Effect of Prior Treatments on the Clinical Activity of Imetelstat in Transfusion-Dependent Patients with Erythropoiesis-Stimulating Agent, Relapsed or Refractory/Ineligible Lower-Risk Myelodysplastic Syndromes

Introduction: Limited treatment options are available for patients with red blood cell (RBC) transfusion-dependent (TD) lower-risk myelodysplastic syndromes (LR-MDS). Imetelstat (IME), a first-in-class, direct, and competitive inhibitor of telomerase activity, was approved by the United States Food and Drug Administration in June 2024 for the treatment of RBC-TD LR-MDS in patients who were relapsed or refractory to or ineligible for erythropoiesis-stimulating agents (ESA) based on the results of the pivotal IMerge trial (NCT02598661). IMerge demonstrated significant and durable efficacy of IME (n=118) versus placebo (n=60) for ≥8-week, ≥24-week, and ≥1-year RBC-transfusion independence (TI), with a generally manageable safety profile in this patient population (Platzbecker U, Santini V, et al. Lancet. 2024). This analysis pooled data from the 3 parts of the IMerge trial (phase 2, phase 3 and QTc study) to investigate the effect of prior therapies on the clinical activity of IME.

Methods: IMerge was a phase 2/3 trial with a clinical QTc study that enrolled patients with heavily RBC-TD LR-MDS who were ESA-ineligible or relapsed/ refractory. IME was administered intravenously every 4 weeks at 7.1 mg/kg (equivalent to 7.5 mg/kg IME sodium). Prior lenalidomide (LEN) and prior hypomethylating agent (HMA) use were exclusion criteria in phase 3 only. In this analysis, IME-treated patients (N=226) were pooled from phase 2, phase 3, and the QTc study of IMerge and analyzed on the basis of prior treatment as follows: ± ESA, luspatercept (LUSP), LEN, and HMA. Prior treatment was not exclusive; patients may have received >1 prior therapy. Outcomes included ≥8-week and ≥24-week RBC-TI, rates of hematologic improvement-erythroid (HI-E) based on the revised International Working Group (IWG) 2018 criteria, transfusion reduction of ≥4 U/8 weeks, and a hemoglobin (Hb) rise of ≥1.5 g/dL for ≥8 weeks.

Results: As previously presented, data from the IMerge phase 3 pivotal analysis demonstrated that patients treated with IME (n=118) had ≥8-week and ≥24-week RBC-TI rates of 40% and 28%, respectively, 42% met HI-E (IWG 2018) criteria, 60% had transfusion reductions of ≥4 U/8 weeks, and 34% had a Hb rise of ≥1.5 g/dL for ≥8 weeks (Platzbecker U, Santini V, et al. Lancet. 2024). In the current analysis of all IME-treated patients pooled in IMerge (N=226), 204 had prior treatment with an ESA and 22 were ineligible for ESAs; 35 had prior LUSP, 26 had prior LEN, and 22 had prior HMA treatment. Of IME-treated patients with prior ESA therapy, 40% and 28% achieved ≥8-week and ≥24-week RBC-TI, respectively, 43% met HI-E, 64% had a transfusion reduction of ≥4 U/8 weeks, and 33% had a Hb rise of ≥1.5 g/dL for ≥8 weeks. In IME-treated patients ineligible for ESA therapy, 36% and 14% achieved ≥8-week and ≥24-week RBC-TI, respectively, 41% met HI-E, 64% had a transfusion reduction of ≥4 U/8 weeks, and 2% had a Hb rise of ≥1.5 g/dL for ≥8 weeks. Of IME-treated patients who had prior treatment with LUSP, 29% and 20% achieved ≥8-week and ≥24-week RBC-TI, respectively, 26% met HI-E, 69% had a transfusion reduction of ≥4 U/8 weeks, and 29% had a Hb rise ≥1.5 g/dL for ≥8 weeks. Of IME-treated patients with prior LEN treatment, 23% and 12% achieved ≥8-week and ≥24-week RBC-TI, respectively, 31% met HI-E, 54% had a transfusion reduction of ≥4 U/8 weeks, and 19% had a Hb rise of ≥1.5 g/dL for ≥8 weeks. Of the 22 IME-treated patients who had prior treatment with HMA, 14% and 9% achieved ≥8-week and ≥24-week RBC-TI, respectively, 18% met HI-E, 50% had a transfusion reduction of ≥4 U/8 weeks, and 14% had a Hb rise of ≥1.5 g/dL for ≥8 weeks.

Conclusions: Patients who were ESA-ineligible or who had prior treatment with LUSP, LEN, or HMA in IMerge experienced clinical benefit from IME treatment, though the number of patients was small. Given the evolving therapeutic landscape for LR-MDS and the limited data available on outcomes in later lines of treatment, these results have important clinical implications, suggesting that IME demonstrates clinical activity regardless of prior therapies.