Targeting pediatric leukemia-propagating cells with anti-CD200 antibody therapy.

Treating refractory pediatric acute lymphoblastic leukemia (ALL) remains a challenge despite impressive remission rates (>90%) achieved in the last decade. The use of innovative immunotherapeutic approaches such as anti-CD19 chimeric antigen receptor T cells does not ensure durable remissions, because leukemia-propagating cells (LPCs) that lack expression of CD19 can cause relapse, which signifies the need to identify new markers of ALL. Here we investigated expression of CD58, CD97, and CD200, which were previously shown to be overexpressed in B-cell precursor ALL (BCP-ALL) in CD34+/CD19+, CD34+/CD19-, CD34-/CD19+, and CD34-/CD19- LPCs, to assess their potential as therapeutic targets. Whole-genome microarray and flow cytometric analyses showed significant overexpression of these molecules compared with normal controls. CD58 and CD97 were mainly co-expressed with CD19 and were not a prerequisite for leukemia engraftment in immune deficient mice. In contrast, expression of CD200 was essential for engraftment and serial transplantation of cells in measurable residual disease (MRD) low-risk patients. Moreover, these CD200+ LPCs could be targeted by using the monoclonal antibody TTI-CD200 in vitro and in vivo. Treating mice with established disease significantly reduced disease burden and extended survival. These findings demonstrate that CD200 could be an attractive target for treating low-risk ALL, with minimal off-tumor effects that beset current immunotherapeutic approaches.

Non-toxic polymer nanovectors for improved delivery of dexamethasone.

Dexamethasone (Dex) is a highly insoluble front-line drug used in cancer therapy. Data from clinical trials indicates that the pharmacokinetics of Dex vary considerably between patients and prolonging drug exposure rather than increasing absolute dose may improve efficacy. Non-toxic, fully biodegradable Dex loaded nanovectors (NV) were formulated, via simple direct hydration within 10 min, as a vehicle to extend exposure and distribution in vivo. Dex-NV were just as effective as the free drug against primary human leukemia cells in vitro and in vivo. Importantly, high levels of DMSO solvent were not required in the NV formulations. Broad distribution of NV was seen rapidly following inoculation into mice. NV accumulated in major organs, including bone marrow and brain, known sanctuary sites for ALL. The study describes a non-toxic, more easily scalable system for improving Dex solubility for use in cancer and can be applied to other medical conditions associated with inflammation.

Large red cell-derived membrane particles are major contributors to hypercoagulability in sickle cell disease.

Sickle cell disease (SCD) is one of the most common inherited single gene disorders. Polymerisation of sickle hemoglobin results in erythrocytes that are inflexible and adherent, leading to coagulation, vascular and cellular activation and resultant blood vessel blockage. Previous studies have observed elevated numbers of red cell-derived particles (RCDP), also denoted extracellular vesicles, in SCD plasma. Here, imaging flow cytometry was used to quantify all RCDP in SCD plasma. A more heterogenous population of RCDP was observed than previously reported. Significantly, large right side-out red cell macrovesicles (MaV), 7 µm in diameter, were identified. Most RCDP were right side-out but a minor population of inside-out vesicles was also present. Electron micrographs confirmed the heterogenous nature of the RCDP detected. All MaV are decorated with prothrombotic phosphatidylserine (PS) and their removal from plasma lengthened clotting times by more than three-fold. Removal of all right side-out RCDP from SCD patient plasma samples resulted in a seven-fold increase in clotting time. These results indicate that MaV comprise a large area of prothrombotic membrane and are thus major contributors to hypercoagulation in SCD. Consequently, controlled removal of MaV and PS exposed RCDP from plasma could provide a novel therapy for managing this disease.

Investigating the response of paediatric leukaemia-propagating cells to BCL-2 inhibitors.

