Targeting bone marrow lymphoid niches in acute lymphoblastic leukemia

Advancements in Personalized CAR-T Therapy: Comprehensive Overview of Biomarkers and Therapeutic Targets in Hematological Malignancies

Chimeric antigen receptor T-cell (CAR-T) therapy is a novel anticancer therapy using autologous or allogeneic T-cells. To date, six CAR-T therapies for specific B-cell acute lymphoblastic leukemia (B-ALL), non-Hodgkin lymphomas (NHL), and multiple myeloma (MM) have been approved by the Food and Drug Administration (FDA). Significant barriers to the effectiveness of CAR-T therapy include cytokine release syndrome (CRS), neurotoxicity in the case of Allogeneic Stem Cell Transplantation (Allo-SCT) graft-versus-host-disease (GVHD), antigen escape, modest antitumor activity, restricted trafficking, limited persistence, the immunosuppressive microenvironment, and senescence and exhaustion of CAR-Ts. Furthermore, cancer drug resistance remains a major problem in clinical practice. CAR-T therapy, in combination with checkpoint blockades and bispecific T-cell engagers (BiTEs) or other drugs, appears to be an appealing anticancer strategy. Many of these agents have shown impressive results, combining efficacy with tolerability. Biomarkers like extracellular vesicles (EVs), cell-free DNA (cfDNA), circulating tumor (ctDNA) and miRNAs may play an important role in toxicity, relapse assessment, and efficacy prediction, and can be implicated in clinical applications of CAR-T therapy and in establishing safe and efficacious personalized medicine. However, further research is required to fully comprehend the particular side effects of immunomodulation, to ascertain the best order and combination of this medication with conventional chemotherapy and targeted therapies, and to find reliable predictive biomarkers.

Abnormal bone marrow microenvironment: the “harbor” of acute lymphoblastic leukemia cells

Bone marrow (BM) microenvironment regulates and supports the production of blood cells which are necessary to maintain homeostasis. In analogy to normal hematopoiesis, leukemogenesis is originated from leukemic stem cells (LSCs) which gives rise to more differentiated malignant cells. Leukemia cells occupy BM niches and reconstruct them to support leukemogenesis. The abnormal BM niches are the main sanctuary of LSCs where they can evade chemotherapy-induced death and acquire drug resistance. In this review, we focus on the protective effects of BM niche cells on acute lymphoblastic leukemia cells.

Targeting CXCR4 in AML and ALL

The interaction of acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL) blasts with the bone marrow microenvironment regulates self-renewal, growth signaling, as well as chemotherapy resistance. The chemokine receptor, CXC receptor 4 (CXCR4), with its ligand chemokine ligand 12 (CXCL12), plays a key role in the survival and migration of normal and malignant stem cells to the bone marrow. High expression of CXCR4 on AML and ALL blasts has been shown to be a predictor of poor prognosis for these diseases. Several small molecule inhibitors, short peptides, antibodies, and antibody drug conjugates have been developed for the purposes of more effective targeting and killing of malignant cells expressing CXCR4. In this review we will discuss recent results and strategies in targeting CXCR4 with these agents in patients with AML or ALL.

The meninges enhance leukaemia survival in cerebral spinal fluid

Central nervous system (CNS) relapse is a common cause of treatment failure in patients with acute lymphoblastic leukaemia (ALL) despite current CNS-directed therapies that are also associated with significant short- and long-term toxicities. Herein, we showed that leukaemia cells exhibit decreased proliferation, elevated reactive oxygen species (ROS) and increased cell death in cerebral spinal fluid (CSF) both in vitro and in vivo. However, interactions between leukaemia and meningeal cells mitigated these adverse effects. This work expands our understanding of the pathophysiology of CNS leukaemia and suggests novel therapeutic approaches for more effectively targeting leukaemia cells in the CNS.

A rare subgroup of leukemia stem cells harbors relapse-inducing potential in acute lymphoblastic leukemia

After initially successful chemotherapy, relapse frequently jeopardizes the outcome of patients with acute leukemia. Because of their adverse characteristics of self-renewal and dormancy, leukemia stem cells have been hypothesized to play a critical role in resistance to antiproliferative chemotherapy and the development of relapse. The high abundance of stem-like cells in acute lymphoblastic leukemia (ALL), however, suggests that not all leukemia-initiating cells carry these adverse characteristics, complicating the biological characterization of relapse-inducing cells in this malignancy. Here, we review sources of therapy resistance and relapse in acute leukemias, which include tumor cell plasticity and reversible characteristics. We discuss the development of patient-derived mouse models that are genetically engineered to mimic long-term dormancy and minimal residual disease in patients. These models allow the tracking and functional characterization of patient-derived ALL blasts that combine the properties of long-term dormancy, treatment resistance, and stemness. Finally, we discuss possible therapeutic avenues to target the functional plasticity of leukemia-initiating cells in ALL.

Regulation of the bone marrow microenvironment by G-CSF: Effects of G-CSF on acute lymphoblastic leukaemia

It has been suggested that disruption of the lymphoid niche by G-CSF may be of therapeutic benefit to patients with acute lymphoblastic leukaemia. We used a xenograft model to determine the effect of G-CSF on ALL progression in a minimal residual disease setting. Consistent with the effects on normal murine B cell progenitors, G-CSF slowed disease in the majority of ALL xenografts tested, suggesting that G-CSF may provide benefits beyond neutrophil recovery for ALL patients. However, two of eight xenografts demonstrated accelerated disease progression. G-CSF could be detrimental for these patients due to expansion of the malignant clone.

