel the niche into a permissive environment favoring leukemic stem cell expansion over normal HSC maintenance, and evidence is accumulating that certain niche alterations can even induce leukemic transformation. Relapse after chemotherapy is still a major challenge during treatment of myeloid malignancies, and cure is only rarely achieved. Recent progress in understanding the niche-imposed chemoresistance mechanisms will likely contribute to the improvement of current therapeutic strategies. This article discusses the role of different niche cells and their stage- and disease-specific roles during progression of myeloid malignancies and in response to chemotherapy.

Bone Marrow Blood Vessels: Normal and Neoplastic Niche

Blood vessels are among the most important factors in the transport of materials such as nutrients and oxygen. This study will review the role of blood vessels in normal bone marrow hematopoiesis as well as pathological conditions like leukemia and metastasis. Relevant literature was identified by a Pubmed search (1992-2016) of English-language papers using the terms bone marrow, leukemia, metastasis, and vessel. Given that blood vessels are conduits for the transfer of nutrients, they create a favorable situation for cancer cells and cause their growth and development. On the other hand, blood vessels protect leukemia cells against chemotherapy drugs. Finally, it may be concluded that the vessels are an important factor in the development of malignant diseases.

Mesenchymal Stem and Progenitor Cells in Normal and Dysplastic Hematopoiesis-Masters of Survival and Clonality?

Myelodysplastic syndromes (MDS) are malignant hematopoietic stem cell disorders that have the capacity to progress to acute myeloid leukemia (AML). Accumulating evidence suggests that the altered bone marrow (BM) microenvironment in general, and in particular the components of the stem cell niche, including mesenchymal stem cells (MSCs) and their progeny, play a pivotal role in the evolution and propagation of MDS. We here present an overview of the role of MSCs in the pathogenesis of MDS, with emphasis on cellular interactions in the BM microenvironment and related stem cell niche concepts. MSCs have potent immunomodulatory capacities and communicate with diverse immune cells, but also interact with various other cellular components of the microenvironment as well as with normal and leukemic stem and progenitor cells. Moreover, compared to normal MSCs, MSCs in MDS and AML often exhibit altered gene expression profiles, an aberrant phenotype, and abnormal functional properties. These alterations supposedly contribute to the “reprogramming” of the stem cell niche into a disease-permissive microenvironment where an altered immune system, abnormal stem cell niche interactions, and an impaired growth control lead to disease progression. The current article also reviews molecular targets that play a role in such cellular interactions and possibilities to interfere with abnormal stem cell niche interactions by using specific targeted drugs.

XBP1 splicing triggers miR-150 transfer from smooth muscle cells to endothelial cells via extracellular vesicles

The interaction between endothelial cells (ECs) and smooth muscle cells (SMCs) plays a critical role in the maintenance of vessel wall homeostasis. The X-box binding protein 1 (XBP1) plays an important role in EC and SMC cellular functions. However, whether XBP1 is involved in EC-SMC interaction remains unclear. In this study, In vivo experiments with hindlimb ischemia models revealed that XBP1 deficiency in SMCs significantly attenuated angiogenesis in ischemic tissues, therefore retarded the foot blood perfusion recovery. In vitro studies indicated that either overexpression of the spliced XBP1 or treatment with platelet derived growth factor-BB up-regulated miR-150 expression and secretion via extracellular vesicles (EVs). The XBP1 splicing-mediated up-regulation of miR-150 might be due to increased stability. The SMC-derived EVs could trigger EC migration, which was abolished by miR-150 knockdown in SMCs, suggesting miR-150 is responsible for SMC-stimulated EC migration. The SMC-derived miR-150-containing EVs or premiR-150 transfection increased vascular endothelial growth factor (VEGF)-A mRNA and secretion in ECs. Both inhibitors SU5416 and LY294002 attenuated EVs-induced EC migration. This study demonstrates that XBP1 splicing in SMCs can control EC migration via SMC derived EVs-mediated miR-150 transfer and miR-150-driven VEGF-A/VEGFR/PI3K/Akt pathway activation, thereby modulating the maintenance of vessel wall homeostasis.