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Background: Current treatment options for red blood cell (RBC) transfusion-dependent (TD) patients with lower risk (LR) myelodysplastic syndromes (MDS) relapsed after or refractory to erythropoiesis-stimulating agents (ESAs) have limited efficacy and durability; new approaches are needed. Imetelstat is a 13-mer lipid-conjugated oligonucleotide that targets the RNA template of human telomerase and is a competitive inhibitor of telomerase enzymatic activity (Asai et al, Cancer Res 2003; Herbert et al, Oncogene 2005). Preclinical, in vivo xenograft models (Dikmen et al, Cancer Res 2005; Hochreiter et al, Clin Cancer Res 2006) and preliminary clinical data from a pilot study conducted at Mayo Clinic (Tefferi et al, Blood Cancer Journal 2016) supported initiation of a study in TD LR MDS patients. A Phase 2 study of imetelstat, IMerge, demonstrated an 8-week RBC transfusion independence (RBC-TI) rate of 42%, 24-week RBC-TI rate of 29%, and 68% erythroid hematologic improvement (HI-E) rate in 38 heavily TD patients (median prior RBC transfusion burden 8 units / 8 weeks over the 16 weeks pre-study period) with LR MDS. Responses were durable with median duration of 8-week RBC-TI of 85.9 weeks by Kaplan Meier estimates (range 8.0-140.9) (Steensma ASH 2018, Fenaux EHA 2019). These Phase 2 results provided further evidence of potential clinical benefit of imetelstat treatment in TD LR MDS, and supported initiation of a Phase 3 trial. Methods: IMerge is two-part, Phase 2/3 study (ClinicalTrials.gov: NCT02598661). The Phase 2 portion of the study described above is closed for enrollment. The Phase 3 portion of the study is open for enrollment of adult patients with International Prognostic Scoring System (IPSS) low or intermediate-1 risk, non-del(5q) MDS, who are TD, are relapsed after or refractory to ESAs, and have not received treatment with lenalidomide or hypomethylating agents. The study is a randomized (2:1) double-blind, placebo-controlled trial to compare efficacy of imetelstat vs. placebo that will enroll approximately 170 patients and will be conducted at approximately 90 centers in North America, Europe, Asia and Middle East. Imetelstat will be administered as 2-hour IV infusion every 4 weeks at 7.5 mg/kg. The primary endpoint of the study is to assess the rate of RBC-TI lasting ≥8 weeks. Secondary endpoints include safety, rate of RBC-TI ≥24 weeks, time to RBC-TI start, RBC-TI duration, rate of HI-E, the amount and relative change in RBC transfusions, rate of CR or PR, overall survival, progression of MDS, pharmacokinetics and effect of treatment on quality of life. Biomarkers relevant to the mechanism of action of imetelstat will be assessed to demonstrate target inhibition and their association with clinical responses. Cytogenetics and mutation analyses will be performed to evaluate the impact of imetelstat on reduction/depletion of malignant clones leading to disease modification. Disclosures Platzbecker: Novartis: Consultancy, Honoraria, Research Funding; Celgene: Consultancy, Honoraria, Research Funding; Abbvie: Consultancy, Honoraria. Steensma:Astex: Consultancy; Arrowhead: Equity Ownership; Summer Road: Consultancy; Onconova: Consultancy; Aprea: Research Funding; Pfizer: Consultancy; Stemline: Consultancy; H3 Biosciences: Other: Research funding to institution, not investigator.. Santini:Celgene Corporation: Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees; Johnson & Johnson: Honoraria; Acceleron: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees; Menarini: Membership on an entity's Board of Directors or advisory committees. Germing:Novartis: Honoraria, Research Funding; Celgene: Honoraria, Research Funding; Jazz Pharmaceuticals: Honoraria; Amgen: Honoraria. Font:Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Pfizer: Membership on an entity's Board of Directors or advisory committees. Díez-Campelo:Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene Corporation: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding. Patnaik:Stem Line Pharmaceuticals.: Membership on an entity's Board of Directors or advisory committees. Sherman:Geron Corporation: Employment, Equity Ownership. Dougherty:Geron Corporation: Employment, Equity Ownership. Feller:Geron Corporation: Employment. Sun:Geron Corporation: Employment, Equity Ownership. Wan:Geron Corporation: Employment, Equity Ownership. Huang:Geron Corporation: Employment, Equity Ownership. Rizo:Geron Corporation: Employment, Equity Ownership. Fenaux:Celgene Corporation: Honoraria, Research Funding; Aprea: Research Funding; Astex: Honoraria, Research Funding; Jazz: Honoraria, Research Funding.

