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Notch3 and Notch4 support survival of primary B-cell acute lymphoblastic leukemia (B-ALL) cells, suggesting a role for Notch signaling in drug response. Here we used in vitro, in silico, and in vivo mouse xenograft model-based approaches to define the role of the Notch pathway in B-ALL chemosensitivity. We observed significant Notch receptor and ligand expression in B-ALL primary cells and cell lines. Primary leukemia cells from high-risk patients overexpressed Notch3, Notch4, and Jagged2 while displaying a reduction in expression levels of Notch1-4 following chemotherapy. We then analyzed in vitro cell survival of B-ALL cells treated with conventional chemotherapeutic agents alone or in combination with Notch signaling inhibitors. Gamma-secretase inhibitors (GSI) and anti-Notch4 were all capable of potentiating drug-induced cell death in B-ALL cells by upregulating intracellular levels of reactive oxygen species, which in turn modulated mTOR, NF-κB, and ERK expression. In NOG-mouse-based xenograft models of B-ALL, co-administration of the Notch inhibitor GSI-XII with the chemotherapeutic agent Ara-C lowered bone marrow leukemic burden compared with DMSO or Ara-C alone, thus prolonging mouse survival. Overall, our results support the potential effectiveness of Notch inhibitors in patients with B-ALL.Significance: Inhibition of Notch signaling enhances the chemosensitivity of B-ALL cells, suggesting Notch inhibition as a potential therapeutic strategy to improve the outcome of patients with B-ALL.

Supplemental Methods describes methods that were not thoroughly described in the main manuscript as well as methods used to produce supplemental data. Table S1 describes characteristics of patients involved in the study. Table S2 describes genes potentially damages in 5 B-ALL patients following DNA sequencing. Table S3 describes, epigenetics patterns of ALL patients as obtained following the processing of methylation data publicly available under accession number GSE49031. Table S4 describes Chi Square analysis of the association between Notch expression level and response to therapy. Table S5 describes B-ALL cell survival upon treatment with Notch ligands. Figure S1 describes expression of Notch target genes and Notch active forms in B-ALL samples. This figure also displays the validation of L5C5 antibody in HEK 293T cells. Figures S2 describes the sensitivity (Annexin V) of B-ALL samples to Ara-C, Doxorubicin and Dexamethasone, each used alone or in combination with anti-Notch3 or anti-Notch4. Figure S3 describes the sensitivity (Annexin V) of B-ALL samples to Ara-C, Doxorubicin and Dexamethasone, each used alone or in combination with different Notch inhibitors. The aim is to screen the most active (in term of cell death) association in vitro, that will then be used in vivo. Figures S4 presents how anti-oxidants NAC and BME protect B-ALL cells from cell death induced by drug treatments.

