Oyster Therapeutics, formerly Kesmalea Therapeutics, has raised $60 million in a Series A financing led by 4BIO Capital, the company said in a November 10, 2026 announcement. The startup is developing oral, brain-penetrant degraders, drugs designed to mark disease-causing proteins for destruction, as a treatment for Alzheimer's disease.
Oyster has raised money before. BioPharma Dive describes the round as an extension of the company's Series A, and Fierce Biotech's funding tracker logs it as Series A-2.
Who put in the money
Both the company's announcement and a 4BIO release distributed on GlobeNewswire name 4BIO as the lead. Oyster's statement lists Actium Group, CE Ventures and TOHO Ventures among the participants. Syncona, an existing investor, refers to some of them by other names in its interim results: Actium Invest, Crescent Enterprises and Global Brain.
S&P Capital IQ, in a report published through MarketScreener on November 10, said Oyster issued convertible preferred stock, and identified MGB Ventures as Mass General Brigham Ventures, LLC. MarketScreener cautioned that it had not independently reconciled the security details with the financing documents.
Much remains unstated. None of the announcements reviewed disclosed a valuation, individual investment amounts, cash runway, tranche structure or a precise start date for first-in-human testing. A TOHO Holdings investor presentation dated November 13, 2026 lists its Oyster investment as completed in October 2026, which suggests the money moved before the public announcement.
Dealroom shows an enterprise-value range of $240 million to $360 million for the company, but without a verified transaction valuation. Readers should not take that range as the price of this round.
The science, and its limits
Degraders are usually large molecules, and size is the problem in the brain: big compounds struggle to swallow-and-survive their way through the gut and then across the blood-brain barrier. Global Brain's November 10 announcement described Oyster's answer as a reversible linker that lets a larger degrader exist as smaller components. Those pieces are meant to cross biological barriers and then assemble into an active bifunctional degrader. The aim is to keep the proven logic of conventional bifunctional degradation while improving oral delivery and penetration of the central nervous system.
The underlying platform, called SELFTAC, predates both the financing and the new name. A November 7, 2024 announcement presented it as a platform for oral, CNS-penetrant degraders, with research spanning central nervous system diseases and oncology. BioPharma Dive reported that Oyster is also exploring applications in cancer and immunology.
Still, the evidence is early. Oyster's announcement disclosed no candidate code, human dosing schedule or human efficacy data, and the research materials do not establish human safety, successful brain delivery in patients or clinical benefit.
Leadership and backers
Robert Johnson is chief executive, and Clive Dix is chairman, according to the company's website. Syncona lists 17 employees at Oyster.
"This financing accelerates our progress towards the clinic," Johnson said in the company's release.
Owen Smith, a partner at 4BIO Capital, struck a more careful note. "Much remains to be shown in the clinic," he said in the financing announcement.
Global Brain said it would work with TOHO Holdings to support Oyster's CNS programs and business development.
Syncona's own account of the company's earlier funding does not quite agree with itself. Its November 13, 2025 interim report says Kesmalea raised £20 million in 2022 and £5 million in 2023, while its updated portfolio page lists £25 million in 2022 plus £5 million in 2023. The discrepancy is small next to the new round, but it leaves the earlier totals unsettled.
A crowded field in tau
Oyster is not alone in going after tau, a protein whose abnormal buildup is associated with Alzheimer's. Arrowhead Pharmaceuticals is pursuing it by a different route. According to Arrowhead's October 14, 2026 presentation, its ARO-MAPT reduces production of the protein through MAPT RNA silencing, whereas Oyster says it will pursue selective degradation of tau already made.
Investor appetite appears strong, at least by Johnson's account. "Big pharma investors are very interested in tau," he told BioPharma Dive in a November 10 interview. He also called it "the next obesity opportunity," an analogy for experimental medicines aimed at large chronic-disease populations rather than a forecast of results.
What comes next
Investor releases, including those from CE Ventures and Global Brain, said the new money is meant to move Oyster's lead tau program toward the clinic. The company has not said when first-in-human testing will begin, and until it does, the pitch rests on promise rather than patient data.
