Kinetics of leukemic cells in 3D culture with stromal cells and with arginine deprivation stress

Brain-Decellularized ECM-Based 3D Myeloid Sarcoma Platform: Mimicking Adaptive Phenotypic Alterations in the Brain

Leukemia circulates in the bloodstream and induces various symptoms and complications. Occasionally, these cells accumulate in non-marrow tissues, forming a tumor-like myeloid sarcoma (MS). When the blast-stage leukemia cells invade the brain parenchyma, intracranial MS occurs, leading to a challenging prognosis owing to the limited penetration of cytostatic drugs into the brain and the development of drug resistance. The scarcity of tissue samples from MS makes understanding the phenotypic changes occurring in leukemia cells within the brain environment challenging, thereby hindering development of effective treatment strategies for intracranial MS. This study presents a novel 3D in vitro model mimicking intracranial MS, employing a hydrogel scaffold derived from the brain-decellularized extracellular matrix in which suspended leukemia cells are embedded, simulating the formation of tumor masses in the brain parenchyma. This model reveals marked phenotypic changes in leukemia cells, including altered survival, proliferation, differentiation, and cell cycle regulation. Notably, proportion of dormant leukemia stem cells increases and expression of multidrug resistance genes is upregulated, leading to imatinib resistance, mirroring the pathological features of in vivo MS tissue. Furthermore, suppression of ferroptosis is identified as an important characteristic of intracranial MS, providing valuable insights for the development of targeted therapeutic strategies.

Macrophage depletion using clodronate liposomes reveals latent dysfunction of the hematopoietic microenvironment associated with persistently imbalanced M1/M2 macrophage polarization in a mouse model of hemophagocytic lymphohistiocytosis

Hemophagocytic lymphohistiocytosis (HLH), a hyperinflammatory syndrome, is caused by the incessant activation of lymphocytes and macrophages, resulting in damage to organs, including hematopoietic organs. Recently, we demonstrated that repeated lipopolysaccharide (LPS) treatment induces HLH-like features in senescence-accelerated (SAMP1/TA-1) mice but not in senescence-resistant control (SAMR1) mice. Hematopoietic failure in LPS-treated SAMP1/TA-1 mice was attributed to hematopoietic microenvironment dysfunction, concomitant with severely imbalanced M1 and M2 macrophage polarization. Macrophages are a major component of the bone marrow (BM) hematopoietic microenvironment. Clodronate liposomes are useful tools for in vivo macrophage depletion. In this study, we depleted macrophages using clodronate liposomes to determine their role in the hematopoietic microenvironment in SAMP1/TA-1 and SAMR1 mice. Under clodronate liposome treatment, the response between SAMR1 and SAMP1/TA-1 mice differed as follows: (1) increase in the number of activated M1 and M2 macrophages derived from newly generated macrophages and M2-dominant and imbalanced M1 and M2 macrophage polarization in the BM and spleen; (2) severe anemia and thrombocytopenia; (3) high mortality rate; (4) decrease in erythroid progenitors and B cell progenitors in the BM; and (5) decrease in the mRNA expression of erythroid-positive regulators such as erythropoietin and increase in that of erythroid- and B lymphoid-negative regulators such as interferon-γ in the BM. Depletion of residual macrophages in SAMP1/TA-1 mice impaired hematopoietic homeostasis, particularly erythropoiesis and B lymphopoiesis, owing to functional impairment of the hematopoietic microenvironment accompanied by persistently imbalanced M1/M2 polarization. Thus, macrophages play a vital role in regulating the hematopoietic microenvironment to maintain homeostasis.