Добірка наукової літератури з теми "Acute myeloid leukemia, Wnt/β-catenin, MSC"

Abstract Galectins are a family of b-galactoside binding proteins with effects on cell adhesion, apoptosis, cell cycle, and mRNA processing. Galectin-3 (LGALS3) is unique among galectins by having an N terminal region of roughly 130 amino acids that allows for multimerization and binding to other proteins independent of carbohydrate binding. In addition to promoting BCL2 gene expression and mitochondrial integrity, LGALS3 (along with LGALS1) positively regulates RAS signaling and thus stabilizes survival proteins dependent on ERK phosphorylation such as MCL-1. The pro-survival functions of LGALS3 and other galectins suggest that their targeting could be therapeutic for cancers including AML. Indeed, LGALS3 expression is a predictor of poor prognosis in acute myeloid leukemia (AML), as reported by Cheng and colleagues (Blood 2013) for patients with non-M3 AML and CN-AML. The modified pectin GCS-100 (La Jolla Pharmaceutical, San Diego, CA), now in a Phase II clinical trial for chronic kidney disease, binds and blocks the function of LGALS3. We report that GCS-100 suppresses the growth of AML cell lines OCI-AML3, THP-1, and HL60 in vitro as a single agent, at doses under the 250 ug/mL (i.e., within clinically-achievable concentrations). Short-term treatment of cells (i.e., < 6 hr) potently suppressed phosphorylation of AKT and ERK and reduced expression of BCL2 and MCL-1. Because LGALS3 positively regulates anti-apoptotic BCL2 family members, the Raz group has suggested targeting galectins to enhance efficacy of BH3 mimetic drugs (Harazano et al Cancer Metastasis Review 2013). We found that GCS-100 potently synergized with ABT-737 to kill OCI-AML3 cells: while 1 uM ABT-737 or 125 ug/mL GCS-100 reduced total viable cells by ~ 30% and induced apoptosis in < 20% of cells after 48 hr as single agents, their combination at those doses and time point reduced viable cells by ~ 94% and induced apoptosis in ~ 70% of cells. Suppression of LGALS3 by lentiviral shRNA reduced BCL2 gene expression as determined by qRT-PCR and augmented killing with ABT-737. Lentiviral suppression of LGALS3 protected cells from GCS-100 at doses of 250 ug/mL but reduction of the galectin failed to protect cells from higher doses of the drug (i.e., 500 ug/mL). This result suggests other galectins are likely inhibited at higher doses of the agent. We used gene expression profiling (GEP) on Illumina HT12v4 human whole-genome arrays to assess more broadly the molecular effects of inhibiting galectins in AML cell lines OCI-AML3 and THP-1 treated with 250 ug/mL or 500 ug/ml GCS-100 for 24 hr. Data were analyzed by Gene Set Enrichment Analysis (GSEA) using gene sets from the Molecular Signatures Database (www.broadinstitute.org/gsea/msigdb/). GSEA suggested that GCS-100 promotes differentiation and inhibits genes associated with proliferation. Multiple upregulated gene sets suggest that there may be a release of a differentiation block as a result of GCS-100 treatment. Furthermore, two gene sets suggest that GCS-100 behaves similar to a GSK3 inhibitor: Known pathways regulated by GSK3 in hematopoietic stem cells are mTOR and Wnt/beta Catenin. Inhibition of Wnt/beta Catenin can release a differentiation block. Consistent with GCS-100 promoting cell differentiation, lentiviral shRNA reduced LGALS3 protein > 90% in THP-1 cells and increased CD11b expression, suggesting increased differentiation, compared to cells with control shRNA. GCS-100 was tested in an in vitro model of the bone marrow microenvironment using BM-derived mesenchymal stromal cell (MSC). MSC can protect leukemia cells from a variety of clinically relevant chemotherapy drugs including AraC. GCS-100 was effective at killing AML cells despite the presence of MSC. Both THP-1 and OCI-AML3 cells exhibited > 80% and > 60% reduction of viable cells, respectively, despite the presence of MSC when treated with 250 ug/mL GCS-100 for 72 hours. In addition, GCS-100 was found to block adhesion of OCI-AML3 cells to MSC suggesting that GCS-100 could be effective in mobilizing AML cells. In summary, our findings suggest that GCS-100 can induce apoptosis in AML cells as a single agent or in combination with the BH3 mimetic ABT-737. The agent is effective even in the presence of MSC suggesting it could be efficacious in the leukemia niche. These findings suggest GCS-100 could be effective for AML therapy. Disclosures Rolke: La Jolla Pharmaceutical Company: Employment. Tidmarsh:La Jolla Pharmaceutical Company: Employment.

