Eisai Inc v. CrySTAl PharmaceuTical SuZhou Co Ltd

1. Case Identification

• Patent #: 10,759,779
• Filed: February 3, 2021
• Petitioner(s): Eisai Inc.
• Patent Owner(s): Crystal Pharmaceutical (Suzhou) Co., Ltd.
• Challenged Claims: 1-4, 7, and 8

2. Patent Overview

• Title: Crystalline Form of Lemborexant
• Brief Description: The ’779 patent is directed to a specific crystalline form of lemborexant, designated "crystalline form CS2," which is a compound used for treating insomnia. The claims define this crystalline form by its characteristic peaks in an X-ray powder diffraction (XRPD) pattern.

3. Grounds for Unpatentability

Ground 1: Inherent Anticipation and Obviousness of Claims 1-4 over the ’109 patent

• Prior Art Relied Upon: Eisai’s ’109 patent (Patent 9,416,109).
• Core Argument for this Ground: Petitioner argued that claims 1-4 are unpatentable under 35 U.S.C. §102 because the claimed subject matter is inherently disclosed in the ’109 patent. Alternatively, Petitioner argued the claims are obvious under §103. The core of the argument is that the claimed "crystalline form CS2" is the natural and inevitable result of following the synthesis and purification procedures for lemborexant explicitly taught in the prior art.
  • Prior Art Mapping: The ’109 patent discloses two distinct procedures in its “Example G” for preparing lemborexant. Petitioner contended that the purification step in both procedures—which involves dissolving lemborexant in a solvent and precipitating it with an anti-solvent—is a crystallization process that necessarily produces the claimed CS2 form.
    • The first procedure involves purification by dissolving lemborexant in ethyl acetate (solvent) and slowly adding n-heptane (anti-solvent) to cause precipitation.
    • The alternate procedure is nearly identical, also using ethyl acetate and n-heptane for purification.
    • Petitioner supported this inherent anticipation argument with two sets of extrinsic evidence: (1) new XRPD testing conducted for the petition by reproducing both Example G procedures, which confirmed the resulting product matched the XRPD peaks of the claimed CS2 form; and (2) internal Eisai records from as early as 2010 showing that manufacturing lemborexant using procedures consistent with Example G consistently produced the same CS2 crystalline form.
    • For process claim 4, Petitioner mapped the claimed steps of dissolving, adding an anti-solvent, and crystallizing directly to the purification steps detailed in both procedures of Example G in the ’109 patent.
  • Motivation to Combine (for §103 grounds): As an alternative to anticipation, Petitioner argued that Example G of the ’109 patent would have rendered claims 1-4 obvious. A person of ordinary skill in the art (POSA) would have been motivated to practice the detailed, efficient, and cost-effective procedures of the prior art to make lemborexant.
  • Expectation of Success (for §103 grounds): Because the ’109 patent provides precise and detailed steps for preparing lemborexant using routine techniques, a POSA would have had a reasonable expectation of success in producing lemborexant, which would inherently possess the claimed crystalline structure.

Ground 2: Obviousness of Claims 7 and 8 over the ’109 patent and the ’995 publication

• Prior Art Relied Upon: Eisai’s ’109 patent (Patent 9,416,109) and Eisai’s ’995 publication (WO 2016/063995).
• Core Argument for this Ground: Petitioner argued that combining the teachings of the ’109 patent and the ’995 publication renders the pharmaceutical composition (claim 7) and method of treatment (claim 8) claims obvious under §103.
  • Prior Art Mapping: The ’109 patent taught a POSA how to make the claimed crystalline form of lemborexant (CS2), as established in Ground 1. The ’995 publication explicitly disclosed using lemborexant to treat insomnia. It taught administering a "therapeutically effective amount" of lemborexant in a pharmaceutical composition with acceptable carriers, diluents, or excipients. The publication also provided results from clinical studies and disclosed effective daily dosage ranges of approximately 1 mg to 15 mg.
  • Motivation to Combine: A POSA would have been motivated to combine these references to create a treatment for insomnia. The ’109 patent provided an effective method for making the active ingredient (lemborexant in its stable crystalline form), and the ’995 publication provided the explicit blueprint for its use: formulating it into a pharmaceutical composition and administering it to patients to treat insomnia. The goal of treating insomnia was already established in the art.
  • Expectation of Success: The ’995 publication’s disclosure of favorable results from clinical studies demonstrating lemborexant’s efficacy in treating insomnia would have provided a POSA with a strong and reasonable expectation of success in creating the claimed pharmaceutical composition and achieving the claimed therapeutic effect.

4. Arguments Regarding Discretionary Denial

• Petitioner argued that the Board should not exercise its discretion to deny institution under §325(d) because the petition raised new art, evidence, and arguments not previously considered by the USPTO.
• The petition contended that the Examiner's review during the expedited prosecution was minimal. The Chinese counterpart to the ’109 patent was cited in an International Search Report, but the Examiner made only a conclusory statement of allowance without any substantive analysis or explanation of how the reference was distinguished. There were no office actions issued.
• Petitioner asserted that its inherent anticipation argument, supported by new XRPD testing evidence, was never before the Examiner. This new evidence demonstrated that the Examiner materially erred by allowing claims to a crystalline form that was the natural result of a prior art process.
• Furthermore, the obviousness ground combining the ’109 patent with the ’995 publication was never considered by the Examiner. The ’995 publication, with its critical disclosures of clinical trial data and therapeutic use, was not evaluated at all.

5. Relief Requested

• Petitioner requested institution of Post-Grant Review and cancellation of claims 1-4, 7, and 8 of the ’779 patent as unpatentable.