Relapse of paediatric acute lymphoblastic leukaemia (ALL) may occur due to persistence of resistant cells with leukaemia-propagating ability (LPC). In leukaemia, the balance of B-cell lymphoma-2 (BCL-2) family proteins is disrupted, promoting survival of malignant cells and possibly LPC. A direct comparison of BCL-2 inhibitors, navitoclax and venetoclax, was undertaken on LPC subpopulations from B-cell precursor (BCP) and T-cell ALL (T-ALL) cases in vitro and in vivo. Responses were compared to BCL-2 levels detected by microarray analyses and Western blotting. In vitro, both drugs were effective against most BCP-ALL LPC, except CD34- /CD19- cells. In contrast, only navitoclax was effective in T-ALL and CD34- /CD7- LPC were resistant to both drugs. In vivo, navitoclax was more effective than venetoclax, significantly improving survival of mice engrafted with BCP- and T-ALL samples. Venetoclax was not particularly effective against T-ALL cases in vivo. The proportions of CD34+ /CD19- , CD34- /CD19- BCP-ALL cells and CD34- /CD7- T-ALL cells increased significantly following in vivo treatment. Expression of pro-apoptotic BCL-2 genes was lower in these subpopulations, which may explain the lack of sensitivity. These data demonstrate that some LPC were resistant to BCL-2 inhibitors and sustained remission will require their use in combination with other therapeutics.

Inhibition of GATA2 restrains cell proliferation and enhances apoptosis and chemotherapy mediated apoptosis in human GATA2 overexpressing AML cells.

GATA2, a zinc finger transcription factor predominantly expressed in hematopoietic cells, acts as an essential regulator of hematopoietic stem cell generation, survival and functionality. Loss and gain of GATA2 expression has been implicated in myelodysplastic syndrome and acute myeloid leukemia (AML) yet the precise biological impact of GATA2 expression on human AML cell fate decisions remains ambiguous. Herein, we performed large-scale bioinformatics that demonstrated relatively frequent GATA2 overexpression in AML patients as well as select human AML (or AML-like) cell lines. By using shRNAi to target GATA2 in these AML cell lines, and an AML cell line expressing normal levels of GATA2, we found that inhibition of GATA2 caused attenuated cell proliferation and enhanced apoptosis exclusively in AML cell lines that overexpress GATA2. We proceeded to pharmacologically inhibit GATA2 in concert with AML chemotherapeutics and found this augmented cell killing in AML cell lines that overexpress GATA2, but not in an AML cell line expressing normal levels of GATA2. These data indicate that inhibition of GATA2 enhances chemotherapy-mediated apoptosis in human AML cells overexpressing GATA2. Thus, we define novel insights into the oncogenic role of GATA2 in human AML cells and suggest the potential utilization of transient GATA2 therapeutic targeting in AML.

DNA damage signalling from the placenta to foetal blood as a potential mechanism for childhood leukaemia initiation.

For many diseases with a foetal origin, the cause for the disease initiation remains unknown. Common childhood acute leukaemia is thought to be caused by two hits, the first in utero and the second in childhood in response to infection. The mechanism for the initial DNA damaging event are unknown. Here we have used in vitro, ex vivo and in vivo models to show that a placental barrier will respond to agents that are suspected of initiating childhood leukaemia by releasing factors that cause DNA damage in cord blood and bone marrow cells, including stem cells. We show that DNA damage caused by in utero exposure can reappear postnatally after an immune challenge. Furthermore, both foetal and postnatal DNA damage are prevented by prenatal exposure of the placenta to a mitochondrially-targeted antioxidant. We conclude that the placenta might contribute to the first hit towards leukaemia initiation by bystander-like signalling to foetal haematopoietic cells.

LEF-1 drives aberrant ß-catenin nuclear localization in myeloid leukemia cells.