Abstract BACKGROUND: Patients with TD lower-risk (LR)-MDS relapsed or refractory to ESA have limited treatment options. Imetelstat is a first-in-class telomerase inhibitor that targets cells with short telomere lengths and active telomerase, characteristics observed in some MDS patients. IMerge is an ongoing global study of imetelstat in RBC TD patients with LR-MDS (IPSS Low or Int-1). In the first 32 patients enrolled, 8-week TI rate was 34%, with 24-week TI of 16%, and HI-E of 59%. The most frequently reported adverse events were reversible grade ≥3 cytopenias (Fenaux et al EHA 2018 Abstr S1157). Higher response rates were observed in patients (n=13) who were LEN and HMA naïve without del(5q). We report here results in an additional 25 LEN and HMA naïve patients without del(5q), with longer term follow-up of the 13 initial patients meeting the same criteria. METHODS: IMerge is a phase 2/3 trial (NCT02598661) that includes LR-MDS patients with a high transfusion burden (≥4 units / 8 weeks) who are relapsed/refractory to ESA or have sEPO >500 mU/mL. The additional 25 were required to be LEN and HMA naïve and lack del(5q). Imetelstat 7.5 mg/kg was administered IV every 4 weeks. In addition to the key endpoints noted above, secondary endpoints include safety, time to and duration of TI. Biomarkers are also being explored, including telomerase activity, hTERT, telomere length, and genetic mutations. RESULTS: Overall, for the 38 LEN/HMA naïve and non-del(5q) patients, median age was 71.5 years and 66% were men. 63% of patients were IPSS Low and 37% Int-1. Median prior RBC transfusion burden was 8.0 (range 4-14) U, and 71% had WHO 2008 RARS or RCMD-RS. 9/37 (24%) patients with evaluable sEPO levels had baseline level >500 mU/mL. As of July 2018, with a median follow-up of 25.8 months for the initial 13 patients, and 5.2 months for the 25 recently included patients, the 8-week RBC-TI rate was 37% (14/38). Durability of 24-week TI responses was demonstrated, with a median duration of 10 months and the longest ongoing response now >2 years. Among the patients achieving durable TI, all showed a Hb rise of ≥3.0 g/dL compared to baseline during the transfusion-free interval. Response rates were similar in RARS/RCMD-RS (33% [9/27]) and other patients (27% [3/11]), and those with baseline EPO levels >500 mU/mL (33% [3/9]) and ≤500 mU/mL (32% [9/28]). Reversible grade ≥3 neutropenia and thrombocytopenia were each reported in 58% of the patients. Liver function test (LFT) elevations were mostly grade 1/2. Reversible grade 3 LFTelevations were observed in 3 (8%) patients on study. An independent Hepatic Review Committee deemed the observed LFT elevations were not imetelstat-related hepatic toxicities. SUMMARY / CONCLUSIONS: In this cohort of 38 non-del(5q) LR-MDS patients with a high RBC transfusion burden who were ESA relapsed/refractory and naïve to LEN/HMA, single-agent imetelstat yielded a TI rate of 37%, with a median duration of 10 months and limited side effects. Durable responses were characterized by transfusion independence >24 weeks and accompanied by Hb rise. Updated data will be presented. Disclosures Steensma: Takeda: Consultancy; Syros: Research Funding; Otsuka: Membership on an entity's Board of Directors or advisory committees; Onconova: Consultancy; Novartis: Membership on an entity's Board of Directors or advisory committees; Kura: Research Funding; Janssen: Consultancy, Research Funding; H3 Biosciences: Research Funding; Celgene: Research Funding; Amphivena: Membership on an entity's Board of Directors or advisory committees; Acceleron: Consultancy. Platzbecker:Celgene: Research Funding. Van Eygen:Janssen: Consultancy, Research Funding; Roche: Research Funding; Amgen: Research Funding. Raza:Kura Oncology: Research Funding; Onconova: Research Funding, Speakers Bureau; Celgene: Research Funding; Novartis: Speakers Bureau; Geoptix: Speakers Bureau; Janssen: Research Funding; Syros: Research Funding. Santini:Amgen: Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria; AbbVie: Membership on an entity's Board of Directors or advisory committees; Otsuka: Consultancy; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Research Funding. Germing:Celgene: Honoraria, Research Funding; Janssen: Honoraria; Novartis: Honoraria, Research Funding. Font:Celgene: Membership on an entity's Board of Directors or advisory committees. Samarina:Janssen: Research Funding. Díez-Campelo:Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau. Bussolari:Janssen: Employment, Equity Ownership. Sherman:Janssen: Employment, Equity Ownership. Sun:Janssen: Employment, Equity Ownership. Varsos:Janssen: Employment, Equity Ownership. Rose:Janssen: Employment, Equity Ownership. Fenaux:Roche: Honoraria; Otsuka: Honoraria, Research Funding; Jazz: Honoraria, Research Funding; Janssen: Honoraria, Research Funding; Celgene: Honoraria, Research Funding.

Abstract Introduction: Patients with RR-AML, particularly older adults, have dismal outcomes and limited therapy options. Given low response rates and high toxicity with salvage intensive chemotherapy, and frequent ineligibility for allogeneic stem cell transplantation (alloSCT), many patients are treated with HMAs. Robust data regarding use of HMAs in AML predominates in the frontline setting, while their use in RR-AML has limited supportive data. Here wesought to analyze theoutcomes and their predictors in patients with RR-AML treated with HMAs. Methods:We collected data, spanning a period from 2006 to 2016, from 7 centers in the United States and 4 centers in Europe regarding patients treated with HMAs for RR-AML. Responses were defined by International Working Group criteria. Kaplan-Meier methods estimated overall survival (OS) from initiation of HMAs to death or end of follow-up. Multivariable logistic regression models estimated odds for response, and multivariable Cox Proportional Hazard (CPH) models estimated hazards ratios (HR) for OS. Covariates considered included HMA received, age at diagnosis (in years), AML classification at diagnosis (AML with myelodysplasia-related changes [AML-MRC], therapy-related [t]-AML), disease status (relapsed vs. refractory), number of therapy lines prior to HMA (1 vs. 2 vs. >=3), duration of first complete remission (CR1), white blood cell count, peripheral blood blast percentage, bone marrow (BM) cellularity (<=20% vs. > 20%), BM blast percentage (<=20% vs. >20%), cytogenetic risk group, and the presence of complex or chromosome 7 abnormalities. Results: Of 514 patients, 217 patients (42.2%) had refractory and 297 (58%) had relapsed AML. By end of study, 415 patients (88.5%) had died. Median follow-up for living patients was 11.6 months.Median age at diagnosis was 64 years (range [R], 16-92). AML-MRC was diagnosed in 29.0% while 8.2% had t-AML. Median number of prior therapies was 2 (R, 1-7), with 48.3% receiving 1 prior line, 30.2% receiving 2 prior lines, and 21.5% receiving >=3 prior lines. Prior alloSCT was performed in 21.2%. Only 1.9% had good