Abstract 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.

Abstract Background: The crosstalk between hematopoietic cells and bone marrow (BM) microenvironment in hematological malignancies is related to disease initiation, maintenance and relapse. BM niche sustains a protective response against currently available treatments that have shown unwanted adverse effects and high levels of toxicity for patients. WNT5a is a glycoprotein secreted by mesenchymal stromal cells (MSC) that activates the WNT non-canonical pathway in hematopoietic cells, modulating important biological processes related to neoplasia development. Aims: To investigate WNT5a mRNA expression, protein levels and methylation pattern in Myelodysplastic Syndrome (MDS) and de novo Acute Myeloid Leukemia (AML) patients and their impact on clinical outcomes, and to analyze effects of Foxy-5 (WNTResearch), a new WNT5a-mimicking compound. Methods: WNT5a mRNA expression was analyzed in mononuclear cells (MC) from 371 AML patients (212 male, median age 61 years [range: 2-87]) (Ohsu, Nature 2018). BMMSC and BM biopsies from 5 healthy donors (HD), 6 MDS and 13 AML patients at diagnosis were submitted to analysis of WNT5a mRNA expression and methylation after Azacytidine (1μM) treatment by real-time PCR, and WNT5a protein levels by immunohistochemistry and immunofluorescence (IF). A panel of myeloid leukemia cell lines (U937, HL60, THP1, KG1a, K562) were treated with Foxy-5 (1 to 100μM) for 72h in monoculture, coculture and 3D-coculture (with MSC) and evaluated for ROS production (DCFDA dye), cell proliferation (Ki-67 stain), autophagy (acridine orange dye), chemotaxis (Transwell), actin polymerization (phalloidin stain), cell cycle (PI/RNAse stain), cell viability (MTT assay), apoptosis (Annexin-V stain) and protein expression (Western blot, WB). MC and CD34+ cells from HD were submitted to cytotoxic assays. Statistical analyzes were performed using ANOVA or Mann-Whitney tests, as appropriate. Results: WNT5a gene expression was reduced in MC from AML patients with adverse cytogenetic risk compared to favorable and intermediate cytogenetic risk (fold-decrease [FD]: 42.9; 18.8, respectively) (P<.05) and in BMMSC from AML compared to HD (FD: 53.3) (P<.05). Accordingly, WNT5a gene expression in MDS and AML BMMSC treated with Azacytidine was restored (fold-increase [FI]: 3.99; 1.50, respectively). WNT5a protein expression were diminished in BMMSC from MDS and AML patients compared to HD onto a 3D-coculture (IF)(P<.05) and immunohistochemically detected in all BM hematopoietic lineages. Foxy-5 reduced ROS production in U937 (FD of mean fluorescence intensity [MFI]: 48.2; 46.6), HL60 (FD: 47.1; 115.0), KG1a (FD: 34.9; 20.7) and K562 (FD: 19.0; 24.3) at 100μM in monoculture and coculture, respectively (P<.05). Foxy-5 also significantly decreased proliferation in U937 (FD: 41.0), HL60 (FD: 18.0), THP1 (FD: 36.0) and K562 (FD: 68.0) at 100μM (P<.05), confirmed by a 3D-coculture containing these cell lines and MSC. Foxy-5 reduced monocyte differentiation and inhibited CD11b expression in U937 (FD: 16.4) and THP1 (FD: 14.4). Cell cycle progression was blocked in sub G0/G1 phase in all cell lines (P<.05) after Foxy-5 treatment, probably mediated by the reduction of cyclin D1 protein levels, as verified