Bussolari, Jacqueline

PURPOSE Patients with lower-risk (LR) myelodysplastic syndromes (MDS) who are RBC transfusion dependent and have experienced relapse after or are refractory to erythropoiesis-stimulating agent (ESA) have limited treatment options. High telomerase activity and human telomerase reverse-transcription expression in clonal hematopoietic cells have been reported in patients with MDS. Imetelstat, a first-in-class competitive inhibitor of telomerase enzymatic activity, targets cells with active telomerase. We report efficacy, safety, and biomarker data for patients with LR MDS who are RBC transfusion dependent and who were relapsed/refractory to ESAs. PATIENTS AND METHODS In this two-part phase II/III study (MDS3001), the primary end point was 8-week RBC transfusion independence (TI) rate, with key secondary end points of 24-week RBC TI rate, TI duration, and hematologic improvement-erythroid. RESULTS Data from the phase II part of the study are reported. Of 57 patients enrolled and treated (overall population), 38 were non-del(5q) and hypomethylating agent and lenalidomide naïve (subset population). The 8- and 24-week RBC TI rates in the overall population were 37% and 23%, respectively, with a median TI duration of 65 weeks. In the subset population, 8- and 24-week RBC TI rates were 42% and 29%, respectively, with a median TI duration of 86 weeks. Eight-week TI rate was observed across all subgroups evaluated. Cytogenetic and mutational data revealed a reduction of the malignant clones, suggesting disease modification activity. The most common adverse events were cytopenias, typically reversible within 4 weeks. CONCLUSION Imetelstat treatment results in a meaningful, durable TI rate across a broad range of heavily transfused patients with LR MDS who are ineligible for or relapsed/refractory to ESAs. Biomarker analyses indicated effects on the mutant malignant clone.

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.

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.