Phosphoproteomics Uncovers Synergy between DNA-PK and FLT3 Inhibitors in Acute Myeloid Leukaemia

*These authors contributed equally to this work Background:Acute Myeloid Leukaemia (AML) is the most common and aggressive form of acute leukaemia, with a 5-year survival rate of just 24%. Activating mutations in the receptor tyrosine kinase FLT3 are the most common driver mutations in AML (25-30% of patients). Inhibiting the FLT3 receptor as a mono-therapeutic strategy in AML has proven difficult however, due to the development of treatment resistance and relapse. In order to identify improved therapeutic targets, the oncogenic signalling pathways downstream of mutant FLT3 require characterisation. Methods:Quantitative, label-based phosphoproteomics was performed on primary blasts from 7 AML patients (4 mutant-FLT3, 3 wildtype-FLT3). Differentially phosphorylated pathways were identified using Ingenuity Pathway Analysis, and kinase activation was assessed by kinase substrate enrichment analysis. Validation of results was performed using targeted mass spectrometry. Proliferation, apoptosis, and cell cycle assays were used to assess drug toxicity; drug synergy was evaluated using Chou-Talalay and Webb analyses. Results:Analysis of differentially expressed phosphoproteins in mutant-FLT3 compared to wildtype-FLT3 AML patient blasts revealed dysregulation of DNA repair pathways. Specifically, mutant-FLT3 samples displayed increased phosphorylation of proteins within the error-prone Non-Homologous End Joining (NHEJ) repair pathway, indicating NHEJ pathway activation. Kinase enrichment analysis predicted increased activity of the NHEJ core kinase, DNA-dependent protein kinase (DNA-PK), in mutant-FLT3 samples. Accordingly, proliferation assays revealed that mutant-FLT3 cell lines were sensitive to inhibition of DNA-PK. FLT3-inhibitor treatment reduced DNA-PK phosphorylation in mutant-FLT3 cells, suggesting that activation of DNA-PK is downstream of FLT3 activation. Inhibition of DNA-PK kinase activity combined with FLT3 inhibitors led to synergistic induction of cell death, selectively in mutant-FLT3 cell lines. DNA-PK inhibitors combined with FLT3 inhibitors also co-operatively induced cell death in mutant-FLT3 primary AML patient samplesex vivo, and significantly prolonged survival compared to either monotherapy in a human AML xenograft mouse model. Conclusions:Mutant-FLT3 AML is associated with activation of the error-prone NHEJ repair pathway, which may contribute to genomic instability. Targeting the NHEJ kinase, DNA-PK, in combination with FLT3 inhibitors has the potential to improve outcomes for this poor-prognosis AML subtype. Disclosures Enjeti: Bayer:Speakers Bureau;AbbVie:Membership on an entity's Board of Directors or advisory committees;Alexion:Speakers Bureau;Novartis:Membership on an entity's Board of Directors or advisory committees;Astellas:Membership on an entity's Board of Directors or advisory committees;Sanofi:Speakers Bureau.

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Functional Defects In Neutrophils Derived From Ezh2 Null Mice

Blood ◽

10.1182/blood.v122.21.1556.1556 ◽

2013 ◽

Vol 122 (21) ◽

pp. 1556-1556

Author(s):

Albert Perez-Ladaga ◽

Bennett Caughey ◽

Huafeng Xie ◽

Stuart H. Orkin ◽

David B. Sykes ◽

...

Keyword(s):

Cell Cycle ◽

Cell Death ◽

Progenitor Cells ◽

Board Of Directors ◽

Cell Lines ◽

Resting Cells ◽

Surface Markers ◽

Advisory Committees ◽

Spontaneous Cell Death

Abstract Introduction We investigate the role of Ezh2 in neutrophil function using murine progenitor cells differentiated into neutrophils lacking the Ezh2 gene. Ezh2 is the catalytic component of the polycomb repressive complex 2, which methylates lysine 27 of histone H3. It is frequently disrupted in myelodysplastic syndromes (MDS) leading to loss of function (Ernst et al., 2010). Mutations in EZH2 are found in 6% of MDS patients and while not strongly linked to cytopenias or blast proportion, they are independently associated with worse overall survival compared to patients with wildtype EZH2 (Bejar R. et al., 2011 and 2012). We hypothesize that Ezh2 mutations may cause qualitative defects in myeloid cells that impact their function and could contribute to the adverse prognosis observed in EZH2 mutant MDS. Methods Bone marrow from Ezh2 null (Ezh2-/-) and littermate control mice (WT) were transduced with HOXB8 fused to the estrogen receptor ligand-binding domain to produce immortalized myeloid progenitor cells. Removal of estrogen from the media allows these cells differentiate into mature neutrophils (Wang G.G., 2006). Differentiated cells were characterized for surface markers by flow cytometry and for gene expression by PCR of mRNA. Spontaneous cell death was measured by annexin/PI staining. Cell cycle patterns were determined by measuring the red emission of PI. Chemotactic function was assessed by counting cells that migrated across a transwell in presence/absence of the attractant zymosan. For phagocytosis experiments, cells were incubated with Fluoresbrite YG carboxylate beads at 37°C or 4°C. Reactive oxygen species (ROS) generation was measured by the oxidation of dihydrorhodamine 123 into fluorescent rhodamine 123. Results Estrogen withdrawal caused differentiation of both WT and Ezh2-/- lines into cells with mature neutrophil morphology after six days (Figure 1a). Both differentiated lines expressed the neutrophil surface markers CD11b and CD62L and the neutrophil-specific genes lactoferrin and Itgb2l. Ezh2 -/- cells had an increased rate of spontaneous cell death compared to WT in undifferentiated (32.81% vs. 20.33%) and mature cells (32.82% vs. 14.23%). Nevertheless, both progenitor cell lines showed similar cell cycle patterns, demonstrating that Ezh2 absence had no other effect on cell cycle progression. Ezh2 -/- neutrophils failed to migrate towards zymosan (Figure 1b). Expression of Tlr2, which binds zymosan, and other Toll-like receptors (Tlr4/5/9) were similar between the differentiated cell lines. Cells incubated with FITC-zymosan at 37°C showed no fluorescence differences between cell lines, indicating similar adherence. Experiments with neutrophils from an MDS patient with homozygous EZH2 mutations demonstrated a similar migration defect. Additional studies in MDS patient samples are ongoing and will be presented. Phagocytosis was reduced in Ezh2-/-cells. Unstimulated, the number of cells ingesting and adhering YG-beads was significantly greater with WT cells than with Ezh2-/-cells. When activated with fMLP, both lines showed increased adherence of YG-beads but the number of phagocytosing Ezh2-/- cells was reduced. The average number of beads ingested by each cell was lower for Ezh2-/- cells compared to WT (5.95 vs 2.94, p < 0.001) in resting cells, and 9.47 vs. 3.73 in fMLP-activated cells, p < 0.01. The fraction of Ezh2-/- neutrophils generating ROS when stimulated with PMA is 2.4-fold higher than for WT cells. ROS production was greatly reduced in the presence of diphenyleneiodonium (DPI), confirming the role of NADPH oxidase in the generation of ROS. Conclusion Our results indicate impaired function of neutrophils derived from Ezh2-/- mice, demonstrating increased spontaneous cell death, impaired migration, decreased phagocytosis, and overproduction of ROS. Qualitative defects observed in neutrophils deficient for EZH2 may help explain the adverse prognosis associated with these mutations in MDS patients. Disclosures: Bejar: Genoptix: Consultancy, Honoraria, Membership on an entity’s Board of Directors or advisory committees; Celgene: Consultancy, Membership on an entity’s Board of Directors or advisory committees.

