4BIO Capital leads $60M Series A financing of Oyster Therapeutics (formerly Kesmalea Therapeutics) to advance next-generation targeted protein degraders for Alzheimer’s and other neurodegenerative diseases

• Proceeds to advance oral, brain-penetrant tau degrader into clinical development as a novel treatment for tau-driven diseases like Alzheimer’s
• Series A led by 4BIO Capital with participation from new investors, including Eli Lilly and Company, alongside existing investors
• Financing supports continued development of proprietary SELFTAC® platform for generating small bifunctional targeted protein degraders with enhanced drug-like properties
• Establishes collaboration with leading tau researcher Dr. Catarina Silva at Massachusetts General Hospital

London, United Kingdom, 10 November 2026 – 4BIO Capital, a specialist biotech venture firm transforming innovative technologies into breakthrough precision therapies, today announces that it has led a $60M Series A financing in Oyster Therapeutics (Oyster), previously known as Kesmalea Therapeutics, a pharmaceutical company developing next-generation targeted protein degraders with an initial focus on tau-driven diseases like Alzheimer’s.

The funds will be used to advance Oyster’s oral, brain-penetrant tau degrader into clinical development and to support continued development of its proprietary SELFTAC® platform for generating small, targeted protein degraders with enhanced drug-like properties.

Alongside the financing, the Company is also announcing its rebranding to Oyster Therapeutics. Oyster’s rebranding reflects its new phase of development and a strong ambition to turn deep scientific insight into medicines that change people’s lives. Just as an oyster builds a rare pearl around a singular focus, Oyster Therapeutics builds on deep scientific insight to shape valuable, next-generation medicines.

Owen Smith, Partner at 4BIO Capital, said: “Alzheimer’s and other tau-driven diseases remain among the hardest problems in medicine and Oyster is taking them on with a clear scientific rationale. Targeted protein degradation has real promise and SELFTAC® is an ambitious effort to solve its critical technical challenges so that degraders can reach the brain. Alongside it, Oyster’s lead program aims to remove disease-associated tau while preserving healthy tau. Much remains to be shown in the clinic, but this is where science meets unmet medical need. At 4BIO Capital we back teams like this with conviction before every question is answered, helping to build companies with the potential to make a real difference in medicine.”

Targeted protein degradation (TPD) is a major area of therapeutic development that involves guiding the natural ‘waste removal’ machinery of the cell to target proteins. Oyster is focused on bringing the potential of TPD to the central nervous system (CNS). Devastating neurodegenerative diseases such as Alzheimer’s and Parkinson’s involve proteins that appear well-suited to clearance via TPD. However, the dominant approach to TPD involves larger molecules that have difficulty penetrating the CNS.

Rob Johnson, Chief Executive Officer of Oyster Therapeutics, added: “This financing accelerates our progress towards the clinic and enables us to validate a new approach to targeted protein degradation, or TPD, that solves some of its major limitations through the use of smaller molecules. Millions of people living with diseases such as Alzheimer’s need new approaches such as TPD to address the root cause of disease. At Oyster we are defining next-generation TPD medicines that can reliably reach the brain and are orally available to better meet the needs of global patient populations. We welcome this support from both new and existing investors for our vision of building the world’s leading neuroscience TPD company.”

Oyster’s most advanced program is a small, oral degrader targeting the protein tau, one of the highest-priority targets in neurodegenerative disease. Abnormal tau buildup is the main feature of diseases called ‘tauopathies’, the best known of which is Alzheimer’s. Oyster’s tau degrader is designed to be small enough to enter the CNS and selectively remove pathological forms of tau while preserving healthy tau. An oral formulation is the preferred approach to diseases affecting large populations such as Alzheimer’s, due to the convenience of oral administration, room-temperature storage and lower-cost manufacturing.

In addition to 4BIO Capital, the round attracted participation from new investors including Eli Lilly and Company, Actium Group, CE Ventures and TOHO Ventures (managed by Global Brain). Existing investors Syncona, Oxford Science Enterprises (OSE), Mission BioCapital and MGB Ventures also participated.

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About 4BIO Capital

4BIO Capital is a global specialist biotech venture firm investing in breakthrough technologies that solve critical healthcare challenges. 4BIO partners with visionary biotech founders, investing with conviction and serving as a therapeutic navigator to guide the transformation of scientific innovation into life-changing therapies. The 4BIO team are specialists with deep scientific expertise and proven commercial track records, strategically matched to portfolio companies that align with their specific areas of knowledge. For more information, connect with us on LinkedIn and X @4biocapital and visit www.4biocapital.com.

About Oyster Therapeutics

Oyster is a pharmaceutical company developing next-generation targeted protein degraders with an initial focus on neurodegenerative diseases such as Alzheimer’s. Oyster’s proprietary SELFTAC® platform is designed to solve the fundamental size limitations of many conventional degraders by transforming them into small molecules. This breakthrough is intended to enable routine oral bioavailability and central nervous system (CNS) penetration, significantly expanding the therapeutic potential of the class. Oyster is based in London, UK. For more information, visit www.oyster-tx.com.

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