by WB. Further, Foxy-5 reduced AKT1/2/3 and ERK1/2 phosphorylation levels, possibly by beta-catenin inhibition, with disruption of actin polymerization (U937 (FD: 65.3), HL60 (FD: 35.9), THP1 (FD: 58.5), K562 (FD: 15.0)) at 100μM (P<.05) and consequent impairment of CXCL12-induced chemotaxis (U937 (FD: 27.9), HL60 (FD: 42.5), THP1 (FD: 82.4), K562 (FD: 45.1)) at 100μM (P<.05). In coculture, cell autophagy was reduced in U937 (FD: 27.8), HL60 (FD: 35.9), KG1a (FD: 16.4) and K562 (FD: 35.8) when treated with Foxy-5 at 100μM (P<.05). Finally, Foxy-5 treatment did not affect cytotoxicity in MC and CD34+ cells from HD. Conclusion: WNT5a downregulation in MDS and AML patients occurs probably by methylation and contributes to poor prognosis. Foxy-5, by restoring WNT5a levels, could represent a strategy to counterbalance several oncogenic processes present in leukemia by reducing ROS production and, consequently, inhibiting cell growth and differentiation, downregulating PI3K and MAPK pathways, disrupting actin polymerization and decreasing autophagy. Thus, Foxy-5 treatment may be an important approach to impair leukemia growth and maintenance and arises as a promising therapeutic target. Disclosures No relevant conflicts of interest to declare.

Abstract 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.

Dysregulated Wnt/β-catenin signal transduction is implicated in initiation, propagation, and poor prognosis in AML. Epigenetic inactivation is central to Wnt/β-catenin hyperactivity, and Wnt/β-catenin inhibitors are being investigated as targeted therapy. Dysregulated Wnt/β-catenin signaling has also been linked to accelerated aging. Since AML is a disease of old age (>60 yrs), we hypothesized age-related differential activity of Wnt/β-catenin signaling in AML patients. We probed Wnt/β-catenin expression in a series of AML in the elderly (>60 yrs) and compared it to a cohort of pediatric AML (<18 yrs). RNA from diagnostic bone marrow biopsies (n = 101) were evaluated for key Wnt/β-catenin molecule expression utilizing the NanoString platform. Differential expression of significance was defined as >2.5-fold difference (p < 0.01). A total of 36 pediatric AML (<18 yrs) and 36 elderly AML (>60 yrs) were identified in this cohort. Normal bone marrows (n = 10) were employed as controls. Wnt/β-catenin target genes (MYC, MYB, and RUNX1) showed upregulation, while Wnt/β-catenin inhibitors (CXXR, DKK1-4, SFRP1-4, SOST, and WIFI) were suppressed in elderly AML compared to pediatric AML and controls. Our data denote that suppressed inhibitor expression (through mutation or hypermethylation) is an additional contributing factor in Wnt/β-catenin hyperactivity in elderly AML, thus supporting Wnt/β-catenin inhibitors as potential targeted therapy.

Wnt/β-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—in vitro and in vivo—the anti-leukemic value of combinatorial treatment between Wnt inhibitors and classic anti-leukemia drugs. Higher levels of β-catenin, Ser675-phospho-β-catenin and GSK-3α (total and Ser 9) were found in AML cells from intermediate or poor risk patients; nevertheless, patients presenting high activity of Wnt/β-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/β-catenin inhibition that may represent a potential new therapeutics strategy in AML.