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Treatment of Hodgkin Lymphoma Xenografts with the Novel PI3K δ/γ Inhibitor RP6530 Suppresses M2 Macrophage Polarization and Results in Potent Antitumor and Antiangiogenic Effects

Blood ◽

10.1182/blood.v128.22.45.45 ◽

2016 ◽

Vol 128 (22) ◽

pp. 45-45 ◽

Cited By ~ 2

Author(s):

Silvia Laura Locatelli ◽

Francesca Maria Consonni ◽

Giuseppa Careddu ◽

Simone Serio ◽

Srikant Viswanadha ◽

...

Keyword(s):

Cell Proliferation ◽

Cell Death ◽

Board Of Directors ◽

Cell Lines ◽

Tumor Vasculature ◽

M2 Macrophage ◽

The Novel ◽

Macrophage Differentiation ◽

Advisory Committees ◽

Human Macrophages

Abstract INTRODUCTION: Primary refractory and early-relapsed patients with Hodgkin lymphoma (HL) experience poor responses to salvage chemotherapy and dismal long-term disease control. Therefore, they represent an unmet medical need urgently requiring not only new diagnostic tools but also novel therapeutic agents to overcome the chemo-refractory phenotype.Tumor-associated macrophages (TAMs) have been implicated in the pathogenesis of HL and have been suggested to negatively impact clinical outcome. The phosphatidylinositol 3-kinase (PI3K) is a major effector pathway mediating tumor and endothelial cell survival and functions, as well as macrophage activation. As PI3Kδ and PI3Kγ are constitutively activated in several hematologic malignancies resulting in cancer development and progression, we hypothesize that the novel dual PI3K δ/γ inhibitor,RP6530, might represent a unique therapeutic opportunity for HL patients. This study aimed at investigating the activity and mechanism(s) of action of RP6530 in preclinical HL models. METHODS: The effects of RP6530 on HL cell lines (L-540, KM-H2, L-428) were investigated by assaying cell proliferation, cell death, and gene expression profiling. Upon treatment with RP6530, human macrophages co-cultured with HL cell lines were assessed by flow cytometry for cell death and expression of M1/M2 macrophage markers. The antitumor efficacy and mechanism(s) of action of RP6530 were also analyzed in NOD/SCID mice bearing HL cell line xenografts. Tumor vasculature was analyzed by in vivo biotinylation of vascular endothelial proteins. RESULTS: Exposure of HL cell lines to RP6530 (1.25 - 10 µM) induced a marked, early, and dose-dependent dephosphorylation of PI3K/Akt and MAPK pathways that was associated with inhibition of cell proliferation (L-540: 40 ± 4%, KM-H2: 33 ± 5% and L-428 30 ± 5%, mean ± SEM) and S phase cell cycle arrest (3-fold reduction, compared to vehicle-controls). Significant levels of caspase-dependent cell death were observed in L-540 (20µM: 61 ± 5 vs. 15 ± 2%), KM-H2 (20µM: 41 ± 4 vs. 12 ± 1%) and L-428 (20µM: 31± 4% vs. 12 ± 1%) cells that were associated with mitochondrial depolarization (up to 40%). Interestingly, microarray gene expression analysis of KM-H2 cell line showed that a 24-hour treatment with RP6530 decreased the amplitude of several gene signatures, including “PI3K signaling in B lymphocytes”, “Tumor cell proliferation”, “Tumor angiogenesis”, and “Macrophages activation”, while genes involved in positive regulation of cell death were upregulated. In KM-H2 co-culture, besides observing cell death of human macrophages (up to 40% following a 24-hour exposure), we found that RP6530 inhibited M2 macrophage differentiation, as suggested by decreased CD209 and CD163 expression, and increased M1 macrophage differentiation by upregulating CD40 and CD80 expression. Compared to vehicle-controls, analysis of RP6530-treated tumor xenografts showed a marked reduction of TAM (-44% and -50%, P ≤.0001 in L-540 and KM-H2, respectively), as well as tumor vessel density (average decrease: 80%), consistent with the role of PI3K signaling in the macrophage-dependent promotion of tumor growth and tumor-induced angiogenesis. This finding was paralleled by the histological detection of tumor vasculature disruption, and inhibition of phospho-Akt and -Erk on both endothelial and tumor cells. Finally, RP6530 treatment (150 mg/kg/BID/3wks) of NOD/SCID mice significantly reduced the growth of KM-H2 nodules (-60%, P ≤.0001) compared to vehicle-controls. Reduction of tumor growth was associated with a strong decrease in Ki-67 expression by tumor cells, increase in tumor apoptosis (1.2- and 12-fold in L-540 and KM-H2, respectively) and tumor necrosis (average increase: 7-fold, P≤.0001). CONCLUSIONS: These results demonstrate that the therapeutic potential of RP6530 in HL is likely due to a reduction of M2 macrophages polarization and inhibition of tumor angiogenesis. Our findings warrant further investigation in future clinical trials. Disclosures Viswanadha: Incozen Therapeutics: Employment. Vakkalanka:Rhizen Pharmaceuticals: Employment, Equity Ownership. Santoro:Roche: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Takeda: Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb: Membership on an entity's Board of Directors or advisory committees; ArQule: Membership on an entity's Board of Directors or advisory committees. Carlo-Stella:Boehringer Ingelheim: Consultancy; Rhizen Pharmaceuticals: Research Funding.

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Methyljasmonate, An Inhibitor of Glycolytic Energy Production, Displays Pre-Clinical Activity against Multiple Myeloma Cells.

Blood ◽

10.1182/blood.v114.22.1741.1741 ◽

2009 ◽

Vol 114 (22) ◽

pp. 1741-1741

Author(s):

Steffen Klippel ◽

Jana Jakubikova ◽

Jake Delmore ◽

Melissa G. Ooi ◽

Douglas McMillin ◽

...

