The Combination of the BCL-2 Antagonist Venetoclax with the CD70-Targeting Antibody Cusatuzumab Synergistically Eliminates Primary Human Leukemia Stem Cells

Introduction Acute myeloid leukemia (AML) is a very heterogeneous hematological malignancy characterized by the accumulation of myeloid blasts. Treatment options for unfit AML patients greater than 65 year of age are still limited and outcomes are dismal. The current standard of care for older AML patients are hypomethylating agents (HMA) or low dose Ara-C. However, even though inducing hematological remissions in up to 30 percent of the patients, responses are not durable and survival of these patients is only marginally prolonged. The poor durability is due to insufficient action on leukemia stem cells (LSC) which drive and maintain the disease and are resistance to therapy (Craddock et al, 2013 and DiNardo et al, 2019). We described how aberrant CD70/CD27 signaling drives stemness of AML LSCs and identified CD70 as potential new target for the treatment of AML patients (Riether et al, 2017). In a recent Phase 1 clinical trial, treatment of older and unfit AML patients with the ADCC-enhanced humanized monoclonal anti CD70 antibody (mAb) cusatuzumab in combination with HMA demonstrated promising clinical activity and a favorable tolerability profile. The BCL-2 antagonist, venetoclax, targets and eliminates LSCs by suppression of oxidative phosphorylation and demonstrated very promising activity in older AML patients in clinical phase I and II studies in combination with standard of care (Pollyea et al, 2018). However, even with novel agents such as venetoclax, there are still patients that become refractory or relapse. We hypothesized that combining venetoclax and cusatuzumab with distinct but complementary mechanisms of action could successfully eliminate LSCs. Experimental design To test this hypothesis, we performed a drug-combination study according to the Chou-Talalay method (Chou 2010) in CD70-expressing AML cell lines such as MOLM-13, MV4-11, and NOMO-1 cells in vitro. In addition, we tested the effect of the cusatuzumab/venetoclax and the cusatuzumab/venetoclax/HMA combination on colony formation and re-plating capacity of primary CD34+CD38- LSCs from newly diagnosed AML patients. Results We first treated MOLM-13, MV4-11, and NOMO-1 AML cells with vehicle, cusatuzumab alone or in combination with venetoclax or decitabine in a constant ratio in the presence of CFSE-labeled NK cells (ratio 1:1). AML cell numbers were assessed 72 hours later. Cusatuzumab in combination with venetoclax or decitabine and NK cells synergistically eliminated CD70-expressing AML cells in a broad dose range (Figure 1). To assess the effect of the cusatuzumab/venetoclax combination on primary human AML LSCs, we treated CD34+ CD38- LSCs with cusatuzumab or venetoclax monotherapy or in combination in the presence of NK cells and assessed colony formation. Cusatuzumab/venetoclax co-treatment was more efficacious than each monotherapy alone and strongly reduced LSCs and leukemia progenitors (Figure 2). To analyze the effect of the cusatuzumab/venetoclax treatment on LSC function in a more stringent way, we performed serial re-plating experiments in vitro. The impaired colony formation after combination treatment observed after the first plating was maintained during subsequent the re-plating, even though cusatuzumab and venetoclax were not present in the re-plating, indicating an effective reduction of LSCs. Mechanistically, we could show that treatment with venetoclax results in up-regulation of CD70 on LSCs, suggesting that venetoclax renders LSCs more susceptible to cytolytic killing with cusatuzumab. In older AML patients, cusatuzumab and venetoclax each have demonstrated promising clinical activity in combination with HMA. We determined whether addition of HMA to the cusatuzumab/venetoclax co-treatment could more effectively eliminate LSCs. The triplet combination cusatuzumab/venetoclax/decitabine did not further reduce growth of AML cell lines in vitro (Figure 1) nor colony and re-plating capacity of human LSCs compared to the cusatuzumab/venetoclax co-treatment. Conclusions Overall, these results indicate that a combination of cusatuzumab with venetoclax eliminates LSCs synergistically and more efficiently than as a monotherapy. Tolerability and efficacy will be tested in mouse models using both primary AML and cell line xenografts. The results suggest that targeting LSCs by combining venetoclax and cusatuzumab treatments is a promising novel treatment strategy in AML. Disclosures Johnson: Janssen R&D: Employment. Drenberg:Janssen R&D: Employment. Syed:Janssen R&D: Employment. Moshir:Argenx: Employment, Equity Ownership. Hultberg:Argenx: Employment. Leupin:Argenx: Employment, Equity Ownership, Patents & Royalties. De Haard:Argenx: Employment, Equity Ownership, Patents & Royalties.

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The Novel mTOR Kinase Inhibitor CC-223 Demonstrates Significant Activity In In Vitro Models Of Multiple Myeloma (MM), Both As a Single Agent and In Combination With The Approved Agents, Dexamethasone, Lenalidomide and Pomalidomide

Blood ◽

10.1182/blood.v122.21.3160.3160 ◽

2013 ◽

Vol 122 (21) ◽

pp. 3160-3160 ◽

Cited By ~ 1

Author(s):

Emily Rychak ◽

Derek Mendy ◽

Karen Miller ◽

Jim Leisten ◽

Rama Krishna Narla ◽

...

Keyword(s):

