FDA tells Magenta to pump the brakes on blood cancer trial before it starts to develop new dosing test

Magenta Therapeutics has been asked by the FDA to pump the brakes on a trial for its blood cancer med before it even got started.

The FDA would like the biotech to develop an additional test to inform dose escalation and safety monitoring in the proposed phase 1/2 clinical trial, according to a Wednesday release. Magenta submitted a regulatory filing last month for the trial to test MGTA-117 in patients with the blood cancers acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS).

Magenta said the additional test is the only request from the clinical hold letter. The agency did not institute any stops related to toxicology or manufacturing of the drug. 

The exact date the study was expected to commence was not disclosed, but Magenta did report during first quarter earnings earlier this year that the company "expects to assess initial safety and pharmacokinetic data internally in the fourth quarter of 2021."

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Work to develop the test has already begun, and Magenta does not anticipate technical challenges in the process, said President and CEO Jason Gardner in a statement. Magenta will work with the FDA to determine the new test's application for dose escalation, the company said.

"We expect to request a ‘Type A’ meeting in the coming weeks and, if successful in resolving this remaining issue, we would anticipate opening the study in Q4 2021," Gardner said. 

The antibody-drug conjugate is meant to selectively deplete hematopoietic stem cells from patients before transplant or stem cell-based gene therapy, which would reduce the need for high-dose or high-intensity chemotherapies, Magenta said. 

MGTA-117 is initially being tested in AML and MDS, pending the FDA's future reassessment of the proposed clinical trial. Magenta believes the therapy has potential for applications across other blood cancers, sickle cell disease, inherited metabolic disorders and other areas. The CD117 receptor targeted by the drug is expressed on the cell surface of hematopoietic stem cells and leukemia cells.

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In May 2020, Magenta linked arms with Avrobio to evaluate the potential use of the drug to condition patients before receiving Avrobio's investigational lentiviral gene therapies. And, last June, the biotech teamed up with Beam Therapeutics on a research and clinical collaboration to assess the potential use of the drug to condition patients with sickle cell disease and beta-thalassemia who are taking Beam's base editing therapies. 

The company had more than $200 million in cash at the end of the second quarter, which is expected to provide a runway to execute on existing plans. Magenta shares were down more than 7%, to $8.25 apiece, as of 10:30 a.m. ET.