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| Trade names | Rytelo |
| Other names | GRN163L |
| AHFS/Drugs.com | Monograph |
| MedlinePlus | a624035 |
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| Routes of administration | Intravenous |
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| Formula | C148H211N68O53P13S13 |
| Molar mass | 4610.18 g·mol−1 |
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Imetelstat, sold under the brand name Rytelo, is an anti-cancer medication used for the treatment of myelodysplastic syndromes with transfusion-dependent anemia. [1] Imetelstat is an oligonucleotide telomerase inhibitor. [1] [2] [3] By blocking telomerase activity, imetelstat causes telomere shortening, inhibits the proliferation of malignant stem and progenitor cells and induces cell death, ultimately leading to a reduction in malignant clones. [2]
The most common adverse reactions include decreased platelets, decreased white blood cells, decreased neutrophils, increased aspartate aminotransferase, increased alkaline phosphatase, increased alanine aminotransferase, fatigue, prolonged partial thromboplastin time, arthralgia/myalgia, COVID-19 infections, and headache. [4]
Imetelstat was approved for medical use in the United States in June 2024. [4] [5] [6] The US Food and Drug Administration (FDA) considers it to be a first-in-class medication. [7]
Imetelstat is indicated for the treatment of adults with low- to intermediate-1 risk myelodysplastic syndromes with transfusion-dependent anemia requiring four or more red blood cell units over eight weeks who have not responded to or have lost response to or are ineligible for erythropoiesis-stimulating agents. [1] [4]
Imetelstat is the first telomerase inhibitor to enter clinical trials. [8]
Chemically, imetelstat is a synthetic conjugate consisting of three parts: GRN163, a thio phosphoramide oligonucleotide, and a palmitoyl lipid group. [8] GRN163 is the pharmacological component with telomerase inhibition based on experiments with poly-G oligonucleotides first conducted at the University of Nebraska Medical Center under contract with Lynx Therapeutics. [9] The palmitic acid moiety is conjugated via a phosphothioate linkage to the backbone of the antisense oligonucleotide.[ medical citation needed ] Telomere shortening and lower cell viability are observed after inhibition of telomerase activity in vitro.[ medical citation needed ] IC50 values ranged from 50 to 200nM for 10 different pancreatic cell lines. [10]
The efficacy of imetelstat was evaluated in IMerge (NCT02598661), a randomized (2:1), double-blind, placebo-controlled multicenter trial in 178 participants with myelodysplastic syndromes. [4] Participants received an intravenous infusion of imetelstat 7.1 mg/kg or placebo in 28-day treatment cycles until disease progression or unacceptable toxicity. [4] Randomization was stratified by prior red blood cell transfusion burden and by International Prognostic Scoring System (IPSS) risk group. [4] All participants received supportive care, which included red blood cell transfusions. [4]
Imetelstat was approved for medical use in the United States in June 2024. [4] The FDA granted the application for imetelstat orphan drug designation. [4] [11] [12]
In December 2024, the Committee for Medicinal Products for Human Use of the European Medicines Agency adopted a positive opinion, recommending the granting of a marketing authorization for the medicinal product Rytelo, intended for the treatment of adults with transfusion-dependent anemia due to very low, low or intermediate risk myelodysplastic syndromes. [2] The applicant for this medicinal product is Geron Netherlands B.V. [2] Imetelstat was authorized for medical use in the European Union in March 2025. [2]
Imetelstat is the international nonproprietary name. [13]