Cell Proliferation ◽

Cell Death ◽

Tumor Growth ◽

Cell Lines ◽

Combination Index ◽

Synergistic Effects ◽

Standard Of Care ◽

Employment Equity ◽

Equity Ownership

Abstract Over expression of the PI3 kinase/mTOR/AKT pathway has been well documented in MM patient biopsies and human MM cell lines, suggesting this pathway plays a key role in the survival and proliferation of malignant plasma cells. Rapamycin and the rapalogs are allosteric inhibitors of the mTORC1 complex (consisting of mTOR, raptor, mLST8 and PRAS40), inducing mainly cytostatic effects but not cell death. Inhibition of mTORC1 prevents a negative feedback loop to the mTORC2 complex (consisting of mTOR, Rictor, mLST8 and Sin 1) leading to the phosphorylation of AKT. Phosphorylated AKT is a key inducer of anti-apoptosis mechanisms and cell cycle progression, which may explain the limited results of the rapalogs in the clinic. Recently developed mTOR kinase inhibitors (i.e., CC-223) target both mTORC1 and mTORC2 complexes in order to inhibit tumor growth and importantly, induce cell death. Here we evaluate the effects of CC-223 on a panel of MM cell lines, in combination with current standard of care agents in MM (the corticosteroid, dexamethasone [DEX] and the IMiD® immunomodulatory drugs, lenalidomide [LEN] and pomalidomide [POM]), as well as in the context of LEN resistance. Single agent CC-223 was shown to inhibit cell proliferation in a panel of 10 MM cell lines achieving IC50 values between 0.1-1 µM following 5 days of treatment. CC-223 also reduced cell viability reaching IC50 values between 0.4-1 µM in 5 out of 10 MM cell lines tested. CC-223 induced concentration-dependent G1 phase arrest within 24h of treatment followed by an induction of cell death by 48h. The anti-MM tumor activity of CC-223 (0.3-10 mg/kg) was further tested in SCID mice with xenotransplants of NCI-H929 grown to approximately 100-150 mm3 in size. A dose-dependent tumor growth inhibition and tumor growth delay was seen with once daily dosing of CC-223. Combination of CC-223 with standard of care therapy compounds was also evaluated in vitro. The combination of CC-223 and DEX demonstrated synergistic effects on the inhibition of cell proliferation in 6 MM cell lines (combination index: 0.0002-0.38) tested over 5 days. CC-223 also had synergistic effects on the same panel of MM cell lines when combined with LEN (combination index: 0.05-0.8). Acquisition of drug resistance in patients receiving standard of care therapies is still one of the major clinical problems in MM. POM, the next generation of IMiD® immunomodulatory agents, has shown clinically meaningful results in patients that are resistant or have relapsed to their drug regimens, including LEN. We have recently developed in vitro cellular models of LEN-resistance using the H929 MM cell line. H929 cells with acquired resistance to LEN (H929 R10-1, R10-2, R10-3 and R10-4) were shown to have one copy number loss of cereblon compared to their matched LEN-sensitive control (H929 D1). In addition to this, protein expression analysis identified that these resistant cell lines also gained the activation of signaling pathways such as PI3K/AKT/mTOR, MEK/MAPK as well as anti-apoptotic factors. For example, S473 AKT phosphorylation was highly elevated in LEN-resistant cell lines which correlated with loss of PTEN protein expression (H929 R10-3 and R10-4). Interestingly, regardless of PI3K/AKT/mTOR pathway status, all LEN-sensitive and resistant H929 cells responded to CC-223 treatment with a strong inhibition of cell proliferation (H929 D1 IC50 0.2 µM, and H929 R10 1-4 IC50 0.2-0.35 µM) and to a lesser effect, induction of cell death, over a 5 day period. Similar to the panel of MM cell lines, G1 arrest occurred after 24h treatment and cell death (Sub-G1) was increased by 72h of treatment. CC-223 treatment reduced S473 pAKT and p-4EBP1 after 1h while total AKT and 4EBP1 remained unchanged in both the sensitive and resistant MM cell lines. Combination treatment of LEN-sensitive and resistant H929 cells with CC-223 and POM had synergistic inhibitory effects on cell proliferation (combination index: 0.35-0.7) and cell viability (combination index: 0.15-0.42). In conclusion, the mTOR kinase inhibitor, CC-223 potently inhibited MM cell proliferation by inducing G1 arrest and cell death in a panel of MM cell lines and reduction of tumor volume in vivo. The combination of LEN, POM or DEX with CC-223 had synergistic effects on MM cell proliferation and viability. Therefore, CC-223 in combination with other standard of care agents could become an important clinical tool for the treatment of MM in the future. Disclosures: Rychak: Celgene Corporation: Employment, Equity Ownership. Mendy:Celgene: Employment, Equity Ownership. Miller:Celgene Corporation: Employment, Equity Ownership. Leisten:Celgene Corporation: Employment, Equity Ownership. Narla:Celgene Corporation: Employment, Equity Ownership. Raymon:Celgene Corporation: Employment, Equity Ownership. Chopra:Celgene: Employment, Equity Ownership. Lopez-Girona:Celgene: Employment, Equity Ownership.

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EZH2 Inhibitors Are Broadly Efficacious in Multiple Myeloma As Single Agent and in Combination with Standard of Care Therapeutics

Blood ◽

10.1182/blood.v128.22.5672.5672 ◽

2016 ◽

Vol 128 (22) ◽

pp. 5672-5672 ◽

Cited By ~ 1

Author(s):

Shilpi Arora ◽

Kaylyn Williamson ◽

Shruti Apte ◽

Srividya Balachander ◽

Jennifer Busby ◽

...

Keyword(s):

Multiple Myeloma ◽

Cell Lines ◽

Single Agent ◽

Standard Of Care ◽

Tumor Growth Inhibition ◽

Sequencing Data ◽

Employment Equity ◽

Chip Sequencing ◽

Equity Ownership

Abstract Post-translational modifications of the histone proteins play a key role in regulating processes that require access to DNA. Specifically, methylation of lysine 27 on histone 3 (H3K27) is intimately linked with transcriptional repression. EZH2, a histone lysine methyl transferase is the catalytic component of the PRC2 complex, which catalyzes H3K27 methylation. EZH2 dysregulation has been observed in different malignancies and inhibition of its catalytic activity has emerged as a novel therapeutic approach to treat human cancers. Potent, selective and reversible EZH2 small molecule inhibitors are currently being tested in Ph. 1 clinical trials. We and others have reported EZH2 dependencies across non-Hodgkin Lymphoma subtypes in cancer cell lines, in xenograft mouse models and in lymphoma patients. We identified Multiple Myeloma as potential clinical application for EZH2 inhibitors. Treatment with EZH2 inhibitors such as CPI-360, CPI-169 and CPI-1205 cause apoptosis in multiple myeloma and plasmacytoma cell models and causes tumor growth inhibition in myeloma xenograft models at well tolerated doses. An EZH2-controlled transcriptional signature across various multiple myeloma was identified using integrated RNA-sequencing and ChIP-sequencing data. Combination studies testing EZH2 inhibitors with standard of care (SOC) agents across a panel of multiple myeloma cell lines showed synergistic responses with several of the SOC agents in vitro and in vivo. Disclosures Arora: Constellation Pharmaceuticals: Employment, Equity Ownership. Williamson:Constellation Pharmaceuticals: Employment, Equity Ownership. Apte:Constellation Pharmaceuticals: Employment, Equity Ownership. Balachander:Constellation Pharmaceuticals: Employment, Equity Ownership. Busby:Constellation Pharmaceuticals: Employment, Equity Ownership. Hatton:Constellation Pharmaceuticals: Employment, Equity Ownership. Bryant:Constellation Pharmaceuticals: Employment, Equity Ownership. Trojer:Constellation Pharmaceuticals: Employment, Equity Ownership.

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Lenalidomide Exhibits Activity in Mantle Cell Lymphoma through Increased NK Cell Mediated Cytotoxicity

Blood ◽

10.1182/blood.v126.23.821.821 ◽

2015 ◽

Vol 126 (23) ◽

pp. 821-821 ◽

Cited By ~ 1

Author(s):

Patrick Hagner ◽

Hsiling Chiu ◽

Maria Ortiz-Estevez ◽

Tsvetan Biyukov ◽

Carrie Brachman ◽

...

