Telomerase Inhibitor Imetelstat Provides Durable Transfusion Independence in Myelodysplastic Syndrome

SUMMARY: It is estimated that in the United States approximately 13,000 people are diagnosed with MyeloDysplastic Syndromes (MDS) each year. MyeloDysplastic Syndromes are a heterogenous group of stem cell disorders characterized by marrow failure resulting in cytopenias with associated cytogenetic abnormalities, and abnormal cellular maturation with morphologic changes in clonal cells. Majority of the individuals diagnosed with MDS are aged 65 years and older and die as a result of infection and/or bleeding, consequent to bone marrow failure. About a third of patients with MDS develop Acute Myeloid Leukemia (AML). Patients with low-risk MDS have an indolent disease course with a median survival of about 6 years with no therapeutic intervention. Patients with intermediate and higher-risk disease however have a shorter median survival even with treatment, with approximately a third of the patients progressing to AML within 3 years. The International Prognostic Scoring System (IPSS) for MDS has 4 risk groups based on Total Risk Score (Low, Intermediate-1, Intermediate-2 and High). The three prognostic factors scored to predict the course of the patient's disease include, percentage of blast cells in the bone marrow, type of chromosomal changes in the marrow cells and number of cytopenias (anemia, neutropenia or thrombocytopenia).

Management of patients with MDS includes supportive care with Erythropoiesis Stimulating Agents (ESAs), hypomethylating agents such as VIDAZA® (Azacitidine) and DACOGEN® (Decitabine), Immunomodulatory agents such as REVLIMID® (Lenalidomide), and Immunosuppressive agents such as AntiThymocyte Globulin (ATG) and Cyclosporine. Symptomatic patients with MDS are often treated with either VIDAZA® or DACOGEN® as these agents have been shown to improve survival in higher-risk MDS patients. It has remained unclear however, if one is better than the other.

Erythropoiesis Stimulating Agents (ESAs) are first-line therapy for anemia associated with lower-risk non-del(5q) MDS. ESAs such as Darbepoetin alfa and Epoetin alfa are re-engineered and recombinant DNA technology products of Erythropoietin (EPO), and they stimulate erythropoiesis by binding and activating the EPO receptor. There are however limited treatment options for RBC Transfusion Dependent (TD), Low Risk (IPSS Low/Int-1) MDS patients, who are Relapsed/Refractory to ESAs. There is therefore an unmet clinical need for safe and effective treatment options, to reduce the RBC transfusion burden in these patients. Imetelstat is a first-in-class Telomerase inhibitor that targets cells with short telomere length and active Telomerase, a feature often observed in some MDS patients across all stages of their disease. Higher Telomerase activity and shorter Telomeres in the blood cells of some patients with lower-risk MDS are known to predict for shorter overall survival.

IMerge is an ongoing global Phase II/III study of Imetelstat in RBC Transfusion Dependent patients with Low Risk-MDS (IPSS Low or Int-1). Previously reported data have demonstrated clinical benefit with Imetelstat in Low Risk-MDS patients inducing durable Transfusion Independence (Steensma et al ASH 2018 Abstr463). The authors now reported updated efficacy data in Low Risk, non-del(5q) MDS patients, Relapsed/Refractory to ESAs and Lenalidomide/HypoMethylating Agents naïve, from the open-label, single-arm Part 1 of IMerge study.

Part 1 of the IMerge study included patients with Low Risk MDS, who were heavily transfused (4 or more units /8wks), were Refractory or Relapsed on ESA or had serum EPO level of more than 500 mU/mL. This part of the study included 38 patients who were non-del(5q) and had not received either Lenalidomide/HypoMethylating Agents. Imetelstat was administered at 7.5 mg/kg IV every 4 weeks. The median patient age was 72 years, median baseline RBC transfusion burden was 8U/8weeks (range 4-14), 37% of the patients had IPSS Intermediate-1 risk score, 71% had WHO 2001 classification RARS (Refractory Anemia with Ringed Sideroblasts) or RCMD-RS (Refractory Cytopenia with Multilineage Dysplasia and Ringed Sideroblast) subtype and 32% with evaluable serum EPO levels had baseline level of more than 500 mU/mL. The Primary endpoint was 8-week Transfusion Independence rate. Secondary endpoints included 24-week Transfusion Independence rate, Safety, Duration of Transfusion Independence, and Hematologic Improvement rate. The median follow up was 12.1 months. The authors in this publication reported long-term efficacy, safety and biomarker data from these 38 patients.

Treatment with single-agent Imetelstat resulted in 8-week Transfusion Independence rate of 45% and the median Transfusion Independence duration was 8.5 months. Among those responding to Imetelstat, 59% remained transfusion free for over 24 weeks. The presence of Ring Sideroblasts or baseline serum EPO levels did not have an impact on 8-week Transfusion Independence rate. The 24-week Transfusion Independence rate was 26%. Erythroid Hematologic Improvement, defined as transfusion reduction by at least 4 units/8 weeks (IWG2006), was achieved in 68% of the patients. All patients (N=6) who had IPSS- Intermediate/poor cytogenetic risk achieved 8-week Transfusion Independence and 2 patients achieved partial cytogenetic response. Post treatment decrease in Telomerase (human Telomerase Reverse Transcriptase-hTERT) RNA level was observed in 73.5% of patients. Further, among patients with pre and post-treatment mutation analyses, six patients had SF3B1 mutations at baseline, and 2 patients who had a decrease in the mutation burden had longest Transfusion Independence duration on study. The most frequently reported adverse events were manageable and reversible grade 3 cytopenias.

It was concluded that treatment with single agent Imetelstat resulted in meaningful and durable Transfusion Independence, in Transfusion Dependent patients with non-del(5q) Lower-Risk MDS, who had relapsed or were refractory to ESA. Transfusion Independence was observed across different clinical subgroups, including patients with Intermediate and Poor cytogenetic risk, with a positive effect on malignant mutant clones. TREATMENT WITH IMETELSTAT PROVIDES DURABLE TRANSFUSION INDEPENDENCE (TI) IN HEAVILY TRANSFUSED NON-DEL(5Q) LOWER RISK MDS (LR-MDS) RELAPSED/REFRACTORY (R/R) TO ERYTHROPOIESIS STIMULATING AGENTS (ESAS). Fenaux P, Steensma DP, Eygen KV, et al. Presentation during European Hematology Association, Jun 15, 2019; 267420; S837