From the niche to malignant hematopoiesis and back: reciprocal interactions between leukemia and the bone marrow microenvironment

Targeting Acute Myeloid Leukemia Using Sphingosine Kinase 1 Inhibitor-Loaded Liposomes

Acute myeloid leukemia (AML) kills 75% of patients and represents a major clinical challenge with a need to improve on current treatment approaches. Targeting sphingosine kinase 1 with a novel ATP-competitive-inhibitor, MP-A08, induces cell death in AML. However, limitations in MP-A08's "drug-like properties" (solubility, biodistribution, and potency) hinder its pathway to the clinic. This study demonstrates a liposome-based delivery system of MP-A08 that exhibits enhanced MP-A08 potency against AML cells. MP-A08-liposomes increased MP-A08 efficacy against patient AML cells (>140-fold) and significantly prolonged overall survival of mice with human AML disease (P = 0.03). The significant antileukemic property of MP-A08-liposomes could be attributed to its enhanced specificity, bioaccessibility, and delivery to the bone marrow, as demonstrated in the pharmacokinetic and biodistribution studies. Our findings indicate that MP-A08-liposomes have potential as a novel treatment for AML.

In vitro simulation of the acute lymphoblastic leukemia niche: a critical view on the optimal approximation for drug testing

Acute lymphoblastic leukemia with the worst prognosis is related to minimal residual disease. Minimal residual disease not only depends on the individual peculiarities of leukemic clones but also reflects the protective role of the acute lymphoblastic leukemia microenvironment. In this review, we discuss in detail cell-to-cell interactions in the 2 leukemic niches, more explored bone marrow and less studied extramedullary adipose tissue. A special emphasis is given to multiple ways of interactions of acute lymphoblastic leukemia cells with the bone marrow or extramedullary adipose tissue microenvironment, indicating observed differences in B- and T-cell-derived acute lymphoblastic leukemia behavior. This analysis argued for the usage of coculture systems for drug testing. Starting with a review of available sources and characteristics of acute lymphoblastic leukemia cells, mesenchymal stromal cells, endothelial cells, and adipocytes, we have then made an update of the available 2-dimensional and 3-dimensional systems, which bring together cellular elements, components of the extracellular matrix, or its imitation. We discussed the most complex available 3-dimensional systems like "leukemia-on-a-chip," which include either a prefabricated microfluidics platform or, alternatively, the microarchitecture, designed by using the 3-dimensional bioprinting technologies. From our analysis, it follows that for preclinical antileukemic drug testing, in most cases, intermediately complex in vitro cell systems are optimal, such as a "2.5-dimensional" coculture of acute lymphoblastic leukemia cells with niche cells (mesenchymal stromal cells, endothelial cells) plus matrix components or scaffold-free mesenchymal stromal cell organoids, populated by acute lymphoblastic leukemia cells. Due to emerging evidence for the correlation of obesity and poor prognosis, a coculture of adipocytes with acute lymphoblastic leukemia cells as a drug testing system is gaining shape.

Periplocin Overcomes Bortezomib Resistance by Suppressing the Growth and Down-Regulation of Cell Adhesion Molecules in Multiple Myeloma

Multiple myeloma (MM) is an incurable hematological malignant disorder of bone marrow. Patients with MM receive multiple lines of chemotherapeutic treatments which often develop bortezomib (BTZ) resistance and relapse. Therefore, it is crucial to identify an anti-MM agent to overcome the BTZ resistance of MM. In this study, we screened a library of 2370 compounds against MM wild-type (ARP1) and BTZ-resistant type (ARP1-BR) cell lines and found that periplocin (PP) was the most significant anti-MM natural compound. We further investigated the anti-MM effect of PP by using annexin V assay, clonogenic assays, aldefluor assay, and transwell assay. Furthermore, RNA sequencing (RNA-seq) was performed to predict the molecular effects of PP in MM followed by verification through qRT-PCR and Western blot analysis. Moreover, ARP1 and ARP1-BR xenograft mice models of MM were established to confirm the anti-MM effects of PP invivo. The results showed that PP significantly induced apoptosis, inhibited proliferation, suppressed stemness, and reduced the cell migration of MM. The expression of cell adhesion molecules (CAMs) was suppressed upon PP treatment in vitro and in vivo. Overall, our data recommend PP as an anti-MM natural compound with the potential to overcome BTZ resistance and downregulate CAMs in MM.

The Potential Role of 3D In Vitro Acute Myeloid Leukemia Culture Models in Understanding Drug Resistance in Leukemia Stem Cells

The complexity of the bone marrow (BM) microenvironment makes studying hematological malignancies in vitro a challenging task. Three-dimensional cell cultures are being actively studied, particularly due to their ability to serve as a bridge of the gap between 2D cultures and animal models. The role of 3D in vitro models in studying the mechanisms of chemotherapeutic resistance and leukemia stem cells (LSCs) in acute myeloid leukemia (AML) is not well-reviewed. We present an overview of 3D cell models used for studying AML, emphasizing the recent advancements in microenvironment modeling, chemotherapy testing, and resistance.