INTRODUCTION: Hematopoietic stem cell transplantation (HSCT) has proven to be effective for the treatment of hematopoietic disorders, including immune deficiencies, bone marrow failure syndromes (BMFS) and leukemia. However, current preparation for HSCT carries significant toxicity due to radiation and/or chemotherapy that put the patients at high risk of life-threatening infections and toxicity. Severe infections frequently present in the immediate post-HSCT period, while complications caused by chemotoxicity and irradiation damage affect multiple organs at the long term. The high mortality and morbidity rates, although acceptable for malignant diseases, make the risk-benefit ratio too high to apply HSCT for young patients with for instance BMFS and immune deficiencies. The low-risk solution that we propose in this report is the engineering and pre-clinically testing of novel antibodies that rapidly and transiently deplete hematopoietic stem cells (HSCs) to create the desired bone marrow (BM) space that allows for sufficient HSC engraftment. Highly effective HSC depleting antibodies that have a controllable activity in the body would be ideal for rapid and efficient treatment of patients. Such antibodies would facilitate BM conditioning without the risk of infections and toxicity. In this project, we developed and tested novel antibodies that target the c-KIT/CD117 receptor, which is a characteristic molecule on HSCs.METHODS: We developed novel anti-CD117 reagents including anti-CD117 IgG Fc-engineered (anti-CD117) antibody and bispecific T-cell engager (BiTE, CD117xCD3). For our experiments we used an anti-CD117 reference antibody, which is currently tested in clinical trials. We first determined the binding capacity and affinity of these novel reagents to human CD117 expressing TF-1 cell line. The in vitro depletion capacity of our anti-CD117 antibody was tested with an antibody-dependent cytotoxicity reporter Bioassay and NK-cell-mediated cell depletion assays using TF-1 cells and human primary BM-CD34+ cells as targets. The cytotoxicity of the BiTE was shown in vitro in a T-cell-mediated cell depletion assay with the same type of target cells. In addition, we determined T-cell activation, T-cell proliferation and inflammatory cytokine levels. Next, we tested our novel reagents in a CD34+ transplanted humanized mouse model (NOD.Cg-PrkdcscidIl2rgtm1Wjl/SzJ) for their ability to deplete human CD117+ HSCs. Mice were treated with our BiTE reagents for three days by multiple injections. The percentage of depleted human HSCs in the BM was determined at various time points by flow cytometry. Finally, the levels of the inflammatory cytokines were tested in the serum with ELLA Simple Plex assays.RESULTS: We demonstrated that our novel anti-CD117 reagents bind specifically to CD117 expressed on TF-1 and human CD34+ cells. Our novel anti-CD117 antibody showed an enhanced antibody-dependent cell-mediated cytotoxicity (ADCC), with a more than 2.5 improved killing of TF-1 cells compared to the reference antibody in vitro. Furthermore, we observed a greater than 4-fold improved killing of human CD34+ cells. We demonstrated that our CD117xCD3 BiTE also binds specifically to human T cells leading to a strong T-cell activation, T-cell proliferation, and upregulation of cytokines, in the presence of human CD117+ target cells. In in vitro cytotoxicity assays using our CD117xCD3 BiTE, we observed an 80% killing of TF-1 within 6 hours and 60% depletion of human CD34+ cells at 24 hours, whereas control BiTE did not induce cell death. We observed up to 80% depletion of human CD117+ HSCs in the BM of humanized mice already at 1 day post-treatment, whereas control-treated mice did not show depletion of CD117+ cells. This depletion was even more pronounced and on average 95% at 5 days post-treatment. Notably, no inflammatory cytokines in the serum or obvious toxicities were found in the treated mice.CONCLUSION: We showed that our novel anti-CD117 antibody and CD117xCD3 BiTE exhibit improved cell depletion in vitro. Furthermore, we showed that the CD117xCD3 BiTE rapidly depletes human HSCs in the BM of humanized mice. Our novel anti-CD117 reagents are promising for further development of safe BM conditioning protocols prior to HSCT.

T-cell prolymphocytic leukemia (T-PLL) is mostly characterized by aberrant expansion of small- to medium-sized prolymphocytes with a mature post-thymic phenotype, high aggressiveness of the disease and poor prognosis. However, T-PLL is more heterogeneous with a wide range of clinical, morphological, and molecular features, which occasionally impedes the diagnosis. We hypothesized that T-PLL consists of phenotypic and/or genotypic subgroups that may explain the heterogeneity of the disease. Multi-dimensional immuno-phenotyping and gene expression profiling did not reveal clear T-PLL subgroups, and no clear T-cell receptor a or β CDR3 skewing was observed between different T-PLL cases. We revealed that the expression of microRNA (miRNA) is aberrant and often heterogeneous in T-PLL. We identified 35 miRNA that were aberrantly expressed in T-PLL with miR-200c/141 as the most differentially expressed cluster. High miR- 200c/141 and miR-181a/181b expression was significantly correlated with increased white blood cell counts and poor survival. Furthermore, we found that overexpression of miR-200c/141 correlated with downregulation of their targets ZEB2 and TGFβR3 and aberrant TGFβ1- induced phosphorylated SMAD2 (p-SMAD2) and p-SMAD3, indicating that the TGFβ pathway is affected in T-PLL. Our results thus highlight the potential role for aberrantly expressed oncogenic miRNA in T-PLL and pave the way for new therapeutic targets in this disease.

Graft-vs-host-disease (GvHD) is currently the main complication of allogeneic hematopoietic stem cell transplantation. Mortality and morbidity rates are particularly high, especially in steroid-refractory acute GvHD (aGvHD). Immune regulatory human bone marrow mesenchymal stromal cells (hMB-MSCs) represent a therapeutic approach to address this issue. Unfortunately, their effect is hardly predictable in vivo due to several variables, that is, MSC tissue origin, concentration, dose number, administration route and timing, and inflammatory status of the recipient. Interestingly, human bone marrow MSC-derived extracellular vesicles (hBM-MSC-EVs) display many of the hBM-MSC immunoregulatory properties due to their content in paracrine factors that greatly varies according to the collection method. In this study, we focused on the immunological characterization of hBM-MSC-EVs on their capability of inducing regulatory T-cells (T-regs) both in vitro and in a xenograft mouse model of aGvHD. We correlated these data with the aGvHD incidence and degree following hBM-MSC-EV intravenous administration. Thus, we first quantified the EV immunomodulation in vitro in terms of EV immunomodulatory functional unit (EV-IFU), that is, the lowest concentration of EVs leading in vitro to at least threefold increase of the T-regs compared with controls. Second, we established the EV therapeutic dose in vivo (EV-TD) corresponding to 10-fold the in vitro EV-IFU. According to this approach, we observed a significant improvement of both mouse survival and control of aGvHD onset and progression. This study confirms that EVs may represent an alternative to whole MSCs for aGvHD prevention, once the effective dose is reproducibly identified according to EV-IFU and EV-TD definition.

