Imetelstat, a novel, first‐in‐class telomerase inhibitor: Mechanism of action, clinical, and translational science

Abstract Most cancers and neoplastic progenitor cells have elevated telomerase activity and preservation of telomeres that promote cellular immortality, making telomerase a rational target for the treatment of cancer. Imetelstat is a first‐in‐class, 13‐mer oligonucleotide that binds with high affinity to the template region of the RNA component of human telomerase and acts as a competitive inhibitor of human telomerase enzymatic activity. Pharmacokinetics, pharmacodynamics, exposure‐response analyses, efficacy, and safety of imetelstat have been evaluated in vitro, in vivo, and clinically in solid tumor and hematologic malignancies, including lower‐risk myelodysplastic syndromes (LR‐MDS) and myeloproliferative neoplasms. Imetelstat was approved in the United States in June 2024 for the treatment of adult patients with LR‐MDS with transfusion‐dependent anemia requiring four or more red blood cell units over 8 weeks who have not responded to or have lost response to or are ineligible for erythropoiesis‐stimulating agents, with a recommended dosing regimen of 7.1 mg/kg administered via 2‐h intravenous infusion every 4 weeks. In the pivotal trial, significantly more patients treated with imetelstat versus placebo achieved ≥8‐week and ≥24‐week red blood cell‐transfusion independence, and imetelstat was associated with a manageable safety profile characterized primarily by short‐lived and manageable neutropenia and thrombocytopenia. This mini‐review summarizes the mechanism of action, pharmacokinetic and pharmacodynamic characteristics, clinical development, and clinical efficacy and safety data of imetelstat.