Magenta Therapeutics’ MGTA-117 blood cancer clinical trial has gone from bad to worse. Weeks after Magenta dropped down a dose level in response to serious adverse events (SAEs), a patient has died after receiving the new, lower dose, prompting the biotech to voluntarily pause the study.
The phase 1/2 clinical trial is studying the anti-CD117 antibody-drug conjugate MGTA-117 in people with relapsed or refractory acute myeloid leukemia and myelodysplastic syndrome. On Dec. 12, Magenta provided an upbeat look at data from 15 patients treated across the first three dose cohorts. No SAEs were deemed drug related, and no dose-limiting toxicities were seen.
Magenta stepped up to the fourth dose—and quickly ran into problems. On Dec. 20, the biotech said it had dropped back down to the third dose level after seeing grade 3 and 4 SAEs in recipients of the higher, 0.13 mg/kg dose.
De-escalating the dose to 0.08 mg/kg has failed to eradicate the safety problems. The latest participant to receive that dose has died after experiencing respiratory failure and cardiac arrest deemed to possibly be related to MGTA-117. Magenta communicated the event to the FDA and voluntarily paused the study while it assesses all of the available data.
Some patients treated with the 0.13 mg/kg dose also developed respiratory problems. Magenta saw a grade 4 respiratory SAE in the second recipient of the highest tested dose. The third recipient of the dose also suffered a respiratory SAE. The dose-limiting toxicities led Magenta to drop down to 0.08 mg/kg.
Shares in Magenta fell 25% to $0.37 in premarket trading. The stock has largely languished below $0.50 since the biotech reported the dose-limiting toxicities late last year. Magenta traded above $3 this time last year but enthusiasm for the biotech waned in the spring, when it laid off 14% of its staff and stopped investing in certain programs to focus its resources on MGTA-117.
Magenta had $128 million to its name at the end of September, a sum it forecast to keep the lights on into the second quarter of 2024.