Keyword(s):

Cell Cycle ◽

Multiple Myeloma ◽

Cell Death ◽

Cancer Cells ◽

Board Of Directors ◽

Cell Lines ◽

Research Funding ◽

Energy Production ◽

Advisory Committees ◽

Normal Cells

Abstract Abstract 1741 Poster Board I-767 Background In contrast to most normal cells, cancer cells typically produce energy predominantly by glycolysis as demonstrated by O. Warburg more than 50 years ago. Methyljasmonate (MJ), a hormone produced by plants in response to biotic & abiotic stresses such as herbivory and wounding, has been shown to prevent the interaction of hexokinase (Hxk) and voltage dependent anion channels (VDACs), thereby significantly impacting the onset of glycolytic energy production. This may explain promising preclinical results observed with MJ against a variety of cancer cells, including myeloid leukemia and B-cell lymphoma cell lines. Methods and Results We tested the potential of MJ against Multiple Myeloma (MM) cells. We first evaluated the response of 16 different MM cell lines to 24 h of exposure to MJ concentrations of 0.5 – 3.5 mM using MTT assays. 15/16 of the MM cell lines tested displayed an IC50 of < 1.5 mM. In contrast, HS-5 stroma cells and peripheral blood mononuclear cells (PBMCs) did not respond to that MJ concentration, and even at a concentration of 2.5 mM MJ showed a maximal reduction of cell viability of 40%. Similarly to MM cell lines, purified CD138+ primary tumor cells of 3 MM patients displayed an IC50 of < 1.5 mM, suggesting that the differential sensitivity of MM vs. normal cells to MJ is not restricted to cell lines, but is also observed with primary tumor cells. Importantly, neither co-culture with HS-5 stroma nor IL-6 protected MM cells against MJ. Cell death commitment assays revealed that 1h exposure of 1.5 mM MJ induced cell death. Annexin V/PI FACS analysis of MJ-exposed MM cells showed that the cell death is mainly driven by apoptosis, evidenced by cleavage of caspases 3, 8 and 9 as well as of PARP. However, pre-incubation of MM cells with specific caspase inhibitors such as 10 mM of AC-DEVD-CHO, Z-IETD-fmk, Z-LEHD-fmk or 50 mM of Z-VAD only minimally protects the cancer cells from MJ exposure. Therefore, the impact of the MJ is not solely due to caspase triggered proteolytic cascades. Measurements of cellular ATP content by cell titer glow (CTG; Promega, Madison, WI) assay showed rapid depletion of ATP triggered by MJ action in sensitive MM cell lines. Additionally, we observed that 1 h exposure to 2 mM MJ modulated signaling pathways including IRS1/PI3K/AKT, MEK1/2, as well as Stat3 and JNK. FACS-based cell cycle analysis after propidium iodide staining did not show cell cycle arrest, but rather a rapid transition of cells to G0/G1 No correlation of sensitivity of MM cell lines and the number of mitochondria per cancer cell, as determined by Mitotracker Green (Invitrogen, Carlsbad, CA) -based flow analysis, was observed. We next examined if MJ exhibits either significant antagonism or synergy with established or novel anti-MM agents, including Bortezomib, Lenalidomide, Doxorubicin, Rapamycin or Dexamethasone, but discovered neither. However, MJ displayed synergy when combined with 2-Deoxyglucose. Finally, MJ was tested in vivo in scid/nod mice irradiated with 150 rads, injected with 1× 106 MM1S cells, and then, treated at 500 mg/kg by IP administration on a 5 days on / 2 days off schedule starting two weeks after tumor cell injection, There was an overall survival advantage of MJ-treated animals over the respective controls, with all treated mice (n=10) still alive but 6/10 control mice dead after 27 d. Conclusions Based on its rapidity of anti-MM action, favorable safety profile in preclinical models, distinct pattern of molecular sequelae, and compatibility with established anti-MM agents, MJ represents a promising investigational anti-MM agent. Disclosures Laubach: Novartis: Consultancy, Honoraria. Richardson:Millennium: (Speakers Bureau up to 7/1/09), Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Celgene: (Speakers Bureau up to 7/1/09), Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Anderson:Millennium: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Consultancy, Honoraria, Research Funding; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Mitsiades:Novartis Pharmaceuticals: Consultancy, Honoraria; Milllennium: Consultancy, Honoraria; Bristol-Myers Squibb : Consultancy, Honoraria; Merck &Co.: Consultancy, Honoraria; Kosan Pharmaceuticals : Consultancy, Honoraria; Pharmion: Consultancy, Honoraria; PharmaMar: Patents & Royalties; Amgen: Research Funding; AVEO Pharma: Research Funding; EMD Serono: Research Funding; Sunesis Pharmaceuticals: Research Funding.

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Role Of Peroxisome Proliferator-Activated Receptor Gamma (PPARγ) and Its Ligands In The Regulation Of Functional OCT-1 Activity In CML Cells

Blood ◽

10.1182/blood.v122.21.1470.1470 ◽

2013 ◽

Vol 122 (21) ◽

pp. 1470-1470

Author(s):

Jueqiong Wang ◽

Chung Hoow Kok ◽

Richard J. D'Andrea ◽

Timothy P. Hughes ◽

Deborah L. White

Keyword(s):

