The United States Court of Appeals for the Federal Circuit has overturned a lower court’s decision in a patent infringement case between Seagen Inc. and Daiichi Sankyo Company, Ltd., along with AstraZeneca Pharmaceuticals LP and AstraZeneca UK Ltd. The appeals court ruled that Seagen’s patent for a type of cancer treatment was invalid due to a lack of proper written description and enablement. This means the court found that the patent didn’t adequately describe the invention or provide enough information for others to recreate it without excessive experimentation.
The Heart of the Matter: Antibody-Drug Conjugates (ADCs)
At the center of the case is a technology called antibody-drug conjugates, or ADCs. These are essentially smart drugs designed to target and kill cancer cells while sparing healthy ones. An ADC is made up of three parts: an antibody, a toxic drug, and a “linker” protein that connects the two. The linker is crucial because it determines when and how the drug is released.
The Seagen patent, U.S. Patent 10,808,039 (the ’039 patent), covers a specific type of ADC. Specifically, the patent claims an ADC where the linker contains a “tetrapeptide” unit composed only of two amino acids: glycine and phenylalanine (a “Gly/Phe-only tetrapeptide”).
The Infringement Claim and the Jury’s Initial Verdict
Seagen sued Daiichi, claiming that Daiichi’s Enhertu®, a cancer drug, infringed on its patent. A jury in the Eastern District of Texas sided with Seagen, finding that Daiichi’s Enhertu infringed the patent and that the infringement was willful. The jury awarded Seagen over $41 million in damages.
However, Daiichi challenged the validity of Seagen’s patent, arguing that it lacked proper written description and enablement. This challenge was the focus of the appeal.
Written Description: Did the Patent Adequately Describe the Invention?
The appeals court focused heavily on whether Seagen’s original patent application (from which the ’039 patent claimed priority) adequately described the specific Gly/Phe-only tetrapeptide claimed in the later patent. The court found it did not.
To gain the benefit of an earlier filing date, a later patent must be supported by the written description provided in the original application. The court explained that the original application described a very broad range of potential peptide units. While the Gly/Phe-only tetrapeptide was *technically* included within this broad range, it was such a small fraction of the possibilities that the original application didn’t provide enough specific detail to show that the inventors actually possessed this specific invention.
The court noted that the original application described over 47 million different tetrapeptide options. The claimed Gly/Phe-only tetrapeptide was just one of the 81 possible combinations within this huge group. The court cited a previous case, *In re Ruschig*, which stated that claims to a particular species or subgenus require “reasonably specific supporting disclosure” to show that the inventor possessed the specific compound. Because the original application didn’t specifically mention or highlight the Gly/Phe-only tetrapeptide, the court decided it failed this requirement.
The court also cited testimony from the inventors, who admitted they hadn’t even conceived of a Gly/Phe-only tetrapeptide until after the public disclosure of Enhertu. This admission further supported the court’s conclusion.
Enablement: Could Others Recreate the Invention?
The court also found that the patent failed the enablement requirement. This part of the law requires that a patent specification must teach those skilled in the art how to make and use the full scope of the claimed invention without undue experimentation.
The appeals court pointed out that the ’039 patent covered ADCs containing any drug moiety (the active ingredient within the drug compound) that is designed to be cleaved inside a patient. However, the court found that the patent didn’t provide enough information about the various drug moieties to allow someone to make and use the invention without excessive trial and error.
The court referenced the Supreme Court case *Amgen v. Sanofi*, which addressed a similar issue in the context of antibodies. The Supreme Court said that if the scope of the patent covered millions of possibilities, but the specification provided limited guidance, the patent was not enabled. The appeals court reasoned that, like in *Amgen*, the Seagen patent required a significant amount of trial and error to determine whether a given ADC with a given drug moiety would meet the functional limitations described in the patent. Thus, the court decided that the patent was not enabled.
The Outcome: Patent Invalidated, Verdict Reversed
Because the appeals court found the Seagen patent invalid due to lack of written description and enablement, it reversed the lower court’s decision. This means that Daiichi and AstraZeneca did not infringe a valid patent. The court also vacated the jury’s finding of willful infringement and the damages award.