Keyword(s):

T Cells ◽

Nk Cells ◽

Cell Lines ◽

Research Funding ◽

Nk Cell ◽

Employment Equity ◽

Mantle Cell ◽

Apoptosis Assay ◽

Equity Ownership

Abstract Introduction: Lenalidomide (Len) is indicated for the treatment of relapsed/refractory (R/R) Mantle Cell Lymphoma (MCL) in the United States and Switzerland. Len binds to the cullin 4 ring E3 ubiquitin ligase complex resulting in ubiquitination and subsequent proteasomal degradation of lymphoid transcription factors Aiolos and Ikaros leading to stimulation of immune cells, such as T-cells. Clinical trial CC-5013-MCL-002 (NCT00875667) is a randomized open-label phase II study in R/R MCL patients in which Len was given orally at 25 mg/day on days 1-21 of each 28-day cycle until progression (N=170). The control arm consisted of investigator choice of single-agent rituximab, gemcitabine, fludarabine, chlorambucil, or cytarabine (N=84). We explored the immune effects of Len treatment in MCL patients enrolled in CC-5013-MCL-002 and further investigated our findings in in vitro MCL co-culture models. Methods: Peripheral blood samples for exploratory analysis were collected at Cycle 1 Day 1 (C1D1, pre-treatment), Cycle 1 Day 4 (C1D4), Cycle 2 Day 15 (C2D15) and at treatment discontinuation. Flow cytometric profiling of T, B and natural killer (NK) cell subsets was performed and differences were analyzed for correlation with clinical outcomes (response rate and progression free survival [PFS]). Cell dependent cytotoxicity was measured in 1) anti-CD3 stimulated peripheral blood mononuclear cells (PBMC) treated with vehicle or 1-10000 nM Len for 3 days and incubated with target tumor cells for an additional 4 hours followed by an apoptosis assay as measured by Annexin V/ToPro-3 flow cytometry and 2) negatively selected CD56+ NK cells stimulated with IL-2 and treated with Len (1 nM to 10 μM) for 18 hrs and incubated with target tumor cells for an additional 4 hours followed by apoptosis assay. Results: At baseline, no significant differences were observed in the absolute levels of immune subsets when comparing non-responders (NR) and responders (R) in either Len (NR=11, R=23) or control (NR=4, R=5) arms. However, in the Len arm, significantly elevated (adj. p < 0.05) proportions of CD3-CD56+CD16+ NK cells (difference of means = 8.73; 95%CI [4.48, 12.98]) were observed at C1D4 compared to baseline in the R (N=19) outcome sub-group compared to NR (N=11). A similar trend in levels of NK subsets was observed at C2D15, however the difference was not significant. In addition, elevated proportions of CD3-CD56+CD16+ NK cells (p≤0.016) at C1D4 relative to total lymphocytes correlated significantly to longer PFS in the Len arm. Immune subset analysis in the control arm did not show any correlation to response or PFS at any visit. The mechanism whereby NK cell modulation contributes to clinical benefit demonstrated by Len in patients was further explored in in vitro co-culture systems with MCL cell lines. Len treated PBMC co-cultured with Jeko-1, Granta-519, and Mino MCL cell lines resulted in 38-47.5% more apoptosis compared to DMSO (p≤0.001). We examined the effect of Len on Aiolos and Ikaros protein expression in CD56+ NK and CD3+ T cells within anti-CD3 antibody stimulated PBMCs treated with DMSO or various concentrations of Len (1 nM to 10 μM) for 72 hours. Degradation of both Aiolos (40%) and Ikaros (95%) was observed after drug treatment in CD56+ NK cells. Aiolos and Ikaros levels were also monitored in CD3+ T cells and showed decreased levels after Len treatment, consistent with previous reports (Gandhi, 2014; Kronke, 2014). Furthermore, purified CD56+ NK cell mediated cytotoxicity produced a similar pro-apoptotic effect as the PBMC assay in all MCL cell lines versus DMSO (p≤0.01). Supernatants from co-cultures of NK cells with MCL cell lines showed significantly elevated granzyme B levels as compared to DMSO controls (p≤0.0001), suggesting that the apoptotic effects observed are induced by granzyme B. Conclusions: Lenalidomide is an immune modulating agent and NK cell modulation in particular may play a role in its clinical activity in MCL. A significant increase in proportions of NK cell subsets (vs total lymphocytes) at C1D4 versus baseline was observed and is a potential response indicator of favorable clinical outcome in R/R MCL patients treated with Len. In vitro, Len enhances cell mediated cytotoxicity of MCL cell lines in two co-culture model systems. Understanding NK cell mediated mechanism(s) has potential to enhance guiding patient selection strategies and rational combination therapies of lenalidomide in MCL. Disclosures Hagner: Celgene: Employment, Equity Ownership. Chiu:Celgene: Employment, Equity Ownership. Ortiz-Estevez:Celgene: Employment, Equity Ownership. Biyukov:Celgene: Employment, Equity Ownership. Brachman:Celgene: Employment, Equity Ownership. Trneny:Celgene: Consultancy, Honoraria, Other: Travel, accommodations, expenses, Research Funding. Morschhauser:Genentech Inc./Roche: Other: Advisory boards. Stilgenbauer:AbbVie, Amgen, Boehringer-Ingelheim, Celgene, Genentech, Genzyme, Gilead, GSK, Janssen, Mundipharma, Novartis, Pharmacyclics, Roche: Consultancy, Honoraria, Research Funding. Milpied:Celgene: Honoraria, Research Funding. Musto:Sandoz: Consultancy; Celgene: Honoraria; Roche: Honoraria; Sanofi: Consultancy; Genzyme: Consultancy; Novartis: Honoraria; Janssen: Honoraria; Mundipharma: Honoraria. Martinelli:AMGEN: Consultancy; Ariad: Consultancy; Pfizer: Consultancy; ROCHE: Consultancy; BMS: Consultancy, Speakers Bureau; Novartis: Consultancy, Speakers Bureau; MSD: Consultancy. Heise:Celgene: Employment, Equity Ownership. Daniel:Celgene: Employment, Equity Ownership. Chopra:Celgene: Employment, Equity Ownership. Carmichael:Celgene: Employment, Equity Ownership. Trotter:Celgene Corporation: Employment. Gandhi:Celgene: Employment, Equity Ownership. Thakurta:Celgene Corporation: Employment, Equity Ownership.