Wnt/&beta, catenin signaling has been reported in Acute Myeloid leukemia, but little is known about its significance as a prognostic biomarker and drug target. In this study, we first evaluated the correlation between expression levels of Wnt molecules and clinical outcome. Then, we studied&mdash, in vitro and in vivo&mdash, the anti-leukemic value of combinatorial treatment between Wnt inhibitors and classic anti-leukemia drugs. Higher levels of &beta, catenin, Ser675-phospho-&beta, catenin and GSK-3&alpha, (total and Ser 9) were found in AML cells from intermediate or poor risk patients, nevertheless, patients presenting high activity of Wnt/&beta, catenin displayed shorter progression-free survival (PFS) according to univariate analysis. In vitro, many pharmacological inhibitors of Wnt signalling, i.e., LRP6 (Niclosamide), GSK-3 (LiCl, AR-A014418), and TCF/LEF (PNU-74654) but not Porcupine (IWP-2), significantly reduced proliferation and improved the drug sensitivity of AML cells cultured alone or in the presence of bone marrow stromal cells. In vivo, PNU-74654, Niclosamide and LiCl administration significantly reduced the bone marrow leukemic burden acting synergistically with Ara-C, thus improving mouse survival. Overall, our study demonstrates the antileukemic role of Wnt/&beta, catenin inhibition that may represent a potential new therapeutics strategy in AML.

The endothelin-1 (ET-1) receptors were recently found to mediate pro-survival functions in multiple myeloma (MM) cells in response to autocrine ET-1. This study investigated the effectiveness of macitentan, a dual ET-1 receptor antagonist, in MM treatment, and the mechanisms underlying its activities. Macitentan affected significantly MM cell (RPMI-8226, U266, KMS-12-PE) survival and pro-angiogenic cytokine release by down-modulating ET-1-activated MAPK/ERK and HIF-1α pathways, respectively. HIF-1α silencing abrogated the ET-1 mediated induction of genes encoding for pro-angiogenic cytokines such as VEGF-A, IL-8, Adrenomedullin, and ET-1 itself. Upon exposure to macitentan, MM cells cultured in the presence of the hypoxia-mimetic agent CoCl2, exogenous ET-1, or CoCl2plus ET-1, down-regulated HIF-1α and the transcription and release of downstream pro-angiogenic cytokines. Consistently, macitentan limited significantly the basal pro-angiogenic activity of RPMI-8226 cells in chorioallantoic membrane assay. In xenograft mouse models, established by injecting NOG mice eitherviaintra-caudal vein with U266 or subcutaneously with RPMI-8226 cells, macitentan reduced effectively the number of MM cells infiltrating bone marrow, and the size and microvascular density of subcutaneous MM tumors. ET-1 receptors targeting by macitentan represents an effective anti-proliferative and anti-angiogenic therapeutic approach in preclinical settings of MM.

The role of Notch signaling in acute myeloid leukemia (AML) is still under investigation. We have previously shown that high levels of Notch receptors and ligands could interfere with drug response. In this study, the protein expression of 79 AML blast samples collected from newly diagnosed patients was examined through flow cytometry. Gamma-secretase inhibitors were used in AML mouse xenograft models to evaluate the contribution of Notch pharmacological inhibition to mouse survival. We used univariate analysis for testing the correlation and/or association between protein expression and well-known prognostics markers. All the four receptors (Notch1&ndash, 4) and some ligands (Jagged2, DLL-3) were highly expressed in less mature subtypes (M0&ndash, M1). Notch3, Notch4, and Jagged2 were overexpressed in an adverse cytogenetic risk group compared to good cytogenetic risk patients. Chi-square analysis revealed a positive association between the complete remission rate after induction therapy and weak expression of Notch2 and Notch3. We also found an association between low levels of Notch4 and Jagged2 and three-year remission following allogeneic stem cell transplantation (HSCT). Accordingly, Kaplan&ndash, Meier analysis showed improved OS for patients lacking significant expression of Notch4, Jagged2, and DLL3. In vivo experiments in an AML mouse model highlighted both improved survival and a significant reduction of leukemia cell burden in the bone marrow of mice treated with the combination of Notch pan-inhibitors (GSIs) plus chemotherapy (Ara-C). Our results suggest that Notch can be useful as a prognostic marker and therapeutic target in AML.

