VE-cadherin Regulates Philadelphia Chromosome Positive Acute Lymphoblastic Leukemia Sensitivity to Apoptosis

Cadherins, Selectins, and Integrins in CAM-DR in Leukemia

The interaction between leukemia cells and the bone microenvironment is known to provide drug resistance in leukemia cells. This phenomenon, called cell adhesion-mediated drug resistance (CAM-DR), has been demonstrated in many subsets of leukemia including B- and T-acute lymphoblastic leukemia (B- and T-ALL) and acute myeloid leukemia (AML). Cell adhesion molecules (CAMs) are surface molecules that allow cell-cell or cell-extracellular matrix (ECM) adhesion. CAMs not only recognize ligands for binding but also initiate the intracellular signaling pathways that are associated with cell proliferation, survival, and drug resistance upon binding to their ligands. Cadherins, selectins, and integrins are well-known cell adhesion molecules that allow binding to neighboring cells, ECM proteins, and soluble factors. The expression of cadherin, selectin, and integrin correlates with the increased drug resistance of leukemia cells. This paper will review the role of cadherins, selectins, and integrins in CAM-DR and the results of clinical trials targeting these molecules.

Pyrvinium Pamoate Use in a B cell Acute Lymphoblastic Leukemia Model of the Bone Tumor Microenvironment

PURPOSE

Pyrvinium pamoate (PP) is an anthelmintic drug that has been found to have anti-cancer activity in several cancer types. In the present study, we evaluated PP for potential anti-leukemic activity in B cell acute lymphoblastic leukemia (ALL) cell lines, in an effort to evaluate the repurposing potential of this drug in leukemia.

METHODS

ALL cells were treated with PP at various concentrations to determine its effect on cell proliferation. Metabolic function was tested by evaluating Extracellular Acidification Rate (ECAR) and Oxygen Consumption Rate (OCR). Lastly, 3D spheroids were grown, and PP was reformulated into nanoparticles to evaluate distribution effectiveness.

RESULTS

PP was found to inhibit ALL proliferation, with varied selectivity to different ALL cell subtypes. We also found that PP's cell death activity was specific for leukemic cells, as primary normal immune cells were resistant to PP-mediated cell death. Metabolic studies indicated that PP, in part, inhibits mitochondrial oxidative phosphorylation. To increase the targeting of PP to a hypoxic bone tumor microenvironment (BTME) niche, we successfully encapsulated PP in a nanoparticle drug delivery system and demonstrated that it retained its anti-leukemic activity in a hemosphere assay.

CONCLUSION

We have demonstrated that PP is a novel therapeutic lead compound that counteracts the respiratory reprogramming found in refractory ALL cells and can be effectively formulated into a nanoparticle delivery system to target the BTME.

Eviction from the sanctuary: Development of targeted therapy against cell adhesion molecules in acute lymphoblastic leukemia

Acute lymphoblastic leukemia (ALL) is a malignant hematological disease afflicting hematopoiesis in the bone marrow. While 80%-90% of patients diagnosed with ALL will achieve complete remission at some point during treatment, ALL is associated with high relapse rate, with a 5-year overall survival rate of 68%. The initial remission failure and the high rate of relapse can be attributed to intrinsic chemoprotective mechanisms that allow persistence of ALL cells despite therapy. These mechanisms are mediated, at least in part, through the engagement of cell adhesion molecules (CAMs) within the bone marrow microenvironment. This review assembles CAMs implicated in protection of leukemic cells from chemotherapy. Such studies are limited in ALL. Therefore, CAMs that are associated with poor outcomes or are overexpressed in ALL and have been shown to be involved in chemoprotection in other hematological cancers are also included. It is likely that these molecules play parallel roles in ALL because the CAMs identified to be a factor in ALL chemoresistance also work similarly in other hematological malignancies. We review the signaling mechanisms activated by the engagement of CAMs that provide protection from chemotherapy. Development of targeted therapies against CAMs could improve outcome and raise the overall cure rate in ALL.

Pediatric precursor B acute lymphoblastic leukemia: are T helper cells the missing link in the infectious etiology theory?

