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

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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VS-4718, a Potent Focal Adhesion Kinase (FAK) Inhibitor, Exhibits Anticancer Activity in Leukemia Models in Vitro and in Vivo

Blood ◽

10.1182/blood.v124.21.982.982 ◽

2014 ◽

Vol 124 (21) ◽

pp. 982-982 ◽

Cited By ~ 2

Author(s):

Winnie F. Tam ◽

Jennifer E. Ring ◽

Anthony F. Trombino ◽

David T. Weaver ◽

Jonathan A. Pachter ◽

...

Keyword(s):

Stem Cells ◽

Focal Adhesion ◽

Myeloid Leukemia ◽

Acute Lymphocytic Leukemia ◽

Vehicle Control ◽

Lymphocytic Leukemia ◽

Employment Equity ◽

Equity Ownership

Abstract Current chemotherapy is effective in killing leukemic blasts in the periphery, but not leukemic stem cells (LSCs) in the bone marrow, which are thought to be responsible for the high relapse rate in leukemia. Thus, new therapies that effectively target LSCs are urgently needed to prevent cancer relapse. Accumulating evidence supports an essential role for adhesion pathways: particularly integrin beta 3 and its downstream focal adhesion kinase (FAK) in the maintenance of LSCs (Miller et al., Cancer Cell 2013; Despeaux et al., Stem Cells 2012). Previously, we have shown that FAK inhibitors preferentially target cancer stem cells in solid tumors (Shapiro et al., Sci Transl Med, 2014; Kolev et al., AACR 2013). We are extending our investigation of FAK inhibitors into hematological malignancies and report here that the FAK inhibitor VS-4718 displays anticancer activity in leukemia models both in vitro and in vivo. VS-4718 is a potent and orally bioavailable small molecule compound that targets cancer stem cells through inhibition of FAK kinase which is currently being tested in a Phase 1 clinical trial (NCT01849744). The anti-proliferative effect of VS-4718 was evaluated in a panel of 10 cell lines derived from patients with acute promyelocytic leukemia (APL), T-cell acute lymphocytic leukemia (T-ALL), B-cell acute lymphocytic leukemia (B-ALL), chronic myeloid leukemia (CML) and acute myeloid leukemia (AML) using a CellTiter-Glo cell viability assay on tissue culture or collagen coated plates. VS-4718 displayed anti-proliferative effects against most of these cell lines, with MV-4-11 AML being the most sensitive with an EC50 value of 200 nM. We further investigated the in vivo efficacy of VS-4718 against AML in both subcutaneous and disseminated models using the MV-4-11 cell line. Nude mice bearing MV-4-11 subcutaneous xenografts were treated orally twice daily with either vehicle control or VS-4718 for 14 days. 75 mg/kg VS-4718 caused 50% tumor growth delay and significantly extended median survival from 28 days to 48 days (p < 0.05). Moreover, tumor regression was observed in 4 out of 10 mice. We extended these observations to a disseminated MV-4-11 AML model to incorporate bone marrow stromal biology. When compared with vehicle control, VS-4718 dosed at 25 or 75 mg/kg, on a twice daily oral dosing schedule for 14 days, resulted in 40% and 76% increase in mouse life span, and significantly extended survival with p values < 0.05 and < 0.001 (log rank test), respectively. The effect of VS-4718 on leukemia stem cells and minimal residual disease (MRD) is currently under investigation. Taken together, results of our preclinical studies suggest that VS-4718 may have activity against leukemia that warrants further investigation. Disclosures Tam: Verastem: Employment. Ring:Verastem: Employment. Trombino:Verastem: Employment. Weaver:Verastem: Employment, Equity Ownership. Pachter:Verastem Inc.: Employment, Equity Ownership. Padval:Verastem: Employment. Xu:Verastem: Employment.

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Persisting Chronic Myeloid Leukemia Stem and Progenitor Cells From Patients in Major Molecular Remission Under Imatinib Are Characterized by Low BCR/ABL Expression.

Blood ◽

10.1182/blood.v114.22.2207.2207 ◽

2009 ◽

Vol 114 (22) ◽

pp. 2207-2207

Author(s):

Ashu Kumari ◽

Cornelia Brendel ◽

Thorsten Volkmann ◽

Sonja Tajstra ◽

Andreas Neubauer ◽

...

Keyword(s):

