Merck Buys Prometheus For $10.8 Billion, Lands Promising Autoimmune Asset

Merck (known as MSD outside the US and Canada) has announced that it is buying Prometheus Biosciences for $200 per share in cash for a total equity valuation of approximately $10.8 billion. The transaction, which will take place through a subsidiary, is expected to close in the third quarter of 2023.  

Prometheus is a clinical-stage biotech based in California. The company’s lead pipeline candidate, PRA023, is a humanized monoclonal antibody (mAb) being developed for the treatment of autoimmune conditions including ulcerative colitis (UC) and Crohn’s disease (CD). 

“The agreement with Prometheus will accelerate our growing presence in immunology where there remains a substantial unmet patient need,” said Robert M. Davis, chairman and CEO of Merck.

“This transaction adds diversity to our overall portfolio and is an important building block as we strengthen the sustainable innovation engine that will drive our growth well into the next decade.”

Related article: Vallon and GRI Bio Strike a Merger Deal, Joining Forces for Innovative NKT Cell Regulators 

Positive Phase 2 Results in UC and CD

PRA023 inhibits both soluble and membrane-associated tumor necrosis factor (TNF)-like ligand 1A (TL1A), which has been linked to intestinal inflammation and fibrosis. 

In December 2022, Prometheus revealed positive readouts for PRA023 from two Phase 2 trials in UC and CD. In the Artemis-UC Phase 2, placebo-controlled study of patients with moderate to severe UC, 26.5% of 68 patients reached clinical remission compared to less than 2% in the placebo arm, clearing the primary endpoint. 36.8% of patients showed improvement in their endoscopy exam, reaching a key secondary endpoint. On the safety front, no serious adverse events were recorded in the study. 

In a Phase 2a, open-label study called Apollo-CD of patients with moderate to severe CD, PRA023 resulted in endoscopic response in 26.0% of patients, while 49.1% achieved clinical remission. The results compared to historical placebo rates of 12% and 16% respectively. No serious adverse events were reported in the study. 

The announcement of the results then sent Prometheus’ stock soaring from $40 per share to $95.80 on the closing date of December 7th, 2022. The findings were recently presented at the 18th Congress of the European Crohn’s and Colitis Organization (ECCO). 

Merck’s latest acquisition puts it head to head against Pfizer and Roivant’s TL1A antibody, RVT-3101, which has generated promising results of its own in a Phase 2b study in UC.

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Joy Lin

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