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

Antiproliferative and Pro-Apoptotic Activity and Tubulin Dynamics Modulation of 1H-Benzimidazol-2-yl Hydrazones in Human Breast Cancer Cell Line MDA-MB-231

(1) Background: The aim of the work is the evaluation of in vitro antiproliferative and pro-apoptotic activity of four benzimidazole derivatives containing colchicine-like and catechol-like moieties with methyl group substitution in the benzimidazole ring against highly invasive breast cancer cell line MDA-MB-231 and their related impairment of tubulin dynamics. (2) Methods: The antiproliferative activity was assessed with the MTT assay. Alterations in tubulin polymerization were evaluated with an in vitro tubulin polymerization assay and a docking analysis. (3) Results: All derivatives showed time-dependent cytotoxicity with IC50 varying from 40 to 60 μM after 48 h and between 13 and 20 μM after 72 h. Immunofluorescent and DAPI staining revealed the pro-apoptotic potential of benzimidazole derivatives and their effect on tubulin dynamics in living cells. Compound 5d prevented tubulin aggregation and blocked mitosis, highlighting the importance of the methyl group and the colchicine-like fragment. (4) Conclusions: The benzimidazole derivatives demonstrated moderate cytotoxicity towards MDA-MB-231 by retarding the initial phase of tubulin polymerization. The derivative 5d containing a colchicine-like moiety and methyl group substitution in the benzimidazole ring showed potential as an antiproliferative agent and microtubule destabilizer by facilitating faster microtubule aggregation and disrupting cellular and nuclear integrity.

An update on the development on tubulin inhibitors for the treatment of solid tumors

INTRODUCTION

Microtubules play a vital role in cancer therapeutics. They are implicated in tumorigenesis, thus inhibiting tubulin polymerization in cancer cells, and have now become a significant target for anticancer drug development. A plethora of drug molecules has been crafted to influence microtubule dynamics and presently, numerous tubulin inhibitors are being investigated. This review discusses the recently developed inhibitors including natural products, and also examines the preclinical and clinical data of some potential molecules.

AREA COVERED

The current review article summarizes the development of tubulin inhibitors while detailing their specific binding sites. It also discusses the newly designed inhibitors that may be useful in the treatment of solid tumors.

EXPERT OPINION

Microtubules play a crucial role in cellular processes, especially in cancer therapy where inhibiting tubulin polymerization holds promise. Ongoing trials signify a commitment to revolutionizing cancer treatment and exploring targeted therapies. Challenges in microtubule modulation, like resistance and off-target effects, demand focused efforts, emphasizing combination therapies and personalized treatments. Beyond microtubules, promising avenues in cancer research include immunotherapy, genomic medicine, CRISPR gene editing, liquid biopsies, AI diagnostics, and stem cell therapy, showcasing a holistic approach for future advancements.

Discovery, synthesis, activities, structure-activity relationships, and clinical development of combretastatins and analogs as anticancer drugs. A comprehensive review

Covering: 1982 to up to the end of 2022Bioassay guided purification of the extracts of Combretum caffrum led to the discovery of six series of combretastatins A-D with cytotoxic activities ranging from sub nM to >50 μM ED50's against a wide variety of cancer cell lines. Of these, cis-stilbenes combretastatins A-4 and A-1 were the most potent, exhibiting in vivo efficacy against a wide variety of tumor types in murine models. These antimitotic agents inhibited tubulin polymerization by reversibly binding to the colchicine binding sites. They inhibited tumor growth by a novel antivascular and antineogenesis mechanism in which they stopped blood flows to the blood vessels causing necrosis. Over 20 clinical trials of the phosphate prodrugs of combretastatin A-4 (CA4P) and A-1 (CA1P) showed objective and stable responses against many tumor types, with increased survival times of many patients along with the confirmed cure of certain patients inflicted with anaplastic thyroid cancers. Medicinal chemistry efforts led to the identification of three new leads (AVE8062, BNC105P, SCB01A) with improved in vitro and in vivo potency and an often-improved cellular spectrum. Unfortunately, these preclinical improvements did not translate clinically in any meaningful way. Objectively, CA4P remained the best compound and has garnered many Orphan drug designations by FDA. Clinical trials with tumor genetic mapping, particularly from previous responders, may help boost the success of these compounds in future studies. A comprehensive review of combretastatin series A-D, including bioassay guided discovery, total syntheses, and structure-activity relationship (SAR) studies, biological and mechanistic studies, and preclinical and clinical evaluations of the isolated combretastatins and analogs, along with the personal perspective of the author who originated this project, is presented.