Stem Cells ◽

Stem Cell ◽

Chronic Myeloid Leukemia ◽

Progenitor Cells ◽

Myeloid Leukemia ◽

Soft Agar ◽

Molecular Remission ◽

Stem And Progenitor Cells ◽

First Diagnosis

Abstract Abstract 2207 Poster Board II-184 Introduction: Treatment with the Abl-kinase specific inhibitor imatinib (IM) is very effective in chronic myeloid leukemia (CML). However, IM presumably fails to eradicate CML stem cells (HSC) leading to disease persistence and relapse after IM-discontinuation. Although causes of CML persistence under imatinib remain ill defined, quiescence and BCR/ABL-overexpression of CML stem and progenitor cells have been suggested as underlying mechanisms. We here set out to identify means to directly study persistence mechanisms in residual BCR/ABL-positive progenitor and stem cell clones from chronic phase CML patients in major molecular remission (mmR) under imatinib. Methods: Bone marrow specimens of twenty-one CML patients in at least major molecular remission (mmR) according to the international scale, first diagnosis (FD) patients (n=5) and healthy donors (n=4) were sorted into HSC, common myeloid progenitors (CMP), granulocyte/macrophage progenitors (GMP) and megakaryocate-erythrocyte progenitors (MEP) and BCR-ABL mRNA expression was directly assessed by quantitative real time (qPCR) and/or nested PCR (mRNA of 4.000 sorted cells). Alternatively, HSC, CMP, GMP and MEP were seeded into soft agar and mRNA was extracted from individual colony forming units (CFU) to assess BCR/ABL-mRNA expression by qPCR. Moreover, CFU of sub-fractions of first diagnosis CML patients were treated in vitro with IM at 3mM and BCR/ABL-expression of surviving CFU was compared with the BCR/ABL expression levels of mock-treated CML-CFU. In total, 595 soft agar colonies were analyzed. Results: By nested PCR, BCR/ABL-mRNA was readily detectable in the HSC compartments of 7 of 10 (7/10) CML patients in mmR. BCR/ABL was also detected in the CMP-, GMP-, and MEP-compartments in 6, 10 and 8 of the 10 patients, respectively. Real time qRT-PCR suggested only a trend toward stronger BCR/ABL positivity of the HSC compartment when compared to the other progenitor compartments (table 1). A detailed analysis of the BCR/ABL-expression of individual CFU from HSC-, CMP-, GMP-, and MEP-compartments of mmR patients revealed that persisting CML-CFU expressed significantly less BCR/ABL than first diagnosis CML-CFU obtained before imatinib therapy (table 1). This finding could be recapitulated in vitro: primary CML-CD34+ cells of first diagnosis CML patients (n=4) were seeded into soft agar in the presence or absence of 3 uM imatinib. After 14 days BCR/ABL expression only of BCR/ABL-positive CFU was compared. BCR/ABL-positive CML-CFU (n=30) that had survived imatinib exposure expressed significantly less BCR/ABL than mock-treated CML-CFU (n=175) (p<0.001). Work is in progress providing in vitro evidence that selection/induction of low BCR/ABL expression in immature progenitor and stem cells is a new mechanism of imatinib persistence in mmR patients via reducing oncogenic addiction from BCR/ABL. Conclusions: We showed that BCR/ABL-persistence is not confined to the quiescent CML-stem cell compartment, but seems to affect also the highly proliferative progenitor compartments. More intriguingly, persisting CML-HSC and -precursor cells express remarkably low levels of BCR/ABL when compared to first diagnosis HSC and progenitors, implying that low BCR/ABL expression reduces imatinib sensitivity in vivo. The simple model of selection / induction of low BCR/ABL expression as mechanism of imatinib persistence in CML would explain the low propensity of disease progression after achieving mmR, and the low genetic instability of CML clones from mmR patients. Disclosures: No relevant conflicts of interest to declare.

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An All Antibody Approach for Conditioning Bone Marrow for Hematopoietic Stem Cell Transplantation with Anti-cKIT and Anti-CD47 in Non-Human Primates

Blood ◽

10.1182/blood-2019-131490 ◽

2019 ◽

Vol 134 (Supplement_1) ◽

pp. 4428-4428

Author(s):

Kristopher D Marjon ◽

James Y Chen ◽

Jiaqi Duan ◽

Timothy S Choi ◽

Kavitha Sompalli ◽

...

Keyword(s):

Bone Marrow ◽

Mast Cell ◽

Stem Cell ◽

Peripheral Blood ◽

Research Funding ◽

Mast Cell Degranulation ◽

Employment Equity ◽

Cell Counts ◽

Equity Ownership

Background Hematopoietic stem cell (HSC) transplantation (HSCT) is a well-established procedure that, with or without gene therapy, is curative for numerous severe life-threatening diseases including genetic blood disorders and blood cancers. While advances have been made, there are still substantial concerns since these chemo- and radiation therapy based procedures cause long-term toxicities such as infertility and secondary malignancies or even result in high mortality. We have previously established in a series of preclinical studies a novel chemo- and radiation-free non-toxic monoclonal antibody (Ab) -based conditioning regimen for autologous and allogeneic HSCT (Czechowicz et al., Akanksha et al. and George et al.). This cKIT-CD47 Ab-based regimen selectively depletes host HSCs for HSCT while sparing off-target toxicities caused by chemotherapy/radiation. By significantly decreasing morbidity/mortality associated with traditional conditioning regimens, antibody-mediated conditioning could expand the patient population eligible to receive HSCT for a variety of disorders. We developed a novel cKIT Ab (FSI-174), with an active Fc, and in combination with our CD47 magrolimab (previously 5F9, blocks the don't eat me pathway) could be utilized to translate the promising preclinical findings into clinical studies for safe and less toxic bone marrow conditioning for HSCT. Here we present the functional characterization of FSI-174 as single Ab and in combination with magrolimab in vitro and in non-human primate (NHP) studies. Methods We tested if FSI-174 could block stem cell factor signaling and we explored if FSI-174 alone or in combination with magrolimab could promote phagocytosis of cKIT positive cells (Kasumi-1). In addition, we determined if FSI-174 could cause mast cell degranulation. Subsequently, we explored the potential of FSI-174 alone (Phase A) or in combination with magrolimab (Phase B) to deplete HSCs in NHPs (rhesus macaques)in vivo. In Phase A, single doses of FSI-174 (0.3, 1, or 3 mg/kg) were administered alone. In Phase B, FSI-174 (0.3 or 3 mg/kg) was administered in combination with magrolimab (5mg/kg priming and 20 mg/kg maintenance dose). Bone marrow aspirates and core biopsies and peripheral blood were sampled before the study start and throughout the study. Frequency of bone marrow HSCs and cKIT receptor occupancy (RO) was determined by flow cytometry. In addition, the PK profile of FSI-174 was determined. Results In-vitro analysis demonstrated that FSI-174 decreases proliferation of HSPCs and enhances phagocytosis of cKIT positive cells, and the addition of magrolimab synergistically enhances the phagocytosis. Strikingly, FSI-174 did not cause mast cell degranulation in vitro. In the NHPs, complete (100%) cKIT receptor occupancy was achieved at all FSI-174 dose levels and was maintained for 1 to 9 days correlating with increasing doses and pharmacokinetics. The FSI-174 Cmax was found to be proportional to dose and mean Cmax increased from 6.25 ug/mL to 49.2 ug/mL. In Phase A, FSI-174 alone did not decrease the frequency of bone marrow HSCs compared to PBS control and had no effect on the peripheral blood cell counts. However, in Phase B, when FSI-174 was combined with magrolimab it significantly decreased the frequency of bone marrow HSCs with the nadir at day 9 and no recovery over 85 days compared to PBS control. Notably, there were no changes in peripheral blood cell counts over the course of the studies with no cytopenias in combination treatment. Conclusions We have developed a novel cKIT Ab (FSI-174) that meets the desired profile of stem cell factor block, promotion of phagocytosis, but without promoting mast cell degranulation. Furthermore, in the NHPs studies we have confirmed our chemo- and radiation-free cKIT-CD47 Ab -based conditioning approach with FSI-174 and magrolimab. As anticipated by our previous preclinical studies, monotherapy with FSI-174 does not deplete bone marrow HSCs in NHPs. Notably, no cytopenias are observed with either monotherapy or combination therapy. These data demonstrate the specificity, efficacy and safety of FSI-174/ magrolimab combination have great potential for conditioning regimen for HSCT in a chemotherapy and radiation free manner. Given the favorable safety profile of magrolimab across several clinical studies, these results are paving the way to the first-in-human trials for this novel conditioning for HSCT. Disclosures Marjon: Forty Seven Inc: Employment, Equity Ownership. Chen:Forty Seven Inc.: Consultancy, Equity Ownership. Duan:Forty Seven Inc.: Employment, Equity Ownership. Choi:Forty Seven inc: Employment, Equity Ownership. Sompalli:Forty Seven Inc: Employment, Equity Ownership. Feng:Forty Seven Inc: Employment, Equity Ownership. Mata:Forty Seven inc: Employment, Equity Ownership. Chen:Forty Seven Inc: Employment, Equity Ownership. Kean:HiFiBio: Consultancy; BlueBirdBio: Research Funding; Gilead: Research Funding; Regeneron: Research Funding; EMDSerono: Consultancy; FortySeven: Consultancy; Magenta: Research Funding; Bristol Meyers Squibb: Patents & Royalties, Research Funding; Kymab: Consultancy; Jazz: Research Funding. Chao:Forty Seven Inc: Employment, Equity Ownership. Chao:Forty Seven, Inc.: Employment, Equity Ownership, Patents & Royalties. Takimoto:Forty Seven, Inc.: Employment, Equity Ownership, Patents & Royalties. Agoram:Forty Seven Inc.: Employment, Equity Ownership. Majeti:FortySeven: Consultancy, Equity Ownership, Other: Board of Director; BioMarin: Consultancy. Weissman:Forty Seven Inc.: Consultancy, Equity Ownership, Patents & Royalties. Liu:Forty Seven Inc: Employment, Equity Ownership, Patents & Royalties. Volkmer:Forty Seven, Inc.: Employment, Equity Ownership, Patents & Royalties.