Precursor B acute lymphoblastic leukemia (BCP-ALL), the most common childhood malignancy, arises from an expansion of malignant B cell precursors in the bone marrow. Epidemiological studies suggest that infections or immune responses to infections may promote such an expansion and thus BCP-ALL development. Nevertheless, a specific pathogen responsible for this process has not been identified. BCP-ALL cells critically depend on interactions with the bone marrow microenvironment. The bone marrow is also home to memory T helper (Th) cells that have previously expanded during an immune response in the periphery. In secondary lymphoid organs, Th cells can interact with malignant cells of mature B cell origin, while such interactions between Th cells and malignant immature B cell in the bone marrow have not been described yet. Nevertheless, literature supports a model where Th cells—expanded during an infection in early childhood—migrate to the bone marrow and support BCP-ALL cells as they support normal B cells. Further research is required to mechanistically confirm this model and to elucidate the interaction pathways between leukemia cells and cells of the tumor microenvironment. As benefit, targeting these interactions could be included in current treatment regimens to increase therapeutic efficiency and to reduce relapses.

VE-cadherin involved in the pulmonary microvascular endothelial cell barrier injury induced by angiotensin II through modulating the cellular apoptosis and skeletal rearrangement

OBJECTIVE

Angiotensin II (AngII) involved in the pathogenesis of pulmonary injury through impairing the integrity of pulmonary microvascular endothelial barrier, but the mechanism is still not clear. We aim to determine the roles of VE-cadherin, playing crucial roles in the adhesion of the vascular endothelial barrier and the barrier function, in the pulmonary microvascular endothelial cell (PMVEC) barrier injury mediated by AngII.

METHODS

Mice acute lung injury (ALI) model was induced through pumping of AngII. The infiltration of macrophages and neutrophils as well as the PMVEC permeability were determined in order to determine the barrier injury in vivo and in vitro. Knockdown of VE-cadherin was established using siRNA technique, and its roles in the apoptosis and skeletal rearrangement in the PMVECs were evaluated.

RESULTS

After AngII interference, the expression of VE-cadherin in the PMVECs and pulmonary tissues in mice was down-regulated. Upon VE-cadherin knockdown through siRNA technique, AngII induced susceptibility of PMVECs to apoptosis. Knockdown of VE-cadherin contributed to the skeletal rearrangement in the endothelial cells, together with increase of permeability.

CONCLUSIONS

VE-cadherin expression is closely related to the apoptosis and skeletal rearrangement of PMVECs induced by AngII.

SOX7 promotes the maintenance and proliferation of B cell precursor acute lymphoblastic cells

B cell precursor acute lymphoblastic leukemia (BCP-ALL) is the most frequent type of cancer in children. Despite progresses in curative treatment, intensive chemotherapy regimens still cause life threatening complications. A better understanding of the molecular mechanisms underlying the emergence and maintenance of BCP-ALL is fundamental for the development of novel therapies. Here, we establish that SOX7 is frequently and specifically expressed in BCP-ALL and that the expression of this transcription factor does not correlate with any specific cytogenetic abnormalities. Using human leukemia model systems, we establish that the down-regulation of SOX7 in BCP-ALL causes a significant decrease in proliferation and clonogenicity in vitro that correlates with a delay in leukemia initiation and burden in vivo. Overall, these results identify a novel and important functional role for the transcription factor SOX7 in promoting the maintenance of BCP-ALL.

Bone Marrow Microenvironment Niche Regulates miR-221/222 in Acute Lymphoblastic Leukemia

