Daiichi Sankyo wins round in Enhertu patent dispute

Daiichi Sankyo has succeeded in a bid to convince the US Patent and Trademark Office (PTO) to take another look at a patent held by Seagen that was previously deemed to have been infringed by its breast cancer drug Enhertu.

The PTO has said it will conduct a post-grant review of whether claims in Seagen’s 10,808,039 patient – which covers antibody-drug conjugates (ADCs) that include auristatin compounds coupled to an antibody via a linker molecule – are valid.

In a nutshell, Daiichi Sankyo’s position is that the ‘039 patent should never have been granted, but until now its attempts to get the PTO to conclude a post-grant review (PGR) of its patentability, first started in 2020, have been thwarted. Last July, PTO advisors granted Seagen’s request to shelve the review.

That has now been reversed, according to Daiichi Sankyo, which in the interim lost a patent infringement suit claiming that AstraZeneca-partnered Enhertu (trastuzumab deruxtecan) infringed the ‘039 patent.

The jury in the case – heard in a district court in Texas – awarded $41.8 million in damages to Seagen last year, based on past royalties that should have been paid on Enhertu sales in the US to date, but declined a request by Seagen to increase the amount, despite concluding that the infringement had been ‘wilful’.

Seagen had also asked the court for royalties on future sales of Enhertu, until the expiry of the '039 patent in November 2024, but so far a decision on that has not been taken.

That could be a sizeable windfall for the Seattle based biotech, as Enhertu is on an upwards growth path, fuelled by a string of new regulatory approvals.

First cleared as a later-line therapy for HER2-positive breast cancer in 2019, Enhertu has steadily seen its label extended to include earlier use, as well as HER2-positive gastric cancer and non-small cell lung cancer (NSCLC).

Last year, it also scored approvals in HER2-low breast cancer – representing a much larger patient population, which some analysts have suggested could be worth $3 billion in sales for the drug on its own. Enhertu had sales of $1.17 billion last year, excluding Japan – more than twice its 2021 revenues – with AZ pocketing $602 million of that total.

There’s no guarantee that the PGR will rule in Daiichi Sankyo’s favour, but the decision keeps its defence of Enhertu alive for the time being.

“We are very pleased that the PGR will be reinstituted, given the PTO’s determination that our petition presented compelling evidence of unpatentability of the ’039 patent,” commented Naoto Tsukaguchi, Daiichi Sankyo’s general counsel.