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A Phase I Study Evaluating the Safety and Persistence of Allorestricted WT1-TCR Gene Modified Autologous T Cells in Patients with High-Risk Myeloid Malignancies Unsuitable for Allogeneic Stem Cell Transplantation

Blood ◽

10.1182/blood-2019-128044 ◽

2019 ◽

Vol 134 (Supplement_1) ◽

pp. 1367-1367

Author(s):

Emma C Morris ◽

Rita Tendeiro-Rego ◽

Rachel Richardson ◽

Thomas A Fox ◽

Francesca Sillito ◽

...

Keyword(s):

T Cells ◽

Stem Cell ◽

T Cell ◽

High Risk ◽

Phase I ◽

Myeloid Leukemia ◽

Research Funding ◽

Post Infusion ◽

Equity Ownership ◽

Acute Myeloid

Background:Patients with acute myeloid leukemia (AML), myelodysplasia (MDS) or tyrosine kinase inhibitor resistant chronic myeloid leukemia (CML) who are unsuitable for consolidative allogeneic stem cell transplantation (alloSCT) have high relapse rates following chemotherapy. Wilms' tumor 1 (WT1) is highly expressed in the majority of acute myeloid leukemias (AML) and in many subtypes of myelodysplasia (MDS) as well as other hematological and solid tumors. WT1 is an intracellular antigen, which makes it difficult to target using current Chimeric Antigen Receptor (CAR)-T cell technologies. The use of genetically modified T cells expressing WT1-specific α/β T cell receptors can re-direct T cell specificity via the recognition of intracellular peptides presented by MHC molecules on the malignant cell surface. Phase I clinical trials of WT1-TCR gene-modified T cells have been conducted in the settings of relapsed disease and post-alloSCT and preliminary data suggests this treatment approach is safe and potentially clinically effective in these cohorts (Tawara et al. Blood. 2017;130(18):1985-94; Chapuis et al, Nat Med. 2019;25(7):1064-72). Methods:We report a phase I/II safety and dose escalation study evaluating WT1-TCR gene-modified autologous T cells in HLA-A*0201 positive patients with AML, MDS and CML, unsuitable for alloSCT (NCT02550535) (Fig 1A). Patient T cells were harvested by leucapheresis and transduced with a retroviral vector construct encoding the codon optimised variable and constant a and bchains of the human pWT126-specific TCR separated by a self-cleaving 2A sequence (Fig 1B). Bulk transduced T cells were analysed by flow cytometry (CD3, CD8 and Vb2.1) prior to infusion and at regular intervals post-infusion. A quantitative PCR assay was developed to identify WT1-TCR expressing T cells in the peripheral blood post infusion. Patients received minimal conditioning with fludarabine and methylprednisolone prior to transfer of transduced T cells. All subjects were followed for a minimum of 12 months or until death. Results:A total of 10 patients (6 AML, 3 MDS and 1 TKI- resistant CML) were recruited. The mean age was 71.3 years (range 64-75) and all had high risk disease (by cytogenetic or clinical criteria). All AML patients were in complete morphological remission at the time of trial entry, whilst MDS patients had ≤ 15% blasts on bone marrow examination. All 10 patients received the gene-modified T cells in dose escalation cohorts (seven patients received £2x107/kg and three patients received £1x108/kg bulk WT1 TCR transduced cells). No adverse events directly attributable to the investigational product were recorded apart from one possible cytokine release syndrome, which was managed without tociluzimab. Transferred T cells demonstrated in vivoproliferation commensurate with maintenance of functional capacity despite ex vivo manipulation (Fig 1C and 1D). The TCR-transduced T cells were detectable in all patients at 28 days and in 7 patients persisted throughout the study period (Fig 1E). All 6 AML patients were alive at last follow up (median 12 months; range 7-12.8 months). The 3 patients with MDS had a median survival of 3 months (range 2.1-3.96 months) post T cell infusion. 2 died from progressive disease and one from other causes. 2 patients discontinued the study early due to disease progression. Conclusions: This is the second reported phase I/II clinical trial of autologous WT1-TCR gene-modified T cells for treatment of AML and MDS in a high-risk cohort of patients not suitable for alloSCT. We have shown that the WT1-TCR T cells demonstrated a strong safety profile without detectable on-target, off-tumour toxicity and no severe adverse events in the ten patients treated. An important cause of treatment failure for adoptive cellular therapies is the lack of persistence of transferred T cells leading to loss of disease specific effects. We demonstrated that autologous WT1-TCR T cells proliferated in vivoand persisted for many months. Recent work within our group (in press) has shown that TCRs modified to include key framework residues, show increased TCR expression and functional improvement. These modifications could be incorporated into future studies to improve efficacy. This data supports the rationale for a larger, phase II trial of WT1-TCR T cells in myeloid malignancies in patients for whom alloSCT is not appropriate, in order to assess clinical efficacy. Figure 1 Disclosures Morris: Quell Therapeutics: Consultancy, Other: Scientific Founder,stock; Orchard Therapeutics: Consultancy. Qasim:CellMedica: Research Funding; Bellicum: Research Funding; UCLB: Other: revenue share eligibility; Autolus: Equity Ownership; Orchard Therapeutics: Equity Ownership; Servier: Research Funding. Mount:Gamma Delta Therapeutics: Employment. Inman:Cellmedica: Employment. Gunter:Cellmedica: Employment. Stauss:Cell Medica: Other: I have stock; Quell Therapeutics: Consultancy, Other: I have stock.

