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Outcomes in patients with high-risk and treatment-resistant myelofibrosis (MF) post-JAK inhibitor therapy remain poor, with no approved drug therapies beyond the JAK inhibitor class. In certain clinical situations, such as severe thrombocytopenia, administration of most JAK inhibitors are contraindicated. Thus, there is an unmet medical need for the development of novel agents for patients with MF. SMAC mimetics [or inhibitor of apoptosis (IAP) antagonists] induce apoptosis in cancer cells. Because these agents are hypothesized to have increased activity in a tumor necrosis factor-α cytokine-rich microenvironment, as is the case with MF, we conducted a single-center, investigator-initiated phase 2 clinical trial, with a monovalent SMAC mimetic LCL161 (oral, starting dose, 1500 mg per week) in patients with intermediate to high-risk MF. In an older group, 66% with ≥2 prior therapies and a median baseline platelet count of 52 × 103/μL and 28% with ASXL1 mutations, we observed a 30% objective response by Revised International Working Group-Myeloproliferative Neoplasms Research and Treatment (IWG-MRT) 2013 criteria. Notably, 6 responding patients achieved clinical improvement of anemia: 4, hemoglobin response; 2, transfusion independence. Median OS was 34 months (range, 2.2-60.1+). Reductions of cIAPs were observed in all responders. The most common toxicity was nausea/vomiting (N/V) in 64% (mostly grade 1/2); fatigue in 46%; and dizziness/vertigo in 30%. There were 4 grade 3/4 adverse events (2, syncope; 1, N/V; 1, skin eruption/pruritis). There were 2 deaths during the study period, both unrelated to the study drug. SMAC mimetics may represent an option for older patients with thrombocytopenia or for those in whom prior JAK inhibitors has failed. This trial was registered at www.clinicaltrials.gov as #NCT02098161.

Background: Prior work from our group has shown that fibrocytes, the cells driving bone marrow (BM) fibrosis in patients with primary myelofibrosis (PMF), are neoplastic (clonal) and derived from monocytes (Verstovsek, J Exp Med 2016). These findings led to the clinical development of PRM-151 (recombinant human pentraxin-2) as an anti-fibrotic agent for patients with myelofibrosis (MF) (Verstovsek, EHA 2019). Our observations were extended by others to show that thrombopoietin receptor (MPL) activation induces fibrocyte differentiation and that blood monocytes highly expressing MPL and signaling lymphocyte activation molecule family member 7 (SLAMF7) were possible fibrocyte precursors (Maekawa, Leukemia 2018). Furthermore, patients with JAK2V617F+ MF have a significantly elevated SLAMF7 high monocyte percentage, which correlates with the JAK2V617F allele burden (Maekawa, Blood 2019). Finally, elotuzumab, a SLAMF7-targeting monoclonal antibody, inhibited the differentiation of MF patient-derived fibrocytes in vitro and romiplostim-induced MF and splenomegaly in vivo. Study design and methods: This is a single-institution, investigator-initiated, pilot phase 2 study of elotuzumab monotherapy in patients with JAK2V617F+ PMF or post-polycythemia vera/essential thrombocythemia MF who need treatment but are not candidates for JAK inhibitor therapy. Baseline BM fibrosis grade must be 2 or 3 per the European consensus (Thiele, Haematologica 2005). Prior JAK inhibitor treatment is permitted. Elotuzumab is dosed intravenously weekly at 10 mg/kg per dose for the first 8 doses, followed by 20 mg/kg every 4 weeks, per the label for its use in multiple myeloma in combination with pomalidomide and dexamethasone. Patients may continue elotuzumab until disease progression or unacceptable toxicity, up to a maximum of 36 cycles. Premedication and management of infusion reactions are carried out according to the elotuzumab package insert. Spleen and liver sizes are measured by palpation