Seagen patent in Daiichi Sankyo ADC dispute nixed by USPTO

There has been another twist in the road for the ongoing legal battle between Seagen and Daiichi Sankyo over patent rights for antibody-drug conjugate (ADC) Enhertu.

The US Patent and Trademark Office (USPTO) has delivered a final decision invalidating a Seagen patent – No. 10,808,039 – which covers auristatin compounds coupled to an antibody via a linker molecule and had been challenged by Daiichi Sankyo.

The Japanese drugmaker had filed a post-grant review proceeding (PGR) in 2020 seeking the invalidation of the ‘039 patent, which is the sole patent involved in the infringement litigation between the parties in the US District Court for the Eastern District of Texas.

Daiichi Sankyo has been ordered to pay an 8% royalty rate on sales of AstraZeneca-partnered breast and gastric cancer therapy Enhertu (trastuzumab deruxtecan) after Seagen won a lawsuit claiming that the ADC infringed the patent.

An initial judgment by the court on 1st April 2022 held that Seagen was in line for damages based on past royalties that should have been paid on Enhertu sales in the US prior to that date. Then, last October, the court decided that Daiichi Sankyo should also pay royalties on Enhertu sales until 4th November 2024, when the ‘039 patent expires.

Seagen – which is heading for a $43 billion takeover by Pfizer – had also sought to increase damage award on the grounds that Daiichi Sankyo’s infringement of the patent was ‘wilful’, but that was denied.

Daiichi Sankyo launched an appeal against those decisions, which is now pending in the US Court of Appeals for the Federal Circuit, and the invalidation of the ‘039 patent bolsters that appeal significantly.

“We are pleased that the USPTO invalidated all challenged claims of the ‘039 patent,” said Naoto Tsukaguchi, Daiichi Sankyo’s corporate officer and general counsel in a statement.

First cleared as a later-line therapy for HER2-positive breast cancer in 2019, Enhertu has expanded into earlier use, as well as HER2-positive gastric cancer and non-small cell lung cancer (NSCLC), and also HER2-low breast cancer that could drive sales to more than $6 billion in 2028, according to Evaluate. Sales in fiscal 2022/23 were almost $1.2 billion, around half of which was booked by AZ.

AZ paid $1.35 billion upfront to license Enhertu in 2019 in a deal that could be worth up to $6.9 billion.