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A Phase 2 Randomized Study of Low Dose Ara-C with or without Glasdegib (PF-04449913) in Untreated Patients with Acute Myeloid Leukemia or High-Risk Myelodysplastic Syndrome

Blood ◽

10.1182/blood.v128.22.99.99 ◽

2016 ◽

Vol 128 (22) ◽

pp. 99-99 ◽

Cited By ~ 26

Author(s):

Jorge E. Cortes ◽

Florian H. Heidel ◽

Michael Heuser ◽

Walter Fiedler ◽

B. Douglas Smith ◽

...

Keyword(s):

Acute Myeloid Leukemia ◽

High Risk ◽

Myeloid Leukemia ◽

Research Funding ◽

Low Dose ◽

P Value ◽

Employment Equity ◽

Equity Ownership ◽

Acute Myeloid

Abstract Background: The Hedgehog signaling pathway (HhP) is aberrantly activated in leukemias and myelodysplastic syndrome (MDS), promoting cancer stem cell maintenance. HhP inhibition reduces leukemic stem cells. Glasdegib is a potent, selective, oral HhP inhibitor, with activity in pre-clinical and clinical studies. The addition of glasdegib to standard chemotherapy (CT) has an acceptable safety profile and appears to have clinical activity in MDS and acute myeloid leukemia (AML). Methods: In this study (NCT01546038), previously untreated AML or high-risk MDS patients (pts) ineligible for intensive CT were randomized 2:1 to receive low-dose cytarabine (LDAC) 20 mg subcutaneously twice a day x 10 days q28 days + oral glasdegib 100 mg daily or LDAC alone for as long as pts received clinical benefit. The primary endpoint was overall survival (OS). The final analysis was conducted after completion of recruitment (Oct 2015) and at least 92 OS events. Results: As of Apr 2016, 132 pts (116 AML, 16 MDS) were randomized to LDAC + glasdegib (n = 88) or LDAC alone (n = 44) (stratified as good/intermediate [int.] vs poor risk) (Table). Demographic and baseline characteristics were similar between arms in median age, baseline cytogenetic risk, and diagnosis. Eighty-four pts received LDAC + glasdegib and 41 pts LDAC alone (7 randomized/not treated pts were followed for survival). Median treatment duration was 83 days for LDAC + glasdegib and 47 days for LDAC alone; median follow up was 14.3 months and 12.4 months, respectively. In the glasdegib arm, 12 pts were continuing treatment and 25 were in follow up; in the LDAC arm, 1 pt was on treatment and 5 in follow up. Cytopenias and gastrointestinal toxicities were the adverse events (AEs) occurring more frequently in the LDAC + glasdegib arm. Hh-associated AEs in the glasdegib arm included dysgeusia (23.8%), muscle spasms (20.2%) and alopecia (10.7%). Serious AEs of febrile neutropenia were more frequent in the glasdegib arm, but sepsis rates were lower and pneumonia rates were similar. The most common cause of death was disease progression in both arms. Grade 2-4 QTcF prolongation was more frequent in the LDAC arm. Investigator-reported complete response (CR) rates were numerically higher for LDAC + glasdegib (n = 17, 15%) vs LDAC alone (n = 1, 2.3%), p-value 0.0142. Based on intent to treat analysis of 96 events, median OS (mOS) for LDAC + glasdegib was 8.3 (80% confidence interval [CI] 6.9, 9.9) vs 4.9 months (80% CI 3.5, 6.0) for LDAC alone (HR 0.511, 80% CI 0.386, 0.675; one-sided log rank p-value 0.0020 stratified by cytogenetic risk). For good/int. risk, mOS for LDAC + glasdegib was 12.2 vs 6.0 months for LDAC alone (HR 0.464, p-value 0.0035). For poor risk, mOS for LDAC + glasdegib was 4.4 vs 2.3 months (HR 0.575, p-value 0.0422). In AML pts, mOS for LDAC + glasdegib was 8.3 vs 4.3 months for LDAC alone (HR 0.462, p-value 0.0004). Conclusions: The addition of glasdegib to LDAC for AML and high-risk MDS pts improved OS compared with LDAC alone. The improvement was consistent among subgroups, particularly in good/int. risk pts. Treatment was associated with an acceptable safety profile. The addition of glasdegib to LDAC may be a treatment option for pts with AML or high-risk MDS. Disclosures Cortes: ARIAD: Consultancy, Research Funding; Bristol-Myers Squib: Consultancy, Research Funding; Novartis: Consultancy, Research Funding; Pfizer: Consultancy, Research Funding; Teva: Research Funding. Heuser:Tetralogic: Research Funding; Celgene: Honoraria; Bayer Pharma AG: Research Funding; Novartis: Consultancy, Research Funding; Pfizer: Research Funding; Karyopharm Therapeutics Inc: Research Funding; BerGenBio: Research Funding. Fiedler:Gilead: Other: Travel; Novartis: Consultancy; Ariad/Incyte: Consultancy; Teva: Other: Travel; Pfizer: Research Funding; Kolltan: Research Funding; Amgen: Consultancy, Other: Travel, Patents & Royalties, Research Funding; GSO: Other: Travel. Smith:Actinium Pharmaceuticals, Inc.: Research Funding. Robak:Pfizer: Research Funding. Montesinos Fernandez:Gamida Cell: Consultancy. Ma:Pfizer: Employment, Equity Ownership. Shaik:Pfizer: Employment, Equity Ownership. Zeremski:Pfizer: Employment, Equity Ownership. O'Connell:Pfizer: Employment, Equity Ownership. Chan:Pfizer: Employment, Equity Ownership.