and the MPN-SAF-TSS questionnaire (Emanuel, J Clin Oncol 2012) is administered on day 1 of each cycle. Patients receive a BM biopsy at screening and every 6 cycles while on-study. Plasma cytokines are measured at baseline and every 3 cycles while on-study. The primary endpoint is overall response rate according to the revised IWG-MRT-ELN criteria (Tefferi, Blood 2013). A total of 15 patients are planned to be enrolled. Elotuzumab is provided by Bristol-Myers Squibb. Adverse events are graded according to the National Cancer Institute's Common Terminology Criteria for Adverse Events (CTCAE), version 5.0. The method of Thall, Simon and Estey (Thall, Stat Med 1995) is used for toxicity monitoring. Correlative studies: These include quantification of SLAMF7 highCD16 neg circulating monocytes by flow cytometry, measurement of serum interleukin-1 receptor alpha (IL-1Rα) concentrations and correlation of these with each other and with the mutant JAK2 allele burden, culture of human fibrocytes from peripheral blood mononuclear cells (PBMCs) in vitro, engraftment of BM cells from patients in non-obese diabetic, severe combined immunodeficient gamma (NSG) mice, and quantitation of fibrocytes in the BM of participants at baseline and every 6 cycles. Current status: The study (clinicaltrials.gov identifier: NCT04517851) is ongoing; 2 participants have been enrolled and treated thus far. Updated enrollment information will be provided. Disclosures Bose: Astellas: Research Funding; Sierra Oncology: Honoraria; Constellation Pharmaceuticals: Research Funding; Novartis: Honoraria; Celgene Corporation: Honoraria, Research Funding; Incyte Corporation: Honoraria, Research Funding; NS Pharma: Research Funding; Promedior: Research Funding; Blueprint Medicines: Honoraria, Research Funding; BMS: Honoraria, Research Funding; Kartos Therapeutics: Honoraria, Research Funding; CTI BioPharma: Honoraria, Research Funding; Pfizer: Research Funding. Jain: TG Therapeutics: Honoraria; Janssen: Honoraria; Servier: Honoraria, Research Funding; Aprea Therapeutics: Research Funding; Bristol Myers Squibb: Honoraria, Research Funding; AbbVie: Honoraria, Research Funding; Beigene: Honoraria; Adaptive Biotechnologies: Honoraria, Research Funding; Genentech: Honoraria, Research Funding; Precision Biosciences: Honoraria, Research Funding; ADC Therapeutics: Honoraria, Research Funding; Pfizer: Research Funding; Cellectis: Honoraria, Research Funding; Fate Therapeutics: Research Funding; AstraZeneca: Honoraria, Research Funding; Incyte: Research Funding; Pharmacyclics: Research Funding. Pemmaraju: Roche Diagnostics: Consultancy; ASH Communications Committee: Membership on an entity's Board of Directors or advisory committees; ASCO Leukemia Advisory Panel: Membership on an entity's Board of Directors or advisory committees; Samus: Other, Research Funding; Springer Science + Business Media: Other; HemOnc Times/Oncology Times: Membership on an entity's Board of Directors or advisory committees; Dan's House of Hope: Membership on an entity's Board of Directors or advisory committees; DAVA Oncology: Consultancy; Clearview Healthcare Partners: Consultancy; Blueprint Medicines: Consultancy; Protagonist Therapeutics, Inc.: Consultancy; Sager Strong Foundation: Other; Cellectis S.A. ADR: Other, Research Funding; Daiichi Sankyo, Inc.: Other, Research Funding; Plexxicon: Other, Research Funding; CareDx, Inc.: Consultancy; Aptitude Health: Consultancy; MustangBio: Consultancy, Other; Abbvie Pharmaceuticals: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other, Research Funding; Celgene Corporation: Consultancy; Stemline Therapeutics, Inc.: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other, Research Funding; LFB Biotechnologies: Consultancy; Novartis Pharmaceuticals: Consultancy, Other: Research Support, Research Funding; Incyte: Consultancy; Affymetrix: Consultancy, Research