Cell Death ◽

Board Of Directors ◽

Cell Lines ◽

Research Funding ◽

K562 Cells ◽

Vehicle Control ◽

Peroxisome Proliferator ◽

Advisory Committees ◽

Peroxisome Proliferator Activated Receptor

Abstract Introduction The human organic cation transporter-1 (hOCT-1) is the primary active influx protein for imatinib in BCR-ABL positive cells. The functional activity of the OCT-1 protein (OCT-1 activity, OA) is predictive of molecular response in de-novo chronic phase chronic myeloid leukemia (CP-CML) patients. We have previously demonstrated that diclofenac, a competitive peroxisome proliferator-activated receptor-γ (PPARγ) antagonist, can significantly increase OA in CML cells 1. However, the role of PPARγ and its ligands in OA regulation remain unknown. Thus, the link between OA and PPARγ in CML cells has been investigated in this study. Methods OA was determined by intracellular uptake and retention assay (IUR) in the presence and absence of the OCT-1 inhibitor, prazosin 2. To assess the effect of PPARγ ligands on OA, BCR-ABL positive cell lines (KU812, K562) were incubated with PPARγ antagonist (GW9662, T0070907) or agonists (GW1929, rosiglitazone) respectively for 1 hour immediately prior to the IUR assays. The OA was also assessed in the mononuclear cells (MNCs) of 77 CP-CML patients enrolled to the TIDEL II trial. PPARγ activity in CML MNC nuclear extracts was determined through the use of a PPARγ Transcription Factor Assay Kits according to the manufacturer's instructions. To assess the effect of PPARγ ligands on cell death, KU812 or K562 cells were stained with AnnexinV and 7-AAD for detection of apoptosis after the co-administration of imatinib and PPARγ ligands for 72 hours. Results A significant increase in OA was observed in KU812 and K562 cells treated with PPARγ antagonists. In contrast, PPARγ agonists significantly decreased the OA in both cell lines (Table 1). A negative link between OA and PPARγ activity was observed in CML MNC samples (R=-0.585, p<0.001). PPARγ activity was significantly elevated in CML patients who had a low OA at diagnosis (less than 4 ng/200,000 cells) compared with those who had higher OA (p<0.001). After 72 hours co-administration with 0.1µM imatinib, KU812 cells treated with PPARγ antagonists (GW9662 and T0070907) showed a significantly lower cell viability (40% and 18% respectively) compared with vehicle control (70%, p<0.001). Similar results were also observed in K562 cells after co-administration with 1.0µM imatinib for 72 hours. K562 cells treated with PPARγ antagonists (GW9662: 51% and T0070907: 47%) showed a significantly lower cell viability (51% and 47% respectively) compared with vehicle control (61%, p<0.05). Conclusion Ligand-activation or inhibition of PPARγ is a regulator of OA in CML cell lines, and the low MNC OCT-1 activity in CML patients is consistent with the high level of PPARγ activity in these cells. Low PPARγ activity may be the key driver for low OA and poor imatinib response observed in a subset of CML patients. Importantly, the enhanced OA as a result of PPARγ antagonist treatment resulted in increased cell death following co-administration with imatinib. Ongoing studies relating to the upstream pathways involved in PPARγ activation aim to reveal the possible mechanism of OA modulation by PPARγ. Enhancement of OA by PPARg antagonists is likely to provide an important axis for clinical application to improve the clinical efficacy of imatinib. This would be particularly important in patients with low OA who currently have inferior outcomes with imatinib therapy. 1. Wang J, Hughes TP, Kok CH, et al. Contrasting effects of diclofenac and ibuprofen on active imatinib uptake into leukaemic cells. British Journal of Cancer. 2012;106(11):1772-1778. 2. White DL, Saunders VA, Dang P, et al. Most CML patients who have a suboptimal response to imatinib have low OCT-1 activity: Higher doses of imatinib may overcome the negative impact of low OCT-1 activity. Blood. 2007;110(12):4064-4072. Disclosures: Hughes: Novartis: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding; BMS: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding; Ariad: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding; CSL: Research Funding. White:Novartis: Research Funding; BMS: Research Funding, Speakers Bureau; Ariad: Research Funding; CSL: Research Funding.

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A New Therapeutic Hypothesis: Nonsense-Mediated Decay Is an Exploitable Target in Multiple Myeloma

Blood ◽

10.1182/blood-2018-99-114801 ◽

2018 ◽

Vol 132 (Supplement 1) ◽

pp. 1937-1937

Author(s):

Alexander Leeksma ◽

Ingrid A.M. Derks ◽

Brett Garrick ◽

Torsten Trowe ◽

Aldo Jongejan ◽

...

Keyword(s):

Multiple Myeloma ◽

Cell Death ◽

Er Stress ◽

Board Of Directors ◽

Cell Lines ◽

Research Funding ◽

Protein Production ◽

Splicing Factors ◽

Advisory Committees ◽

Nonsense Mediated Decay

Abstract Background Nonsense-mediated decay (NMD) is a cellular quality control system that degrades mRNAs containing premature termination codons (PTCs) as well as ~10% of normal mRNAs (Kurosaki and Maquat, 2016). NMD thus prevents translation of misfolded proteins, and potential activation of the unfolded protein response (UPR). Mutations in splicing factors such as SF3B1, SRSF2, U2AF1 and ZRSR2 found in hematological as well as solid tumors, can lead to generation of aberrant mRNAs that contain PTCs. Aberrant splicing patterns in cancer cells can possibly result in increased pressure on the NMD machinery. CC-115, a potent inhibitor of mTOR kinase (TORK) and of DNA-dependent protein kinase, (DNA-PK; Mortensen et al., 2015; Tsuji et al., 2017), is in clinical development for the treatment of solid and hematologic malignancies (Thijssen et al., 2016). Preclinical data revealed an additional target of CC-115 and its differential effect on NMD. Our hypothesis was that a subset of tumor cells, especially hematologic tumors with high protein production and/or splicing factor mutations, would be susceptible to NMD inhibition by CC-115. Methods In total, 141 cell lines were screened for sensitivity to CC-115-mediated inhibition of proliferation and induction of cell death, in comparison to specific inhibition of TORK (CC-223). Isogenic DNA-PK knockout cell lines HCT116/HCT116 DNA-PK-/- and M059K/M059J DNA-PK-/- were treated with CC-115 and CC-223. Activity on NMD in vivo was tested using HCT-116 xenograft tumors treated with Vehicle or CC-115. Dependence on CC-115 sensitivity was determined using CRISPR/Cas9 technology of apoptosis or UPR genes in various MM cell lines. RNA sequencing was used for identification of potential targets in sensitive and resistant cell lines. Results A subset of cancer cell lines underwent cell death at sub-micromolar concentrations of CC-115 due to inhibition of NMD, but this was independent of mutations in splicing factors such as SF3B1. We next focused on MM cells as these generally produce high levels of (immunoglobulin) proteins and are prone to ER stress, and therefore potentially susceptible to NMD inhibition. Indeed, treatment with CC-115 resulted in activation of the UPR independent of TORK and DNA-PK inhibition, and cell death in 11/12 MM cell lines. Activity of CC-115 correlated strongly with cell death by the known ER-stress inducer, thapsigargin. Cell death by CC-115 occurred by the mitochondrial pathway of apoptosis, as it depended on caspase activity and the presence of Bax-Bak. Analysis of RNA sequencing data is ongoing and has indicated potential targets dictating sensitivity to CC-115-mediated cell death. Conclusions We describe that hematologic tumors with high protein production are specifically sensitive to CC-115, a novel and clinically exploitable inhibitor of NMD. This might lead to application in malignancies that depend on NMD to avoid excessive protein stress, such as multiple myeloma. Disclosures Garrick: Celgene: Employment. Trowe:Celgene: Employment. Kater:Acerta: Membership on an entity's Board of Directors or advisory committees, Research Funding; Abbvie: Membership on an entity's Board of Directors or advisory committees, Research Funding; Roche/Genentech: Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Research Funding; Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding. Eldering:Celgene: Research Funding. Filvaroff:Celgene: Employment.