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Inecalcitol and Decitabine Synergize to Inhibit Cell Proliferation and to Induce Differentiation of Human Acute Myeloid Leukemia Cell Lines

Blood ◽

10.1182/blood-2018-99-118125 ◽

2018 ◽

Vol 132 (Supplement 1) ◽

pp. 5234-5234

Author(s):

Enguerran Mouly ◽

Emilie Rousseau ◽

Cecile Planquette ◽

Remi Delansorne

Keyword(s):

Cell Proliferation ◽

Cell Line ◽

Cell Lines ◽

Myeloid Leukemia ◽

Employment Equity ◽

Elderly Aml ◽

Equity Ownership ◽

Inhibit Cell Proliferation ◽

Stimulation Of

Abstract Decitabine (DAC) is a hypomethylating agent indicated as front-line therapy for de novo or secondary acute myeloid leukemia (AML) in newly diagnosed patients aged 65 years or older unfit for standard induction chemotherapy (Kantarjian et al., 2012, Malik & Cashen, 2014, Nieto et al., 2016, He et al., 2017). Its mechanism of action at the DNA level mostly results in inhibition of cell proliferation. Cellular differentiation can also be involved in some extent in a fraction of the leukemic cell population, as reported in initial pharmacological studies (Creusot et al., 1982; Pinto et al., 1984). Overall survival advantage is nevertheless limited to several more months and the next challenge is to combine DAC with other drugs to improve it further (Kubasch & Platzbecker, 2018). Inecalcitol (INE: 14epi-,19nor-,23yne-,1,25dihydroxy-cholecalciferol) is a vitamin D receptor agonist characterized by potent anti-proliferative and pro-differentiating general properties on cancer cells and by a low calcemic potential (Okamoto et al., 2012; Ma et al., 2013; Medioni et al. 2014), and especially on AML cell lines (AACR 2017, 2018). INE is currently being tested in combination with DAC in this category of elderly AML patients unfit for standard chemotherapy. The aim of the present report was to look for synergies in vitro between DAC and INE on four non-APL human AML cell lines (MOLM-13, U-937, THP-1, OCI-AML2) both on inhibition of proliferation and induction of differentiation. After 72 hours of incubation, cells were counted and labeled for CD11b and CD14 at the cell surface as biomarkers of monocytic/macrophagic differentiation. The range of DAC concentrations had to adapted to each cell line to avoid maximal cytotoxicity: 1.2 nM to 100 nM on MOLM-13, 3 nM to 250 nM on U-937 and THP-1, and 31 nM to 500 nM on OCI-AML2. The same range of 0.12 to 10 nM INE concentrations was tested on each cell line. Each concentration of INE was tested in combination with each concentration of DAC. Synergy was calculated as the excess over the highest single agent (HSA) using the open source Combenefit software (Di Veroli et al., 2016). The highest concentration of DAC alone (MOLM-13: 100 nM, U-937 and THP-1: 250 nM; OCI-AML2: 500 nM) induced a decrease in cell count of 30% of THP-1 cells, 50% of OCI-AML2 cells, 65% of U-937 cells and 80% of MOLM-13 cells. The highest concentration of INE alone (10 nM) induced a decrease in cell count of 20% of U-937 and THP-1 cells, 60% of OCI-AML2 cells and 70% of MOLM-13 cells. The antiproliferative effects of DAC and INE were at least additive in all combinations tested. Significant HSA synergy indexes were found for the decrease in cell number in all four cell lines, ranging from 12% to 23% depending on cell lines and combinations of concentrations. The highest concentration of DAC alone had no (U-937, THP-1) or limited activity (<+12% of labeled MOLM-13 or OCI-AML2 cells) to induce either CD11b or CD14 on the cell surface. By contrast, the highest concentration of INE alone (10 nM) stimulated the expression of CD11b and CD14 in up to 70% to 95% of the cells depending on the cell line (except the CD14 labeling of U-937 cells which remained < 8%). The respective EC50 of INE for CD11b and CD14 induction was 1 and 3 nM on THP-1 cells, 4 and 3 nM on MOLM-13 cells, 3 and 3 nM on OCI-AML2 cells and 1 nM on U-937 cells (50% not reached for CD14). There was no antagonistic effect of DAC towards the pro-differentiating properties of INE. A significant HSA synergy index in the 16% to 26% range was observed for both CD11b and CD14 in MOLM-13 cells and for CD14 in OCI-AML2 cells. A very high HSA synergy index of 75% was observed for the stimulation of CD14 in U-937 cells. In summary, DAC exerted more antiproliferative activity than INE which was more potent to induce monocytic/macrophagic differentiation of four non-APL human AML cell lines. The combination of DAC and INE systematically resulted in a synergy to inhibit cell proliferation, and the strong stimulation of cell differentiation induced by INE alone was in some cases boosted by DAC. These in vitro results provide the mechanistic basis for the potential interest of treating elderly AML patients with INE in addition to DAC in the ongoing double-blind placebo-controlled Phase II clinical trial (NCT02802267). Disclosures Mouly: Hybrigenics: Employment. Rousseau:Hybrigenics: Employment. Planquette:Hybrigenics: Employment, Equity Ownership, Patents & Royalties: inventor, but no royalties. Delansorne:Hybrigenics: Employment, Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties: inventor, but no royalties.