Bone Marrow Microenvironment-On-Chip for Culture of Functional Hematopoietic Stem Cells

Hematopoiesis takes place in the bone marrow and is supported by a complex cellular and molecular network in the bone marrow microenvironment. Commonly used models of the human bone marrow microenvironment include murine models and two-dimensional and three-dimensional tissue cultures. While these model systems have led to critical advances in the field, they fail to recapitulate many aspects of the human bone marrow. This has limited our understanding of human bone marrow pathophysiology and has led to deficiencies in therapy for many bone marrow pathologies such as bone marrow failure syndromes and leukemias. Therefore, we have developed a modular murine bone marrow microenvironment-on-chip using a commercially available microfluidic platform. This model includes a vascular channel separated from the bone marrow channel by a semi-porous membrane and incorporates critical components of the bone marrow microenvironment, including osteoblasts, endothelial cells, mesenchymal stem cells, and hematopoietic stem and progenitor cells. This system is capable of maintaining functional hematopoietic stem cells in vitro for at least 14 days at frequencies similar to what is found in the primary bone marrow. The modular nature of this system and its accessibility will allow for acceleration of our understanding of the bone marrow.

Bone Marrow Niches and Tumour Cells: Lights and Shadows of a Mutual Relationship

The bone marrow (BM) niche is the spatial structure within the intra-trabecular spaces of spongious bones and of the cavity of long bones where adult haematopoietic stem cells (HSCs) maintain their undifferentiated and cellular self-renewal state through the intervention of vascular and nervous networks, metabolic pathways, transcriptional and epigenetic regulators, and humoral signals. Within the niche, HSCs interact with various cell types such as osteoblasts, endothelial cells, macrophages, and mesenchymal stromal cells (MSCs), which maintain HSCs in a quiescent state or sustain their proliferation, differentiation, and trafficking, depending on body needs. In physiological conditions, the BM niche permits the daily production of all the blood and immune cells and their admittance/ingress/progression into the bloodstream. However, disruption of this delicate microenvironment promotes the initiation and progression of malignancies such as those included in the spectrum of myeloid neoplasms, also favouring resistance to pharmacological therapies. Alterations in the MSC population and in the crosstalk with HSCs owing to tumour-derived factors contribute to the formation of a malignant niche. On the other hand, cells of the BM microenvironment cooperate in creating a unique milieu favouring metastasization of distant tumours into the bone. In this framework, the pro-tumorigenic role of MSCs is well-documented, and few evidence suggest also an anti-tumorigenic effect. Here we will review recent advances regarding the BM niche composition and functionality in normal and in malignant conditions, as well as the therapeutic implications of the interplay between its diverse cellular components and malignant cells.

Leukemia’s Next Top Model? Syngeneic Models to Advance Adoptive Cellular Therapy

In recent years, there has been an emphasis on harnessing the immune system for therapeutic interventions. Adoptive cell therapies (ACT) have emerged as an effective option for B-cell derived hematological malignancies. Despite remarkable successes with ACT, immune dysregulation and the leukemia microenvironment can critically alter clinical responses. Therefore, preclinical modeling can contribute to the advancement of ACT for leukemias. Human xenografts, the current mainstay of ACT in vivo models, cannot evaluate the impact of the immunosuppressive leukemia microenvironment on adoptively transferred cells. Syngeneic mouse models utilize murine tumor models and implant them into immunocompetent mice. This provides an alternative model, reducing the need for complicated breeding strategies while maintaining a matched immune system, stromal compartment, and leukemia burden. Syngeneic models that evaluate ACT have analyzed the complexity of cytotoxic T lymphocytes, T cell receptor transgenics, and chimeric antigen receptors. This review examines the immunosuppressive features of the leukemia microenvironment, discusses how preclinical modeling helps predict ACT associated toxicities and dysfunction, and explores publications that have employed syngeneic modeling in ACT studies for the improvement of therapy for leukemias.

Endocan in Acute Leukemia: Current Knowledge and Future Perspectives

Endocan is a soluble dermatan sulfate proteoglycan expressed by endothelial cells and detected in serum/plasma. Its expression is increased in tumors/tumor vessels in several human malignancies, and high expression (high serum/plasma levels or tumor levels) has an adverse prognostic impact in several malignancies. The p14 endocan degradation product can also be detected in serum/plasma, but previous clinical studies as well as previously unpublished results presented in this review suggest that endocan and p14 endocan fragment levels reflect different biological characteristics, and the endocan levels seem to reflect the disease heterogeneity in acute leukemia better than the p14 fragment levels. Furthermore, decreased systemic endocan levels in previously immunocompetent sepsis patients are associated with later severe respiratory complications, but it is not known whether this is true also for immunocompromised acute leukemia patients. Finally, endocan is associated with increased early nonrelapse mortality in (acute leukemia) patients receiving allogeneic stem cell transplantation, and this adverse prognostic impact seems to be independent of the adverse impact of excessive fluid overload. Systemic endocan levels may also become important to predict cytokine release syndrome after immunotherapy/haploidentical transplantation, and in the long-term follow-up of acute leukemia survivors with regard to cardiovascular risk. Therapeutic targeting of endocan is now possible, and the possible role of endocan in acute leukemia should be further investigated to clarify whether the therapeutic strategy should also be considered.