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Targeting Polo-like Kinase 4 Triggers Polyploidy and Apoptotic Cell Death in TP53-Mutant Acute Myeloid Leukemia

Blood ◽

10.1182/blood-2021-153436 ◽

2021 ◽

Vol 138 (Supplement 1) ◽

pp. 1167-1167

Author(s):

Edward Ayoub ◽

Rafael Heinz Montoya ◽

Vakul Mohanty ◽

Wencke Walter ◽

Tallie Patsilevas ◽

...

Keyword(s):

Cell Death ◽

Board Of Directors ◽

Cell Lines ◽

Intellectual Property Rights ◽

Research Funding ◽

Apoptotic Cell ◽

Apoptotic Cell Death ◽

Advisory Committees ◽

Grant Support ◽

Support Research

Abstract Background: TP53 mutations in acute myeloid leukemia (AML) are associated with complex karyotype, high incidence of minimal residual disease (MRD), and high risk of relapse (Döhner et al., 2017; Giacomelli et al., 2018). While numerous novel treatment regimens, including the combination of the BCL2 inhibitor venetoclax (VEN) and hypomethylating agents (HMA), have emerged as partially effective treatments and resulted in higher remission rates in patients with TP53-mutant AML, full clearance of the mutant TP53 clone is rarely achieved and the majority of patients relapse (Short et al., 2021; Takahashi et al., 2016). The mechanisms responsible for response and relapse in TP53-mutant AML remain unclear and investigating novel mechanisms is critical to develop more effective therapies. Results: In order to shed light on the defective p53 signaling pathways underlying TP53 mutant AML, and to better understand mechanisms of resistance, we performed RNA-sequencing (RNA-seq) on FACS-sorted subpopulations using samples collected from TP53-mutant or TP53-wt high-risk AML patients. Samples were collected at diagnosis (DX) and post-treatment (POSTTX) (total number of samples n= 67, TP53-mutant=36, TP53-wt=31). Diagnostic samples include bulk AML, leukemic stem cells (LSCs), and post-treatment samples including bulk mononuclear cells (MNCS) and patient specific MRD (total n= 67, DX_Bulk=15, DX_LSCs=15, POSTTX_MNCs=14, POSTTX_MRD=23). Differential gene expression analysis of TP53-mutant samples indicates a positive enrichment of the following pathways: G2/M checkpoint, MYC targets, and mitotic spindle, among others. We focused here on genes associated with TP53-mutant AML enriched pathways, and identified a key regulator of centriole biogenesis, one of E2F targets: Polo-like kinase 4 (PLK4) as a potential target highly expressed in TP53-mutant AML samples . Previous publications showed that PLK4 is transcriptionally repressed by p53 and induces apoptosis upon RNAi silencing (Fischer et al., 2014; Li et al., 2005). Here we show that TP53-mutant AML samples lack the p53-dependent PLK4 repression and have higher levels of PLK4 compared to TP53-wt AML. To test the rigor of this finding, we interrogated the Munich Leukemia Laboratory (MLL) data base and analyzed their clinically annotated (e.g. karyotype, survival, complete blood counts, previous treatments ... etc) RNA-seq dataset of 726 AML samples (TP53-mutant=72, TP53-wt=654). TP53-mutant AML samples consistently showed significant PLK4 upregulation (p= 0.0003). We analyzed PLK4 expression and its correlation with TP53 mutations in The Cancer Dependency Map project dataset (1375 cell lines in 35 different types of cancers) (p= 0.004). Furthermore, we found significantly higher PLK4 protein levels in TP53-mutant AML MOLM13 cell lines when compared with syngeneic TP53-wt AML MOLM13 cells. Experimentally, we found that PLK4 inhibition using 25nM CFI-400945 in TP53-mutant AML MOLM13 cell lines triggers polyploidy > 2-fold higher than in TP53-wt AML MOLM13 cell lines 72 hours post treatment (Fig.1A p< 0.0001). Finally, we show that polyploidy is not reversible after drug removal and results in significantly increased levels of apoptotic cell death in TP53-mutant AML MOLM13 cells (Fig.1B). Conclusion: Our data suggest that TP53-mutant AML expresses higher levels of PLK4 in comparison to TP53-wt AML, and targeting PLK4 triggers polyploidy and apoptotic cell death in TP53-mutant AML. A clinical trial is ongoing testing the efficacy of PLK4 inhibition (CFI-400945) in AML (Clinical Trial ID: NCT04730258, TWT-202). Figure 1 Figure 1. Disclosures Issa: Kura Oncology: Consultancy, Research Funding; Syndax Pharmaceuticals: Research Funding; Novartis: Consultancy, Research Funding. Borthakur: Takeda: Membership on an entity's Board of Directors or advisory committees; ArgenX: Membership on an entity's Board of Directors or advisory committees; Ryvu: Research Funding; Astex: Research Funding; University of Texas MD Anderson Cancer Center: Current Employment; Protagonist: Consultancy; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees; GSK: Consultancy. Konopleva: Ascentage: Other: grant support, Research Funding; Novartis: Other: research funding pending, Patents & Royalties: intellectual property rights; Stemline Therapeutics: Research Funding; KisoJi: Research Funding; Eli Lilly: Patents & Royalties: intellectual property rights, Research Funding; Sanofi: Other: grant support, Research Funding; AstraZeneca: Other: grant support, Research Funding; Ablynx: Other: grant support, Research Funding; AbbVie: Consultancy, Honoraria, Other: Grant Support, Research Funding; F. Hoffmann-La Roche: Consultancy, Honoraria, Other: grant support; Reata Pharmaceuticals: Current holder of stock options in a privately-held company, Patents & Royalties: intellectual property rights; Rafael Pharmaceuticals: Other: grant support, Research Funding; Genentech: Consultancy, Honoraria, Other: grant support, Research Funding; Cellectis: Other: grant support; Calithera: Other: grant support, Research Funding; Agios: Other: grant support, Research Funding; Forty Seven: Other: grant support, Research Funding. Haferlach: MLL Munich Leukemia Laboratory: Other: Part ownership. Andreeff: Senti-Bio: Consultancy; ONO Pharmaceuticals: Research Funding; Glycomimetics: Consultancy; Aptose: Consultancy; Breast Cancer Research Foundation: Research Funding; Oxford Biomedica UK: Research Funding; Karyopharm: Research Funding; Medicxi: Consultancy; Amgen: Research Funding; AstraZeneca: Research Funding; Daiichi-Sankyo: Consultancy, Research Funding; Syndax: Consultancy; Novartis, Cancer UK; Leukemia & Lymphoma Society (LLS), German Research Council; NCI-RDCRN (Rare Disease Clin Network), CLL Foundation; Novartis: Membership on an entity's Board of Directors or advisory committees; Reata, Aptose, Eutropics, SentiBio; Chimerix, Oncolyze: Current holder of individual stocks in a privately-held company.