Natural-Product-Inspired Discovery of Trimethoxyphenyl-1,2,4-triazolosulfonamides as Potent Tubulin Polymerization Inhibitors

An approach of natural product-inspired strategy and incorporation of an NP-privileged motif has been investigated for the discovery of new tubulin polymerization inhibitors. Two series, N-Arylsulfonyl-3-arylamino-5-amino-1,2,4-triazole derivatives, and their isomers were considered. The compounds were synthesized by construction of the N-aryl-1,2,4-triazole-3,5-diamine motif and sulfonylation. Although the chemo- and regioselectivity in sulfonylation were challenging due to multiple ring-tautomerizable-NH and exocyclic NH2 functionalities present in the molecular motifs, the developed synthetic method enabled the preparation of designed molecular skeletons with biologically important motifs. The approach also led to explore interesting molecular regio- and stereochemical aspects valuable for activity. The X-ray crystallography study indicated that the hydrogen bonding between the arylamine-NH and the arylsulfonyl-"O" unit and appropriate molecular-functionality topology allowed the cis-locking of two aryls, which is important for tubulin-binding and antiproliferative properties. All synthesized compounds majorly showed characteristic antiproliferative effects in breast cancer cells (MCF-7), and four compounds exhibited potent antiproliferative activity. One compound potently bound to tubulin at the colchicine site and inhibited tubulin polymerization in vitro. The compound significantly depolymerized microtubules in MCF-7 cells, arrested the cells at the G2/M phase, and induced cell death. This study represents the importance of the design strategy in medicinal chemistry and the molecular structural features relevant to anticancer anti-tubulin properties. The explored molecules have the potential for further development.

Phytochemicals and bioactive compounds effective against acute myeloid leukemia: A systematic review

This systematic review identified various bioactive compounds which have the potential to serve as novel drugs or leads against acute myeloid leukemia. Acute myeloid leukemia (AML) is a heterogeneous hematopoietic malignancy that arises from the dysregulation of cell differentiation, proliferation, and cell death. The risk factors associated with the onset of AML include long-term exposure to radiation and chemicals such as benzene, smoking, genetic disorders, blood disorders, advancement in age, and others. Although novel strategies to manage AML, including a refinement of the conventional chemotherapy regimens, hypomethylating agents, and molecular targeted drugs, have been developed in recent years, resistance and relapse remain the main clinical problems. In this study, three databases, PubMed/MEDLINE, ScienceDirect, and Google Scholar, were systematically searched to identify various bioactive compounds with antileukemic properties. A total of 518 articles were identified, out of which 59 were viewed as eligible for the current report. From the data extracted, over 60 bioactive compounds were identified and divided into five major groups: flavonoids, alkaloids, organosulfur compounds, terpenes, and terpenoids, and other known and emerging bioactive compounds. The mechanism of actions of the analyzed individual bioactive molecules differs remarkably and includes disrupting chromatin structure, upregulating the synthesis of certain DNA repair proteins, inducing cell cycle arrest and apoptosis, and inhibiting/regulating Hsp90 activities, DNA methyltransferase 1, and histone deacetylase 1.

Discovery of a novel Coumarin-Dihydroquinoxalone derivative MY-673 as a tubulin polymerization inhibitor capable of inhibiting the ERK pathway with potent anti-gastric cancer activities