Abstract Eradication of minimal residual disease is a key goal in AML treatment. It has been found that interaction between leukaemic blasts and different cells of the bone marrow niche contributes to AML drug resistance. Previously we have demonstrated that β-catenin may mediate drug resistance in both short and long-term stromal co-culture assays. β-catenin is known to correlate with poor prognosis in AML. β-catenin has dual roles as both a central effector molecule of the canonical Wnt signalling pathway and a component of adherens junction. The role of Wnt/β-catenin in AML has been well established, but the mechanism through which it mediates adhesion in AML remains unclear. Using a human:human co-culture adhesion model, β-catenin was found to be significantly up-regulated on HS5 and AML derived mesenchymal stromal cell (MSC). Lentivirus mediated β-catenin knock-down in AML cells significantly reduced their adhesion on HS5 and primary normal MSC and AML MSC (n=3, P<0.001). β-catenin knock-down also significantly reduced the proliferation of AML cells either on their own or in suspension from co-culture with primary normal MSC and AML MSC (P<0.001, n=3). In order to dissect the mechanisms underlying β-catenin mediated blast cell adhesion phenotype, KG-1a cells were chosen based on their primitive phenotype, high adhesion to human stroma and β-catenin nuclear translocation ability.KG-1a β-catenin knock-down and control cells were co-cultured with HS5 cells for 24hr and soluble factors in supernatants were harvested and analysed by Luminex bead arrays. β-catenin knock down induced reciprocal feedback signals in both KG-1a cells and HS5 cells. KG-1a catenin knockdown cells displayed increased levels of pro-inflammatory and adhesion pathways including: Galectin-3, N-CAM, NCAM1-1, CEACAM-1, osteonectin, CCL3, C5a, CCL4 and TNFα. Other soluble factors, including S100A8, TIMP-1, CD44, IL-2 and MMP3, were found to be down-regulated in KG-1a cells with β-catenin knock down and co-culture with HS5 abrogated these changes, clearly demonstrating stromal compensation in response to β-catenin knockdown. KG-1a β-catenin knock down and control cells were co-cultured with HS5 cells and suspension and adherent fractions harvested for nuclear and cytoplasmic protein extraction. Proteomic analysis of protein lysates using TMT labelling revealed that significant knock down of catenin target and adhesion molecule CD44 was observed in both cytoplasmic and nuclear fractions in both suspension and adherent KG-1a cells with beta-catenin knock down, suggesting canonical Wnt signalling is universally affected regardless of cellular context. Reduced CD44 production in catenin knockout cell lines was also confirmed in the soluble secretory factors from supernatants analysed by Luminex bead arrays, which also showed a significant reduction in soluble CD44 in β-catenin knock down lines (p<0.01). CD44 was also found to be significantly downregulated on KG-1a cell surface by flow cytometry in both suspension and adherent cells with β-catenin knock down(P<0.01), although adherent KG-1a cells showed considerably higher reduction in CD44 compared with suspension KG-1a cells (P<0.001). Proteomic data further demonstrated the upregulation of nuclear CD44 in adherent fractions, compared with suspension fractions, in both β-catenin knock down cells and control cells, suggesting activated and internalized CD44. Previous publications have shown that nuclear CD44 activates stemness factors, such as Nanog, SOX2 and Oct-4 and also PI3K/AKT and MAPK/ERK signal pathways which might contribute to the stroma mediated drug resistance we observed before. In conclusion, stromal feedback drives an AML blast adhesion phenotype through the Catenin/CD44 signalling axis, which is a contributing mechanism underlying the β-catenin-mediated stromal drug protection in AML. This finding indicates the recent development of novel Wnt inhibitors may be insufficient as a monotherapy to eradicate minimal residual disease in AML and further investigation of stromal-specific Wnt/CD44 targeting combinations is required to tackle this resistance mechanism. Disclosures Ottmann: Fusion Pharma: Consultancy, Research Funding; Celgene: Consultancy, Research Funding; Novartis: Consultancy; Incyte: Consultancy, Research Funding; Takeda: Consultancy; Pfizer: Consultancy; Amgen: Consultancy.

