GSK's Efimosfermin Opens Two Phase 3 Trials Targeting MASH Cirrhosis, Signaling a Shift Toward Disease-Modifying Outcomes
核心洞察
GSK initiated two Phase 3 trials (NEBULA-1 and NEBULA-2) for efimosfermin alfa, an FGF21 analog, targeting compensated cirrhosis (fibrosis stage F4) due to MASH.
NEBULA-1 plans to enroll 1,740 patients with a primary endpoint of time to first liver-related clinical composite outcome, while NEBULA-2 plans 380 patients assessing fibrosis improvement without MASH worsening at 96 weeks.
The move signals a competitive shift in the MASH field from intermediate fibrosis stages toward cirrhosis, a population with no currently approved pharmacological treatment options.
GSK has opened recruitment for two Phase 3 trials of efimosfermin alfa, an analog of fibroblast growth factor 21 (搜索) (FGF21), both targeting compensated cirrhosis caused by metabolic dysfunction-associated steatohepatitis (搜索) (MASH), corresponding to fibrosis stage F4. The two trials, NEBULA-1 and NEBULA-2, were initiated on July 22 and moved to recruiting status this week, marking a notable expansion of the MASH competitive landscape from intermediate fibrosis stages into cirrhosis.
Efimosfermin alfa is designed for once-monthly subcutaneous administration and regulates glucose and lipid metabolism. GSK acquired the asset from Boston Pharmaceuticals in 2025 for $1.2 billion upfront, with up to $2 billion including milestones. The drug has received Breakthrough Therapy designation from the US FDA and PRIME designation from the European EMA.
Trial Designs and Endpoints
NEBULA-1 plans to enroll 1,740 patients, with the primary endpoint being the time to the first occurrence of liver-related clinical composite outcomes, and completion expected in 2033. NEBULA-2 plans to enroll 380 patients, with the primary endpoint for Part A being at least a one-stage improvement in fibrosis without worsening of MASH at 96 weeks.
The preceding ZENITH-1 and ZENITH-2 trials targeting fibrosis stages F2/F3 are also ongoing. Phase 2 results reported a 45.2% improvement in fibrosis by at least one stage and 67.7% MASH resolution without worsening of fibrosis.
Strategic Significance
The decision to conduct outcome trials with liver-related event suppression as the primary endpoint indicates that GSK is positioning efimosfermin not as a symptomatic fibrosis-improving drug, but as a drug that changes the course of the disease itself. F4 compensated cirrhosis represents the stage just before progression to liver transplantation or liver cancer, and it has previously been considered the most difficult population in which to demonstrate drug efficacy.
Market Context and Unmet Need
In the Japanese market, semaglutide was approved domestically for MASH on June 19, 2026, but its target is limited to non-cirrhotic F2/F3 patients, with facility requirements such as the involvement of hepatologists. Resmetirom is not yet approved in Japan. As a result, there are currently no approved pharmacological treatment options for F4 cirrhosis, and Japan is a market where a certain number of patients exist with cirrhosis and liver cancer progressed from fatty liver. If efimosfermin demonstrates efficacy in F4, it would directly fill this domestic gap. However, the readout is expected in the 2030s, positioning the asset on the competitive map rather than as an immediate investment decision.