FDA pauses Mersana’s clinical trial after patient dies

The FDA has paused Mersana Therapeutics’ Phase I clinical trial for a cancer treatment after a patient died, the biotech said Monday morning.

The death was deemed to be related to its drug, the Cambridge, MA-based biotech said.

The patient who died was the second to be dosed in Mersana’s clinical trial for a STING agonist — a drug target that scientists believe can boost immune response against tumors but has seen a number of challenges over the years, from low efficacy to nixed programs.

Mersana’s drug, XMT-2056, is an antibody-drug conjugate meant to target cells that express HER2 and activate STING signaling in those cells. Mersana started the trial in late January, looking to enroll patients with solid tumor cancers that were HER2 positive.

In August, GSK paid Mersana $100 million upfront for an option to co-develop and commercialize XMT-2056, which Mersana touted as the “biggest preclinical ADC deal ever.” GSK said in an emailed statement that it was “aware of the clinical hold.”

Anna Protopapas

Since the Phase I study was a dose escalation trial, the patient was dosed at the lowest dose that Mersana set out to test. As a result of the FDA’s clinical hold, no more patients will be dosed or enrolled in the trial. Mersana CEO Anna Protopapas said in a statement the company will be “undertaking the work required to fully analyze this SAE and consider potential next steps for development.”

Mersana declined to comment beyond the press release.

The biotech specializes in antibody-drug conjugates, a type of treatment where an antibody acts as the homing beacon for a cancer drug. Mersana’s lead candidate, upifitamab rilsodotin, is an ADC for ovarian cancer that is currently in Phase III.

Mersana’s stock $MRSN was paused briefly Monday morning but eventually slid about 5% after the opening bell.

therapeutics
antibody-drug conjugates
biotech
fda