Canonical Wnt/ß-catenin signaling is frequently dysregulated in myeloid leukemias and is implicated in leukemogenesis. Nuclear-localized ß-catenin is indicative of active Wnt signaling and is frequently observed in acute myeloid leukemia (AML) patients; however, some patients exhibit little or no nuclear ß-catenin even where cytosolic ß-catenin is abundant. Control of the subcellular localization of ß-catenin therefore represents an additional mechanism regulating Wnt signaling in hematopoietic cells. To investigate the factors mediating the nuclear-localization of ß-catenin, we carried out the first nuclear/cytoplasmic proteomic analysis of the ß-catenin interactome in myeloid leukemia cells and identified putative novel ß-catenin interactors. Comparison of interacting factors between Wnt-responsive cells (high nuclear ß-catenin) versus Wnt-unresponsive cells (low nuclear ß-catenin) suggested the transcriptional partner, LEF-1, could direct the nuclear-localization of ß-catenin. The relative levels of nuclear LEF-1 and ß-catenin were tightly correlated in both cell lines and in primary AML blasts. Furthermore, LEF-1 knockdown perturbed ß-catenin nuclear-localization and transcriptional activation in Wnt-responsive cells. Conversely, LEF-1 overexpression was able to promote both nuclear-localization and ß-catenin-dependent transcriptional responses in previously Wnt-unresponsive cells. This is the first ß-catenin interactome study in hematopoietic cells and reveals LEF-1 as a mediator of nuclear ß- catenin level in human myeloid leukemia.

Biodegradable, Drug-Loaded Nanovectors via Direct Hydration as a New Platform for Cancer Therapeutics.

The stabilization and transport of low-solubility drugs, by encapsulation in nanoscopic delivery vectors (nanovectors), is a key paradigm in nanomedicine. However, the problems of carrier toxicity, specificity, and producibility create a bottleneck in the development of new nanomedical technologies. Copolymeric nanoparticles are an excellent platform for nanovector engineering due to their structural versatility; however, conventional fabrication processes rely upon harmful chemicals that necessitate purification. In engineering a more robust (copolymeric) nanovector platform, it is necessary to reconsider the entire process from copolymer synthesis through self-assembly and functionalization. To this end, a process is developed whereby biodegradable copolymers of poly(ethylene glycol)-block-poly(trimethylene carbonate), synthesized via organocatalyzed ring-opening polymerization, undergo assembly into highly uniform, drug-loaded micelles without the use of harmful solvents or the need for purification. The direct hydration methodology, employing oligo(ethylene glycol) as a nontoxic dispersant, facilitates rapid preparation of pristine, drug-loaded nanovectors that require no further processing. This method is robust, fast, and scalable. Utilizing parthenolide, an exciting candidate for treatment of acute lymphoblastic leukemia (ALL), discrete nanovectors are generated that show strikingly low carrier toxicity and high levels of specific therapeutic efficacy against primary ALL cells (as compared to normal hematopoietic cells).

Investigating chemoresistance to improve sensitivity of childhood T-cell acute lymphoblastic leukemia to parthenolide.

Current therapies for childhood T-cell acute lymphoblastic leukemia have increased survival rates to above 85% in developed countries. Unfortunately, some patients fail to respond to therapy and many suffer from serious side effects, highlighting the need to investigate other agents to treat this disease. Parthenolide, a nuclear factor kappa (κ)B inhibitor and reactive oxygen species inducer, has been shown to have excellent anti-cancer activity in pediatric leukemia xenografts, with minimal effects on normal hemopoietic cells. However, some leukemia initiating cell populations remain resistant to parthenolide. This study examined mechanisms for this resistance, including protective effects conferred by bone marrow stromal components. T-cell acute leukemia cells co-cultured with mesenchymal stem cells demonstrated significantly enhanced survival against parthenolide (73±11%) compared to cells treated without mesenchymal stem cell support (11±9%). Direct cell contact between mesenchymal cells and leukemia cells was not required to afford protection from parthenolide. Mesenchymal stem cells released thiols and protected leukemia cells from reactive oxygen species stress, which is associated with parthenolide cytotoxicity. Blocking cystine uptake by mesenchymal stem cells, using a small molecule inhibitor, prevented thiol release and significantly reduced leukemia cell resistance to parthenolide. These data indicate it may be possible to achieve greater toxicity to childhood T-cell acute lymphoblastic leukemia by combining parthenolide with inhibitors of cystine uptake.