As a class of microtubule targeting agents, colchicine binding site inhibitors (CBSIs) are considered as promising drug candidates for cancer therapy. However, due to adverse reactions, there are currently no CBSIs approved by FDA for cancer treatment. Therefore, extensive efforts are still encouraged to find novel CBSIs with different chemical structures and better anticancer efficacies. In this work, we designed and synthesized a new coumarin-dihydroquinoxalone derivative, MY-673, and evaluated its anticancer potency in vitro and in vivo. We confirmed that MY-673 was a potent CBSI that it not only inhibited tubulin polymerization, but also exhibited significant inhibitory potency on the growth of 13 cancer cells with IC₅₀ values from 11.7 nM to 395.9 nM. Based on the results of kinase panel screening, MY-673 could inhibit ERK (extracellular regulated protein kinases) pathways-related kinases. We further confirmed that MY-673 could inhibit ERK signaling pathway in MGC-803 and HGC-27 cells, and then affected the expression level of SMAD4 protein in TGF-β (transforming growth factor β) /SMAD (small mother against decapentaplegic) signaling pathway using the western blotting assay. In addition, compound MY-673 could effectively inhibit cell proliferation, migration and induce cell apoptosis. We also further confirmed the in vivo efficacy of MY-673 in inhibiting tumor growth using the MGC-803 xenograft tumor model. At 20 mg/kg, the TGI rate was 85.9%, and it did not cause obvious toxicity to the main organs of mice. Together, the results we report here indicated that MY-673 was a promising CBSI for cancer treatment, which was capable of inhibiting the ERK pathway with potent antiproliferative activities in vitro and in vivo.

Breaking the niche: multidimensional nanotherapeutics for tumor microenvironment modulation

Most of the current antitumor therapeutics were developed targeting the cancer cells only. Unfortunately, in the majority of tumors, this single-dimensional therapy is found to be ineffective. Advanced research has shown that cancer is a multicellular disorder. The tumor microenvironment (TME), which is made by a complex network of the bulk tumor cells and other supporting cells, plays a crucial role in tumor progression. Understanding the importance of the TME in tumor growth, different treatment modalities have been developed targeting these supporting cells. Recent clinical results suggest that simultaneously targeting multiple components of the tumor ecosystem with drug combinations can be highly effective. This type of "multidimensional" therapy has a high potential for cancer treatment. However, tumor-specific delivery of such multi-drug combinations remains a challenge. Nanomedicine could be utilized for the tumor-targeted delivery of such multidimensional therapeutics. In this review, we first give a brief overview of the major components of TME. We then highlight the latest developments in nanoparticle-based combination therapies, where one drug targets cancer cells and other drug targets tumor-supporting components in the TME for a synergistic effect. We include the latest preclinical and clinical studies and discuss innovative nanoparticle-mediated targeting strategies.

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.

Polyphenols: Chemoprevention and therapeutic potentials in hematological malignancies

Polyphenols are one of the largest plant-derived natural product and they play an important role in plants' defense as well as in human health and disease. A number of them are pleiotropic molecules and have been shown to regulate signaling pathways, immune response and cell growth and proliferation which all play a role in cancer development. Hematological malignancies on the other hand, are cancers of the blood. While current therapies are efficacious, they are usually expensive and with unwanted side effects. Thus, the search for newer less toxic agents. Polyphenols have been reported to possess antineoplastic properties which include cell cycle arrest, and apoptosis via multiple mechanisms. They also have immunomodulatory activities where they enhance T cell activation and suppress regulatory T cells. They carry out these actions through such pathways as PI3K/Akt/mTOR and the kynurenine. They can also reverse cancer resistance to chemotherapy agents. In this review, i look at some of the molecular mechanism of action of polyphenols and their potential roles as therapeutic agents in hematological malignancies. Here i discuss their anti-proliferative and anti-neoplastic activities especially their abilities modulate signaling pathways as well as immune response in hematological malignancies. I also looked at clinical studies done mainly in the last 10-15 years on various polyphenol combination and how they enhance synergism. I recommend that further preclinical and clinical studies be carried out to ensure safety and efficacy before polyphenol therapies be officially moved to the clinics.

