PIPELINE

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• Efimosfermin alfa (BOS-580) is a long-acting, once-monthly FGF21 analogue under development for the treatment of metabolic dysfunction-associated steatohepatitis (MASH), previously known as non-alcoholic steatohepatitis (NASH).

• Efimosfermin is currently being studied in Phase 2 clinical trials in participants at risk for or with biopsy-confirmed MASH

Efimosfermin is an investigational fusion protein based on human IgG and FGF21, modified to provide an extended systemic half-life. Efimosfermin is produced in mammalian cells, which is known to improve the quality of glycosylation. The molecule has demonstrated specificity for three FGF21 receptors in non-clinical studies which suggests efimosfermin may allow for a balanced pharmacological effect.

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a highly prevalent, silent disease. MASLD is also closely associated with metabolic co-morbidities such as diabetes mellitus 2 (T2D) and hypertension. Metabolic dysfunction-associated steatohepatitis (MASH) is a severe form of MASLD.

MASH is a growing global epidemic fueled by increasing levels of obesity and metabolic disease. It is estimated that 3 to 5% of the global population is affected by MASH, though the disease is underdiagnosed. Prevalence of MASH will increase by 15-56% depending on region by 2030. The potential ability of FGF21-based MASH therapies to treat patients with T2D could be particularly important given the prevalence of T2D in MASH patients and the role of FGF21 in improving glycemic control. If MASH is left untreated and progresses to advanced fibrosis (cirrhosis), which can lead to liver failure, liver cancer or death.

In a Phase 2a trial, reductions in markers of liver injury and fibrosis in phenotypic MASH patients and improvements in markers of metabolic health were observed with once-monthly dosing of efimosfermin. To date, efimosfermin has demonstrated low discontinuation rates in clinical trials. The most commonly observed adverse events have been of GI in nature.

• BOS-342 is an investigational bispecific antibody directed against Glypican-3 (GPC3) and 4-1BB (CD137) bispecific antibody being developed for patients with hepatocellular carcinoma (HCC). 4-1BB is a member of the tumor necrosis factor receptor family and is expressed by activated CD8 and CD4 T cells.

• BOS-342 is currently under clinical evaluation. The treatment involves an intravenously administered dose once every two weeks.

BOS-342 is an investigational, intravenously administered, first-in-class Glypican-3 (GPC3) bispecific antibody for treatment of patients with hepatocellular carcinoma (HCC) that progressed on at least one prior treatment. The antibody is comprised of a GPC3 antibody (tumor target) linked to a 4-1BB (CD137) agonistic anticalin protein (immune receptor).

Hepatocellular carcinoma is the most common form of liver cancer, accounting for 80-90% of liver cancer. HCC is a cancer of hepatocytes, which are the most abundant cell type in the liver and are responsible for the liver’s primary functions.

GPC3 is an oncofetal glycoprotein attached to the cell membrane by a glycophosphatidylinositol anchor. GPC3 is overexpressed in the majority of hepatocellular carcinoma tumors, and GPC3 is implicated in processes such as cell growth, differentiation, and migration.

Preclinical studies indicate that BOS-342 selectively binds to tumors expressing GPC3 to exert tumor killing activity through the recruitment and activation of T-cells. BOS-342 binds with high affinity GPC3 positive tumor cells, where it will then activate 4-1BB on the tumor infiltrating immune cells.

Phase 1/2 clinical trial for HCC started in 2023. The study is open and enrolling.

Opportunities exist for potential expansion into other solid tumors with GPC3 overexpression.