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SL-401, a Targeted Therapy Directed to the Interleukin-3 Receptor (CD123), and SL-801, a Reversible Inhibitor of Exportin-1 (XPO1), Display Synergistic Anti-Tumor Activity Against Hematologic Malignancies in Vitro

Blood ◽

10.1182/blood.v128.22.4724.4724 ◽

2016 ◽

Vol 128 (22) ◽

pp. 4724-4724 ◽

Cited By ~ 1

Author(s):

John Gionco ◽

Janice Chen ◽

Ross Lindsay ◽

Vince Macri ◽

Christopher L. Brooks

Keyword(s):

Cell Line ◽

Cell Lines ◽

Single Agent ◽

Hematologic Malignancies ◽

Clinical Activity ◽

Employment Equity ◽

Equity Ownership ◽

Rpmi 8226 ◽

Anti Tumor Activity

Abstract Background: Novel combination therapies have shown success in combating tumor heterogeneity and drug resistance. SL-401 is a targeted therapy directed to the interleukin-3 receptor (CD123), which is overexpressed on numerous hematologic malignancies. SL-401 has demonstrated high single agent response rates in an ongoing Phase 2 trial of blastic plasmacytoid dendritic cell neoplasm (BPDCN) and is also being evaluated in the clinic for additional cancers, including acute myeloid leukemia (AML) and myeloproliferative neoplasms (MPNs) as a single agent, and multiple myeloma (MM) in combination with other agents. While SL-401 has demonstrated robust single agent clinical activity in patients with BPDCN, its unique mechanism of action and non-overlapping side effect profile with other agents may lend itself to combination therapy as well. Another class of drugs that has demonstrated clinical activity against several hematologic and solid malignancies is Exportin-1 (XPO1) inhibitors. SL-801 is a novel oral small molecule that reversibly inhibits XPO1 and has shown potent in vitro and in vivo anti-tumor activity against a broad range of hematologic and solid malignancies. SL-801 is currently being evaluated in a Phase 1 trial of patients with advanced solid tumors, and a Phase 1 trial in advanced hematologic cancers is planned. Here, we investigated the in vitro effect of combination treatment of SL-401 and SL-801 against cell lines of chronic myeloid leukemia (CML), AML, MM, and Hodgkin's lymphoma (HL). Methods: The human K562 CML cell line, MV4-11 AML cell line, RPMI-8226 MM cell line, and L-428 HL cell line were treated with varying concentrations of SL-401 and SL-801 alone or in combination for 48 hours. Cell viability was assessed by the CellTiter Glo in vitro cytotoxicity assay. Combination index (CI) values were calculated using CompuSyn software by the method of Chou and Talalay, and treatment was considered to be synergistic when CI < 1. Caspase activation was measured using the Caspase-Glo 3/7 assay, and lactate dehydrogenase (LDH) release was measured using the CytoTox 96 Non-Radioactive Cytotoxicity Assay. Results: As single agents, SL-401 and SL-801 demonstrated anti-tumor activity in all four cell lines tested. MV4-11 cells were the most sensitive to both drugs, with an IC50 of 34 pM for SL-401 and 21 nM for SL-801. In the other cell lines, the IC50s for SL-401 were 17 nM in K562 cells, 25 nM in RPMI-8226 cells, and 100 nM in L-428 cells, and the IC50s for SL-801 were 99 nM in K562 cells, 51 nM in RPMI-8226 cells, and 494 nM in L-428 cells. When combined with each other, SL-401 and SL-801 potently inhibited cell growth in all cell lines, and CI calculations indicated that the interaction between the two drugs was synergistic at most dose combinations. Notably, CI values < 0.3 were observed in MV4-11 and L-428 cells, indicative of strong synergy. Consistent with these observations, the combination of SL-401 and SL-801 also induced higher levels of caspase activation and LDH release in MV4-11 and L-428 cells than either drug alone. Conclusion: These findings demonstrate that SL-401 and SL-801, when combined, act synergistically in their in vitro anti-tumor activity against CML, AML, MM, and HL cells. Investigations into the molecular mechanisms underlying the observed synergy are in progress. These promising results provide rationale for further development of SL-401 and SL-801 combination therapy in the treatment of a broad range of hematologic malignancies. Disclosures Gionco: Stemline Therapeutics, Inc.: Employment. Chen:Stemline Therapeutics, Inc.: Employment, Equity Ownership. Lindsay:Stemline Therapeutics, Inc.: Employment, Equity Ownership. Macri:Stemline Therapeutics, Inc.: Employment, Equity Ownership. Brooks:Stemline Therapeutics, Inc.: Employment, Equity Ownership, Patents & Royalties.

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Clinical Pharmacodynamic Markers and Combinations with SY1425 (tamibarotene) in a Genomically-Defined Subset of Non-APL AML

Blood ◽

10.1182/blood.v128.22.2898.2898 ◽

2016 ◽

Vol 128 (22) ◽

pp. 2898-2898

Author(s):

Michael R McKeown ◽

Christopher Fiore ◽

Emily Lee ◽

Matthew L Eaton ◽

Christian C. Fritz

Keyword(s):