risk (core binding factor) karyotype, while 56.2% had intermediate risk karyotype, and 41.9% had poor risk karyotype. Azacitidine was used in 45.8% and decitabine in 54.2%; median number of azacitidine cycles was 4 (Interquartile range [IQR], 2-6) compared to 2 for decitabine (IQR, 1-4, p <0.001). Best response to HMAs was CR in 11.7% (95%CI, 9%-14%), CRi in 6.4% (95%CI, 4.3%-8.8%), hematologic improvement (HI) in 8% (95%CI, 5.7%-10.5%), stable disease (SD) in 9.8% (95%CI, 7.2%-12.5%), while 64.1% (95%CI, 57.7%-66.2%) had progressive disease (PD). Median OS from HMA initiation for all patients was 6.9 months (IQR, 3.0-13.3). There was a significant difference in OS based on best response achieved [Figure 1]. Unadjusted OS showed an insignificant trend for worsening with increasing number of prior lines of therapy [Figure 2A]. In unadjusted analyses, there was no difference in OS based on HMA received in all patients [Figure 2B] or the subset who received only 1 prior line of therapy (median OS: Azacitidine vs. decitabine 8.4 vs 7.3 months, p=0.88). Following HMA therapy, the median number of subsequent therapies was 0 (R, 0-6), and only 12.8% underwent alloSCT. In multivariate CPH models, HMA used was not significantly associated with OS (HR=0.80, 95%CI, 0.42-1.51, p=0.49), while increasing age, and presence of complex cytogenetics and chromosome 7 abnormalities were significantly associated with risk of death [Table 1]. In multivariable logistic regression models, HMA used was not associated with achieving CR+CRi (Odds ratio=0.56, p=0.32). Conclusions: In this largest reported cohort of patients with RR-AML treated with HMAs, we found that HMAs are often used as alast line of therapy, with a minority of patients receiving subsequent treatment. Nonetheless, the minority of patients who achieve CR (11.7%) with HMA therapy had a median OS of 25.6 months. Therefore, use of HMAs for management of RR-AML is a reasonable intervention in the absence of clinical trial options. There appears to be no difference in OS or probability of achieving CR+CRi based on HMA used. Ongoing analyses in this dataset include further evaluations of predictors, including genetic mutations, and the development of prediction tools for clinical outcomes with HMA therapy. Figure 1. Figure 1. Disclosures Podoltsev: Ariad: Consultancy, Honoraria; Incyte: Consultancy, Honoraria. Ritchie:Novartis: Honoraria; Incyte: Speakers Bureau; Arian: Speakers Bureau; Pfizer: Honoraria; Celgene: Speakers Bureau. Sekeres:Millenium/Takeda: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees. Komrokji:Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Consultancy, Speakers Bureau. Al-Kali:Onconova Therapeutics, Inc.: Research Funding; Celgene: Research Funding. Santini:Celgene: Consultancy, Honoraria, Research Funding; Janssen: Consultancy, Honoraria; Novartis: Consultancy, Honoraria; Onconova: Consultancy; Amgen: Consultancy; Astex: Consultancy. Roboz:Cellectis: Research Funding; Agios, Amgen, Amphivena, Astex, AstraZeneca, Boehringer Ingelheim, Celator, Celgene, Genoptix, Janssen, Juno, MEI Pharma, MedImmune, Novartis, Onconova, Pfizer, Roche/Genentech, Sunesis, Teva: Consultancy. Fenaux:Celgene, Janssen,Novartis, Astex, Teva: Honoraria, Research Funding. Prebet:celgene: Consultancy, Honoraria; Novartis: Consultancy, Honoraria. Gore:celgene: Consultancy, Honoraria. Zeidan:Ariad: Consultancy, Honoraria; Pfizer: Consultancy, Honoraria; Incyte: Consultancy, Honoraria; Celgene: Consultancy, Honoraria.

