
Biogen and City Therapeutics are to partner for the development of new RNA interference (RNAi) therapies.
Leveraging tissue-enhanced delivery technologies, the partnership will concentrate on one target associated with central nervous system diseases, aiming to facilitate systemic administration of medicines.
City Therapeutics will utilise its RNAi engineering technologies for trigger molecule development, which will be joined with Biogen’s drug delivery technology.
Biogen will pay City Therapeutics $46m, which includes $16m upfront and $30m investment for a convertible note.
Biogen will record the upfront payment as an acquired in-process research and development (R&D) expense in the second quarter of 2025.
If the initial programme meets specific development and commercial goals, City Therapeutics could receive up to $1bn in potential milestone payments and is eligible for tiered royalties based on net sales.

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By GlobalDataBiogen will handle the investigational new drug (IND)-enabling trials, worldwide clinical development, regulatory submissions and commercialisation activities, and has the option to choose an additional target for the partnership, contingent on an extra payment and target availability.
Biogen Research head Jane Grogan stated: “This collaboration underscores Biogen’s new strategic research approach of balancing our differentiated internal capabilities with external investments in cutting-edge science.
“With this effort, we are further expanding the modalities in our R&D toolbox to potentially reach our targets of interest more precisely by adding an RNAi-based approach.”
City Therapeutics was jointly founded by RNAi scientists and executives. The company has secured $135m in funding from life sciences investors.
In April 2025, Biogen, in partnership with Eisai, secured marketing authorisation from the European Commission for Leqembi (lecanemab) for Alzheimer’s disease treatment.