Abstract Abstract 912 BCR-ABL tyrosine kinase inhibitors (TKI) do not eliminate leukemia stem cells (LSC) in chronic myeloid leukemia (CML), which remain a potential source of relapse. TKI treatment effectively inhibits BCR-ABL kinase activity in CML LSC, indicating that additional kinase-independent mechanisms contribute to LSC preservation. We investigated the role of signals from the bone marrow (BM) microenvironment in protecting chronic phase (CP) CML stem/progenitor cells from TKI treatment. Culture with human BM mesenchymal stromal cells (MSC), immortalized by ectopic expression of telomerase, significantly inhibited apoptosis in CP CML CD34+CD38- primitive and CD34+CD38+ commited progenitors treated with imatinib (5μM, p<0.01), nilotinib (5μM, p<0.01), or dasatinib(150nM, p<0.05). MSC coculture reduced TKI-mediated apoptosis in both dividing and non-dividing CD34+CD38- cells, defined using CFSE labeling, and increased the percentage of undivided CD34+CD38- cells (p<0.05). MSC coculture also enhanced colony forming ability of CML CD34+CD38- (p<0.05) and CD34+CD38+ (p<0.05) cells treated with TKI. Importantly MSC coculture, with or without imatinib treatment, significantly enhanced engraftment of CML CD34+ cells in immunodeficient NSG mice, both at 4 weeks (without IM: 27.2±5% human CD45+ cells without stroma, 52.8±8% with stroma, p<0.001; with IM: 4.9±2% without stroma, 10.1±2% with stroma, p<0.05) and at 10 weeks post-transplant (without IM : 1.48±0.2% human CD45+ cells without stroma, 2.37±0.4% with stroma, p=0.07; with IM : 0.74±0.2% without stroma, 1.2±0.3% with stroma, p<0.05). CML progenitors cultured in a transwell insert over MSC showed increased apoptosis following TKI exposure compared to cells cultured in direct contact with MSC (p<0.05). An increased proportion of CML progenitors adhered to MSC after 4 days of TKI treatment (22±4% without IM, 42±5% with IM, p<0.05). Antibody or peptide (NCDH) mediated blockade of the N-Cadherin receptor reduced adhesion of CML progenitors to MSC (p<0.05), and increased apoptosis of TKI-treated CML progenitors cocultured with MSC (p<0.05), indicating an important role for N-Cadherin in MSC-mediated protection of CML progenitors from TKI. Although N-Cadherin expression measured by flow cytometry, Western blot and Q-RT-PCR was lower in CML compared to normal CD34+CD38- and CD34+CD38+ cells, we observed significantly increased N-Cadherin expression in CML cells remaining after 4 days culture with IM and MSC (p<0.05). We observed enhanced β-catenin activity in CML progenitors cocultured with MSC, with and without TKI treatment, as manifested by increased β-catenin protein levels and nuclear localization, enhanced expression of β-catenin target genes, and increased TCF/LEF reporter activity. β-catenin levels and target gene expression were increased primarily in MSC-adherent CML progenitors compared to non-adherent cells, and were significantly reduced by antibody or peptide-mediated inhibition of N-Cadherin-mediated adhesion. Using the Duolink labeling technology, we demonstrated increased protein-protein interactions between N-cadherin and β-catenin in CML progenitors cocultured with MSC, with or without TKI treatment. Finally, we showed that addition of exogenous Wnt1 protected CML progenitors from TKI treatment, whereas inhibition of Wnt receptors by DKK1, or inhibition of β-catenin signaling by the small molecule inhibitor ICG001, enhanced apoptosis of CML progenitors cocultured with MSC, suggesting an important role for exogenous Wnt signaling in MSC-mediated protection of CML progenitors from TKI-induced apoptosis. Microarray analysis of gene expression confirmed enrichment of Wnt/β-catenin and Cadherin related gene sets in CML CD34+ cells cultured on MSC with or without IM, as well as enrichment of genes related to hematopoietic stem cell (HSC) self-renewal, HSC quiescence, and cytokine signaling. In conclusion, our studies reveal an important role for exogenous Wnt-β-catenin signaling, and a close interplay between N-Cadherin and β-catenin, in microenvonment-mediated resistance of CML stem and progenitor cells to TKI treatment. These findings support further development of novel treatment strategies to eradicate residual LSC in TKI-treated CML patients through inhibition of Wnt secretion or blockade of Wnt or N-Cadherin receptors. Disclosures: No relevant conflicts of interest to declare.

