John O. Mascarenhas, MD, on Myelofibrosis: Novel Combination of Imetelstat Plus Ruxolitinib

The IMproveMF study is a study of imetelstat, the telomerase inhibitor, the first in class telomerase inhibitor, which is an infusional agent in patients with myelofibrosis that are on a stable dose of ruxolitinib with the add-on metals stat to try to improve upon response, spleen, symptom, and biomarkers of response. So this is a phase one B study dose escalation starting at 4.7 milligrams per kilogram IV every four weeks added onto the stable dose of ruxolitinib. The patients had to been on for at least 12 weeks and a stable dose for four weeks. And what we saw in this phase one B study all the way up to 9.4 milligrams per kilogram was no dose limiting toxicity. So we didn't see significant myelosuppression, GI toxicity, or any other non hematologic toxicity. Any hematologic toxicity we saw was both transient and recoverable, allowing us to continue dosing imetelstat. So it really did prove that imetelstat which is approved, I should say in lower risk transfusion dependent MDS patients with an anemia goal in myelofibrosis can be delivered as an add-on strategy to ruxolitinib safely. We're now beginning to look at the readout of efficacy. We gave some preliminary results showing that at the higher doses of imetelstat 9.4 milligram per kilogram, which is the dose I should point out, that's being evaluated in the phase three randomized. Phase three is a single agent in the relapse refractory setting is a well tolerated dose and has shown already some preliminary activity in terms of reduction in spleen and symptom burden above and beyond what we were seeing with the single agent ruxolitinib initially. So we need to expand this cohort, continue to follow the patients for outcome measures like progression-free survival, maybe even overall survival, and make sure these responses are durable, and that's the next step. We'll also add a cohort of patients that will likely be treatment naive patients, so adding imetelstat plus ruxolitinib upfront rather than this delayed add-on strategy. So more to come with imetelstat. And of course we're still waiting for the randomized phase three single agent in the relapse refractory setting to read out. Hopefully by 2026.