Efimosfermin alfa (BOS-580), a long-acting FGF21 analogue, in participants with phenotypic metabolic...

Metabolic dysfunction-associated steatohepatitis (MASH) is a progressive disease characterised by steatosis, inflammation, and liver fibrosis. Efimosfermin alfa (efimosfermin, formerly BOS-580) is a long-acting, engineered variant of FGF21 designed to have a prolonged half-life. We aimed to assess the safety and tolerability of multiple efimosfermin doses and dosing regimens compared with placebo and to evaluate exploratory biomarkers of efficacy in participants with phenotypic MASH.

This multicentre, randomised, double-blind, placebo-controlled, phase 2a trial was conducted at 12 centres in the USA. Individuals with phenotypic MASH, aged 18-75 years and with a BMI of 30-45 kg/m², were eligible for the study. Participants were randomly assigned, using a centralised interactive randomisation system with no stratification factors, to one of five dosing cohorts: efimosfermin 75 mg once every 4 weeks, 75 mg once every 2 weeks, 150 mg once every 4 weeks, 150 mg once every 2 weeks, or 300 mg once every 4 weeks, for a 12-week treatment period. Participants were assigned 1:1:1:1 to all cohorts except efimosfermin 150 mg once every 4 weeks, which was initiated after assignment to the other cohorts was complete. Within each cohort, participants were randomly assigned 4:1 to receive efimosfermin or placebo, via subcutaneous injection, in fixed blocks of size five. Investigators and participants were masked to group assignment and treatment allocation. The primary endpoint was safety and tolerability and was assessed throughout the 12-week treatment period and at the follow-up visit 4 weeks after the final dose in the full analysis set, defined as enrolled participants who received at least one dose of study medication. Part A (reported here) of this phase 2 study is complete, while other parts of the phase 2 study are ongoing. This trial is registered with ClinicalTrials.gov (NCT04880031).

Between Aug 27, 2021, and July 22, 2022, 360 individuals were screened, of whom 102 were eligible and were randomly assigned to receive placebo (n=37) or efimosfermin 75 mg every 4 weeks (n=8), 75 mg every 2 weeks (n=14), 150 mg every 4 weeks (n=15), 150 mg every 2 weeks (n=15), or 300 mg every 4 weeks (n=13), for a total of 12 weeks. 45 (44%) of the 102 participants were female and 57 (56%) were male, with a mean age of 53 years (SD 11) and mean BMI of 36·5 kg/m² (SD 4·1). Of 65 participants treated with efimosfermin, 43 (66%) had treatment-emergent adverse events (TEAEs): four (50%) of eight participants receiving 75 mg every 4 weeks, ten (71%) of 14 participants receiving 75 mg every 2 weeks, six (40%) of 15 participants receiving 150 mg every 4 weeks; 12 (80%) of 15 participants receiving 150 mg every 2 weeks, and 11 (85%) of 13 participants receiving 300 mg every 4 weeks; TEAEs were recorded in 18 (49%) of 37 participants receiving placebo. TEAEs were typically mild-to-moderate in severity and resolved spontaneously. The most frequent TEAEs were gastrointestinal in nature, reported by nine (24%) of 37 participants in the placebo group and 26 (40%) of 65 participants who received efimosfermin: two (25%) of eight participants receiving 75 mg every 4 weeks, eight (57%) of 14 participants receiving 75 mg every 2 weeks, two (13%) of 15 participants receiving 150 mg every 4 weeks, eight (53%) of 15 participants receiving 150 mg every 2 weeks, and six (46%) of 13 participants receiving 300 mg every 4 weeks. The most common gastrointestinal events were nausea, vomiting, and diarrhoea. There were no treatment-related deaths. At week 12, 47 (89%) of 53 participants receiving efimosfermin for whom data were available had at least a 30% reduction in hepatic fat fraction: five (63%) of eight participants receiving 75 mg every 4 weeks, 11 (92%) of 12 participants receiving 75 mg every 2 weeks, nine (90%) of ten participants receiving 150 mg every 4 weeks, 11 (92%) of 12 participants receiving 150 mg every 2 weeks, and all 11 (100%) participants receiving 300 mg every 4 weeks, compared with two (7%) of 30 participants receiving placebo.

In participants with phenotypic MASH, efimosfermin had a favourable safety profile and showed improvements in indicators of hepatic steatosis. These results help to inform future studies of efimosfermin in this important disease state.

Boston Pharmaceuticals.