- Magenta Therapeutics on Wednesday said it has paused a clinical trial after a participant died following treatment with the company’s experimental conditioning drug regimen.
- The adult study volunteer experienced respiratory failure and cardiac arrest potentially related to the company’s experimental medicine, called MGTA-117 and meant to prepare patients for stem cell transplants. The trial is testing increasing dose levels of the medicine to assess its safety in patients with relapsed or refractory acute myeloid leukemia or myelodysplastic syndrome.
- The death comes a month after Magenta stopped enrolling for a higher dose due to side effects. The company has reported the death to the Food and Drug Administration and voluntarily paused dosing in the trial, saying it is “working to evaluate the totality of available data and determine next steps for the development of MGTA-117.”
Launched in 2016, the Cambridge, Massachusetts biotechnology company is one of several companies trying to develop better ways to condition or prepare patients ahead of stem cell transplants or gene therapies.
Decades-old regimens used to deplete target cells in the blood or bone marrow before treatment have toxic side effects that can be fatal. This has drawn interest to Magenta’s technology, an antibody-drug conjugate, a type of targeted therapy designed to more safely or effectively ready patients for the procedure.
MGTA-117, Magenta’s lead treatment, latches onto CD117-expressing hematopoietic stem cells and progenitor cells and kills them with its linked payload, a toxin called amanitin. The treatment has drawn interest from gene therapy developers Beam Therapeutics and Avrobio, which signed agreements in 2020 to use the conditioning treatment with their programs in hemoglobinopathies and lysosomal storage disorders, respectively.
Last month, Magenta reported preliminary results for early-phase testing of MGTA-117 that the company said showed it quickly depleted target cells and was well tolerated by patients. Through early December, the trial had dosed a total of 15 participants with MGTA-117. Eleven had completed a 21-day observation period for dose-limiting toxicity, while four had discontinued treatment for reasons unrelated to the conditioning regimen.
But a week later, the company said it stopped giving its second highest dose, 0.13 milligram per kilogram, after two of three participants treated with it experienced serious adverse effects. One had elevated liver enzyme counts and another had a respiratory-related side effect.
The company’s statement Wednesday was brief, noting few other details about the patient’s death. The participant had received an 0.08 milligram per kilogram dose of MGTA-117, the next highest dose Magenta has tested. Investigators judged the death to be “possibly related” to treatment, leading Magenta to stop further dosing.
Shares in Magenta fell by more than 10% in Thursday morning trading on the news. At less than $0.50 apiece, the stock has lost nearly all its worth since the company’s 2019 initial public offering.
Like many biotechs, the company is also facing funding challenges. In April, it laid off 14% of its workforce and reprioritized its portfolio to extend its cash runway through mid-2024.
Editor’s Note: This story has been updated to include mention of Magenta halting enrollment for a higher level dosing in December.