Imetelstat — Drug Monograph

Brand names: Rytelo

Drug class: Other

Mechanism of Action

First-in-class telomerase inhibitor. Imetelstat is a 13-mer thio-phosphoramidate oligonucleotide that covalently binds to the RNA template component (hTR) of telomerase, blocking telomerase enzymatic activity. Malignant hematopoietic stem cells in MDS and myelofibrosis have short telomeres and high telomerase dependence, making them selectively vulnerable. Inhibition of telomerase leads to progressive telomere shortening and apoptosis of malignant clones while sparing normal long-telomere hematopoietic cells.

FDA Indications

• Transfusion-dependent anemia in adults with low- to intermediate-1-risk myelodysplastic syndromes (MDS) after failure of erythropoiesis-stimulating agents (ESAs) (FDA approved June 2024; IMerge: 40% transfusion independence ≥8 weeks vs 15% placebo; 28% transfusion independence ≥24 weeks vs 3% placebo)

Common Side Effects

• Thrombocytopenia (77%)
• Neutropenia (68%)
• Anemia worsening (18%)
• Fatigue (17%)
• Nausea (16%)
• Infusion-related reactions (12%)
• Elevated AST/ALT

Clinical Pearl

Imetelstat represents a novel first-in-class mechanism for MDS anemia — telomerase inhibition. Unlike luspatercept (which promotes erythroid maturation) or ESAs (which stimulate erythropoiesis), imetelstat targets the malignant clone directly. The major limiting toxicity is myelosuppression (neutropenia and thrombocytopenia), which requires CBC monitoring before every cycle.

Related Therapies & Mechanisms

• Arsenic Trioxide (Trisenox) — Other · Leukemia
• Brexucabtagene autoleucel (Tecartus) — Other · Leukemia
• Enasidenib (Idhifa) — Other · Leukemia
• Glasdegib (Daurismo) — Other · Leukemia