An immortalized adult human erythroid line facilitates sustainable and scalable generation of functional red cells.

With increasing worldwide demand for safe blood, there is much interest in generating red blood cells in vitro as an alternative clinical product. However, available methods for in vitro generation of red cells from adult and cord blood progenitors do not yet provide a sustainable supply, and current systems using pluripotent stem cells as progenitors do not generate viable red cells. We have taken an alternative approach, immortalizing early adult erythroblasts generating a stable line, which provides a continuous supply of red cells. The immortalized cells differentiate efficiently into mature, functional reticulocytes that can be isolated by filtration. Extensive characterization has not revealed any differences between these reticulocytes and in vitro-cultured adult reticulocytes functionally or at the molecular level, and importantly no aberrant protein expression. We demonstrate a feasible approach to the manufacture of red cells for clinical use from in vitro culture.

Functionalized Triblock Copolymer Vectors for the Treatment of Acute Lymphoblastic Leukemia.

The chemotherapeutic Parthenolide is an exciting new candidate for the treatment of acute lymphoblastic leukemia, but like many other small-molecule drugs, it has low aqueous solubility. As a consequence, Parthenolide can only be administered clinically in the presence of harmful cosolvents. Accordingly, we describe the synthesis, characterization, and testing of a range of biocompatible triblock copolymer micelles as particle-based delivery vectors for the hydrophobic drug Parthenolide. The drug-loaded particles are produced via an emulsion-to-micelle transition method, and the effects of introducing anionic and cationic surface charges on stability, drug sequestration, biocompatibility, and efficacy are investigated. Significantly, we demonstrate high levels of efficacy in the organic solvent-free systems against human mesenchymal stem cells and primary T-acute lymphoblastic leukemia patient cells, highlighting the effectiveness of the delivery vectors for the treatment of acute lymphoblastic leukemia.

pH-Sensitive O6-Benzylguanosine Polymer Modified Magnetic Nanoparticles for Treatment of Glioblastomas.

Nanoparticle-mediated delivery of chemotherapeutics has demonstrated potential in improving anticancer efficacy by increasing serum half-life and providing tissue specificity and controlled drug release to improve biodistribution of hydrophobic chemotherapeutics. However, suboptimal drug loading, particularly for solid core nanoparticles (NPs), remains a challenge that limits their clinical application. In this study we formulated a NP coated with a pH-sensitive polymer of O6-methylguanine-DNA methyltransferase (MGMT) inhibitor analog, dialdehyde modified O6-benzylguanosine (DABGS) to achieve high drug loading, and polyethylene glycol (PEG) to ameliorate water solubility and maintain NP stability. The base nanovector consists of an iron oxide core (9 nm) coated with hydrazide functionalized PEG (IOPH). DABGS and PEG-dihydrazide were polymerized on the iron oxide nanoparticle surface (IOPH-pBGS) through acid-labile hydrazone bonds utilizing a rapid, freeze-thaw catalysis approach. DABGS polymerization was confirmed by FTIR and quantitated by UV-vis spectroscopy. IOPH-pBGS demonstrated excellent drug loading of 33.4 ± 5.1% by weight while maintaining small size (36.5 ± 1.8 nm). Drug release was monitored at biologically relevant pHs and demonstrated pH dependent release with maximum release at pH 5.5 (intracellular conditions), and minimal release at physiological pH (7.4). IOPH-pBGS significantly suppressed activity of MGMT and potentiated Temozolomide (TMZ) toxicity in vitro, demonstrating potential as a new treatment option for glioblastomas (GBMs).