Funding; Bristol-Myers Squibb Co.: Consultancy; ImmunoGen, Inc: Consultancy; Pacylex Pharmaceuticals: Consultancy. Kantarjian: Amgen: Honoraria, Research Funding; Pfizer: Honoraria, Research Funding; NOVA Research: Honoraria; Precision Biosciences: Honoraria; Astra Zeneca: Honoraria; KAHR Medical Ltd: Honoraria; Ipsen Pharmaceuticals: Honoraria; Daiichi-Sankyo: Research Funding; Jazz: Research Funding; Immunogen: Research Funding; BMS: Research Funding; Astellas Health: Honoraria; AbbVie: Honoraria, Research Funding; Ascentage: Research Funding; Novartis: Honoraria, Research Funding; Aptitude Health: Honoraria; Taiho Pharmaceutical Canada: Honoraria. Verstovsek: Blueprint Medicines Corp: Research Funding; Promedior: Research Funding; PharmaEssentia: Research Funding; Protagonist Therapeutics: Research Funding; CTI BioPharma: Research Funding; Celgene: Consultancy, Research Funding; Genentech: Research Funding; NS Pharma: Research Funding; Ital Pharma: Research Funding; Incyte Corporation: Consultancy, Research Funding; Gilead: Research Funding; Sierra Oncology: Consultancy, Research Funding; Roche: Research Funding; AstraZeneca: Research Funding; Novartis: Consultancy, Research Funding; Constellation: Consultancy; Pragmatist: Consultancy. OffLabel Disclosure: Elotuzumab is a monoclonal antibody targeting SLAMF7, previously known as CS-1. It is approved for the treatment of multiple myeloma in combination with an IMiD and dexamethasone. This trial studies it as a single agent in patients with myelofibrosis.

Background Anemia is common in patients (pts) with myeloproliferative neoplasm (MPN)-associated myelofibrosis (MF). Furthermore, anemia is an on-target effect of therapeutic Janus kinase 2 (JAK2) inhibition, and may be the most frequent cause of ruxolitinib (rux) discontinuation (d/c) in clinical practice (Kuykendall, Ann Hematol 2018). Current therapies for anemia of MF (erythropoietin and analogs, danazol, IMiDs®) are unsatisfactory. Sotatercept (ACE-011) is a first-in-class, activin receptor type IIA ligand trap that may improve anemia by sequestering stromal transforming growth factor beta superfamily ligands that suppress terminal erythropoiesis (Iancu-Rubin, Exp Hematol 2013). Methods This is a phase 2, investigator-initiated, open-label, single institution study of sotatercept, administered subcutaneously every 3 weeks, in 2 cohorts of anemic pts (Hgb Results A total of 53 pts have been treated; one pt received only 0.3 mg/kg of sotatercept and is not considered further. Thirty one pts received sotatercept alone and 21 in combination with rux. Baseline characteristics appear in Table 1, panel A. Sixteen TD and 15 non-TD pts received sotatercept alone for a median of 5 (1-67) cycles. Thirteen pts received 0.75 mg/kg and 18, 1 mg/kg. Seven of 24 (29%) evaluable pts responded. Of these, 4 were anemia responses; 3 TD pts achieved TI. Five responses occurred at the 0.75 mg/kg dose, and 2 at the 1 mg/kg dose. Median time to response (TTR) was 21 (1-22) days and median duration of response (DOR) 13 (3.9-56.4) months. Seven pts (22.6%) received The combination cohort comprised 15 non-TD pts and 6 TD pts. The median number of cycles was 8 (2-43). Five of 17 (29%) evaluable pts in the combination cohort responded, all non-TD pts. Median TTR was 14 (7-147) days and median DOR 34.6 (3.1-47.9) months. Four pts (19%) received Several non-response-evaluable pts in both cohorts achieved ≥1.5 g/dl increments in Hgb from baseline that were not sustained for ≥12 wks because of early d/c of sotatercept. An additional pt in the combination cohort required a rux dose increase, leading to failure to sustain a ≥1.5 g/dl Hgb improvement. Across both cohorts, several responding pts required multiple protocol-specified drug holidays because of Hgb levels ≥11.5 g/dl, with resumption of sotatercept once Hgb was Sotatercept was well-tolerated (Table 1, panel B). Grade 3 adverse events possibly related to sotatercept were HTN (n=7), limb (bone/muscle/joint) pain (n=3) and headache (1). Conclusions Sotatercept is safe and effective against anemia of MPN-associated MF, both in non-TD and TD pts, with a response rate of 29% both when used alone and in conjunction with a stable dose of rux. A total of 60 pts are planned to be treated on this trial (NCT01712308). Disclosures Bose: Blueprint Medicines Corporation: Honoraria, Research Funding; NS Pharma: Research Funding; Constellation Pharmaceuticals: Research Funding; Astellas Pharmaceuticals: Research Funding; Pfizer, Inc.: Research Funding; Incyte Corporation: Consultancy, Honoraria, Research Funding, Speakers Bureau; Celgene Corporation: Honoraria, Research Funding; CTI BioPharma: Honoraria, Research Funding; Promedior, Inc.: Research Funding; Kartos Therapeutics: Honoraria, Research Funding. Pemmaraju:Samus Therapeutics: Research Funding; AbbVie: Honoraria, Research Funding; MustangBio: Honoraria; SagerStrong Foundation: Other: Grant Support; Roche Diagnostics: Honoraria; Pacylex Pharmaceuticals: Consultancy; Plexxikon: Research Funding; Daiichi Sankyo: Research Funding; Stemline Therapeutics: Honoraria, Research Funding; Celgene: Honoraria; Incyte Corporation: Honoraria; Cellectis: Research Funding; Blueprint Medicines: Honoraria; Affymetrix: Other: Grant Support, Research Funding; Novartis: Honoraria, Research Funding; LFB Biotechnologies: Honoraria; DAVA Oncology: Honoraria. Daver:Fate Therapeutics: Research Funding; Bristol-Myers Squibb: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Karyopharm: Research Funding; Servier: Research Funding; Genentech: Research Funding; AbbVie: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Astellas: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novimmune: Research Funding; Gilead: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Trovagene: Research Funding; Daiichi Sankyo: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; KITE: Consultancy, Membership on an entity's Board of Directors or advisory committees; Agios: Consultancy, Membership on an entity's Board of Directors or advisory committees; ImmunoGen: Research Funding; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees; Jazz: Consultancy, Membership on an entity's Board of Directors or advisory committees; Trillium: Consultancy, Membership on an entity's Board of Directors or advisory committees; Syndax: Consultancy, Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees. Jabbour:BMS: Other: Advisory role, Research Funding; Amgen: Other: Advisory role, Research Funding; Pfizer: Other: Advisory role, Research Funding; AbbVie: Other: Advisory role, Research Funding; Takeda: Other: Advisory role, Research Funding; Adaptive Biotechnologies: Other: Advisory role, Research Funding; Genentech: Other: Advisory role, Research Funding. Kadia:Astellas: Research Funding; Pulmotec: Research Funding; Incyte: Research Funding; Ascentage: Research Funding; JAZZ: Honoraria, Research Funding; Cyclacel: Research Funding; Amgen: Research Funding; Celgene: Research Funding; Cellenkos: Research Funding; Genentech: Honoraria, Research Funding; BMS: Honoraria, Research Funding; Pfizer: Honoraria, Research Funding; Novartis: Honoraria; Abbvie: Honoraria, Research Funding; Astra Zeneca: Research Funding. Andreeff:Daiichi-Sankyo; Jazz Pharmaceuticals; Celgene; Amgen; AstraZeneca; 6 Dimensions Capital: Consultancy; Amgen: Research Funding; Daiichi-Sankyo; Breast Cancer Research Foundation; CPRIT; NIH/NCI; Amgen; AstraZeneca: Research Funding; Centre for Drug Research & Development; Cancer UK; NCI-CTEP; German Research Council; Leukemia Lymphoma Foundation (LLS); NCI-RDCRN (Rare Disease Clin Network); CLL Founcdation; BioLineRx; SentiBio; Aptose Biosciences, Inc: Membership on an entity's Board of Directors or advisory