GSK to acquire efimosfermin, a phase III-ready potential best-in-class specialty medicine to treat and prevent progression of steatotic liver disease (SLD) 
 
   -- Affecting up to 5% of the global population, SLD represents an area of 
      significant unmet medical need with limited treatment options 
 
   -- Phase II data show potential of efimosfermin to reverse liver fibrosis, 
      demonstrated in metabolic dysfunction-associated steatohepatitis (a form 
      of SLD) 
 
   -- Unique properties offer potential for efimosfermin to be a new 
      standard-of-care 
 
   -- Significantly expands GSK's hepatology pipeline aimed at addressing 
      steatotic and viral drivers of liver disease, offering multiple 
      development options and potential first launch in 2029 
 
 
CAMBRIDGE, Mass.--(BUSINESS WIRE)--May 14, 2025-- 
 
   GSK plc (LSE/NYSE: GSK) and Boston Pharmaceuticals, a leading clinical 
stage biopharmaceutical company developing highly targeted therapies for 
patients with serious liver diseases, today announced that they have 
entered into an agreement under which GSK will acquire Boston 
Pharmaceuticals' lead asset, efimosfermin alfa. Efimosfermin is a phase 
III-ready, potential best-in-class, investigational specialty medicine 
to treat and prevent progression of steatotic liver disease (SLD). Under 
the agreement, GSK will pay $1.2 billion upfront, with potential for 
additional success-based milestone payments totalling $800 million. 
 
 
   Efimosfermin is a novel, once-monthly fibroblast growth factor 21 
(FGF21) analog therapeutic in clinical development for the treatment of 
metabolic dysfunction-associated steatohepatitis (MASH), including 
cirrhosis, and future development in alcohol-related liver disease $(ALD.AU)$, 
both forms of SLD. Given efimosfermin's direct antifibrotic mechanism of 
action and GSK's data-driven insights from work in human genetics and 
disease phenotyping, it has potential to address more advanced stages of 
SLD and opportunity in combination with GSK'990, a siRNA therapeutic in 
development for other subsets of patients with SLD. 
 
 
   The acquisition of efimosfermin is highly aligned to GSK's R&D focus on 
science related to the immune system and is further evidence of the 
company's intent to build on its deep understanding of fibrosis and 
auto-inflammation to develop precision interventions that stop and 
reverse disease progression. 
 
 
   SLD represents an area of significant unmet medical need affecting 
approximately 5% of the global population with limited therapeutic 
options for patients.(1) SLD, including MASH and ALD, is characterised 
by the accumulation of fat in the liver (steatosis), with associated 
inflammation and fibrosis. ALD affects about 26 million patients 
globally, and together with MASH, is the leading cause of liver 
transplant in the US, representing a significant burden and cost on 
healthcare utilisation.(1,3) Substantial and disproportionate costs are 
associated with end-stage liver disease. Interventions that reduce 
moderate-to-advanced fibrosis to prevent progression of cirrhosis, liver 
cancer, hospitalisations and transplant could save the US healthcare 
system between $40 - 100 billion over the next two decades.(4) 
 
 
   Recent data from a phase II trial of efimosfermin, designed to assess 
the efficacy and safety of a monthly subcutaneous dose in participants 
with biopsy-confirmed moderate-to-advanced (F2 or F3) MASH, showed that 
efimosfermin rapidly and significantly reversed liver fibrosis and 
stopped its progression, with a manageable tolerability profile. These 
data suggest potentially greater fibrosis improvement compared to that 
seen with other therapeutic approaches and with benefit expected 
independent of background glucagon-like peptide-1 (GLP-1) therapy. In 
addition, efimosfermin could offer triglyceride reduction and improved 
glycaemic control, important considerations for MASH patients who 
frequently face cardiometabolic co-morbidities. Efimosfermin's unique 
properties, including low immunogenicity and an extended half-life, also 
offer the potential for a monthly dosing regimen and improved patient 
convenience. Full data from the trial was presented at the American 
Association for the Study of Liver Diseases (AASLD) Meeting in November 
2024.(5) 
 
 
   Tony Wood, Chief Scientific Officer, GSK said: "The FGF21 class has 
shown some of the most exciting data in MASH including first-in-disease 
evidence of cirrhosis reversal, and efimosfermin has the potential to 
define a new standard-of-care with its monthly dosing and tolerability 
profile. Efimosfermin will significantly expand our hepatology pipeline 
and provide us the opportunity to develop a new potential best-in-class 
medicine with first launch expected in 2029. It complements GSK'990, 
also in development for ALD and MASH, offering GSK options to develop 
both monotherapy and potential combinations to improve patient 
outcomes." 
 