// Paul Takam Kamga 1 , Giada Dal Collo 1 , Giulio Bassi 1 , Martina Midolo 1 , Massimo Delledonne 2, 3 , Marco Chilosi 4 , Massimiliano Bonifacio 1 and Mauro Krampera 1 1 Stem Cell Research Laboratory, Section of Hematology, Department of Medicine, University of Verona, Verona, Italy 2 Department of Biotechnology, University of Verona, Verona, Italy 3 Personal Genomics S.R.L., Verona, Italy 4 Section of Pathology, Department of Diagnostics and Public Health, University of Verona, Verona, Italy Correspondence to: Mauro Krampera, email: mauro.krampera@univr.it Keywords: Notch signaling; B-acute lymphoblastic leukemia; B-ALL; Alagille syndrome; ALGS Received: January 02, 2018 Accepted: March 11, 2018 Published: April 06, 2018 ABSTRACT Notch signaling contribution to B-cell acute lymphoblastic leukemia (B-ALL) development is still under investigation. The serendipitous onset of B-ALL in a patient affected by the germinal Notch mutation-dependent Alagille syndrome allowed us to establish a B-ALL cell line (VR-ALL) bearing a genetic loss of function in components of Notch signaling. VR-ALL is a common-type B-ALL cell line, grows in conventional culture medium supplemented with 10% serum, and gives rise, once injected into immunodeficient NOG mice, to a mouse xenograft model of B-ALL. Exome sequencing revealed deleterious mutations in some components of Notch signaling, including Jagged1, Notch1, and Notch2. In addition, VR-ALL is sensitive both in vitro and in vivo to γ-secretase inhibitors (GSIs) as well as conventional anti-leukemic drugs. For all these reasons, VR-ALL may help to gain more insights into the role of Notch signaling in B-ALL.

Notch3 and Notch4 support survival of primary B-cell acute lymphoblastic leukemia (B-ALL) cells, suggesting a role for Notch signaling in drug response. Here we used in vitro, in silico, and in vivo mouse xenograft model-based approaches to define the role of the Notch pathway in B-ALL chemosensitivity. We observed significant Notch receptor and ligand expression in B-ALL primary cells and cell lines. Primary leukemia cells from high-risk patients overexpressed Notch3, Notch4, and Jagged2 while displaying a reduction in expression levels of Notch1-4 following chemotherapy. We then analyzed in vitro cell survival of B-ALL cells treated with conventional chemotherapeutic agents alone or in combination with Notch signaling inhibitors. Gamma-secretase inhibitors (GSI) and anti-Notch4 were all capable of potentiating drug-induced cell death in B-ALL cells by upregulating intracellular levels of reactive oxygen species, which in turn modulated mTOR, NF-κB, and ERK expression. In NOG-mouse-based xenograft models of B-ALL, co-administration of the Notch inhibitor GSI-XII with the chemotherapeutic agent Ara-C lowered bone marrow leukemic burden compared with DMSO or Ara-C alone, thus prolonging mouse survival. Overall, our results support the potential effectiveness of Notch inhibitors in patients with B-ALL. Significance: Inhibition of Notch signaling enhances the chemosensitivity of B-ALL cells, suggesting Notch inhibition as a potential therapeutic strategy to improve the outcome of patients with B-ALL.