Demonstrating Tumor Vascular Disrupting Activity of the Small-Molecule Dihydronaphthalene Tubulin-Binding Agent OXi6196 as a Potential Therapeutic for Cancer Treatment

The vascular disrupting activity of a promising tubulin-binding agent (OXi6196) was demonstrated in mice in MDA-MB-231 human breast tumor xenografts growing orthotopically in mammary fat pad and syngeneic RENCA kidney tumors growing orthotopically in the kidney. To enhance water solubility, OXi6196, was derivatized as its corresponding phosphate prodrug salt OXi6197, facilitating effective delivery. OXi6197 is stable in water, but rapidly releases OXi6196 in the presence of alkaline phosphatase. At low nanomolar concentrations OXi6196 caused G2/M cell cycle arrest and apoptosis in MDA-MB-231 breast cancer cells and monolayers of rapidly growing HUVECs underwent concentration-dependent changes in their morphology. Loss of the microtubule structure and increased bundling of filamentous actin into stress fibers followed by cell collapse, rounding and blebbing was observed. OXi6196 (100 nM) disrupted capillary-like endothelial networks pre-established with HUVECs on Matrigel®. When prodrug OXi6197 was administered to mice bearing orthotopic MDA-MB-231-luc tumors, dynamic bioluminescence imaging (BLI) revealed dose-dependent vascular shutdown with >80% signal loss within 2 h at doses ≥30 mg/kg and >90% shutdown after 6 h for doses ≥35 mg/kg, which remained depressed by at least 70% after 24 h. Twice weekly treatment with prodrug OXi6197 (20 mg/kg) caused a significant tumor growth delay, but no overall survival benefit. Similar efficacy was observed for the first time in orthotopic RENCA-luc tumors, which showed massive hemorrhage and necrosis after 24 h. Twice weekly dosing with prodrug OXi6197 (35 mg/kg) caused tumor growth delay in most orthotopic RENCA tumors. Immunohistochemistry revealed extensive necrosis, though with surviving peripheral tissues. These results demonstrate effective vascular disruption at doses comparable to the most effective vascular-disrupting agents (VDAs) suggesting opportunities for further development.

Styryl Group, a Friend or Foe in Medicinal Chemistry

The styryl (Ph-CH=CH-R) group is widely represented in medicinally important compounds, including drugs, clinical candidates, and molecular probes as it positively impacts the lipophilicity, oral absorption, and biological activity. The analysis of matched molecular pairs (styryl vs. phenethyl, phenyl, methyl, H) for the biological activity indicates the superiority aspect of styryl compounds. However, the Michael acceptor site in the styryl group makes it amenable to the nucleophilic attack by biological nucleophiles and transformation to the toxic metabolites. One of the downsides of styryl compounds is isomerization that impacts the molecular conformation and directly affects biological activity. The impact of cis-trans isomerism and isosteric replacements on biological activity is exemplified. We also discuss the styryl group-bearing drugs, clinical candidates, and fluorescent probes. Overall, the present review reveals the utility of the styryl group in medicinal chemistry and drug discovery.

Angiogenesis and anti-leukaemia activity of novel indole derivatives as potent colchicine binding site inhibitors

The screened compound DYT-1 from our in-house library was taken as a lead (inhibiting tubulin polymerisation: IC₅₀=25.6 µM, anti-angiogenesis in Zebrafish: IC₅₀=38.4 µM, anti-proliferation against K562 and Jurkat: IC₅₀=6.2 and 7.9 µM, respectively). Further investigation of medicinal chemistry conditions yielded compound 29e (inhibiting tubulin polymerisation: IC₅₀=4.8 µM and anti-angiogenesis in Zebrafish: IC₅₀=3.6 µM) based on tubulin and zebrafish assays, which displayed noteworthily nanomolar potency against a variety of leukaemia cell lines (IC₅₀= 0.09–1.22 µM), especially K562 cells where apoptosis was induced. Molecular docking, molecular dynamics (MD) simulation, radioligand binding assay and cellular microtubule networks disruption results showed that 29e stably binds to the tubulin colchicine site. 29e significantly inhibited HUVEC tube formation, migration and invasion in vitro. Anti-angiogenesis in vivo was confirmed by zebrafish xenograft. 29e also prominently blocked K562 cell proliferation and metastasis in blood vessels and surrounding tissues of the zebrafish xenograft model. Together with promising physicochemical property and metabolic stability, 29e could be considered an effective anti-angiogenesis and -leukaemia drug candidate that binds to the tubulin colchicine site.

