Boston Pharmaceuticals Presents Data at NASH-TAG 2024 Demonstrating Low Immunogenicity Over Time With Long-acting FGF21 Analogue, BOS-580, for MASH

Boston Pharmaceuticals, a clinical-stage biopharmaceutical company developing differentiated molecules addressing serious liver diseases, today announced additional Phase 2 data supporting the low risk of immunogenicity and positive clinical effects associated with BOS-580, the company's investigational, long-acting fibroblast growth factor 21 (FGF21) analogue for the treatment of metabolic dysfunction-associated steatohepatitis (MASH), also known as non-alcoholic steatohepatitis (NASH). The data were presented at NASH-TAG 2024 (Jan. 4-6, 2024) in Park City, Utah.

"These encouraging results indicate that BOS-580 is unlikely to generate anti-drug antibodies, which is a key feature for drug developers working on FGF21 analogues in the field of MASH, as patients need sustained powerful efficacy over time," said Sophie Kornowski, CEO of Boston Pharmaceuticals. "This low immunogenicity distinguishes BOS-580 from other FGF21 analogues currently in development."

Another analysis of data from Boston Pharmaceuticals' Phase 2a trial demonstrated the impact of BOS-580 treatment on several non-invasive indicators of fibrosis based on markers of liver injury and fibrosis in MASH patients.

"Our latest data highlight that BOS-580 has great potential to become a backbone in the treatment of patients suffering from MASH. We are committed to advancing once-monthly BOS-580 to pivotal clinical trials in the near term. We believe BOS-580 may offer a compelling and convenient treatment option for people living with MASH," said Juan Carlos Lopez-Talavera, M.D., Ph.D., CMO of Boston Pharmaceuticals.

Low Immunogenicity Reported in Patients with Phenotypic MASH Treated with BOS-580
Protein-based therapeutics can trigger an immune response that can alter or reduce their efficacy and may be associated with adverse effects. Researchers assessed the impact of BOS-580 treatment (once-monthly and bi-weekly dosing regimens) on the formation of anti-drug antibodies (ADAs), a clinical measure of protein therapeutic immunogenicity, in patients with phenotypic MASH enrolled in Part A of a randomized, double-blind, placebo-controlled Phase 2a study (N=102).

Results indicate:

• BOS-580 showed low and transient ADA responses, detected at one or two measurements
• Titers for anti?BOS-580 and anti?FGF-21 antibodies were low
• One out of 65 patients (1.5%) exposed to BOS-580 had consecutive increasing anti-FGF21 antibodies, which had no impact on the drug's pharmacokinetic or pharmacodynamic parameters

BOS-580 Treatment Resulted in Significant Reductions in Composite Biomarkers Associated with Fibrosis
An analysis of data from Boston Pharmaceuticals' Phase 2a trial demonstrated the efficacy of BOS-580 on biomarkers of liver injury and fibrosis in MASH patients. With the high prevalence of metabolic dysfunction-associated steatotic liver disease (MASLD), also known as non-alcoholic fatty liver disease (NAFLD), which can lead to MASH, there is an urgent need to identify non-invasive methods to avoid the use of biopsies.

Results of this analysis show treatment with BOS-580 led to significant reductions across composite scores for Fibroscan-AST (FAST), Fibrosis-4 Index (FIB-4), Aspartate aminotransferase-to-platelet ratio index (APRI) and ADAPT. The responses observed were rapid, within one to two weeks, and were sustained over the 12-week study, suggesting BOS-580 treatment may lead to clinical benefit in MASH patients.

Details of the NASH-TAG 2024 presentations are as follows:

Title: Low Immunogenicity Rates in Phenotypic MASH Patients Treated for 12 Weeks With Once-Monthly and Bi-weekly Subcutaneous Dosing of BOS-580 (Poster Presentation)
Abstract Number: 42
Session Date, Time: Saturday, Jan. 6, 2024
Presenter: Swapan K Chowdhury, Boston Pharmaceuticals

Title: Improvement in FAST and FIB-4 Composite Biomarker Scores in Phenotypic MASH Patients Treated for 12 Weeks With Monthly and Bi-weekly Subcutaneous Dosing of BOS-580? (Oral Presentation)
Abstract Number: 46
Session Date, Time: Saturday, Jan. 6, 2024 at 11:45 a.m. MST
Presenter: Rohit Loomba, M.D., MHSc, Professor of Medicine, Chief in the Division of Gastroenterology and Hepatology, and Director of MASLD Research Center at University of California, San Diego

About BOS-580
BOS-580 is a once-monthly subcutaneous injectable of a long-acting, highly engineered variant of human fibroblast growth factor 21 (FGF21) that regulates various metabolic pathways to decrease liver fat and ameliorate liver inflammation and damage in patients with metabolic dysfunction-associated steatohepatitis (MASH), also known as non-alcoholic steatohepatitis (NASH).

About Boston Pharmaceuticals
Boston Pharmaceuticals is a clinical stage biopharmaceutical company that leverages an experienced and committed drug development team to advance a portfolio of highly differentiated therapies that may address important unmet medical needs in serious liver diseases, with MASH as the focus of its lead asset. The Company has significant expansion opportunities through its portfolio of promising drug development candidates that were acquired through partnerships with proven, innovative biotechnology and pharmaceutical companies. Boston Pharmaceuticals applies rigorous decision making to advance programs to deliver differentiated medicines to patients in need of new options, while creating value for all parties involved in the journey.

For more information, please visit www.bostonpharmaceuticals.com and follow us on LinkedIn.

About B-Flexion
Boston Pharmaceuticals is a portfolio company of B-Flexion, a private entrepreneurial investment firm that partners with sophisticated capital to deliver exceptional value over the generations, while also contributing positively to society. Chaired by Ernesto Bertarelli and with offices across Europe and the United States, B-Flexion seeds, acquires and builds investment partnerships, principally in the fields of Private Equity, Venture & Growth Capital, Real Assets, Hedge Funds, Credit, and Public Securities. As well as these partnerships, B-Flexion makes principal investments in operating businesses in transformative industries with a focus on Healthcare, Planet, Consumer and Technology.

For more information, please visit www.bflexion.com.