committees. Cortes:Bristol-Myers Squibb: Research Funding; Pfizer: Consultancy, Research Funding; Takeda: Consultancy, Research Funding; Sun Pharma: Research Funding; BioPath Holdings: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Telios: Research Funding; Astellas: Research Funding; Amphivena Therapeutics: Research Funding; Arog: Research Funding; BiolineRx: Consultancy, Research Funding; Daiichi Sankyo: Consultancy, Research Funding; Jazz Pharmaceuticals: Consultancy, Research Funding; Merus: Research Funding; Immunogen: Research Funding; Novartis: Consultancy, Research Funding. Jain:BMS: Research Funding; Pharmacyclics: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Verastem: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Adaptive Biotechnologies: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Cellectis: Research Funding; TG Therapeutics: Honoraria, Membership on an entity's Board of Directors or advisory committees; Aprea Therapeutics: Research Funding; Precision Bioscienes: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Servier: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Fate Therapeutics: Research Funding; AstraZeneca: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Incyte: Research Funding; BeiGene: Honoraria, Membership on an entity's Board of Directors or advisory committees; ADC Therapeutics: Research Funding; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Genentech: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; AbbVie: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Pfizer: Research Funding. Borthakur:Nkarta Therapeutics: Consultancy; Treadwell Therapeutics: Consultancy; PTC Therapeutics: Research Funding; Jannsen: Research Funding; Abbvie: Research Funding; Novartis: Research Funding; Incyte: Research Funding; Polaris: Research Funding; Xbiotech USA: Research Funding; Oncoceutics: Research Funding; Curio Science LLC: Consultancy; FTC Therapeutics: Consultancy; Argenx: Consultancy; PTC Therapeutics: Consultancy; BioLine Rx: Consultancy; BioTherix: Consultancy; Cyclacel: Research Funding; GSK: Research Funding; BioLine Rx: Research Funding; BMS: Research Funding; AstraZeneca: Research Funding. Alvarado:Sun Pharma: Research Funding; Astex Pharmaceuticals: Research Funding; MEI Pharma: Research Funding; Daiichi-Sankyo: Research Funding; Tolero Pharmaceuticals: Research Funding; FibroGen: Research Funding; Jazz Pharmaceuticals: Research Funding; BerGenBio ASA: Research Funding. Huynh-Lu:Incyte Corporation: Speakers Bureau. Nguyen-Cao:Incyte Corporation: Speakers Bureau. Garcia-Manero:Acceleron Pharmaceuticals: Consultancy, Honoraria; Celgene: Consultancy, Honoraria, Research Funding; Jazz Pharmaceuticals: Consultancy; Novartis: Research Funding; Onconova: Research Funding; Helsinn Therapeutics: Consultancy, Honoraria, Research Funding; Merck: Research Funding; AbbVie: Honoraria, Research Funding; H3 Biomedicine: Research Funding; Astex Pharmaceuticals: Consultancy, Honoraria, Research Funding; Bristol-Myers Squibb: Consultancy, Research Funding; Genentech: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Amphivena Therapeutics: Research Funding. Kantarjian:Oxford Biomedical: Honoraria; Actinium: Honoraria, Membership on an entity's Board of Directors or advisory committees; Delta Fly: Honoraria; Janssen: Honoraria; Ascentage: Research Funding; BioAscend: Honoraria; Amgen: Honoraria, Research Funding; Aptitute Health: Honoraria; Immunogen: Research Funding; Jazz: Research Funding; Novartis: Honoraria, Research Funding; Sanofi: Research Funding; Pfizer: Honoraria, Research Funding; Daiichi-Sankyo: Honoraria, Research Funding; BMS: Research Funding; Adaptive biotechnologies: Honoraria; Abbvie: Honoraria, Research Funding. Verstovsek:Sierra Oncology: Consultancy, Research Funding; Gilead: Research Funding; Celgene: Consultancy, Research Funding; CTI Biopharma Corp: Research Funding; Roche: Research Funding; NS Pharma: Research Funding; Promedior: Research Funding; Novartis: Consultancy, Research Funding; AstraZeneca: Research Funding; ItalPharma: Research Funding; Protagonist Therapeutics: Research Funding; PharmaEssentia: Research Funding; Incyte Corporation: Consultancy, Research Funding; Blueprint Medicines Corp: Research Funding; Genentech: Research Funding.

