Recent findings of a phase II clinical trial of imetelstat, a telomerase inhibitor, demonstrate that it could be a promising treatment approach for patients with essential thrombocythemia, which raises platelets to dangerous levels.
Myeloproliferative neoplasms are a group of disorders caused by an overproduction of a particular blood cell type. For example, essential thrombocythemia (ET) causes an abnormal increase in the number of platelets produced in the blood and bone marrow. Although most patients have a normal life expectancy, ET may develop into acute myeloid leukemia. Currently available drugs help manage symptoms and offer protection from heart attack or strokes, but more treatment options are necessary for those patients who are not responsive or who experienced adverse side effects.
Recently, researchers reported success of a phase II clinical trial of a novel-acting drug, imetelstat, which could be a promising treatment approach for ET . Imetelstat is an oligonucleotide sequence that targets the RNA template of the enzyme telomerase, thereby directly inhibiting its activity. If telomerase is active, a cell will continue to grow and divide. Most cancers have a high level of telomerase activity compared to normal cells, and thus exhibit a selective growth advantage. Inhibition of telomerase would prevent cancer cells from dividing uncontrollably. Thus, telomerase is a great target for new cancer treatments.
In their study, 18 ET patients who were unresponsive or intolerant to other treatments received weekly injections of imetelstat, followed by less frequent doses during the course of the trial. All patients demonstrated reduced platelet levels, and 16 achieved complete normalization of blood cell counts. In addition, they were responsive to the drug for more than a year. Overall, adverse events were manageable and reversible.
Imetelstat is the first telomerase inhibitor to advance to clinical development. The findings of this study could be potentially applied to other myeloproliferative neoplasms, including myelofibrosis or polycythemia vera.
HemaCare is a leading provider of platelets and other blood cell types for research purposes. We look forward to the application of this novel-acting drug for treatment of myeloproliferative disorders.
 Baerlocher, G. M. et al. Telomerase Inhibitor Imetelstat in Patients with Essential Thrombocythemia. The New England Journal of Medicine 373, 920-928, doi:10.1056/NEJMoa1503479 (2015).