Cancer Drug Patent Claims Upheld by CAFC

The U.S. Court of Appeals for the Federal Circuit (CAFC) issued a precedential decision on Monday in Exelixis, Inc. v. MSN Laboratories Private Ltd., affirming a district court finding that certain patent claims covering a cancer treatment satisfy the written description requirement under 35 U.S.C. Section 112(a). The court also granted a motion to dismiss a separate portion of the appeal as moot and vacated the underlying district court judgment on that issue.

Exelixis holds the New Drug Application for Cabometyx, a tablet containing the active pharmaceutical ingredient cabozantinib (L)-malate, that is indicated for the treatment of kidney, liver, and differentiated thyroid cancers. A 2015 submission to the Food and Drug Administration reported that cabozantinib (L)-malate exists in two closely related crystalline forms, designated N-1 and N-2, and that no other crystalline forms had been identified. Exelixis later obtained patents on those two forms before filing the patents at issue, which is referred to as the Malate Salt Patents. U.S. Patent Nos. 11,091,439, 11,091,440, and 11,098,015 share a specification and separately claim crystalline cabozantinib (L)-malate salts, pharmaceutical formulations containing those salts, and methods of treating cancer with them. Additionally, a fourth patent, U.S. Patent No. 11,298,349, covers compositions that are essentially free of a genotoxic impurity generated during the compound’s synthesis.

MSN Laboratories Private Limited and MSN Pharmaceuticals, Inc. submitted an Abbreviated New Drug Application seeking approval for generic cabozantinib (L)-malate tablets, using a different crystalline form on which MSN separately holds its own patent. Exelixis filed two lawsuits against MSN in the U.S. District Court for the District of Delaware, later consolidated, alleging infringement of the Malate Salt Patents and the ‘349 patent. MSN conceded infringement of the Malate Salt Patents but challenged their written description, while separately contesting infringement and validity of claim 3 of the ‘349 patent.

After a bench trial, the district court found written description support for the Malate Salt Patents claims, applying the framework set out in Ariad Pharmaceuticals, Inc. v. Eli Lilly & Co. Under that framework, a specification adequately supports a claimed genus by disclosing either a representative number of species within the genus or structural features common to genus members sufficient to allow a skilled artisan to visualize or recognize them. The district court found that the specification’s disclosure of the chemical name, formula, and crystalline structure of cabozantinib (L)-malate satisfied this standard, analogizing the case to GlaxoSmithKline LLC v. Banner Pharmacaps, Inc. On the ‘349 patent, the district court found no infringement and further found that MSN had not proven claim 3 invalid, since MSN failed to establish that a prior art reference inherently disclosed a composition essentially free of the relevant impurity.

MSN appealed the written description finding as to claim 4 of the ‘439 patent, claim 3 of the ‘440 patent, and claim 2 of the ‘015 patent. Circuit Judge Stoll, writing for the court, rejected MSN’s argument that the district court had improperly relied on cursory disclosures that failed to identify structural features distinguishing the claimed genus. The court found no clear error in treating the disclosure of the chemical name, formula, and crystalline structure of cabozantinib (L)-malate salt as an identification of structural features shared by genus members, noting that the claims are no broader than the written description since they require a crystalline structure. The court reaffirmed that under Ariad, “adequate written description requires a precise definition, such as by structure, formula, chemical name, physical properties, or other properties.”

The court also found MSN’s reliance on the differing physical properties of the N-1 and N-2 polymorphs unpersuasive, since MSN did not explain how those unclaimed properties undermined the district court’s structural analysis, distinguishing the case from AbbVie Deutschland GmbH & Co. v. Janssen Biotech, Inc. The court also rejected MSN’s argument that the district court applied a heightened standard to functional claims. However, it found that the district court merely recognized that functional claims can present additional written description challenges without applying a different legal standard to the structural claims at issue.

Furthermore, MSN had initially challenged the district court’s finding that claim 3 of the ‘349 patent was not proven invalid for lack of inherency. After Exelixis dismissed its own cross-appeal challenging the noninfringement finding on that same claim, the CAFC required MSN and Exelixis to address whether MSN retained standing to pursue the invalidity issue. MSN then moved to dismiss that portion of its appeal as moot and to vacate the underlying judgment.

The court also cited Cardinal Chemical Co. v. Morton International, Inc. in finding that Exelixis’s asserted interest in preserving the inherency ruling for use in separate litigation involving a related patent presented only speculative collateral consequences insufficient to confer standing. The court applied vacatur principles from United States v. Munsingwear, Inc. and U.S. Bancorp Mortgage Co. v. Bonner Mall Partnership, explaining that vacatur is appropriate when mootness results from the unilateral action of the litigant that prevailed below, since “a party who seeks review of the merits of an adverse ruling but is frustrated by the vagaries of circumstance ought not in fairness be forced to acquiesce in the judgment.”

Ultimately, the CAFC affirmed the district court’s finding of written description support under Section 112(a) for the asserted claims of the ‘439, ‘440, and ‘015 patents. The court also granted MSN’s motion to dismiss its appeal as to claim 3 of the ‘349 patent and vacated the district court’s judgment of nonobviousness on that claim.

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