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BCL-2, a Therapeutic Target for High Risk Hypodiploid B-Cell Acute Lymphoblastic Leukemia

Blood ◽

10.1182/blood.v128.22.280.280 ◽

2016 ◽

Vol 128 (22) ◽

pp. 280-280 ◽

Cited By ~ 5

Author(s):

Ernesto Diaz-Flores ◽

Evan Q. Comeaux ◽

Kailyn Kim ◽

Kyle Beckman ◽

Kara L. Davis ◽

...

Keyword(s):

Cell Death ◽

Acute Lymphoblastic Leukemia ◽

Board Of Directors ◽

Cell Lines ◽

Research Funding ◽

Lymphoblastic Leukemia ◽

Advisory Committees ◽

Chromosomal Number ◽

Patient Derived Xenograft

Abstract Acute lymphoblastic leukemia (ALL) is the most common cancer of childhood. Specific genetic subsets, including hypodiploid ALL, are associated with particularly high rates of relapse. Despite the poor outcomes of hypodiploid B-ALL with traditional therapeutic approaches, there have been no known effective alternative therapies or novel candidates tested to improve outcome. We hypothesized that new therapeutic targets could by identified by integrated biochemical and genomic profiling, combined with functional drug assays in order to determine which pathways play an essential role in transformation. For biochemical profiling, we analyzed multiple pathways commonly deregulated in leukemias using phosphoflowcytometry (including receptor tyrosine kinases, JAK/STAT, MAPK, PI3K, PTEN, Bcl-2 survival and pro-apoptotic family members and p53). We subjected hypodiploid cell lines (NALM-16, MHH-CALL2) and patient derived xenograft samples in vitro to inhibitors against each of these pathways (PP2:Src family;Ruxolitinib: JAK/STAT; PD235901/CI1040: MAPK; GDC-0941, PI-90, PI-103, p110 (a, b, g, d): PI3K isoform specific; PP-242:mTOR; ABT-263/ABT-737: Bcl-2/Bcl-xl, and ABT-199: Bcl-2 specific). We found that the Bcl-2 inhibitors (ABT-263, ABT-737 and ABT-199) and to a lesser extent PI3K pathway inhibitors GDC-0941 and PP-242, but not the MAPK or RTK inhibitors, efficiently reduced proliferation of hypodiploid cells. However, only ABT-263/ABT-199 induced high levels of apoptosis at nanomolar concentrations. Based on the consistent efficacy observed with ABT-199 against hypodiploid patient-derived cells and cell lines in culture, we selected eight cryopreserved, previously xenografted (F3 generation) hypodiploid patient samples (4 low hypodiploid, chromosomal number between 32 and 39; and 4 Near Haploid, chromosomal number between 24 and 31) and three non-hypodiploid patient samples (Ph-positive,Ph-Like and Erg+) for a preclinical trial in immunodeficient mice. Each patient sample was engrafted into six mice, which were randomized to receive vehicle or ABT-199 daily over 60 days (Figure 1). Treatment started when the peripheral blood (PB) human CD45 count reached 15%. A rapid decrease in PB blasts was noted at 7 days (Figure 1). Eighty-five percent of the hypodiploid xenografts survived 60 days with either undetectable or low levels of leukemia in the PB. In contrastPh+ andPh-Like xenografts died within 10-20 days regardless of treatment. Importantly, hypodiploid leukemic blasts gradually emerged after discontinuing ABT-199 after 60 days. Additionally, despite low or undetectable levels of leukemic blasts in PB and reduced levels in bone marrow and spleen, all mice had high percentages of leukemic cells in the liver (Figure 2). In conclusion we have identified the survival protein Bcl-2 as a promising molecular target in hypodiploid B-ALL. ABT-199 for dramatically reduced leukemia cells in vitro and in vivo in patient-derived xenograft models of hypodiploid B-ALL. However, the liver represented a protective niche for these leukemias. In addition, our biochemical characterization of the organ infiltrating blasts collected from mice on trial indicate that the sensitivity of hypodiploid ALL to ABT-199 relies not only on high levels of Bcl-2 and deficiency for other survival proteins such as Bcl-xl but also on high levels of proapoptotic proteins, providing two different signatures that correlate with response to ABT-199. Using genome editing (CRISPR/Cas9) we interrogated the necessity for individual proapoptotic genes, including PUMA, NOXA, and BAD, for ABT-199-induced cell death. This study provides encouraging preclinical data that Bcl-2 may be a promising target for the treatment of hypodiploid B-ALL. Our studies identify signature biomarkers that correlate with drug response and identify essential proteins mediating ABT-199-induced cell death. Importantly, this report also identifies the limitations of using ABT-199 as single drug, and provides the rationale for using combinatorial therapies in order to improve the efficacy of the drug. Disclosures Mullighan: Loxo Oncology: Research Funding; Amgen: Speakers Bureau; Incyte: Membership on an entity's Board of Directors or advisory committees. Loh:Bristol Myers Squibb: Membership on an entity's Board of Directors or advisory committees; Abbvie: Research Funding.

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BET Bromodomain Inhibition Targets Both c-Myc and IL7R in Acute Lymphoblastic Leukemia

Blood ◽

10.1182/blood.v120.21.672.672 ◽

2012 ◽

Vol 120 (21) ◽

pp. 672-672

Author(s):

Nadja Kopp ◽

Christopher J. Ott ◽

Liat Bird ◽

Ronald Paranal ◽

Jun Qi ◽

...

Keyword(s):