Background: Outcomes in patients (pts) with relapsed/refractory (R/R) myelofibrosis (MF) post JAK inhibitor are poor [overall survival (OS) 13-14 months] (Newberry K, Blood 2017; Kuykendall A, Ann Hematol 2018). There are no approved therapies beyond JAK inhibitors for pts with MF. In certain clinical situations, such as severe thrombocytopenia, administration of JAK inhibitors may be difficult or even contraindicated. SMAC mimetics (or IAP antagonists), a novel class of anti-cancer therapeutics, lead to apoptotic cancer cell death through targeting of IAPs. Because these agents are hypothesized to be particularly effective in a TNFα-rich micro-environment, such as in pts with MF, a group known to have markedly increased cytokines including TNFα (Fleischman A Blood 2011; Heaton W, Leukemia 2018; Tefferi A, JCO 2011), we conducted an investigator-initiated phase 2 clinical trial with LCL161 in pts with intermediate to high risk PMF or post-ET/PV MF. Objectives: Primary: overall response rate (ORR) by IWG-MRT 2013; secondary and exploratory: time to response, response duration, safety, improvement in symptom burden by MPN-SAF TSS, measurement of cIAP1/2, XIAP, and mutational profiling via next-generation sequencing. Clinical Trial Design: LCL161 is an oral monovalent SMAC mimetic, administered once weekly, starting dose 1500 mg with 2 dose level reductions (DL-1, 1200mg; DL-2, 900 mg) in pts with MF. One cycle was 28 days. Pts age ≥18, PS 0-2, who were not candidates for, intolerant to, or R/R to JAK inhibitors were eligible. After 3 cycles, bone marrow biopsy/response evaluations were performed. There was no minimum platelet count for eligibility, and prior allogeneic stem cell transplant (SCT) was allowed. Results: The study has completed enrollment. A total of 47 pts were treated with a median age of 72 years [56-85]. The median baseline platelet count was 51 x 109/L [6-1365]. The median baseline spleen size was 12 cm among 28 pts with enlarged spleen at baseline. 70% of the pts had ≥2 prior therapies; 55% had a prior JAK inhibitor, 2 pts had prior SCT. 75% were IPSS high-risk. Driver mutations: 64% JAK2 V167F; 13% CALR; 11% MPL W515L; 5 pts had triple negative MF. Mutation analysis revealed the three most common additional mutations: ASXL1 (23%); TET2 (15%); DNMT3a (11%). ORR was 32% (15/47 pts); 15 pts exhibited a total of 19 objective responses (4 pts met criteria for 2 separate IWG 2013 responses): Clinical improvement (CI) symptoms (n=11); CI anemia (n=6); CI spleen (n=1), cytogenetic response (n=1). At a median follow-up of 21.1 months (mo) [3.9-49.7+], the median number of cycles received was 5 [1-52+], the median time to response was 1.4 mo [0.9-9.1] and median response duration (mo) was 31.5 [3.6-48.8+]. Long-term responders: n=8 for ≥1 year; n=4 for ≥2 years/ongoing. Importantly, median OS is not yet reached on this study (Figure). The most common non-hematologic toxicities (grade 1/2): nausea/vomiting (60%); fatigue syndrome (49%), dizziness/vertigo (32%); non-hematologic Grade 3/4: syncope (n=2); nausea/vomiting (n=1). Hematologic toxicities (grade 3/4): thrombocytopenia n=3 (6%); anemia n=2 (4%). 