Transcription Factor ◽

Cell Lines ◽

Binding Sites ◽

Clinical Studies ◽

High Cell ◽

Preclinical Models ◽

Employment Equity ◽

Equity Ownership ◽

Maximal Induction

Abstract SY-1425, a potent and selective agonist of the retinoic acid receptor RARα, is being investigated in a Ph2 trial in a novel genomically-defined subset of non-APL AML and MDS patients (clinicaltrials.gov NCT02807558). RARa is a nuclear hormone receptor and transcription factor that regulates genes involved in cell differentiation and proliferation. We identified a super-enhancer (SE) at the RARA locus, the gene encoding RARa, in a subset of primary non-APL AML blasts. Preclinical models demonstrated a correlation between the presence of a RARA SE and sensitivity to SY-1425, providing the rationale for clinical investigation. Further research has investigated pharmacodynamics (PD) markers and combinations of drugs to support clinical development of SY-1425. In this study we identified DHRS3mRNA induction as a measure of RARα target engagement with SY-1425. We also demonstrated synergy in preclinical models with SY-1425 and hypomethylating agents. Since RARα is a transcription factor that regulates target genes when bound by a retinoid, we characterized the dynamic expression changes of a panel of RARA enhancer- high and - low non-APL AML cell lines (hereafter referred to as RARA-high and -low) in response to SY-1425 treatment. DHRS3 showed the largest expression increase following treatment in 3 RARA-high cell lines, with a range of 29 to 115 fold. In contrast, there was a much lower DHRS3 induction in 3 RARA-low cell lines (range of 1.6 to 6.1 fold). Induction was found to be both time- and dose-dependent with maximal induction at approximately 6 hours and half maximal induction near the EC50 for the anti-proliferative effect in RARA-high cell lines. DHRS3 encodes dehydrogenase/reductase (SDR family) member 3, a metabolic enzyme involved in maintaining cellular retinol homeostasis and had previously been shown to be induced by retinoids. Thus, DHRS3induction in tumor cells represents a potentially useful PD marker for clinical studies of SY-1425. To better understand the mechanism of induction of DHRS3 by SY-1425 we examined the chromosomal localization of RARα as well as the epigenomic state of the DHRS3 locus by ChIP-seq for RARα and H3K27 acetylation, the latter being an indicator of active enhancers and promoters. In the untreated state, OCI-AML3 (a typical RARA-high AML cell line) was found to have multiple RARα binding sites both within and distal to the DHRS3 gene but minimal H3K27 acetylation. Following treatment with SY-1425, the level of H3K27 acetylation at DHRS3 increased, resulting in the formation of a SE. Moreover, the SE encompassed the RARα binding sites, consistent with the model in which SY-1425 converts RARα into an activator of DHRS3expression. Similar results were seen for the CD38 locus in which SY-1425 treatment increased expression, H3K27 acetylation, and RARα binding. CD38 is a cell surface antigen and marker of myeloid maturation readily analyzed by FACS analysis, suggesting it could be an additional PD marker to be used in clinical studies. Indeed, it was found that SY-1425 induced CD38 cell surface expression at similar levels in RARA-high AML cell lines and the NB-4 APL cell line, but not in RARA-low cell lines. We also investigated combinations of SY-1425 with approved or investigational AML and MDS agents in in vitro and in vivo models to inform future clinical studies and to further explore potential PD markers unique to the combined action of the drugs. Several standard of care agents and drugs in current development were found to have synergistic interactions with SY-1425 in RARA-high but not RARA-low cell lines. In particular, azacitidine and decitabine each showed strong in vitro synergy with SY-1425. Evaluation of SY-1425 plus azacitidine in a RARA-high PDX model of non-APL AML demonstrated a better response compared to either agent alone. Additional genome-wide ChIP-seq and expression studies of RARA-high cells treated with various combinations are being investigated to identify optimal PD markers for these combinations. These studies support the use of DHRS3 mRNA induction in tumor cells as a PD marker in the recently initiated Ph2 study of SY-1425 in genomically-defined non-APL AML and MDS patients (clinicaltrials.gov NCT02807558) and further exploration as a PD marker for future combination studies. Disclosures McKeown: Syros Pharmaceuticals: Employment, Equity Ownership. Fiore:Syros Pharmaceuticals: Employment, Equity Ownership. Lee:Syros Pharmaceuticals: Employment, Equity Ownership. Eaton:Syros Pharmaceuticals: Employment, Equity Ownership. Fritz:Syros Pharmaceuticals: Employment, Equity Ownership.

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Differential Effects of Milatuzumab On Human Antigen-Presenting Cells in Comparison to Malignant B Cells.

Blood ◽

10.1182/blood.v114.22.2744.2744 ◽

2009 ◽

Vol 114 (22) ◽

pp. 2744-2744

Author(s):

Xiaochuan Chen ◽

Rhona Stein ◽

Chien-Hsing Chang ◽

David M. Goldenberg

Keyword(s):

T Cell ◽

B Cells ◽

Cell Lines ◽

Hairy Cell ◽

Employment Equity ◽

Cross Presentation ◽

Equity Ownership ◽

Antigen Presenting

Abstract Abstract 2744 Poster Board II-720 Introduction: The humanized anti-CD74 monoclonal antibody (mAb), milatuzumab, is in clinical evaluation as a therapeutic mAb for non-Hodgkin lymphoma, chronic lymphocytic leukemia (CLL), and multiple myeloma after preclinical evidence of activity in these tumor types. In addition to its expression in malignant cells, CD74 is also expressed in normal B cells, monocytes, macrophages, Langerhans cells, follicular and blood dendritic cells. A question therefore arises whether milatuzumab is toxic to or affects the function of these immune cells. This has important implications, not only for safe therapeutic use of this mAb, but also for its potential application as a novel delivery modality for in-vivo targeted vaccination. Methods: We assessed the binding profiles and functional effects of milatuzumab on human antigen-presenting cell (APC) subsets. Studies on the effect of milatuzumab on antigen presentation and cross-presentation are included. In addition, binding and cytotoxicity on a panel of leukemia/lymphoma cell lines and CLL patient cells were tested to demonstrate the range of malignancies that can be treated with this mAb. Results: Milatuzumab bound efficiently to different subsets of blood dendritic cells, including BDCA-1+ myeloid DCs (MDC1), BDCA-2+ plasmacytoid DCs (PDC), BDCA-3+ myeloid DCs (MDC2), B lymphocytes, monocytes, and immature DCs derived from human monocytes in vitro, but not LPS-matured DCs, which correlated well with their CD74 expression levels. In the malignant B-cells tested, milatuzumab bound to the surface of 2/3 AML, 2/2 mantle cell (MCL), 4/4 ALL, 1/1 hairy cell leukemia, 2/2 CLL, 7/7 NHL, and 5/6 multiple myeloma cell lines, and cells of 4/6 CLL patient specimens. Significant cytotoxicity (P<0.05) was observed in 2/2 MCL, 2/2 CLL, 3/4 ALL, 1/1 hairy cell, 2/2 NHL, and 2/2 MM cell lines, and 3/4 CD74-positive CLL patient cells, but not in the AML cell lines following incubation with milatuzumab. In contrast, milatuzumab had minimal effects on the viability of DCs or B cells that normally express CD74. The DC maturation and DC-mediated T-cell functions were not altered by milatuzumab treatment, which include DC-induced T-cell proliferation, CD4+CD25+FoxP3+ Treg expansion, and CD4+ naïve T-cell polarization. Moreover, milatuzumab had little effect on CMV-specific CD8- and CD8+ T cell interferon-g responses of peripheral blood mononuclear cells stimulated in vitro with CMV pp65 peptides or protein, suggesting that milatuzumab does not influence antigen presentation or cross-presentation. Conclusion: These results demonstrate that milatuzumab is a highly specific therapeutic mAb against B-cell malignancies with potentially minimal side effects. It also suggests that milatuzumab may be a promising novel delivery mAb for in vivo targeted vaccinations, given its efficient binding, but lack of cytotoxicity and functional disruption on CD74-expressing normal APCs. (Supported in part by NIH grant PO1-CA103985.) Disclosures: Chang: Immunomedics Inc.: Employment, Equity Ownership, Patents & Royalties. Goldenberg:Immunomedics, Inc.: Employment, Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties.