Cell Death ◽

Acute Lymphoblastic Leukemia ◽

Board Of Directors ◽

Cell Lines ◽

Lymphoblastic Leukemia ◽

Janus Kinase ◽

Cytokine Receptor ◽

Advisory Committees ◽

Equity Ownership

Abstract Abstract 672 Long-term disease-free survival is achieved in over 80% of children with B-cell acute lymphoblastic leukemia (B-ALL) but only 40% of adults. Particular genomic alterations in B-ALL, including rearrangements of MLL and the cytokine receptor subunit CRLF2, confer a poor prognosis in both children and adults. In addition, current therapies for B-ALL are associated with significant short- and long-term toxicities, highlighting the critical need for new therapeutics. The novel compound JQ1 inhibits the BET class of human bromodomain proteins from mediating the assembly of macromolecular protein complexes that are required for transcriptional activation and polymerase elongation. In hematologic and epithelial tumors, JQ1 can downregulate the expression of c-MYC and thereby suppress malignant growth and survival. We investigated the therapeutic potential of JQ1 across multiple genetically-defined subsets of B-ALL. JQ1 potently induced apoptotic cell death (IC50∼30–300 nM) in all B-ALL cell lines (697, CEMO-1 NALM-6, MHH-CALL4, MUTZ-5, Reh, RS4;11, SEMK2) studied. Among the most sensitive lines (IC50<50 nM) were MUTZ-5 and MHH-CALL4, which both harbor IGH@-CRLF2 translocations as well as activating mutations in JAnus Kinase 2 (JAK2). CRLF2 heterodimerizes with the IL7 receptor (IL7R) subunit in response to thymic stromal lymphopoietin, which induces JAK/STAT, MAP kinase and AKT signaling. To identify mechanisms through which JQ1 induces cell death in MUTZ-5 and MHH-CALL4 cells, we quantified transcript and protein levels for relevant targets in the presence of JQ1 500 nM or vehicle (DMSO). Chromatin immunoprecipitation was also performed with antibodies against BRD4 followed by PCR to determine the effects of JQ1 on BRD4 binding at relevant promoters. As previously observed, JQ1 induced the downregulation of MYC mRNA, loss of BRD4 at the MYC promoter, and reduced the expression of c-Myc target genes. Immunoblotting with phospho-specific antibodies demonstrated almost complete loss of JAK2 and STAT5 phosphorylation in cells treated with JQ1, suggesting that JQ1 also blocks signaling downstream of CRLF2/IL7R. While the levels of CRLF2 mRNA were unaffected by JQ1 in MUTZ-5 and MHH-CALL4 cells, JQ1 markedly downregulated IL7R mRNA and depleted BRD4 from the IL7R promoter in both lines. The reduction in IL7R mRNA levels led to dramatic decreases in IL7R surface expression. Genome-wide expression profiling demonstrated a highly restricted effect of JQ1, with IL7R and MYC being the 7th and 23rd most downregulated genes, respectively. In fact, IL7R was the only cytokine receptor in both CRLF2-rearranged B-ALL lines that was significantly downregulated by JQ1 treatment. In addition, JQ1 potently reduced IL7R mRNA across other B-ALL cell lines with diverse cytogenetics. To determine whether JQ1 could suppress the growth of human B-ALL in vivo, we xenografted a human CRLF2-rearranged B-ALL primary sample into Nod.SCID.IL2RG−/− mice. Upon the development of >30% bone marrow involvement by human CD45+/CRLF2+ B-ALL cells, mice were randomized to receive JQ1 (50mg/kg intraperitoneally daily) or vehicle (DMSO). After 5 days of treatment, sentinel mice were sacrificed for pharmacodynamic endpoints. Spleens from mice treated with JQ1 had markedly reduced c-Myc expression and STAT5 phosphorylation compared with spleens from vehicle-treated mice. In survival cohorts (n=9 per arm), treatment with JQ1 significantly prolonged overall survival (p=0.0002) compared with vehicle. These results demonstrate that BET bromodomain inhibition is a promising therapeutic strategy for patients with B-ALL, including subsets with high-risk cytogenetics. Moreover, the surprising finding that JQ1 also targets IL7R expression suggests that bromodomain inhibitors may be especially useful in malignant and nonmalignant disorders dependent on IL7R. Disclosures: Bradner: Tensha Therapeutics: Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Acetylon Pharmaceuticals: Equity Ownership, Membership on an entity's Board of Directors or advisory committees; SHAPE Pharmaceuticals: Equity Ownership, Membership on an entity's Board of Directors or advisory committees. Weinstock:Novartis: Consultancy, Research Funding.

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Identification of Gene Networks Associated with the Anti-Leukemic Effect of Anti-Inflammatory Drugs on Acute Myeloid Leukemia Cell Lines

Blood ◽

10.1182/blood-2021-153903 ◽

2021 ◽

Vol 138 (Supplement 1) ◽

pp. 4343-4343

Author(s):

Victória Tomaz ◽

Karina Griesi-Oliveira ◽

Renato D Puga ◽

Fabio Pires de Souza Santos ◽

Nelson Hamerschlak ◽

...

Keyword(s):

Cell Cycle ◽

Cell Death ◽

Board Of Directors ◽

Cell Lines ◽

Rna Splicing ◽

Gene Networks ◽

Functional Enrichment ◽

Advisory Committees ◽

Cycle Arrest ◽

Anti Inflammatory

Abstract Introduction Despite recent advances in therapy, acute myeloid leukemia (AML) remain a medical challenge with high morbidity and mortality rates. For most patients, allogeneic hematopoietic stem cell transplantation remain the only curative option, but due to the advanced age at diagnosis, a significant proportion of patients are not elegible to this form of therapy. Nevertheless, novel therapies are warranted. There is preclinical evidence that anti-inflammatory compounds, such as COX-2 inhibitors and steroids, may have anti-neoplastic activity in different tumor types, including AML; nevertheles the mechanisms associated with its anti-neoplastic activity are not clear. Therefore, the aim of this work was to evaluate the anti-leukemic effect of the anti-inflammatory compounds nimesulide and prednisolone in AML cell lines and to identify genes and molecular pathways associated with cytotoxicity through transcriptome analysis. Methods The leukemic cell lines HL-60, THP-1, OCI-AML2 and OCI-AML3 were treated with nimesulide and prednisolone at 100 µM alone and in combination and with cytarabine at 2.5 µM. Twenty four hours after treatment , we measured the amount of cell death using Annexin V Apoptosis Detection Kit FITC (ThermoFisher) and the cell cycle was analized after fixing the cells with 70% alcohol and incubation with propidium iodide (1mg/ml) and RNAse (10mg/ml). In another experiment, we harvested the cells after 4 hours of treatment for transcriptome analysis. RNA was extracted from control (DMSO) and treatment groups (1 - nimesulide, 2 - prednisolone , 3 - nimesulide and prednisolone) with RNeasy Mini Kit (Qiagen). The Illumina® NEBNext® Ultra II Directional RNA Library Prep Kit was used for library preparation, following the manufacturer protocol using Poly(A) mRNA Magnetic Isolation Module. Equimolar amount of libraries was sequenced using an Illumina NextSeq 500, following the manufacturer's instructions, on the Oklahoma Medical Research Foundation Genomics Core (USA). The sequences obtained with the RNA-Seq technique were aligned in the human genome of reference GRCh37.75 by the software Spliced Transcripts Alignment to a Reference (STAR) v2.5 and to obtain normalized counts in FPKM, the software Expectation-Maximization (RSEM) v1.3.0 was used. To identify network of genes correlated with the treatment (modules), we used the Weighted Correlation Network Analysis (WGCNA). Functional enrichment analysis of the WGCNA differentially expressed modules was performed using the Integrated Annotation, Visualization and Discovery Database (DAVID) v6.8 in order to correlate with biological processes. Results In the cell cycle analysis, we observed a significant increase (p < 0.05) in the sub-G0 phase (cell death) after treatment with nimesulide alone, and in combination with prednisolone (figure 1). No effect was observed in the prednisolone only group. The cell cycle effect induced by nimesulide on HL-60 and OCI-AML2 was similar to the induced by cytarabine, a standard chemotherapy agent for AML that in known to induce arrest in the S phase. In addition, the cell line arrest in THP-1 was greater with nimesulide than with cytarabine, while OCI-AML3 was less sensitive to both nimesulide and cytarabine. Regarding cell death mechanism, treatment with nimesulide induced predominantly an increase in late apoptosis that was potentiated after combined treatment with nimesulide and cytarabine (figure 2). After the demonstration of cell cycle arrest and apoptosis induction after treatment with nimesulide, we performed whole transcriptome sequencing followed by WGCNA analysis. We have identified gene modules that were significantly correlated with anti-inflammatory treatments, being 1 module down-regulated (lightyellow with p = 0.00052) and 2 modules up-regulated (lightcyan with p = 0 .00025 and tan with p = 0.000038). Analysis of functional enrichment using DAVID showed up-regulation of gene networks associated with apoptotic processes and autophagy and down- regulation of gene networks associated with cell cycle and RNA splicing pathways Conclusions The COX-2 inhibitor nimesulide caused cell cycle arrest and apoptosis in AML cell lines and potentiated the cytotoxic effects of cytarabine. This treatment was associated with up- regulation of autophagy and apoptosis and down-regulation of cell cycle and RNA splicing gene networks. Figure 1 Figure 1. Disclosures Santos: Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding; Amgen: Membership on an entity's Board of Directors or advisory committees; Abbvie: Membership on an entity's Board of Directors or advisory committees; Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees. Campregher: Astellas: Consultancy.