Background: Growing evidences from both preclinical and clinical investigations reveal the critical role of Wnt signalling for the development of many cancers and for their response to chemotherapy. Although recent studies suggest that aberrant Wnt signalling can be involved in the neoplastic myeloid cell growth, the contribution of the Wnt/β-catenin pathway to AML survival and chemoresistance is still unclear. Aims: In this study, we investigated the contribution of WNT/β-CATENIN signalling to AML survival and chemoresistance. For this purpose we tested different modulators of Wnt/β-Catenin pathway for their ability to influence AML cells proliferation and response to Cytarabine (Ara-C) or Idarubicin treatment. Methods: AML primary blast cells(30 samples) or AML cell lines cultured alone or in presence of human bone marrow mesenchymal stromal cells (hBM-MSCs), were treated with with Cytarabine (Ara-C) or Idarubicin, in presence or absence of Wnt modulators, including ligands (Wnt3a, Wnt5a/5b), Porcupine inhibitors (IWP-2), LRP6 inhibitors (Niclosamide), or antagonists of TCF/β-catenin (PKF118-310, PNU-74654). Results: In silico analysis showed the enrichment of Wnt signalling components in AML samples. Western Blot and flow cytometry showed the presence of total β-catenin only in about 2/3 of primary samples analyzed, while . β-catenin positive samples had different degree of activation of the pathway, as revealed by the expression of active forms of β-catenin, including (Ser675)β-catenin and non-phospho-(Ser33/37/Thr41) β-catenin. Notably, we found that active forms of β-catenin increased in AML samples in co-culture with hBM-MSCs, thus suggesting that Wnt signalling could be involved in the crosstalk between bone marrow stroma and AML cells. The addition of Wnt or pharmacological inhibitors, such as IWP-2, PNU-74654 and Niclosamide, to the culture medium of β-catenin-positive AML samples, either cultured alone or in co-culture with hBM-MSCs, reduced AML cell proliferation with slight effect on cell death. When associated to Idarubicin, all Wnt inhibitors except IWP-2 synergycally induced a dramatic cell death in AML cells in both culture conditions. However, when Idarubicin was replaced by Ara-C the synergism was observed only with Niclosamide and PKF. Cell death was mainly due to apoptosis, as shown by Annexin-V staining. Conclusion: Overall our data show that Wnt inhibitors reduce proliferation and chemoresistance of AML cells in culture or co-culture with bone marrow stroma cells. Wnt/β-catenin signalling may represent a potential therapeutic strategy to improve AML treatment, overcoming bone marrow stromal-mediated anti-apoptotic and chemoresistance effects. Disclosures Bonifacio: Ariad Pharmaceuticals: Consultancy; Pfizer: Consultancy; Bristol Myers Squibb: Consultancy; Novartis: Research Funding; Amgen: Consultancy.

Background: GSK-3 is a serine-threonine kinase involved in metabolic regulation as well as in the control of many pathways associated to cancer development, including Notch Wnt/β-catenin, Hedgehog, and AKT. It has been demonstrated that association of GSK-3 inhibitors with All-trans-retinoic acid (ATRA) significantly improves ATRA-mediated differentiation and cell death of acute promyelocytic (APL) leukaemia cells. However, little is currently known about the contribution of GSK-3 role to non-promyelocytic AML cell response to treatment with chemotherapeutic agents. Aims: In this study, we aim to validate GSK-3 signalling as potent successful therapeutic target in non-promyelocytic AML. For this purpose we tested different GSK-3 for their ability to influence AML cells proliferation and response to Cytarabine (Ara-C) or Idarubicin treatments. Methods: GSK-3 expression was analyzed by Western blot or flow cytometry inAML cell lines (HL-60, THP1, U937) or primary non-promyelocyticAML blast cells (30 samples). AML cellscultured alone or in presence ofhuman bone marrow mesenchymal stromal cells (hBM-MSCs) were treated with GSK-3 inhibitors, including LiCL, AR-A014418, SB 216763, in association or not with Cytarabine (Ara-C) or Idarubicin. Cell proliferation and cell death were measured by CFSE dilution and TOPRO-3/Annexin-V staining, respectively. Results: Flow cytometry and Western blot analysis in AML samples revealed high expression levels of all GSK-3forms, including total GSK-3α, (Ser21) GSK-3α, total GSK-3β, and (Ser 21) GSK-3β; theseforms were all down-modulated when AML cells were cultured in presence of hBM-MSCs, thus suggesting that GSK-3 plays an important role in transducting micro-environmental signals in AML cells interacting with bone marrow stroma. The treatment of AML cells with increasing concentrations of each GSK-3 inhibitors decreased AML cell viability in a dose-dependent manner; interestingly, hBM-MSCs or peripheral blood mononuclear cells were less sensitive to GSK-3inhibitors. The addition of each inhibitor increased dramatically the AML cell apoptotic rate induced by the addition of Ara-C or Idarubicin in vitro. Notably, LiCl and AR-A014418 were capable of abrogating hBM-MSC-mediated AML cell resistance to apoptosis induced by Ara-C or Idarubicin. Conclusion: Overall our data clearly demonstrated that inhibition of GSK-3 reduced proliferation and chemoresistance of non promyelocytic AML cells. Thus GSK-3 inhibition represents a therapeutic strategy not only for APL but also for other AML subtypes. Disclosures Bonifacio: Ariad Pharmaceuticals: Consultancy; Pfizer: Consultancy; Bristol Myers Squibb: Consultancy; Novartis: Research Funding; Amgen: Consultancy.