Epigenetic drug combination overcomes osteoblast-induced chemoprotection in pediatric acute lymphoid leukemia

Although there has been much progress in the treatment of acute lymphoblastic leukemia (ALL), decreased sensitivity to chemotherapy remains a significant issue. Recent studies have shown how interactions with the bone marrow microenvironment can protect ALL cells from chemotherapy and allow for the persistence of the disease. Epigenetic drugs have been used for the treatment of ALL, but there are no reports on whether these drugs can overcome bone marrow-induced chemoprotection. Our study investigates the ability of the DNA methyltransferase inhibitor azacitidine and the histone deacetylase inhibitor panobinostat to overcome chemoprotective effects mediated by osteoblasts. We show that the combination of azacitidine and panobinostat has a synergistic killing effect and that this combination is more effective than cytarabine in inducing ALL cell death in co-culture with osteoblasts. We also show that this combination can be used to sensitize ALL cells to chemotherapeutics in the presence of osteoblasts. Finally, we demonstrate that these effects can be replicated ex vivo in a number of mouse passaged xenograft lines from both B-ALL and T-ALL patients with varying cytogenetics. Thus, our data provides evidence that azacitidine and panobinostat can successfully overcome osteoblast-induced chemoprotection in vitro and ex vivo in both B-ALL and T-ALL cells.

Mimicking the Acute Myeloid Leukemia Niche for Molecular Study and Drug Screening

Bone marrow niche is a major contributing factor in leukemia development and drug resistance in acute myeloid leukemia (AML) patients. Although mimicking leukemic bone marrow niche relies on two-dimensional (2D) culture conditions, it cannot recapitulate complex bone marrow structure that causes introduction of different three-dimensional (3D) scaffolds. Simultaneously, microfluidic platform by perfusing medium culture mimic interstitial fluid flow, along with 3D scaffold would help for mimicking bone marrow microenvironment. In this study TF-1 cells were cocultured with bone marrow mesenchymal stem cells (BM-MSCs) in 2D and 3D microfluidic devices. Phenotype maintenance during cell culture and proliferation rate was assayed and confirmed by cell cycle analysis. Morphology of cells in 2D and 3D culture conditions was demonstrated by scanning electron microscopy. After these experiments, drug screening was performed by applying azacitidine and cytarabine and cytotoxicity assay and quantitative reverse transcription-polymerase chain reaction (qRT-PCR) for B cell lymphoma 2 (BCL2) were done to compare drug resistance in 2D and 3D culture conditions. Our result shows leukemic cells in 3D microfluidic device retaining their phenotype and proliferation rate was significantly higher in 3D culture condition in comparison to 2D culture condition (p < 0.05), which was confirmed by cell cycle analysis. Cytotoxicity assay also illustrated drug resistance in 3D culture condition and qRT-PCR demonstrated higher BCL2 expression in 3D microfluidic device in contrast to 2D microfluidic device (p < 0.05). On balance, mimicking bone marrow niche would help the target therapy and specify the role of niche in development of leukemia in AML patients.

Pro-inflammatory-Related Loss of CXCL12 Niche Promotes Acute Lymphoblastic Leukemic Progression at the Expense of Normal Lymphopoiesis

Pediatric oncology, notably childhood acute lymphoblastic leukemia (ALL), is currently one of the health-leading concerns worldwide and a biomedical priority. Decreasing overall leukemia mortality in children requires a comprehensive understanding of its pathobiology. It is becoming clear that malignant cell-to-niche intercommunication and microenvironmental signals that control early cell fate decisions are critical for tumor progression. We show here that the mesenchymal stromal cell component of ALL bone marrow (BM) differ from its normal counterpart in a number of functional properties and may have a key role during leukemic development. A decreased proliferation potential, contrasting with the strong ability of producing pro-inflammatory cytokines and an aberrantly loss of CXCL12 and SCF, suggest that leukemic lymphoid niches in ALL BM are unique and may exclude normal hematopoiesis. Cell competence ex vivo assays within tridimensional coculture structures indicated a growth advantage of leukemic precursor cells and their niche remodeling ability by CXCL12 reduction, resulting in leukemic cell progression at the expense of normal niche-associated lymphopoiesis.

Concise Review: The Malignant Hematopoietic Stem Cell Niche

Hematopoietic stem cell (HSC) proliferation, self-renewal, and trafficking are dependent, in part, upon signals generated by stromal cells in the bone marrow. Stromal cells are organized into niches that support specific subsets of hematopoietic progenitors. There is emerging evidence that malignant hematopoietic cells may generate signals that alter the number and/or function of specific stromal cell populations in the bone marrow. At least in some cases, the resulting alterations in the bone marrow microenvironment confer a competitive advantage to the malignant HSC and progenitor cells and/or render them less sensitive to chemotherapy. Targeting these signals represents a promising therapeutic strategy for selected hematopoietic malignancies. In this review, we focus on two questions. How do alterations in bone marrow stromal cells arise in hematopoietic malignancies, and how do they contribute to disease pathogenesis? Stem Cells 2017;35:3-8.