Superior survival of ex vivo cultured human reticulocytes following transfusion into mice.

The generation of cultured red blood cells from stem cell sources may fill an unmet clinical need for transfusion-dependent patients, particularly in countries that lack a sufficient and safe blood supply. Cultured red blood cells were generated from human CD34+ cells from adult peripheral blood or cord blood by ex vivo expansion, and a comprehensive in vivo survival comparison with standard red cell concentrates was undertaken. Significant amplification (>105-fold) was achieved using CD34+ cells from both cord blood and peripheral blood, generating high yields of enucleated cultured red blood cells. Following transfusion, higher levels of cultured red cells could be detected in the murine circulation compared to standard adult red cells. The proportions of cultured blood cells from cord or peripheral blood sources remained high 24 hours post-transfusion (82±5% and 78±9%, respectively), while standard adult blood cells declined rapidly to only 49±9% by this time. In addition, the survival time of cultured blood cells in mice was longer than that of standard adult red cells. A paired comparison of cultured blood cells and standard adult red blood cells from the same donor confirmed the enhanced in vivo survival capacity of the cultured cells. The study herein represents the first demonstration that ex vivo generated cultured red blood cells survive longer than donor red cells using an in vivo model that more closely mimics clinical transfusion. Cultured red blood cells may offer advantages for transfusion-dependent patients by reducing the number of transfusions required.

Investigating CD99 Expression in Leukemia Propagating Cells in Childhood T Cell Acute Lymphoblastic Leukemia.

A significant number of children with T-lineage acute lymphoblastic leukemia (T-ALL) fail to respond to therapy and experience early relapse. CD99 has been shown to be overexpressed on T-ALL cells and is considered to be a reliable detector of the disease. However, the relevance of CD99 overexpression in ALL has not been investigated in a functional context. The aim of this study was to investigate the functional capacity of CD99+ cells in childhood ALL and determine the suitability of CD99 as a therapeutic target. Flow cytometric analyses confirmed higher expression of CD99 in ALL blasts (81.5±22.7%) compared to normal hemopoietic stem cells (27.5±21.9%) and T cells (3.1±5.2%, P≤0.004). When ALL cells were sorted and assessed in functional assays, all 4 subpopulations (CD34+/CD99+, CD34+/CD99-, CD34-/CD99+ and CD34-/CD99-) could proliferate in vitro and establish leukemia in NSG mice. Leukemia propagating cell frequencies ranged from 1 in 300 to 1 in 7.4x104 but were highest in the CD34+/CD99- subpopulation. In addition, all four subpopulations had self-renewal ability in secondary NSG mice. Cells in each subpopulation contained patient specific TCR rearrangements and karyotypic changes that were preserved with passage through serial NSG transplants. Despite high levels of CD99 antigen on the majority of blast cells, leukemia initiating capacity in vivo was not restricted to cells that express this protein. Consequently, targeting CD99 alone would not eliminate all T-ALL cells with the ability to maintain the disease. The challenge remains to develop therapeutic strategies that can eliminate all leukemia cells with self-renewal capacity in vivo.

Junctional Adhesion Molecule-A Is Highly Expressed on Human Hematopoietic Repopulating Cells and Associates with the Key Hematopoietic Chemokine Receptor CXCR4.