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Inhibitory Effects of Homoharringtonine on Leukemic Stem Cells and BCR-ABL Induced Chronic Myeloid Leukemia and Acute Lymphoblastic Leukemia in Mice.

Blood ◽

10.1182/blood.v110.11.2912.2912 ◽

2007 ◽

Vol 110 (11) ◽

pp. 2912-2912 ◽

Cited By ~ 1

Author(s):

Yaoyu Chen ◽

Yiguo Hu ◽

Shawnya Michaels ◽

Dennis Brown ◽

Shaoguang Li

Keyword(s):

Stem Cells ◽

Stem Cell ◽

Acute Lymphoblastic Leukemia ◽

Chronic Myeloid Leukemia ◽

Myeloid Leukemia ◽

Lymphoblastic Leukemia ◽

Leukemia Cells ◽

Leukemic Stem Cells ◽

Lymphoid Leukemia

Abstract The Abl tyrosine kinase inhibitors (TKIs) imatinib mesylate (IM) and dasatinib, targeting BCR-ABL for the treatment of Philadelphia-positive (Ph+) leukemia including chronic myeloid leukemia (CML) and B-cell acute lymphoblastic leukemia (B-ALL), have produced impressive results in terms of therapeutic outcome and safety for patients. However, clinical resistance to these TKIs likely at the level of leukemic stem cell negates curative results in Ph+ leukemia. At present, an anti-stem cell strategy has not been developed for treating these leukemia patients. Homoharringtonine (HHT) (omacetaxine mepesuccinate - USAN/INN designation) has shown significant clinical activity in CML in combination with IM or alone for patients failing IM. However, little is known about whether HHT has an inhibitory effect on leukemic stem cells. The purpose of this study is to determine whether HHT inhibits BCR-ABL-expressing leukemic stem cells (Lin-c-Kit+Sca-1+) that we identified previously (Hu et al. Proc Natl Acad Sci USA 103(45):16870–16875, 2007) and to evaluate therapeutic effects of HHT on CML and B-ALL in mice. We find that in our in vitro stem cell assay, greater than 90% of leukemic stem cells were killed after being treating with HHT (12.5, 25, and 50 nM) for 6 days, and in contrast, greater than 75% or 92% of leukemic stem cells survived the treatment with dasatinib (100 nM) or imatinib (2 mM). We next treated CML mice with HHT (0.5 mg/kg, i.p., once a day). 4 days after the treatment, FACS analysis detected only 2% GFP+Gr–1+ myeloid leukemia cells in peripheral blood of HHT -treated CML mice and in contrast, 41% GFP+Gr–1+ myeloid leukemia cells in placebo-treated mice. We also treated mice with BCR-ABL induced B-ALL with HHT, and found that only 0.78% GFP+B220+ lymphoid leukemia cells were detected in peripheral blood compared to 34% GFP+B220+ lymphoid leukemia cells in placebo-treated mice. Furthermore, HHT significantly inhibited in vitro proliferation of K562 and B-lymphoid leukemic cells isolated from mice with B-ALL induced by BCR-ABL wild type and BCR-ABL-T315I resistant to both imatinib and dasatinib. In sum, HHT has an inhibitory activity against CML stem cells, and is highly effective in treating CML and B-ALL induced by BCR-ABL in mice.

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Preclinical Development of Triptolide Derivative MRx102 as a Therapeutic Agent for Acute Myeloid Leukemia

Blood ◽

10.1182/blood.v116.21.3271.3271 ◽

2010 ◽

Vol 116 (21) ◽

pp. 3271-3271

Author(s):

John M. Fidler ◽

Jinhua An ◽

John H. Musser ◽

Duncan H. Mak ◽

Bing Carter ◽

...

Keyword(s):

