CAFC Kills Cancer Treatment Patent Claims Due to Lack of Written Description, Enablement

Today, the U.S. Court of Appeals for the Federal Circuit issued a precedential ruling in Seagen Inc. v. Daiichi Sankyo Co., Ltd., reversing the Eastern District of Texas’ denial of judgment as a matter of law (JMOL) that Seagen’s patent claims lacked both written description support and enablement. Applying precedent from both the U.S. Supreme Court and the Federal Circuit’s predecessor, the Court of Customs and Patent Appeals (CCPA), the appellate court found that Seagen’s disclosure on the original patent application claiming its antibody-drug conjugate cancer treatment was too broad to give the later-filed patent-at-issue the original application’s priority date, and also required undue experimentation to discover effective drug combinations.

In July 2019, Seagen filed a continuation patent application resulting in the issuance of U.S. Patent No. 10808039, Monomethylvaline Compounds Capable of Conjugation to Ligands. The parent patent application, filed in 2004, claims a cancer treatment with a peptide subcomponent of a protein linking an antibody with a cytotoxic drug. The drug moiety containing the cytotoxic cell-killing drug is released after the cancer cell is targeted by the antibody, improving selectivity in treatment. The continuation application resulting in the ‘039 patent, which encompasses AstraZeneca’s Enhertu cancer treatment, explicitly discloses a “Gly/Phe-only tetrapeptide,” a four-amino-acid-long unit where each amino acid is either glycine or phenylalanine, a protein not disclosed in the 2004 application.

Tetrapeptide Disclosure in 2004 Application Too Broad to Support ‘039 Patent’s Subgenus

At trial in Eastern Texas, the parties disputed whether the ‘039 patent was entitled to the priority date of the 2004 patent application, which would result in Enhertu infringing the asserted patent claims, or if Enhertu was instead invalidating prior art made publicly known in December 2015. Following the jury’s willful infringement verdict, which awarded an upfront royalty of $41,820,000 and an 8% running royalty, Daiichi Sankyo filed for JMOL, arguing the written description and enablement issues under 35 U.S.C. § 112 discussed in today’s CAFC ruling.

The Federal Circuit’s 1997 ruling in Lockwood v. American Airlines establishes that, for a later-filed patent “to gain the benefit” of an earlier application’s priority date, that application must disclose the invention “in the manner provided by [Section 112].” On appeal, Daiichi Sankyo argued that the 2004 application did not sufficiently disclose the Gly/Phe-only tetrapeptide corresponding to claim 1’s recitation of a “–W_W–unit” serving as the linker protein.

As described in the 2004 patent application, the Federal Circuit noted that the W_W unit, “when present,” could include anywhere from two to twelve amino acids. When considering the different amino acids that could determine the identity of the W_w unit and their isomers, “just with respect to tetrapeptides, over 47 million different tetrapeptide units” are encompassed, a point confirmed by expert witnesses for both sides. The appellate court acknowledged its own case law consistently finds that the disclosure of a broad genus does not satisfy the written description requirement for claims directed to a particular subgenus.

Reviewing cases by its predecessor court, the Federal Circuit found instructive the CCPA’s 1967 ruling in In re Ruschig, which involved a claim reciting a single compound from the half-million possible compounds disclosed by the specification. In Ruschig, the CCPA required a “reasonably specific supporting disclosure” showing possession of the specific compound. In Seagen’s case, “although the 81 claimed Gly/Phe-tetrapeptides are ‘encompassed’ within those 47 million,…they are merely an infinitesimal
fraction of those peptide units generally included” in the patent’s specification, said the CAFC. As such, the ‘039 patent could not claim priority to the earlier application, leading the Federal Circuit to invalidate its claims as anticipated by Enhertu.

Testimony on ‘Straightforward Leap’ by Skilled Artisan Dooms ‘Blaze Marks’ Theory

The Federal Circuit dismissed arguments raised by Seagen from the CCPA’s 1977 ruling in In re Driscoll, in which the CCPA found written description support for a specific drug moiety in a later-filed patent among the 14 moieties disclosed in an earlier application. However, not only were Seagen’s “effectively countless peptide units… a far cry from [Driscoll’s] 14 moieties,” the claimed Gly/Phe-tetrapeptide subgenus is never discussed by the 2004 patent application and thus not “clearly discernible in the generalized formula.” This was supported by testimony from inventors listed on the ‘039 patent application, who admitted to first observing the claimed tetrapeptides in Enhertu.

Seagen also argued that the 2004 application contained “blaze marks” directing skilled artisans to the claimed Gly/Phe-tetrapeptide subgenus. At trial, Seagen’s expert on this issue claimed that a skilled artisan would find it a “straightforward leap” to change the glycine-phenylalanine-leucine-glyice (GFLG) exemplary tetrapeptide from the 2004 application to the Gly/Phe-tetrapeptide claimed by the ‘039 patent. As the appellate court noted, “that testimony dooms Seagen’s case” as it admits that a skilled artisan would not understand the inventors of the 2004 application to be in possession of the ‘039 patent’s tetrapeptides, providing insufficient evidence for a reasonable jury to find written description support. “In sum, the 2004 application’s broad disclosure of effectively countless options for the peptide unit fails to show the subgenus of Gly/Phe-only tetrapeptides claimed in the ’039 patent,” said the CAFC.

The Federal Circuit also ruled that no reasonable jury could find that the ‘039 patent enabled a skilled artisan to make and use the full scope of the claimed invention. The appellate court analogized to the U.S. Supreme Court’s ruling in Amgen v. Sanofi (2023), in which the Court found that Amgen’s entire genus of antibodies for a claimed cholesterol treatment was not enabled by the specification’s disclosure of two methods for testing if particular antibodies performed recited functions. Due to the unpredictability of antibody science, the Court found that without disclosing “a quality common to every functional embodiment,” Amgen’s patent required trial-and-error discovery by skilled artisans. Here, due to similar unpredictability in intracellular cleaving of drug moieties, the Federal Circuit found that “a skilled artisan would be left to perform far-ranging ‘trial-and-error discovery’ to make and use the [antibody-drug conjugates] within the scope of the ’039 patent.”

Finding the remaining arguments unpersuasive, the CAFC concluded that the ‘039 patent is invalid for failing to meet the written description and enablement requirements. The appellate court vacated the jury’s willful infringement and damages verdict.

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Author: almoond