Daiichi sues Seattle Genetics over tech used in high-profile ADC

Office building showing Daiichi Sankyo logo
Daiichi Sankyo's legal action against Seattle Genetics affects the antibody-drug conjugate covered by Daiichi's $6.9B deal with AstraZeneca. (Daiichi Sankyo)

Daiichi Sankyo has started legal action against Seattle Genetics. The case centers on linker technology used in antibody-drug conjugates (ADCs) including Daiichi’s AstraZeneca-partnered DS-8201.

In 2008, Seattle Genetics granted Daiichi a license to use its cytotoxin and linker technology in an ADC against a single antigen. The agreement ended in 2015, but Daiichi retained an interest in ADCs, going on to take the HER2-targeting DS-8201—also known as [fam-] trastuzumab deruxtecan—deep enough into the clinic to land a $1.35 billion upfront payment from AstraZeneca. 

Seattle Genetics thinks it is the rightful owner of ADC technology used in DS-8201 and other Daiichi candidates. Daiichi disagrees. The disagreement became public this week when Daiichi revealed it has filed a declaratory judgement action in the District Court of Delaware.


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Daiichi took the action in response to communications from Seattle Genetics, which was using the dispute resolution process baked into the 2008 deal to secure rights to its former partner’s ADCs. Rather than carry on with that process, Daiichi has decided to get the courts involved, earning itself a chiding from Seattle Genetics in the process. 

“By filing this lawsuit, Daiichi Sankyo has circumvented the process underway between the parties pursuant to these provisions,” Seattle Genetics wrote in a statement responding to the legal action. 

Both parties think they are in the right. In its statement, Daiichi said Seattle Genetics’ claim to rights to its ADCs are “without merit.” In response, Seattle Genetics said ADC technology, including the all-important linker, used in DS-8201 and other Daiichi candidates are “improvements” to technology covered by the 2008 agreement, making it the rightful owner of the key intellectual property.

A lot is resting on the outcome of the dispute. DS-8201 has emerged as a key part of Daiichi’s plans, landing it a deal worth up to $6.9 billion with AstraZeneca on the strength of its potential to rack up blockbuster breast cancer sales. AstraZeneca and Daiichi hope to win FDA approval for the drug in the second quarter.

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