Drug Development ◽

Cell Lines ◽

Myeloid Leukemia ◽

Leukemia Cell ◽

Employment Equity ◽

Toxicology Study ◽

Leukemia Cell Lines ◽

Equity Ownership ◽

Anti Tumor Activity

Abstract Abstract 3271 Acute Myeloid Leukemia (AML) is the most common form of adult acute leukemia and the second most common childhood leukemia. AML has the lowest survival rate among leukemias, and the frequency is increasing as the population ages. Current therapies are inadequate, and a need exists for better therapeutic agents to treat AML, both as initial treatment for newly diagnosed patients and for those who have failed current therapy and relapsed. Natural products, such as taxol, have shown activities in a variety of disease states, including cancer. Triptolide is a natural product diterpenoid derived from Tripterygium wilfordii Hook f, and has shown anti-cancer activity in a broad range of solid tumors in preclinical models. It induces apoptosis in various leukemic cell lines and primary AML blasts (Carter, B et al, Blood 2006). Derivatives of triptolide with improved pharmacokinetics and bioavailability offer the opportunity to optimize the activity of triptolide for clinical application in AML. MRx102 is a triptolide derivative that is more hydrophobic than triptolide. It has potent in vitro cytotoxic activity with human tumor and leukemia cell lines, an unusual result for triptolide derivatives because they are usually much less active in vitro than the parent compound. Designed as a prodrug, MRx102 exerts cytotoxic activity with human AML cell lines and other human leukemia cell lines without pre-incubation with plasma esterases (IC50 of 51.0 and 37.1 nM with MV4-11 AML cells at 48 and 72 hours, respectively, ∼55% and ∼36% of the activity of triptolide, respectively). MRx102 decreases the viable CD34+ blasts of AML patient samples (a mean of 79.8 ± 8.8% specific apoptosis at 100 nM, n=3), and overcomes the apoptosis protection by co-cultivated stromal cells (with a similar mean of 74.1 ± 8.5%). MRx102 shows dose-dependent anti-tumor activity with the MV4-11 cell line in nude mouse human AML tumor xenografts. After 42 days of MRx102 dosing at 1.35 mg/kg/day i.p., tumor volume was inhibited by 99.7%. Tumors removed from several mice appeared to be Matrigel pellets rather than vascularized tumors, suggesting that many of the tumors were completely eliminated. In studies with the OCI-AML3 human AML cell line xenograft model, the group receiving MRx102 at 1.35 mg/kg/day i.p. showed similar high activity, with mean tumor volume reduced by as much as 99.2% on day 23 compared to the vehicle control group. Tumors of 7 of 10 mice were smaller than the day 0 volumes at the day 28 end of the study. As part of drug development, toxicology testing with MRx102 was initiated with an acute single dose rat toxicology study with no deaths and no adverse signs up to the top dose of 3.0 mg/kg MRx102 in DMSO/PBS administered i.v. The maximum tolerated dose (MTD) is greater than 3 mg/kg of MRx102, and the no observable adverse effect level (NOAEL) is at least 3 mg/kg. A 7-day subacute rat toxicology study of MRx102 showed no deaths and no adverse signs up to the top dose of 1.5 mg/kg/day MRx102 in DMSO/PBS administered daily i.v. for 7 days. The histopatholgy report shows no findings related to administration of the test article. The MRx102 MTD is greater than 1.5 mg/kg/day, and the NOAEL is at least 1.5 mg/kg/day. Previously observed NOAELs for related compounds have been less than 0.1 mg/kg/day. The current studies show potent anti-tumor activity as well as an unusually positive safety profile for MRx102 when compared to triptolide and other triptolide derivatives. Further MRx102 drug development is underway, with the intention of submitting an Investigational New Drug application to the Food and Drug Administration leading to clinical evaluation of MRx102 in AML patients. Updated results on current drug development activities will be presented at the meeting. This work is supported in part by NCI SBIR Contract HHSN261200900061C to MyeloRx LLC. Disclosures: Fidler: MyeloRx LLC: Employment, Equity Ownership, PI for an NCI Contract to MyeloRx LLC, Patents & Royalties. An:MyeloRx LLC: Employment, Equity Ownership, participant in research under an NCI SBIR Contract to MyeloRx LLC. Musser:MyeloRx LLC: Employment, Equity Ownership, Patents & Royalties, participant in research under an NCI SBIR Contract to MyeloRx LLC. Mak:MyeloRx LLC: participant in research under an NCI SBIR Contract to MyeloRx LLC. Carter:MyeloRx LLC: participant in research under an NCI SBIR Contract to MyeloRx LLC. Andreeff:MyeloRx LLC: Consultancy, participant in research under an NCI SBIR Contract to MyeloRx LLC.

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439 Dual modes of action for anti-TIM-3 antibody MBG453 in myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML): preclinical evidence for immune-mediated and anti-leukemic activity

Journal for ImmunoTherapy of Cancer ◽

10.1136/jitc-2020-sitc2020.0439 ◽

2020 ◽

Vol 8 (Suppl 3) ◽

pp. A465-A465

Author(s):

Catherine Sabatos-Peyton ◽

Tyler Longmire ◽

Lisa Baker ◽

Nidhi Patel ◽

Anne-Sophie Wavreille ◽

...

Keyword(s):

Stem Cells ◽

Acute Myeloid Leukemia ◽

Stem Cell ◽

High Risk ◽

Myeloid Leukemia ◽

Leukemic Stem Cells ◽

Self Renewal ◽

Immune Mediated ◽

Acute Myeloid ◽

Cell Stem Cell

BackgroundTIM-3 is expressed on leukemic stem cells (LSCs) and blasts in AML,1 2 and TIM-3 expression on MDS blasts correlates with disease progression.3 Functional evidence for TIM-3 in AML was established with an anti-TIM-3 antibody which inhibited engraftment and development of human AML in immuno-deficient murine hosts.1 TIM-3 promotes an autocrine stimulatory loop via the TIM-3/Galectin-9 interaction, supporting LSC self-renewal.4 In addition to its cell-autonomous role on LSCs/blasts, TIM-3 also has a critical role in immune system regulation, in adaptive (CD4+ and CD8+ T effector cells, regulatory T cells) and innate (macrophages, dendritic cells, NK cells) immune responses.5 MBG453 is a high-affinity, humanized anti-TIM-3 IgG4 antibody (Ab) (stabilized hinge, S228P), which blocks the binding of TIM-3 to phosphatidylserine (PtdSer). Recent results from a multi-center, open label phase Ib dose-escalation study (NCT03066648) in patients with high-risk MDS and no prior hypomethylating agent therapy evaluating MBG453 in combination with decitabine demonstrated encouraging preliminary efficacy with an overall response rate of 58%,6 and MBG453 combined with azacitidine also showed encouraging response rates.7 Preclinical experiments were undertaken to define the mechanism of action of the hypomethylating agent and anti-TIM-3 combination.MethodsTHP-1 cells (a human monocytic AML cell line) were pre-treated with decitabine and co-cultured with anti-CD3 activated healthy human donor peripheral blood mononuclear cells (PBMCs) in an Incucyte-based assay to measure cell killing. The ability of MBG453 to mediate antibody-dependent cellular phagocytosis (ADCP) was measured by determining the phagocytic uptake of an engineered TIM-3-overexpressing Raji cell line in the presence of MBG453 by phorbol 12-myristate 13-acetate (PMA)-activated THP-1 cells. Patient-derived AML xenograft studies were undertaken in immune-deficient murine hosts to evaluate the combination of decitabine and MBG453.ResultsMBG453 was determined to partially block the TIM-3/Galectin-9 interaction in a plate-based MSD (Meso Scale Discovery) assay, supported by a crystal structure of human TIM-3.8 Pre-treatment of THP-1 cells with decitabine enhanced sensitivity to immune-mediated killing in the presence of MBG453. MBG453 was determined to mediate modest ADCP, relative to controls. MBG453 did not enhance the anti-leukemic activity of decitabine in patient-derived xenograft studies in immuno-deficient hosts.ConclusionsTaken together, these results support both direct anti-leukemic effects and immune-mediated modulation by MBG453. Further studies are ongoing to determine: (1) whether MBG453 can mediate physiologically relevant ADCP of TIM-3-expressing leukemic cells; and (2) the potential of MBG453 to impact the autocrine feedback loop of TIM-3/Galectin-9.Ethics ApprovalThe human tissue used in these studies was under the Novartis Institutes of BioMedical Research Ethics Board IRB, Approval Number 201252867.ReferencesKikushige Y, Shima T, Takayanagi S, et al. TIM-3 is a promising target to selectively kill acute myeloid leukemia stem cells. Cell Stem Cell 2010;7(6):708–717.Jan M, Chao MP, Cha AC, et al. Prospective separation of normal and leukemic stem cells based on differential expression of TIM3, a human acute myeloid leukemia stem cell marker. Proc Natl Acad Sci USA 2011; 108(12): 5009–5014.Asayama T, Tamura H, Ishibashi M, et al. Functional expression of Tim-3 on blasts and clinical impact of its ligand galectin-9 in myelodysplastic syndromes. Oncotarget 2017;8(51): 88904–88917.Kikushige Y, Miyamoto T, Yuda J, et al. A TIM-3/Gal-9 autocrine stimulatory loop drives self-renewal of human myeloid leukemia stem cells and leukemic progression. Cell Stem Cell 2015; 17(3):341–352.Acharya N, Sabatos-Peyton C, Anderson AC. Tim-3 finds its place in the cancer immunotherapy landscape. J Immunother Cancer 2020; 8(1):e000911.Borate U, Esteve J, Porkka K, et al. Phase Ib Study of the Anti-TIM-3 Antibody MBG453 in combination with decitabine in patients with high-risk myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML). Blood 2019;134 (Supplement_1):570.Borate U, Esteve J, Porkka K, et al. Abstract S185: Anti-TIM-3 antibody MBG453 in combination with hypomethylating agents (HMAs) in patients (pts) with high-risk myelodysplastic syndrome (HR-MDS) and acute myeloid leukemia (AML): a Phase 1 study. EHA 2020.Sabatos-Peyton C. MBG453: A high affinity, ligand-blocking anti-TIM-3 monoclonal Ab. AACR 2016.

