The US Food and Drug Administration (FDA) has removed the full clinical hold placed on the investigational new drug application for the telomerase inhibitor imetelstat.
The hold, which was placed in March, suspended a phase 2 study of imetelstat in patients with essential thrombocythemia (ET) or polycythemia vera (PV), as well as a phase 2 study of the drug in patients with multiple myeloma (MM).
The hold also delayed a planned phase 2 trial in patients with myelofibrosis (MF).
And it temporarily suspended an investigator-sponsored trial of imetelstat in MF. The FDA lifted the hold on the investigator-sponsored trial in June.
The FDA halted these trials due to reports of persistent, low-grade liver function test (LFT) abnormalities observed in the phase 2 study of ET/PV patients and the potential risk of chronic liver injury following long-term exposure to imetelstat. The FDA expressed concern about whether these LFT abnormalities are reversible.
Now, data provided by the Geron Corporation, the company developing imetelstat, has convinced the FDA to lift the hold on all trials.
The FDA said the proposed clinical development plan for imetelstat, which is focused on high-risk myeloid disorders such as MF, is acceptable. Geron Corporation has said it does not intend to conduct further studies with, or develop imetelstat for, patients with ET or PV.
To address the clinical hold, the FDA required Geron to provide follow-up information from imetelstat-treated patients who experienced LFT abnormalities until such abnormalities resolved to normal or baseline.
Geron obtained follow-up information from patients in the previously ongoing company-sponsored phase 2 trials in ET/PV and MM. These data were submitted to the FDA as part of the company’s complete response.
The company’s analysis of these data showed that, in the ET/PV trial, LFT abnormalities resolved to normal or baseline in 14 of 18 follow-up patients. For the remaining 4 patients, at the time of the data cut-off, 3 patients showed improvement in LFT abnormalities, and 1 patient had unresolved LFT abnormalities. Two of the remaining 4 patients continue in follow-up.
In the MM trial, LFT abnormalities resolved to normal or baseline in all 9 follow-up patients. In addition, no emergent hepatic adverse events were reported during follow-up for either study.
The FDA also requested information regarding the reversibility of liver toxicity after chronic imetelstat administration in animals. Geron submitted data from its non-clinical toxicology studies, which included a 6-month study in mice and a 9-month study in cynomolgus monkeys.
In these studies, no clinical pathology changes indicative of hepatocellular injury were observed, and no clear signal of LFT abnormalities were identified.
With the clinical hold lifted, a multicenter phase 2 trial in MF is projected to begin in the first half of 2015.