Background:There are limited treatment options for red blood cell (RBC) transfusion dependent (TD) LR (IPSS Low/Int‐1) MDS patients who are relapsed/refractory to ESAs. Imetelstat is a first‐in‐class telomerase inhibitor that targets cells with short telomeres and active telomerase, characteristics observed in some MDS patients across all disease stages. Preliminary results show that imetelstat is effective treatment in LR‐MDS patients inducing durable TI (Steensma et al ASH 2018 Abstr463).Aims:We report updated efficacy data with a median follow‐up of 12.1 months in 38 LR non‐del(5q) MDS patients, R/R to ESA and LEN/HMA naive from the open‐label, single‐arm Part 1 of IMerge, an ongoing phase 2/3 study (NCT02598661).Methods:Part 1 of the IMerge study included patients with LR MDS, who were heavily transfused (≥4U/8wks), were R/R to ESA or had sEPO >500 mU/mL. Imetelstat 7.5 mg/kg was administered IV every 4 weeks. The primary endpoint was 8‐week TI rate; key secondary endpoints included 24‐week TI rate, safety, duration of TI, and hematologic improvement (HI) rate. Among the initially enrolled patients, higher 8‐week TI rate was observed in the non‐del5q, LEN/HMA naive patients. Therefore, the study was amended to subsequently enroll only these patients. From a total of 57 patients enrolled in Part 1, 38 were non‐del(5q), LEN/HMA naïve patients (13 in the initial and 25 in the expansion cohort). Here we report long‐term efficacy, safety and biomarker data from these 38 patients.Results:Median baseline RBC transfusion burden was 8U/8weeks (range 4–14), 37% of the patients had IPSS Int‐1; 71% had WHO 2001 RARS or RCMD‐RS subtype and 32% with evaluable sEPO levels had baseline level >500 mU/mL.As of 23 January 2019, median follow‐up was 12.1 months for the 38 patients, representing 30.4 and 11.6 months for the initial 13 and additional 25 patients, respectively. The 8‐week TI rate was 45% (17/38) and median TI duration was 8.5 months (range 1.8–32.4). Of the 17 responding patients, 10 (59%) remained transfusion free for over 24 weeks. The 8‐week TI rate did not differ based on the presence of ring sideroblasts or baseline sEPO levels. The 24‐week TI rate was 26% (10/38). Erythroid HI, defined as transfusion reduction by at least 4 units /8 weeks (IWG2006), was achieved in 68% (26/38) of the patients. The most frequently reported adverse events were manageable and reversible grade ≥3 cytopenias. 6/38 patients had IPSS‐R intermediate/poor cytogenetic risk. All 6 patents achieved 8‐week TI; 2/6 patients achieved partial cytogenetic response. Post treatment decrease in telomerase hTERT RNA level was observed in 25/34 (73.5%) patients with available sample. Among 7 patients with pre‐ and post‐treatment mutation analyses, six had SF3B1 mutations at baseline, and a decrease in the mutation VAF was observed in 2 patients that had longest TI duration on study.Summary/Conclusion:In high RBC transfusion burden patients with non‐del(5q) LR‐MDS R/R to ESA and naive to LEN/HMA, single‐agent imetelstat yielded 8‐week TI rate of 45%, with a median duration of 8.5 months (range 1.8–32.4). The 24‐week TI rate was 26%. HI‐E rate was 68%. All patients with IPSS‐R intermediate and poor cytogenetic risk responded. Biomarker analyses of telomerase activity and mutation allele burden indicate an effect on the malignant mutant clone. These data support Part 2 of IMerge, Phase 3 placebo‐controlled, randomized portion of the study, expected to open mid‐2019.

Key Points In the largest study of HMAs in RR-AML to date, 16% of patients achieved CR/CRi and experienced a median OS of 21 months. Low proliferative disease (peripheral blood blasts <5%) was associated with improved response and OS.

Abstract Myelodysplastic syndromes (MDS) and myeloproliferative neoplasms (MPN) are hematologically diverse stem cell malignancies sharing phenotypic features of both myelodysplastic syndromes and myeloproliferative neoplasms. There are currently no standard treatment recommendations for most adult patients with MDS/MPN. To optimize efforts to improve the management and disease outcomes, it is essential to identify meaningful clinical and biologic end points and standardized response criteria for clinical trials. The dual dysplastic and proliferative features in these stem cell malignancies define their uniqueness and challenges. We propose response assessment guidelines to harmonize future clinical trials with the principal objective of establishing suitable treatment algorithms. An international panel comprising laboratory and clinical experts in MDS/MPN was established involving 3 independent academic MDS/MPN workshops (March 2013, December 2013, and June 2014). These recommendations are the result of this collaborative project sponsored by the MDS Foundation.