Abstract Abstract 1573 Wnt proteins are important developmental regulators and are known to play a role in maintenance of hematopoietic stem cells (HSC). Wnt signaling has also been identified as one of the most frequently dysregulated processes associated with acute myeloid leukemia (AML), though the significance of this observation is as yet poorly understood. Here we investigate the role of two Wnt signaling proteins; β-catenin and γ-catenin and their respective roles in both normal human hematopoiesis and in AML. These proteins have dual and overlapping roles as transcriptional activators of Wnt target genes in the nucleus, and as structural components of the cytoskeleton. To determine the potential scope of influence of these proteins, we first examined their expression levels and subcellular location throughout normal human hematopoiesis using multi-parameter flow cytometric analysis and confocal microscopy. As expected β-catenin was strongly expressed in human cord blood derived HSC (212 MFI ±124, n=6) and at lower levels in differentiated subsets; surprisingly however β-catenin expression was maintained in granulocytic (1182 MFI±568) and monocytic cells (284 MFI±107). Nuclear localization was independent of cytoplasmic expression level, being strongly nuclear-localized in early progenitors and predominantly cytoplasmic in differentiated cells (58%±5 nuclear-localized in CD34+ cells vs 27%±1 in granulocytes, P=0.008). The expression pattern of γ-catenin was similar to β-catenin but showed a reciprocal pattern of subcellular localization, with levels of nuclear γ-catenin strongest in differentiated cells (10%±2 in CD34+ cells vs 44%±3 in monocytes P=0.0005). These data imply complementary roles for β and γ-catenin in normal hematopoiesis and show that nuclear localization of these proteins is regulated independently and irrespective of their expression level. In AML patients, β-catenin dysregulation has been previously reported; however, we also observed frequent overexpression of γ-catenin (over 5 fold in 25% of patients). This overexpression was associated with lower remission rates (OR 1.23 per log increase, P=0.03, CI 1.02–1.49) arising from resistant disease (OR 1.57 per log increase, P=0.003, CI 1.16–2.14) in a cohort of 243 AML patients adjusted for baseline diagnostic variables. In contrast to normal hematopoiesis, we found that nuclear localization of γ-catenin correlated with nuclear localization of β-catenin in AML (R=0.5, n=59) suggesting that the capacity to independently regulate the nuclear entry/retention of these catenins is disrupted in AML. To investigate this, we examined the effect of ectopic overexpression of γ-catenin in normal cord blood derived CD34+ cells and AML cell lines. Three-fold overexpression of γ-catenin failed to induce nuclear translocation of γ- or β-catenin in normal progenitors, which exhibited no major developmental defects. In contrast, in 3 of 4 AML cell lines, overexpression of γ-catenin strongly promoted its nuclear localization (9-16 fold) and was associated with a block in agonist-induced differentiation - a phenotype previously associated with β-catenin. In accord with this, we found that as in primary AML, nuclear translocation of γ-catenin in AML cell lines was associated with translocation of β-catenin (2-22 fold). In conclusion, we propose that in normal hematopoiesis, nuclear translocation of β- and γ-catenin is tightly and independently regulated for each catenin. In contrast, most AML cells lack this regulation resulting in correlated nuclear levels of β- and γ-catenin. In addition, we found while overexpression of γ-catenin has little consequence for normal cells; in malignant cells γ-catenin facilitates nuclear translocation of β-catenin. Disclosures: No relevant conflicts of interest to declare.