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Targeting Hypersumoylation in Mantle Cell Lymphoma

Blood ◽

10.1182/blood-2019-127363 ◽

2019 ◽

Vol 134 (Supplement_1) ◽

pp. 4060-4060 ◽

Cited By ~ 1

Author(s):

Walter Hanel ◽

Liudmyla Tsyba ◽

Dennis Huszar ◽

Alex Prouty ◽

Xiaoli Zhang ◽

...

Keyword(s):

Cell Cycle ◽

Cell Death ◽

Board Of Directors ◽

Cell Lines ◽

Research Funding ◽

Advisory Committees ◽

Human B Cells ◽

Mantle Cell ◽

Normal Human ◽

Protein Sumoylation

Mantle cell lymphoma (MCL) is an aggressive and incurable subtype of B-cell Non-Hodgkin's lymphoma (NHL) characterized by genetic dysregulation of CyclinD1. Despite the improvement in response rates with current therapies, MCL patients inevitably relapse and outcomes remain poor. This is particularly true for MCL patients progressing on novel targeted therapies such as ibrutinib, highlighting the continued need for new therapeutic approaches. SUMOylation is a post-translational modification regulated by SUMO Activating Enzymes 1 and 2 (SAE1/2) affecting function, stability, and subcellular localization of a multitude of proteins such as Cyclin D1 and regulating multiple cellular functions such as cell cycle control and DNA damage response. While not yet explored in MCL, it is known that hyper-SUMOylation is associated with augmented cell proliferation and tumor growth of a number of cancers including B-cell NHL. We evaluated the expression levels of SAE1/2, total SUMO1, and SUMO 2/3 in normal human B cells, primary MCL patient samples, and a panel of 8 MCL cell lines via immunoblotting. We found significantly increased levels of SAE1/2 and total protein SUMOylation in 4 out of 5 MCL patient samples and all MCL cell lines compared to normal human B-cells. To validate the SAE complex as a potential therapeutic target in MCL, we performed genetic knockdown of SAE1 and SAE2 using both shRNA and an inducible CRISPR/Cas9 system and found significant reduction in viability of MCL cells (p < 0.001) thus confirming that SUMOylation is essential for MCL survival. TAK-981 (Takeda Pharmaceuticals) is a potent and selective inhibitor of the SAE1/2 complex currently in a phase 1 clinical trial (NCT036483). We found that treatment of MCL cell lines with TAK-981 resulted in time- and dose-dependent cell death in 7 of 8 MCL cell lines (IC50 17 - 62.5 nM at 72 hr) which was associated with relevant decrease in protein sumoylation. MCL cells were sensitive to TAK regardless of ATM or p53 mutations. Finally, TAK-981 treatment prolonged the survival of SCID mice engrafted with a human MCL cell line (Jeko) compared with placebo control [median overall survival (OS): TAK-981, 34 days; placebo, 29 days, p = 0.008] and also extended the survival of a novel patient derived xenograft (PDX) mouse model of ibrutinib-resistant MCL (median OS: TAK-981, 60 days; placebo, 55 days, p = 0.001), thus establishing the in vivo efficacy of TAK-981 in models of aggressive MCL. Mechanistically, 24 hours of treatment with TAK-981 resulted in a profound G2M cell cycle arrest in 6 out of 7 TAK-981-sensitive MCL cell lines. Cell synchronization with palbociclib followed by release into TAK-981 showed significant apoptosis upon G2M re-entry. In addition, in p53-deficient MCL cell lines, we found rapid accumulation of polyploid and aneuploid cells followed by rapid cell death following 48 hours of drug exposure. These findings strongly support mitotic catastrophe as a significant mechanism of tumor cell death mediated by TAK-981. Upon fractionation of cells at distinct phases of the cell cycle, we found significantly increased levels of protein SUMOylation by both SUMO1 and SUMO2/3 at the G2M transition. Further mechanistic data will be presented at the meeting. Given the multiple immune dampening mechanisms of SUMOylation, we are currently studying the anti-MCL immune effects of TAK-981. To do this, we are employing a novel immunocompetent mouse model of MCL in which murine lymphoma cells from Eμ-SOX11/CCND1 double transgenic animals are adoptively transferred into syngeneic mice. These mice develop a systemic lymphoma with morphological, molecular, and phenotypic features characteristic of MCL resulting in death within 3-4 weeks. Preliminary results with this model show that treatment with TAK-981 leads to decrease in lymphoma burden and significant prolongation of survival. Studies into the immune mediated anti-lymphoma effects of TAK-981 using this model are ongoing and will be presented at the meeting. Together, our data strongly support further development of TAK-981 as a novel MCL therapeutic. Disclosures Huszar: Takeda Pharmaceuticals: Employment, Equity Ownership. Parekh:Karyopharm Inc.: Research Funding; Foundation Medicine Inc.: Consultancy; Celgene Corporation: Research Funding. Maddocks:BMS: Research Funding; Pharmacyclics: Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Research Funding; Merck: Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees; Teva: Membership on an entity's Board of Directors or advisory committees. Baiocchi:Prelude: Consultancy.

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