 
   Elias Zerhouni MD, Chair of the Board, Boston Pharmaceuticals, said: "I 
am very proud of today's agreement with GSK, a company I know and admire, 
and of the outstanding work of the Boston Pharmaceuticals team led by 
Sophie Kornowski. Notably, this would not have been possible without the 
impressive, sustained and long-term strategic commitment to leading edge 
science and biotechnology ventures of the Bertarelli family, which led 
to the development of our Efimosfermin alfa as a potential best-in-class 
therapy in its therapeutic field. We are delighted that GSK, a global 
leader, recognized Efimosfermin's potential to address a growing global 
public health concern and unmet medical need. Together, we look forward 
to Efimosfermin alfa's ongoing journey to become a best-in-class 
treatment for patients with SLD." 
 
 

Sophie Kornowski Pharm D, Chief Executive Officer, Boston Pharmaceuticals said: "Today marks a pivotal moment for Boston Pharmaceuticals and Efimosfermin alfa, as we begin a new chapter with GSK, a global organization with proven expertise in liver disease, and a shared commitment to patients. Our accomplishments were made possible thanks to the dedicated Boston Pharmaceuticals team, who focused on our mission to develop Efimosfermin with a great sense of urgency. I am especially grateful to Ernesto Bertarelli for his unflinching support and the commitment of his expertise over the last few years."

 
 
   The addition of efimosfermin further strengthens GSK's hepatology 
pipeline of specialty medicines aimed at addressing both viral (chronic 
hepatitis B) and steatotic (SLD) drivers of fibrotic liver diseases. 
 
 
   Financial considerations 
 
 
   Under the terms of the agreement, GSK will acquire BP Asset IX, Inc., a 
subsidiary of Boston Pharmaceuticals, to access efimosfermin. GSK will 
pay up to $2 billion of total cash consideration, comprising an upfront 
payment of $1.2 billion and up to $800 million in success-based 
milestone payments. GSK will also be responsible for success-based 
milestone payments as well as tiered royalties for efimosfermin owed to 
Novartis Pharma AG. 
 
 
   GSK will account for the transaction as a business combination. This 
transaction is subject to customary conditions, including applicable 
regulatory agency clearances under the Hart-Scott-Rodino Act in the US. 
 
 
   For GSK, Evercore Partners International LLP is acting as exclusive 
financial advisor and Cleary Gottlieb Steen & Hamilton LLP as legal 
counsel. 
 
 
   For Boston Pharmaceuticals, Centerview Partners LLC is acting as 
exclusive financial advisor and Sullivan & Cromwell LLP as legal 
counsel. 
 
 
   About efimosfermin alfa 
 
 
   Efimosfermin is an investigational, once-monthly subcutaneous injection 
of a long-acting variant of FGF21 that is designed to regulate key 
metabolic pathways to decrease liver fat, ameliorate liver inflammation, 
and reverse liver fibrosis in patients with MASH. Efimosfermin is 
currently in trials for moderate to advanced fibrosis, including 
cirrhosis and is not available for prescription anywhere in the world. 
 
 
   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. Boston 
Pharmaceuticals is a portfolio company of B-Flexion, a private, 
entrepreneurial investment firm which manages the combined funds and 
investments associated with the Bertarelli family and also partners with 
sophisticated capital to meet the shared goal of delivering exceptional 
value over the generations, while also contributing positively to 
society. 
 
 
   About GSK 
 
 
   GSK is a global biopharma company with a purpose to unite science, 
technology, and talent to get ahead of disease together. Find out more 
at gsk.com. 
 
 
   Cautionary statement regarding forward-looking statements 
 
 
   GSK cautions investors that any forward-looking statements or 
projections made by GSK, including those made in this announcement, are 
subject to risks and uncertainties that may cause actual results to 
differ materially from those projected. Such factors include, but are 
not limited to, those described in the "Risk Factors" section in GSK's 
Annual Report on Form 20-F for 2024, and GSK's Q1 Results for 2025. 
 
   Registered in England & Wales: 
 
 
   No. 3888792 
 
   Registered Office: 
 
   79 New Oxford Street 
 
   London 
 
 
   WC1A 1DG 
 
   References 
 
   1 Global Burden of Disease Study 2017 Cirrhosis collaborators. 2020 
 
   2 Allen et al. Postgraduate Medicine. 2024, Vol 136, No. 3, 229--245. 
 
   3 Younossi et al. Hepatol Commun. 2023 Dec 22;8(1):e0352 
 
   4 Wallace, Carolyn et al. Journal of Hepatology, Volume 0, Issue 0 
 
 
   5 Hepatology (2004) Late-Breaking Abstract Supplement p28-30 
TLM2024LBA_20241115A.pdf 
 
 
 

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