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Stroma-Free Ex Vivo Expanded, CD34+ Cord Blood-Derived NK Cells Retain Lytic Activity After Long-Term Engraftment in NSGS Mice

Blood ◽

10.1182/blood.v120.21.580.580 ◽

2012 ◽

Vol 120 (21) ◽

pp. 580-580

Author(s):

Mark Wunderlich ◽

Mahesh Shrestha ◽

Lin Kang ◽

Eric Law ◽

Vladimir Jankovic ◽

...

Keyword(s):

Nk Cells ◽

Research Funding ◽

Nk Cell ◽

Ex Vivo ◽

Employment Equity ◽

Cell Product ◽

Equity Ownership ◽

Cellular Therapeutics

Abstract Abstract 580 Generating a large number of pure, functional immune cells that can be used in human patients has been a major challenge for NK cell-based immunotherapy. We have successfully established a cultivation method to generate human NK cells from CD34+ cells isolated from donor-matched cord blood and human placental derived stem cells, which were obtained from full-term human placenta. This cultivation method is feeder-free, based on progenitor expansion followed by NK differentiation supported by cytokines including thrombopoietin, stem cell factor, Flt3 ligand, IL-7, IL-15 and IL-2. A graded progression from CD34+ hematopoietic progenitor cells (HSC) to committed NK progenitor cells ultimately results in ∼90% CD3-CD56+ phenotype and is associated with an average 10,000-fold expansion achieved over 35 days. The resulting cells are CD16- and express low level of KIRs, indicating an immature NK cell phenotype, but show active in vitro cytotoxicity against a broad range of tumor cell line targets. The in vivo persistence, maturation and functional activity of HSC-derived NK cells was assessed in NSG mice engineered to express the human cytokines SCF, GM-CSF and IL-3 (NSGS mice). Human IL-2 or IL-15 was injected intraperitoneally three times per week to test the effect of cytokine supplementation on the in vivo transferred NK cells. The presence and detailed immunophenotype of NK cells was assessed in peripheral blood (PB), bone marrow (BM), spleen and liver samples at 7-day intervals up to 28 days post-transfer. Without cytokine supplementation, very few NK cells were detectable at any time-point. Administration of IL-2 resulted in a detectable but modest enhancement of human NK cell persistence. The effect of IL-15 supplementation was significantly greater, leading to the robust persistence of transferred NK cells in circulation, and likely specific homing and expansion in the liver of recipient mice. The discrete response to IL-15 versus IL-2, as well as the preferential accumulation in the liver have not been previously described following adoptive transfer of mature NK cells, and may be unique for the HSC-derived immature NK cell product. Following the in vivo transfer, a significant fraction of human CD56+ cells expressed CD16 and KIRs indicating full physiologic NK differentiation, which appears to be a unique potential of HSC-derived cells. Consistent with this, human CD56+ cells isolated ex vivo efficiently killed K562 targets in in vitro cytotoxicity assays. In contrast to PB, spleen and liver, BM contained a substantial portion of human cells that were CD56/CD16 double negative (DN) but positive for CD244 and CD117, indicating a residual progenitor function in the CD56- fraction of the CD34+ derived cell product. The BM engrafting population was higher in NK cultures at earlier stages of expansion, but was preserved in the day 35- cultured product. The frequency of these cells in the BM increased over time, and showed continued cycling based on in vivo BrdU labeling 28 days post-transfer, suggesting a significant progenitor potential in vivo. Interestingly, DN cells isolated from BM could be efficiently differentiated ex vivo to mature CD56+CD16+ NK cells with in vitro cytotoxic activity against K562. We speculate that under the optimal in vivo conditions these BM engrafting cells may provide a progenitor population to produce a mature NK cell pool in humans, and therefore could contribute to the therapeutic potential of the HSC-derived NK cell product. The in vivo activity of HSC-derived NK cells was further explored using a genetically engineered human AML xenograft model of minimal residual disease (MRD) and initial data indicates significant suppression of AML relapse in animals receiving NK cells following chemotherapy. Collectively, our data demonstrate the utility of humanized mice and in vivo xenograft models in characterizing the biodistribution, persistence, differentiation and functional assessment of human HSC-derived cell therapy products, and characterize the potential of HSC-derived NK cells to be developed as an effective off-the-shelf product for use in adoptive cell therapy approaches in AML. Disclosures: Wunderlich: Celgene Cellular Therapeutics: Research Funding. Shrestha:C: Research Funding. Kang:Celgene Cellular Therapeutics: Employment, Equity Ownership, Patents & Royalties. Law:Celgene Cellular Therapeutics: Employment, Equity Ownership, Patents & Royalties. Jankovic:Celgene Cellular Therapeutics: Employment, Equity Ownership, Patents & Royalties. Zhang:Celgene Cellular Therapeutics: Employment, Equity Ownership, Patents & Royalties. Herzberg:Celgene Cellular Therapeutics: Employment, Equity Ownership, Patents & Royalties. Abbot:Celgene Cellular Therapeutics: Employment, Equity Ownership, Patents & Royalties. Hariri:Celgene Cellular Therapeutics: Employment, Equity Ownership, Patents & Royalties. Mulloy:Celgene Cellular Therapeutics: Research Funding.

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BH3 Profiling As Predictor Of 5-Azacytidine and Decitabine Clinical Responses

Blood ◽

10.1182/blood.v122.21.603.603 ◽

2013 ◽

Vol 122 (21) ◽

pp. 603-603 ◽

Cited By ~ 1

Author(s):

Raoul Tibes ◽

Steven M. Kornblau ◽

William E. Pierceall ◽

Ryan Lena ◽

Yi Hua Qiu ◽

...