Post-hoc Analysis of Pharmacodynamics and Single-Agent Activity of CD3xCD123 Bispecific Antibody APVO436 in Relapsed/Refractory AML and MDS Resistant to HMA or Venetoclax Plus HMA

APVO436 is a recombinant bispecific antibody designed to direct host cytotoxic T-cells to CD123-expressing blast cells in patients with hematologic malignancies. APVO436 showed promising tolerability and single-agent activity in relapsed or refractory (R/R) acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS). The primary purpose of this post-hoc analysis was to evaluate the therapeutic and pharmacodynamic effects of APVO436 in 14 R/R AML/MDS patients who had failed treatment with hypomethylating agents (HMA) or venetoclax plus HMA prior to being enrolled in the APVO436 Phase 1 dose-escalation study that was recently completed. Eight of these 14 patients had R/R AML and had failed treatment with HMA (N=2) or venetoclax plus HMA (N=6). The remaining 6 patients had R/R MDS and had also failed treatment with HMA (N=5) or venetoclax plus HMA (N=1). They were treated with APVO436 at submicrogram dose levels >0.08 mcg/kg that were active in preclinical NOD/SCID mouse xenograft models of AML. APVO436 activated patients' T-cells as evidenced by reduced numbers of circulating CD123⁺CD34⁺ and CD33⁺CD34⁺ peripheral blasts. Single-agent activity was observed at dose levels ranging from 0.1 mcg/kg to 0.7 mcg/kg in 4 R/R AML patients (50%), including 3 patients with prolonged stable disease (SD) and one patient with complete remission (CR). Likewise, 3 MDS patients had SD (50%) and 3 additional MDS patients (50%) had a marrow CR at dose levels ranging from 0.1 mcg/kg to 0.8 mcg/kg. The median survival for the combined group of 14 R/R AML/MDS patients was 282 days. This early evidence of single-agent activity of APVO436 in R/R AML/MDS patients who failed HMA with or without venetoclax provides proof of concept supporting its in vivo immunomodulatory and anti-leukemic activity and warrants further investigation of its clinical impact potential.

A Clinical Phase 1B Study of the CD3xCD123 Bispecific Antibody APVO436 in Patients with Relapsed/Refractory Acute Myeloid Leukemia or Myelodysplastic Syndrome

APVO436 is a recombinant T cell-engaging humanized bispecific antibody designed to redirect host T cell cytotoxicity in an MHC-independent manner to CD123-expressing blast cells from patients with hematologic malignancies and has exhibited single-agent anti-leukemia activity in murine xenograft models of acute myeloid leukemia (AML). In this first-in-human (FIH) multicenter phase 1B study, we sought to determine the safety and tolerability of APVO436 in R/R AML/myelodysplastic syndrome (MDS) patients and identify a clinically active recommended phase 2 dose (RP2D) level for its further clinical development. A total of 46 R/R AML/MDS patients who had failed 1-8 prior lines of therapy received APVO436 as weekly intravenous (IV) infusions at 10 different dose levels, ranging from a Minimum Anticipated Biological Effect Level (MABEL) of 0.3 mcg to 60 mcg. APVO436 exhibited a favorable safety profile with acceptable tolerability and manageable drug-related adverse events (AEs), and its maximum tolerated dose (MTD) was not reached at a weekly dose of 60 mcg. The most common APVO436-related AEs were infusion-related reactions (IRR) occurring in 13 (28.3%) patients and cytokine release syndrome (CRS) occurring in 10 (21.7%). The single dose RP2D level was identified as 0.2 mcg/kg. Preliminary efficacy signals were observed in both AML and MDS patients: Prolonged stable disease (SD), partial remissions (PR), and complete remissions (CR) were observed in R/R AML patients as best overall responses to APVO436 at the RP2D level. Three of six evaluable MDS patients had marrow CRs. The safety and preliminary evidence of efficacy of APVO436 in R/R AML and MDS patients warrant further investigation of its clinical impact potential.

