On October 20, 2021 AstraZeneca reported that it has paused an active phase 1 trial of AZD5991, a direct inhibitor of MCL-1, citing the need to suss out a potential safety issue (Press release, AstraZeneca, OCT 20, 2021, View Source [SID1234591820]).

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The trial suspension, noted only through ClinicalTrials.gov, came Oct. 19: "The study has been put on hold to allow further evaluation of safety related information," the brief update said. AstraZeneca did not immediately respond to a request for comment on the trial’s suspension.

The trial was assessing the drug, known as AZD5991, either alone or combined with AbbVie/Roche’s approved blood cancer medicine Venetoclax in relapsed or refractory hematologic malignancies. The drug works by targeting apoptosis, the process of programmed cell death, specifically in blood cancer.

RELATED: Amgen shares hit after analysts expose buried FDA trial halt

This class has seen safety issues before: Back in 2019, Amgen’s oral small-molecule MCL-1 inhibitor AMG 397 was hit with an FDA halt given a "safety signal for cardiac toxicity."

And that’s not all: After AMG 397 showed some potential safety issues, Amgen then voluntarily halted enrollment for another early-stage test for AMG 176, given that it too is an MCL-1 inhibitor. Enrollment was, however, then opened back up.

Back in February, work on AMG 397 was stopped, and the focus shifted to AMG 176, which is now in phase 1 for blood cancers and uses an intravenous route of administration.