Keyword(s):

Cell Lines ◽

Statistical Significance ◽

Family Members ◽

Specific Inhibitor ◽

Hypomethylating Agents ◽

Employment Equity ◽

Number Of Patients ◽

Clinical Responses ◽

Equity Ownership

Abstract Hypomethylating agents have changed treatment and outcomes in MDS and are active in AML patients. However a significant number of patients do not respond to 5-Azacytidine or Decitabine and there is no clinically validated assay that predicts response to 5-Azacytidine (5-Aza) or Decitabine (DAC). Clinical parameters and recently TET2 mutations have been identified as genetic predictors of response to 5-Aza. Several recent papers report on the possible predictive value of anti-apoptotic proteins, for example BCL2L10. In previous genome-scale RNA-interference (RNAi) screens anti-apoptotic BCL-2 family members, most potently BCL-XL, were identified as top targets whose down-regulation sensitize to 5-Aza. Results were confirmed with the BCL-XL and BCL-2 inhibitor ABT-737, as well as the BCL-2-specific inhibitor ABT-199, both of which sensitized myeloid cells to 5-Aza. Although it is expected that interfering with anti-apoptotic genes would sensitize to hypomethylating similar to cytotoxics, few of the other >900 genes from our RNAi sensitizer screens, including few of the 571 kinases, sensitized to 5-Aza as potently as inhibition of BCL-XL. Thus BCL-2 family members constitute an especially potent context to modulate the activity of 5-Aza. To assess if protein expression of the top targets BCL-XL, BCL-2 or MCL-1 correlate with and may explain a preferential sensitization, 577 primary AML samples were examined by Reverse Phase Protein Array (RPPA). There was substantial overlap of expression across and within FAB subgroups and cytogenetics, and expression of neither of these genes/proteins could explain the observed effects. This may be expected due to functional redundancies amongst the different anti-apoptotic BCL-2 family members, as well as distinct, yet overlapping binding affinities between anti- and pro-apoptotic BCL-2 proteins and BH3 peptides. Thus, we next aimed to functionally interrogate the overall balance of pro- and anti-apoptotic BCL-2 family members, also described as “primedness” by BH3 profiling. This assay uses peptides derived from pro-apoptotic BH3-only proteins to determine the capacity of cells to initiate apoptosis in response to pro-apoptotic BH3 molecules [anti-apoptotic BCL-2 molecules like BCL-XL and BCL-2 bind and inhibit BH3-only molecules]. This assay is a broad functional readout that incorporates many parameters including the consequences of varying BCL2L10 expression. To establish a proof-of-concept that the functional interrogation of specific apoptotic thresholds may be an optimal readout for 5-Aza response, we first assessed a broad panel of 13 AML-derived cell lines by BH3 profiling and in parallel 5-Aza drug dose response experiments. Several BH3 profiling metrics, including NOXA plus BIM, significantly correlated with 5-Aza sensitivity in vitro (Figure 1). Next, to correlate actual clinical responses to 5-Aza with BH3 profiling, specimens from 28 AML, MDS and MDS/MPN overlap patients treated with 5-Aza or DAC-based regimens and for whom clinical outcome was available, were assayed in BH3 assays. In the clinic, the best BH3 metrics were combined values from NOXA and BIM peptides similar to cell lines. NOXA plus BIM discriminated clinical responses defined as achieving any response (sensitive) versus a patient being resistance/refractory to 5-Aza/DAC based regimens with statistical significance (Mann-Whitney two-tailed p = 0.001). This was true for the entire group of patients (5-Aza- and DAC- regimens) with a Receiver Operating Characteristic (ROC) of an AUC=0.875, with a further increase for patients treated only with 5-Aza based regimens with an AUC=0.95.Figure 1BH3 metrics distinguish cell lines with higher EC 50 (> 2uM) from those with lower EC50 (generally < 1uM).Figure 1. BH3 metrics distinguish cell lines with higher EC 50 (> 2uM) from those with lower EC50 (generally < 1uM). In conclusion, due to significant expression overlap and functional redundancies of the BCL-2 family proteins, expression does not correlate with 5-Aza clinical or in vitro responses. However, BH3 profiling as a general functional readout of apoptotic primedness, significantly discriminated responses in patients as well as in vitro. Thus, BH3 profiling incorporates the entirety of pro- and anti-apoptotic molecules (including BCL2L10) and is promising to predict responses to hypomethylating agents. We propose to prospectively validate BH3 profiling as a predictive biomarker assay for 5-Aza or DAC based regimens. Disclosures: Pierceall: Eutropics: Employment, Equity Ownership. Lena:Eutropics: Employment, Equity Ownership. Cardone:Eutropics: Employment, Equity Ownership. Elashoff:Eutropics: Employment. Blake:Noel Blake: Employment, Equity Ownership.

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Coltuximab Ravtansine (SAR3419) Demonstrates Enhanced Activity in Combination with Bendamustine, Gemcitabine and Novel Targeted Agents Such As PI3K Inhibitors in Pre-Clinical Models of Relapsed and/or Refractory Non-Hodgkins Lymphoma (NHL)

Blood ◽

10.1182/blood.v126.23.5125.5125 ◽

2015 ◽

Vol 126 (23) ◽

pp. 5125-5125

Author(s):

Callum M Sloss ◽

Katie O'Callaghan ◽

Jutta Deckert ◽

Jenny Tsui ◽

Leanne Lanieri ◽

...

Keyword(s):

Cell Lines ◽

Single Agent ◽

Targeted Agents ◽

Employment Equity ◽

Pi3k Inhibitors ◽

Xenograft Models ◽

Equity Ownership ◽

Chemotherapy Agents

Abstract Introduction: Relapsed/refractory B-cell NHL remains an area of significant medical need. CD19 is broadly expressed on B-cell malignancies making it an ideal target for antibody-drug conjugate (ADC) based therapy. Coltuximab ravtansine is a CD19-targeting ADC consisting of a CD19-targeting antibody conjugated to the maytansinoid anti-mitotic DM4. In preclinical studies, coltuximab ravtansine has shown potent, targeted activity against NHL cell lines and xenograft models. In early clinical trials, it has been well tolerated and has shown promising signs of efficacy as both a single agent and in combination with rituximab. In the STARLYTE Phase 2 trial coltuximab ravtansine monotherapy resulted in an ORR of 44% in R/R-DLBCL that included an ORR of 21% in hard-to-treat primary refractory patients (NCT01472887). Here we describe studies aimed at the identification of combination partners for coltuximab ravtansine to further optimize clinical benefit to R/R-NHL patients. We are employing a dual approach where we investigate combination of coltuximab ravtansine with multiple, novel targeted therapy partners whilst in parallel also investigating the combination of coltuximab ravtansine with chemotherapies commonly used in the late stage R/R-NHL setting. Methods: Coltuximab ravtansine and the DM4 payload were evaluated in a high throughput screen both as single agents and in combination with a selection of novel, emerging targeted agents across a panel of twenty NHL cell lines. The combinations were evaluated in a dose-response matrix and a statistical method was used to identify combination synergies significantly superseding baseline additivity values. The in vivo efficacy of coltuximab ravtansine was additionally assessed in combination with various clinically relevant chemotherapy agents in subcutaneous xenograft models of NHL. Results: Coltuximab ravtansine and DM4 both showed potent single agent activity against the entire panel of NHL cell lines with median GI50's of 770pM and 100pM, respectively. We observed a significant correlation in the cell line sensitivity of the two compounds suggesting that sensitivity to coltuximab ravtansine is driven, at least in part, by inherent sensitivity of cells to the cytotoxic effects of the DM4 payload. In vitro combination studies for coltuximab ravtansine were performed to identify targets or pathways that result in the most prominent combination effects across the cell line panel. Analysis of the in vitro combination dose-matrix revealed particularly strong synergy between coltuximab ravtansine and various inhibitors of the PI3K/AKT/mTOR axis. Studies to examine the synergism between coltuximab ravtansine and PI3K inhibitors in in vivo models of NHL are ongoing. In order to further determine the utility of coltuximab ravtansine as part of a potential combination regimen for the treatment of R/R-NHL, we assessed the combination of coltuximab ravtansine with the chemotherapy agents bendamustine and gemcitabine in vivo. As gemcitabine is typically used in combination we assessed the efficacy of a coltuximab ravtansine with rituximab and gemcitabine in vivo. In both cases the combination with coltuximab ravtansine was significantly more efficacious than the standard-of-care alone arms. Conclusions: Coltuximab ravtansine demonstrates synergistic activity in combination with multiple PI3K pathway inhibitors across a large panel of NHL cell lines. Additionally, we have shown that combination of coltuximab ravtansine with clinically relevant late stage treatments such as bendamustine and rituximab + gemcitabine is more efficacious than the chemotherapy regimens alone. These results support the continued development of coltuximab ravtansine in R/R-NHL in combination with chemotherapy regimens and suggest that a combination of coltuximab ravtansine with PI3K inhibitors may also be of interest in the clinical setting. Disclosures Sloss: ImmunoGen, Inc.: Employment, Equity Ownership. O'Callaghan:ImmunoGen, Inc.: Employment, Equity Ownership. Deckert:ImmunoGen, Inc.: Employment, Equity Ownership. Tsui:ImmunoGen, Inc.: Employment, Equity Ownership. Lanieri:ImmunoGen, Inc.: Employment, Equity Ownership. Romanelli:ImmunoGen, Inc.: Employment, Equity Ownership.