Hematopoietic stem/progenitor cells (HSPCs) reside in specialized bone marrow microenvironmental niches, with vascular elements (endothelial/mesenchymal stromal cells) and CXCR4-CXCL12 interactions playing particularly important roles for HSPC entry, retention, and maintenance. The functional effects of CXCL12 are dependent on its local concentration and rely on complex HSPC-niche interactions. Two Junctional Adhesion Molecule family proteins, Junctional Adhesion Molecule-B (JAM)-B and JAM-C, are reported to mediate HSPC-stromal cell interactions, which in turn regulate CXCL12 production by mesenchymal stromal cells (MSCs). Here, we demonstrate that another JAM family member, JAM-A, is most highly expressed on human hematopoietic stem cells with in vivo repopulating activity (p < .01 for JAM-A(high) compared to JAM-A(Int or Low) cord blood CD34(+) cells). JAM-A blockade, silencing, and overexpression show that JAM-A contributes significantly (p < .05) to the adhesion of human HSPCs to IL-1ß activated human bone marrow sinusoidal endothelium. Further studies highlight a novel association of JAM-A with CXCR4, with these molecules moving to the leading edge of the cell upon presentation with CXCL12 (p < .05 compared to no CXCL12). Therefore, we hypothesize that JAM family members differentially regulate CXCR4 function and CXCL12 secretion in the bone marrow niche. Stem Cells 2016;34:1664-1678.

Interleukin-15 enhances cellular proliferation and upregulates CNS homing molecules in pre-B acute lymphoblastic leukemia.

Genome-wide association studies have consistently implicated the interleukin-15 (IL-15) gene in acute lymphoblastic leukemia (ALL) biology, including associations with disease susceptibility, and increased risk of central nervous system (CNS) involvement. However, whether pre-B ALL blasts directly respond to IL-15 is unknown. Here, we show that most pre-B ALL primary samples and cell lines express IL-15 and components of its receptor and that primary pre-B ALL cells show increased growth in culture in response to IL-15. Investigation of mechanisms of action using IL-15-responsive SD-1 cells shows this growth advantage is maximal under low-serum conditions, mimicking those found in cerebrospinal fluid. IL-15 also upregulates PSGL-1 and CXCR3, molecules associated with CNS trafficking. Investigation of downstream signaling pathways indicates that IL-15 induces signal transducer and activator of transcription 5 (STAT5), extracellular signal-regulated kinase (ERK) 1/2, and to a lesser extent phosphatidylinositol 3-kinase (PI3K) and nuclear factor κB (NF-κB) phosphorylation. The IL-15-mediated growth advantage is abolished by mitogen-activated protein kinase kinase/extracellular signal-regulated kinase (MEK/ERK), PI3K, and NF-κB inhibitors but preserved in the presence of STAT5 inhibition. Together, these observations provide a mechanistic link between increased levels of IL-15 expression and leukemogenesis, high-risk disease, and CNS relapse and suggest potential therapeutic targets.

Parthenolide eliminates leukemia-initiating cell populations and improves survival in xenografts of childhood acute lymphoblastic leukemia.

Approximately 20% of children with acute lymphoblastic leukemia (ALL) relapse because of failure to eradicate the disease. Current drug efficacy studies focus on reducing leukemia cell burden. However, if drugs have limited effects on leukemia-initiating cells (LICs), then these cells may expand and eventually cause relapse. Parthenolide (PTL) has been shown to cause apoptosis of LIC in acute myeloid leukemia. In the present study, we assessed the effects of PTL on LIC populations in childhood ALL. Apoptosis assays demonstrated that PTL was effective against bulk B- and T-ALL cells, whereas the CD34(+)/CD19(-), CD34(+)/CD7(-), and CD34(-) subpopulations were more resistant. However, functional analyses revealed that PTL treatment prevented engraftment of multiple LIC populations in NOD/LtSz-scid IL-2Rγ(c)-null mice. PTL treatment of mice with established leukemias from low- and high-risk patients resulted in survival and restoration of normal murine hemopoiesis. In only 3 cases, disease progression was significantly slowed in mice engrafted with CD34(+)/CD19(-) or CD34(+)/CD7(-) and CD34(-) cells, but was not prevented, demonstrating that individual LIC populations within patients have different responses to therapy. These observations indicate that PTL may have therapeutic potential in childhood ALL and provide a basis for developing effective therapies that eradicate all LIC populations to prevent disease progression and reduce relapse.