Leukemia stem cell-bone marrow microenvironment interplay in acute myeloid leukemia development

Despite the advances in intensive chemotherapy regimens and targeted therapies, overall survival (OS) of acute myeloid leukemia (AML) remains unfavorable due to inevitable chemotherapy resistance and high relapse rate, which mainly caused by the persistence existence of leukemia stem cells (LSCs). Bone marrow microenvironment (BMM), the home of hematopoiesis, has been considered to play a crucial role in both hematopoiesis and leukemogenesis. When interrupted by the AML cells, a malignant BMM formed and thus provided a refuge for LSCs and protecting them from the cytotoxic effects of chemotherapy. In this review, we summarized the alterations in the bidirectional interplay between hematopoietic cells and BMM in the normal/AML hematopoietic environment, and pointed out the key role of these alterations in pathogenesis and chemotherapy resistance of AML. Finally, we focused on the current potential BMM-targeted strategies together with future prospects and challenges. Accordingly, while further research is necessary to elucidate the underlying mechanisms behind LSC–BMM interaction, targeting the interaction is perceived as a potential therapeutic strategy to eradicate LSCs and ultimately improve the outcome of AML.

Therapeutic Targeting of the Leukaemia Microenvironment

In recent decades, the conduct of uniform prospective clinical trials has led to improved remission rates and survival for patients with acute myeloid leukaemia and acute lymphoblastic leukaemia. However, high-risk patients continue to have inferior outcomes, where chemoresistance and relapse are common due to the survival mechanisms utilised by leukaemic cells. One such mechanism is through hijacking of the bone marrow microenvironment, where healthy haematopoietic machinery is transformed or remodelled into a hiding ground or "sanctuary" where leukaemic cells can escape chemotherapy-induced cytotoxicity. The bone marrow microenvironment, which consists of endosteal and vascular niches, can support leukaemogenesis through intercellular "crosstalk" with niche cells, including mesenchymal stem cells, endothelial cells, osteoblasts, and osteoclasts. Here, we summarise the regulatory mechanisms associated with leukaemia-bone marrow niche interaction and provide a comprehensive review of the key therapeutics that target CXCL12/CXCR4, Notch, Wnt/b-catenin, and hypoxia-related signalling pathways within the leukaemic niches and agents involved in remodelling of niche bone and vasculature. From a therapeutic perspective, targeting these cellular interactions is an exciting novel strategy for enhancing treatment efficacy, and further clinical application has significant potential to improve the outcome of patients with leukaemia.

Leukemia Chemoprevention and Therapeutic Potentials: Selected Medicinal Plants with Anti-Leukemic Activities

Haematological malignancies account for more than one million cases of all cancers yearly worldwide. While survival has improved due to newer drugs used in their management, relapsed/refractory disease remains a challenge, and treatment modalities come with side effects and morbidities. The management of leukaemias with medicinal plants and their natural products remain a viable option. Numerous studies have shown the potentials and viability of medicinal plants and their natural products as good options against leukaemias. However many of these natural products face peculiar challenges such as low systemic bioavailability, hydrophobic nature and displayed toxicities when given at different pharmacologic doses, while the medicinal plants face the threat of extinction. The development of semi-synthetic analogues and better regulations have helped overcome some of these challenges. This review briefly analyzes four medicinal plants and their different natural products that are used traditionally in the management of cancers, and have been scientifically proven to have some form of activity against leukemia. These plants include Tanacetum parthenium, Garcinia hanburyi, Scutellaria baicalensis, and Combretum caffrum. This review discusses these medicinal plants and their natural products under the following headings: ethnobotany, phytochemistry, mechanism of action, antileukaemic activity and toxicity.

The Dynamic Interface Between the Bone Marrow Vascular Niche and Hematopoietic Stem Cells in Myeloid Malignancy

Hematopoietic stem cells interact with bone marrow niches, including highly specialized blood vessels. Recent studies have revealed the phenotypic and functional heterogeneity of bone marrow endothelial cells. This has facilitated the analysis of the vascular microenvironment in steady state and malignant hematopoiesis. In this review, we provide an overview of the bone marrow microenvironment, focusing on refined analyses of the marrow vascular compartment performed in mouse studies. We also discuss the emerging role of the vascular niche in “inflamm-aging” and clonal hematopoiesis, and how the endothelial microenvironment influences, supports and interacts with hematopoietic cells in acute myeloid leukemia and myelodysplastic syndromes, as exemplar states of malignant myelopoiesis. Finally, we provide an overview of strategies for modulating these bidirectional interactions to therapeutic effect in myeloid malignancies.