Acute lymphoblastic leukemia (ALL) has many features in common with normal B-cell progenitors, including their ability to respond to diverse signals from the bone marrow microenvironment (BMM) resulting in regulation of cell-cycle progression and survival. Bone marrow-derived cues influence many elements of both steady state hematopoiesis and hematopoietic tumor cell phenotypes through modulation of gene expression. miRNAs are one regulatory class of small noncoding RNAs that have been shown to be increasingly important in diverse settings of malignancy. In the current study, miRNA profiles were globally altered in ALL cells following exposure to primary human bone marrow niche cells, including bone marrow stromal cells (BMSC) and primary human osteoblasts (HOB). Specifically, mature miR-221 and miR-222 transcripts were decreased in ALL cells cocultured with BMSC or HOB, coincident with increased p27 (CDKN1B), a previously validated target. Increased p27 protein in ALL cells exposed to BMSC or HOB is consistent with accumulation of tumor cells in the G₀ phase of the cell cycle and resistance to chemotherapy-induced death. Overexpression of miR-221 in ALL cells during BMSC or HOB coculture prompted cell-cycle progression and sensitization of ALL cells to cytotoxic agents, blunting the protective influence of the BMM. These novel observations indicate that BMM regulation of miR-221/222 contributes to marrow niche-supported tumor cell quiescence and survival of residual cells.

IMPLICATIONS

Niche-influenced miR-221/222 may define a novel therapeutic target in ALL to be combined with existing cytotoxic agents to more effectively eradicate refractory disease that contributes to relapse. Mol Cancer Res; 14(10); 909-19. ©2016 AACR.

Chemosensitizing AML cells by targeting bone marrow endothelial cells

Refractory disease is the greatest challenge in treating patients with acute myeloid leukemia (AML). Blood vessels may serve as sanctuary sites for AML. When AML cells were co-cultured with bone marrow endothelial cells (BMECs), a greater proportion of leukemia cells were in G0/G1. This led us to a strategy of targeting BMECs with tubulin-binding combretastatins, causing BMECs to lose their flat phenotype, degrade their cytoskeleton, cease growth, and impair migration despite unchanged BMEC viability and metabolism. Combretastatins also caused downregulation of BMEC adhesion molecules known to tether AML cells, including vascular cell adhesion molecule (VCAM)-1 and vascular endothelial (VE)-cadherin. When AML-BMEC co-cultures were treated with combretastatins, a significantly greater proportion of AML cells dislodged from BMECs and entered the G2/M cell cycle, suggesting enhanced susceptibility to cell cycle agents. Indeed, the combination of combretastatins and cytotoxic chemotherapy enhanced additive AML cell death. In vivo mice xenograft studies confirmed this finding by revealing complete AML regression after treatment with combretastatins and cytotoxic chemotherapy. Beyond highlighting the pathologic role of BMECs in the leukemia microenvironment as a protective reservoir of disease, these results support a new strategy for using vascular-targeting combretastatins in combination with cytotoxic chemotherapy to treat AML.

Modeling Chemotherapy Resistant Leukemia In Vitro

It is well established that the bone marrow microenvironment provides a unique site of sanctuary for hematopoietic diseases that both initiate and progress in this site. The model presented in the current report utilizes human primary bone marrow stromal cells and osteoblasts as two representative cell types from the marrow niche that influence tumor cell phenotype. The in vitro co-culture conditions described for human leukemic cells with these primary niche components support the generation of a chemoresistant subpopulation of tumor cells that can be efficiently recovered from culture for analysis by diverse techniques. A strict feeding schedule to prevent nutrient fluxes followed by gel type 10 cross-linked dextran (G10) particles recovery of the population of tumor cells that have migrated beneath the adherent bone marrow stromal cells (BMSC) or osteoblasts (OB) generating a "phase dim" (PD) population of tumor cells, provides a consistent source of purified therapy resistant leukemic cells. This clinically relevant population of tumor cells can be evaluated by standard methods to investigate apoptotic, metabolic, and cell cycle regulatory pathways as well as providing a more rigorous target in which to test novel therapeutic strategies prior to pre-clinical investigations targeted at minimal residual disease.

