Another setback for Magenta Therapeutics' MGTA-117

In the second setback in the space of a little over a month, Magenta Therapeutics (Nasdaq: MGTA) saw its shares crash 23.3% to $0.38 pre-market today, after the US biotech revealed that the latest participant dosed at the Cohort 3 level (0.08mg/kg) in the ongoing MGTA-117 Phase I/II dose-escalation clinical trial in relapsed/refractory acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS) experienced a Grade 5 serious adverse event (SAE) (respiratory failure and cardiac arrest resulting in death) deemed to be possibly related to MGTA-117.

The known information has been reported to the US Food and Drug Administration (FDA) as a suspected unexpected serious adverse reaction (SUSAR). After consultation with the trial’s safety Cohort Review Committee and with the highest regard for patient safety, Magenta has voluntarily paused dosing in the clinical trial and is working to evaluate the totality of available data and determine next steps for the development of MGTA-117.

In December last year, shares in Magenta tumbled as much as 53% after the company said it stopped dosing participants in its Phase I/II trial of MGTA-117 in relapsed/refractory acute myeloid leukemia and myelodysplastic syndrome at one of the doses being tested. The move followed the occurrence of dose-limiting toxicities (DLTs) in two of three patients in cohort 4, where subjects were given MGTA-117 at a dose of 0.13mg/kg.