36% pts had a dose reduction; the most common cause was fatigue (n=10). Overall, 81% pts are now off study [Stable disease/no objective response (n=16); progressive disease (n=9); toxicity (n=5), pt's choice/other (n=6), proceeded to SCT (n=2)]. Correlative analysis: Preliminary analysis demonstrates on-target inhibition of cIAP1 observed in all responding pts analyzed; high levels of XIAP and/or XIAP increases were observed in many pts with resistance/disease progression. Anemia responders: 6 pts achieved CI anemia (n=4 hemoglobin responses, n=2 achievement of transfusion independence). Among these 6 pts: median time to response (mo): 3.1 [0.9-9.1]; median response duration (mo): 8.4 [5.5-28.6]. Conclusion: In an older group of pts with 70% with ≥2 prior therapies (55% JAK inhibitor-exposed), median baseline platelet count of 51, ASXL1-mutated in 23%, we observed a 32% ORR. The median OS has not yet been reached. Oral SMAC mimetics may represent a possible option for older pts, those who have failed prior JAK inhibitor, and those with thrombocytopenia limiting entry onto other trials. Future directions include combination studies with hypomethylating agents and JAK inhibitors for pts with myeloid malignancies. This clinical trial is registered at ClinicalTrials.gov as NCT02098161. Figure Disclosures Pemmaraju: sagerstrong: Research Funding; plexxikon: Research Funding; Daiichi-Sankyo: Research Funding; novartis: Consultancy, Research Funding; samus: Research Funding; abbvie: Consultancy, Honoraria, Research Funding; cellectis: Research Funding; celgene: Consultancy, Honoraria; incyte: Consultancy, Research Funding; affymetrix: Research Funding; Stemline Therapeutics: Consultancy, Honoraria, Research Funding; mustangbio: Consultancy, Research Funding. Carter:Amgen: Research Funding; AstraZeneca: Research Funding; Ascentage: Research Funding. Kantarjian:Amgen: Honoraria, Research Funding; Astex: Research Funding; Cyclacel: Research Funding; Actinium: Honoraria, Membership on an entity's Board of Directors or advisory committees; Ariad: Research Funding; BMS: Research Funding; Takeda: Honoraria; Agios: Honoraria, Research Funding; Pfizer: Honoraria, Research Funding; AbbVie: Honoraria, Research Funding; Jazz Pharma: Research Funding; Immunogen: Research Funding; Daiichi-Sankyo: Research Funding; Novartis: Research Funding. Cortes:Sun Pharma: Research Funding; Forma Therapeutics: Consultancy, Honoraria, Research Funding; Daiichi Sankyo: Consultancy, Honoraria, Research Funding; BiolineRx: Consultancy; Jazz Pharmaceuticals: Consultancy, Research Funding; Biopath Holdings: Consultancy, Honoraria; Astellas Pharma: Consultancy, Honoraria, Research Funding; Novartis: Consultancy, Honoraria, Research Funding; Merus: Consultancy, Honoraria, Research Funding; Takeda: Consultancy, Research Funding; Immunogen: Consultancy, Honoraria, Research Funding; Pfizer: Consultancy, Honoraria, Research Funding; Bristol-Myers Squibb: Consultancy, Research Funding. Bose:CTI BioPharma: Research Funding; Promedior: Research Funding; NS Pharma: Research Funding; Astellas: Research Funding; Pfizer: Research Funding; Incyte Corporation: Consultancy, Research Funding, Speakers Bureau; Celgene Corporation: Consultancy, Research Funding; Blueprint Medicine Corporation: Consultancy, Research Funding; Kartos: Consultancy, Research Funding; Constellation: Research Funding. Kadia:Amgen: Membership on an entity's Board of Directors or advisory committees, Research Funding; Bioline RX: Research Funding; Pfizer: Membership on an entity's Board of Directors or advisory committees, Research Funding; Jazz: Membership on an entity's Board of Directors or advisory committees, Research Funding; BMS: Research Funding; Celgene: Research Funding; Genentech: Membership on an entity's Board of Directors or advisory committees; Pharmacyclics: Membership on an entity's Board of Directors or advisory committees; Takeda: Membership on an entity's Board of Directors or advisory committees; AbbVie: Consultancy, Research Funding. Garcia-Manero:Merck: Research Funding; Novartis: Research Funding; AbbVie: Research Funding; Celgene: Consultancy, Research Funding; Astex: Consultancy, Research Funding; Onconova: Research Funding; H3 Biomedicine: Research Funding; Amphivena: Consultancy, Research Funding; Helsinn: Research Funding. Bueso-Ramos:Incyte: Consultancy. DiNardo:jazz: Honoraria; celgene: Consultancy, Honoraria; abbvie: Consultancy, Honoraria; agios: Consultancy, Honoraria; medimmune: Honoraria; syros: Honoraria; notable labs: Membership on an entity's Board of Directors or advisory committees; daiichi sankyo: Honoraria. Popat:Bayer: Research Funding; Incyte: Research Funding; Jazz: Consultancy. Konopleva:Genentech: Honoraria, Research Funding; Ascentage: Research Funding; Kisoji: Consultancy, Honoraria; Reata Pharmaceuticals: Equity Ownership, Patents & Royalties; Ablynx: Research Funding; Astra Zeneca: Research Funding; F. Hoffman La-Roche: Consultancy, Honoraria, Research Funding; Amgen: Consultancy, Honoraria; Agios: Research Funding; Cellectis: Research Funding; AbbVie: Consultancy, Honoraria, Research Funding; Eli Lilly: Research Funding; Forty-Seven: Consultancy, Honoraria; Stemline Therapeutics: Consultancy, Honoraria, Research Funding; Calithera: Research Funding. Borthakur:Oncoceutics, Inc.: Research Funding; PTC Therapeutics: Consultancy; BioLine Rx: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Strategia Therapeutics: Research Funding; Xbiotech USA: Research Funding; Tetralogic Pharmaceuticals: Research Funding; GSK: Research Funding; Argenx: Membership on an entity's Board of Directors or advisory committees; Arvinas: Research Funding; BioTheryX: Membership on an entity's Board of Directors or advisory committees; Eisai: Research Funding; Cantargia AB: Research Funding; AbbVie: Research Funding; FTC Therapeutics: Membership on an entity's Board of Directors or advisory committees; Incyte: Research Funding; Cyclacel: Research Funding; Polaris: Research Funding; NKarta: Consultancy; Agensys: Research Funding; Merck: Research Funding; Bayer Healthcare AG: Research Funding; AstraZeneca: Research Funding; Janssen: Research Funding; Novartis: Research Funding; Oncoceutics: Research Funding; BMS: Research Funding; Eli Lilly and Co.: Research Funding. Jain:Precision Biosciences: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Adaptive Biotechnologies: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Cellectis: Research Funding; Verastem: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Servier: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; AstraZeneca: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen Pharmaceuticals, Inc.: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Genentech: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; BMS: Research Funding; Pfizer: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; ADC Therapeutics: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Incyte: Research Funding; AbbVie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Pharmacyclics, an AbbVie company: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Jabbour:BMS: Consultancy, Research Funding; Amgen: Consultancy, Research Funding; AbbVie: Consultancy, Research Funding; Adaptive: Consultancy, Research Funding; Pfizer: Consultancy, Research Funding; Cyclacel LTD: Research Funding; Takeda: Consultancy, Research Funding. Verstovsek:Incyte: Research Funding; Roche: Research Funding; NS Pharma: Research Funding; Celgene: Consultancy, Research Funding; Gilead: Research Funding; Promedior: Research Funding; CTI BioPharma Corp: Research Funding; Genetech: Research Funding; Blueprint Medicines Corp: Research Funding; Novartis: Consultancy, Research Funding; Sierra Oncology: Research Funding; Pharma Essentia: Research Funding; Astrazeneca: Research Funding; Ital Pharma: Research Funding; Protaganist Therapeutics: Research Funding; Constellation: Consultancy; Pragmatist: Consultancy. OffLabel Disclosure: LCL161- not yet FDA approved drug; investigational agent = SMAC mimetic /IAP antagonist