Bone marrow microenvironment modulation of acute lymphoblastic leukemia phenotype

Acute lymphoblastic leukemia (ALL) treatment regimens have dramatically improved the survival of ALL patients. However, chemoresistant minimal residual disease that persists following cessation of therapy contributes to aggressive relapse. The bone marrow microenvironment (BMM) is an established "site of sanctuary" for ALL, as well as myeloid-lineage hematopoietic disease, with signals in this unique anatomic location contributing to drug resistance. Several models have been developed to recapitulate the interactions between the BMM and ALL cells. However, many in vitro models fail to accurately reflect the level of protection afforded to the most resistant subset of leukemic cells during coculture with BMM elements. Preclinical in vivo models have advantages, but can be costly, and are often not fully informed by optimal in vitro studies. We describe an innovative extension of 2-D coculture wherein ALL cells uniquely interact with bone marrow-derived stromal cells. Tumor cells in this model bury beneath primary human bone marrow-derived stromal cells or osteoblasts, termed "phase dim" ALL, and exhibit a unique phenotype characterized by altered metabolism, distinct protein expression profiles, increased quiescence, and pronounced chemotherapy resistance. Investigation focused on the phase dim subpopulation may more efficiently inform preclinical design and investigation of the minimal residual disease and relapse that arise from BMM-supported leukemic tumor cells.

Coordinate regulation of stem cell competition by Slit-Robo and JAK-STAT signaling in the Drosophila testis

Stem cells in tissues reside in and receive signals from local microenvironments called niches. Understanding how multiple signals within niches integrate to control stem cell function is challenging. The Drosophila testis stem cell niche consists of somatic hub cells that maintain both germline stem cells and somatic cyst stem cells (CySCs). Here, we show a role for the axon guidance pathway Slit-Roundabout (Robo) in the testis niche. The ligand Slit is expressed specifically in hub cells while its receptor, Roundabout 2 (Robo2), is required in CySCs in order for them to compete for occupancy in the niche. CySCs also require the Slit-Robo effector Abelson tyrosine kinase (Abl) to prevent over-adhesion of CySCs to the niche, and CySCs mutant for Abl outcompete wild type CySCs for niche occupancy. Both Robo2 and Abl phenotypes can be rescued through modulation of adherens junction components, suggesting that the two work together to balance CySC adhesion levels. Interestingly, expression of Robo2 requires JAK-STAT signaling, an important maintenance pathway for both germline and cyst stem cells in the testis. Our work indicates that Slit-Robo signaling affects stem cell function downstream of the JAK-STAT pathway by controlling the ability of stem cells to compete for occupancy in their niche.

Stromal cells attenuate the cytotoxicity of imatinib on Philadelphia chromosome-positive leukemia cells by up-regulating the VE-cadherin/β-catenin signal

β-Catenin is a key regulator of leukemia stem cell maintenance and drug resistance. Herein, we investigated the protective effects of the stromal cell-mediated VE-cadherin-β-catenin signal on Ph+ leukemia cells during imatinib treatment. We found stromal cells could desensitize imatinib and up-regulate VE-cadherin expression on Ph+ leukemia cells (K562 and SUP-B15 cells), which further stabilized and activated β-catenin. Knockdown of VE-cadherin with shRNA diminished the β-catenin protein and partly resensitized Ph+ leukemia cells to imatinib despite the presence of stromal cells, suggesting VE-cadherin is a potential target in the treatment of Ph+ leukemia.

Bone marrow mesenchymal stromal cells affect the cell cycle arrest effect of genotoxic agents on acute lymphocytic leukemia cells via p21 down-regulation

The effect of bone marrow microenvironment on the cell cycle of acute lymphocytic leukemia (ALL) and the underlying mechanism has not been elucidated. In this study, we found that in normal condition, bone marrow mesenchymal stromal cells (BM-MSCs) had no significant effect on the cell cycle and apoptosis of ALL; in the condition when the cell cycle of ALL was blocked by genotoxic agents, BM-MSCs could increase the S-phase cell ratio and decrease the G2/M phase ratio of ALL. Besides, BM-MSCs could protect ALL cells from drug-induced apoptosis. Then, we proved that BM-MSCs affect the cell cycle arrest effect of genotoxic agents on ALL cells via p21 down-regulation. Moreover, our results indicated that activation of Wnt/β-catenin and Erk pathways might be involved in the BM-MSC-induced down-regulation of p21 in ALL cells. Targeting microenvironment-related signaling pathway may therefore be a potential novel approach for ALL therapy.