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A Novel Cereblon E3 Ligase Modulator Eradicates Acute Myeloid Leukemia Stem Cells through Degradation of Translation Termination Factor GSPT1

Blood ◽

10.1182/blood-2019-128450 ◽

2019 ◽

Vol 134 (Supplement_1) ◽

pp. 3940-3940 ◽

Cited By ~ 1

Author(s):

Liqing Jin ◽

Nathan Mbong ◽

Stanley W.K. Ng ◽

Jean C.Y. Wang ◽

Mark D. Minden ◽

...

Keyword(s):

Stem Cells ◽

Stem Cell ◽

High Risk ◽

Translation Initiation ◽

Myeloid Leukemia ◽

Translation Termination ◽

Employment Equity ◽

Equity Ownership ◽

Translation Termination Factor

Acute myeloid leukemia (AML) is a clonal malignant disease initiated and propagated by leukemia stem cells (LSCs). Both LSCs and normal hematopoietic stem cells (HSCs) share many biological properties including self-renewal and quiescence. One such shared property that we have recently established involves the pro-survival features of proteostatic stress signaling. Stem cells have reduced protein translation initiation due to scarcity of the eIF2α translation initiation complex (van Galen et al Nature 2014; Cell Reports 2018). This in turn, increases the activity of activating transcription factor 4 (ATF4) uniquely in HSCs and LSCs. In homeostasis, this level of ATF4 facilitates stem cell persistence and survival, but upon stronger stress activation stem cell apoptosis ensues. This mechanism predicts that agonists of the integrated stress response (ISR) could provide a novel therapeutic approach to eradicate LSCs. Here we report that the novel cereblon E3 ligase modulator (CELMoD) CC-90009, which causes degradation of the translation termination factor G1 to S phase transition protein 1 (GSPT1) and downstream activation of ISR, is potent against primary AML both in vitro and in vivo, and reduces self-renewing LSCs in preclinical xenograft models for human AML. We first carried out in vitro assays to evaluate the effect of CC-90009 on primary AML samples. We found that CC-90009 degraded GSPT1 in primary AML cells and induced leukemic cell apoptosis in 24 hours. Leukemic colony forming progenitors were also reduced by CC-90009 in a dose-dependent manner. We next tested the efficacy of CC-90009 against primary AML samples in xenografts in NOD/SCID mice. Leukemia cells were transplanted intrafemorally 21 days prior to CC-90009 treatment. Mice were treated with vehicle or CC-90009 at 2.5mg/kg BID for 4 weeks. Heterogeneous responses to the CC-90009 treatment were observed. Of 35 AML samples tested, 16 were highly responsive to CC-90009 with >75% reduction of AML engraftment, 10 showed moderate response between 45% and 75% reductions, and 9 showed reductions of <25%. AML is clinically characterized by accumulation of blasts that are impaired for differentiation and maturation. We observed that, in addition to the reduction of total AML graft, CC-90009 also induced myeloid differentiation of AML blasts in the CC-90009 responders, as evidenced by increases in late myeloid cell surface markers (CD14, CD15 and CD11b) and reductions of the immature marker CD34. To determine the efficacy of CC-90009 against AML cases at high risk of relapse following standard induction chemotherapy, we assessed CC-90009 efficacy vs. the status of an expression-based 17-gene leukemia stem cell score (the LSC17 score) that was recently implemented for rapid risk stratification of AML patients (Ng et al, Nature 2016). LSC17-high patients are predicted to have poor treatment response and poor clinical outcome. We found that, while 8 out of 9 poor responders to CC-90009 had high LSC17 scores, 20 out of 28 samples that had high LSC17 scores responded well to CC-90009, indicating that the drug is able to target high risk cases. Serial transplantation utilizing limiting dilution analysis showed that CC-90009 targeted self-renewing LSCs. Our data established that a new CELMoD CC-90009 has anti-proliferative effects on human primary AML cells and self-renewing LSCs evaluated in xenograft assays. These observations provide important implications for CC-90009 in its clinical development as a new therapeutic agent to treat AML patients with high risk disease when treated with standard of care therapies. Currently, a phase I study evaluating CC-90009 in relapsed or refractory AML is ongoing (CC-90009-AML-001; NCT02848001). Disclosures Jin: Trillium Therapeutics: Other: licensing agreement. Ng:Celgene: Research Funding. Wang:Pfizer AG Switzerland: Honoraria, Other: Travel and accommodation; Trilium therapeutics: Other: licensing agreement, Research Funding; NanoString: Other: Travel and accommodation; Pfizer International: Honoraria, Other: Travel and accommodation. Minden:Trillium Therapetuics: Other: licensing agreement. Fan:Celgene Corporation: Employment, Equity Ownership. Pierce:Celgene Corporation: Employment, Equity Ownership. Pourdehnad:Celgene Corporation: Employment, Equity Ownership.

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