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SL-501, a Next-Generation Targeted Therapy Directed to the IL-3 Receptor (IL-3R), Possesses Preclinical Anti-Tumor Activity Against Hodgkin’s and Non-Hodgkin’s Lymphoma

Blood ◽

10.1182/blood.v124.21.4500.4500 ◽

2014 ◽

Vol 124 (21) ◽

pp. 4500-4500 ◽

Cited By ~ 1

Author(s):

Janice Chen ◽

Vince Macri ◽

Pedro Herrera ◽

Christopher Brooks ◽

Eric Rowinsky

Keyword(s):

Targeted Therapy ◽

Cell Lines ◽

Myeloid Leukemia ◽

Hodgkin’S Lymphoma ◽

Hodgkin's Lymphoma ◽

Next Generation ◽

Employment Equity ◽

Equity Ownership ◽

Anti Tumor Activity

Abstract While Hodgkin’s lymphoma (HL) is among the most curable lymphomas, a significant percentage of patients relapse after frontline therapy or have primary refractory disease. Patients that remain resistant after second or third line chemotherapy or autologous stem cell transplantation (ASCT) have very limited treatment options. Non-Hodgkin’s lymphoma (NHL) comprises a wide array of clinical subtypes, which have indolent to aggressive clinical courses. Multiple lines of chemotherapy and ASCT are part of the NHL treatment strategy, but indolent forms frequently recur, and patients can develop resistance to therapies that were previously effective. The prognosis for patients with HL and NHL who fail to achieve durable remission with approved therapeutics or transplantation is poor. Therefore, new treatment strategies for such patients are desperately needed. The interleukin-3 receptor (IL-3R) alpha chain (CD123) is overexpressed on the tumor bulk and cancer stem cells (CSCs) of multiple hematologic malignancies. In particular, CD123 has been shown to be upregulated on a variety of leukemias and lymphomas, including HL and certain NHLs. We previously showed that SL-401, a novel IL-3R-targeted therapy comprised of IL-3 fused to a truncated diphtheria toxin payload, possesses cytotoxic activity against IL-3R-expressing HL and NHL cells. SL-501 is a next-generation IL-3R targeted therapy with increased binding affinity for the IL-3R and enhanced potency against both tumor bulk and CSCs of acute myeloid leukemia (AML) and chronic myeloid leukemia (CML). Here, the anti-tumor activity of SL-501 against HL and NHL cells was investigated. Our flow cytometry assessment of CD123 showed that the receptor was expressed on two nodular sclerosing HL cell lines (L-428 and HDLM2), one mixed cellularity HL line (L-1236), and two mantle cell lymphoma lines (Mino and JeKo-1). CD123 was expressed to varying extents, ranging from high expression in HDLM-2 (99.5%) and L-428 (89.1%), to moderate-to-low expression in Mino (25.4%), L-1236 (19.5%) and JeKo-1 (2.9%). In this study, the activity of SL-501 was tested against this panel of cell lines. Cell were treated with SL-501 (range: 6.3 pM – 1.5 mM) for 48 hours and then assessed for viability using the CellTiter Glo® in vitro cytotoxicity assay. We found that SL-501 reduced the viability of all cell lines tested in a dose-dependent fashion. In particular, SL-501 showed very high potency against the HDLM2 and L-1236 lines, with IC50 values in the sub-nanomolar range (0.139 nM and 0.191 nM, respectively). SL-501 was also cytotoxic against L-428, JeKo-1, and Mino cell lines, with IC50s of 91 nM, 97 nM, and 116 nM, respectively. Taken together, these findings demonstrate that SL-501, a novel next-generation IL-3R-targeted therapeutic, possesses potent in vitro anti-cancer activity against a variety of HL and NHL cell lines. Additional functional studies are ongoing. These promising results provide a rationale for further development of SL-501 in HL and NHL. Disclosures Chen: Stemline Therapeutics: Employment, Equity Ownership. Macri:Stemline Therapeutics: Employment, Equity Ownership. Herrera:Stemline Therapeutics: Employment. Brooks:Stemline Therapeutics: Employment, Equity Ownership. Rowinsky:Stemline Therapeutics: Consultancy, Employment, Equity Ownership.

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