London biotech Oyster Therapeutics, previously known as Kesmalea Therapeutics, has closed a $60m Series A-2 led by 4BIO Capital, with Eli Lilly among four new investors. The round follows £30m raised across a 2022 Series A and a 2023 top-up, most of it from Syncona.
Oyster is developing small-molecule targeted protein degraders for diseases of the central nervous system, starting with tau-driven conditions such as Alzheimer's. The company announced the financing and its change of name on Tuesday.
Targeted protein degradation turns the cell's own disposal system against disease-causing proteins. Most degraders in development are large bifunctional molecules that struggle to cross the blood-brain barrier, which has limited their reach in neurology.
Oyster's SELFTAC platform addresses that with a reversible linker. The drug enters as two smaller molecules that can pass into the brain, then assembles into a working degrader. Its lead programme is an oral degrader designed to clear the abnormal forms of tau while leaving healthy tau in place.
The round was led by London-based specialist investor 4BIO Capital. Eli Lilly, CE Ventures, Actium Group and TOHO Ventures, which is managed by Global Brain, came in as new investors, while existing backers Syncona, Oxford Science Enterprises, Mission BioCapital and MGB Ventures followed on. The valuation and the size of individual cheques were not disclosed.
The A-2 label reflects the company's funding history. Syncona led a £25m Series A in 2022, committing £20m alongside Oxford Science Enterprises, and put up £4m of a further £5m raised in 2023, according to its portfolio disclosures. That made Syncona the source of £24m of the £30m raised in those two rounds, or 80%.
The new financing widens that shareholder base. Lilly's participation puts a drugmaker that already markets an Alzheimer's treatment on the register as Oyster moves towards its first clinical studies.
"This financing accelerates our progress towards the clinic," said chief executive Rob Johnson, who described the goal as building a leading neuroscience degrader company. Owen Smith, a partner at 4BIO Capital, said that "much remains to be shown in the clinic".
Proceeds will take the tau degrader into clinical development and fund further work on the SELFTAC platform, which the company says supports faster, cheaper hit screening than conventional degrader design.
Oyster has also signed a sponsored research agreement with Massachusetts General Hospital. The deal gives it access to patient-derived neuronal cell lines and methods for generating and detecting oligomeric tau, the form widely regarded as most toxic to neurons, under the supervision of Dr Catarina Silva of the Mass General Brigham Neuroscience Institute.
The deal follows two seed rounds 4BIO led in September: €40m for Aptadir Therapeutics and $33m for Cloverleaf Bio.
Original source: Business Wire — https://www.businesswire.com/news/home/20261109552229/en/Kesmalea-Therapeutics-Announces-%2460-Million-Series-A-Financing-to-Advance-Next-Generation-Targeted-Protein-Degraders-for-Alzheimers-and-Other-Neurodegenerative-Diseases-and-Rebrands-as-Oyster-Therapeutics
