PTAB

IPR2022-00125

Hope Medical Enterprises Inc v. Fennec Pharmaceuticals Inc

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Key Events
Petition
petition

1. Case Identification

2. Patent Overview

  • Title: Anhydrous Sodium Thiosulfate and Formulations Thereof
  • Brief Description: The ’363 patent is directed to compositions of anhydrous sodium thiosulfate (STS), methods for synthesizing anhydrous STS, and methods for measuring its binding capacity to platinum-based chemotherapeutics like cisplatin.

3. Grounds for Unpatentability

Ground 1: Claims 1-4 are obvious over Benda.

  • Prior Art Relied Upon: Benda (a 1979 German scientific publication titled "On Polymorphism of Na₂S₂O₃").
  • Core Argument for this Ground:
    • Prior Art Mapping: Petitioner argued that Benda, a 1979 scientific article, discloses the characterization of anhydrous STS using X-ray powder diffraction (XRPD) with copper Kα radiation. Petitioner asserted that Benda's published table of XRPD peaks discloses at least 14 peaks that fall within the ±0.2 degree margin of error for the peaks recited in independent claim 1 and dependent claim 2. For claim 3, which recites thermal characteristics, Petitioner contended these are inherent properties of the same anhydrous STS disclosed by Benda. For claim 4, which recites specific purity levels, Petitioner argued that Benda's disclosure of the molecular structure of a pure STS crystal renders the claim obvious, as a POSITA would have been motivated to use known purification techniques to remove common impurities to achieve a clinically useful substance.
    • Motivation to Combine (for §103 grounds): This ground relied on a single reference. The motivation argument for claim 4 was based on achieving a clinically useful substance by removing known impurities from the STS disclosed in Benda, which was a routine objective for a POSITA.
    • Expectation of Success (for §103 grounds): A POSITA would have reasonably expected that purifying the known compound from Benda using conventional techniques would successfully reduce impurity levels.

Ground 2: Claims 5-21 are obvious over Levenson in view of Sherman and Edwards.

  • Prior Art Relied Upon: Levenson (Patent 2,763,531), Sherman (Patent 8,496,973), and Edwards (a 1985 article titled "Hydrates of Sodium Thiosulphate").
  • Core Argument for this Ground:
    • Prior Art Mapping: Petitioner alleged that the combination of these references teaches all steps of the challenged method claims for synthesizing anhydrous STS. Levenson taught reacting sodium sulfite with sulfur in the presence of a cationic surface-active agent (e.g., cetylpyridinium halides) to accelerate the reaction. Sherman taught conventional methods for crystallizing the resulting STS, including using an anti-solvent and subsequently washing and drying the product. Edwards taught that acetone is a suitable anti-solvent for precipitating STS and, critically, disclosed the final step of dehydrating STS pentahydrate using methanol to obtain the claimed anhydrous form. Together, Petitioner argued these references disclose reacting the components with a surface-active agent (Levenson), crystallizing and washing the product with acetone (Sherman and Edwards), and dehydrating it with methanol to produce the final anhydrous STS (Edwards).
    • Motivation to Combine (for §103 grounds): A POSITA would combine Levenson with Sherman's general synthesis method to improve reaction speed, a known benefit taught by Levenson. It would have been obvious to then incorporate the dehydration step from Edwards because the anhydrous form of STS was known, and a POSITA seeking to create it would have logically applied Edwards' conventional dehydration methods to the intermediate STS pentahydrate produced by the Levenson/Sherman process.
    • Expectation of Success (for §103 grounds): A POSITA would have had a high expectation of success as each step—synthesis, crystallization, and dehydration—was conventional and their combination was predictable.

Ground 3: Claims 22-27 are obvious over Elferink.

  • Prior Art Relied Upon: Elferink (a 1986 article in Clinical Chemistry titled "Interaction of cisplatin and carboplatin with sodium thiosulfate: reaction rates and protein binding").
  • Core Argument for this Ground:
    • Prior Art Mapping: Petitioner asserted that Elferink taught a method for measuring the binding capacity of STS for cisplatin that rendered claims 22-27 obvious. Elferink described mixing a predetermined quantity of cisplatin with various molar ratios of STS (including a 10:1 ratio as claimed), incubating the mixture for various time periods (including up to 3 and 24 hours, encompassing the claimed ranges), and analyzing the concentration of cisplatin over time to determine reaction rates. Petitioner argued Elferink's use of a liquid chromatography system with a UV detector for this analysis directly corresponds to the "HPLC and UV detection" limitation in claim 27.
    • Motivation to Combine (for §103 grounds): This ground relied on a single reference that allegedly disclosed all claimed elements.
    • Expectation of Success (for §103 grounds): Not applicable as this was presented as a single-reference obviousness case where Elferink's disclosed methods directly mapped to the challenged claims.

4. Key Claim Construction Positions

  • "Acetone Wash" (Claim 5): Petitioner proposed this term means using acetone as an anti-solvent to promote crystallization of the STS product. This construction was central to combining Sherman's teaching of using an anti-solvent with Edwards' specific disclosure of using acetone for that purpose.
  • "Washing with Acetone" / "Washed with Acetone" (Claims 13, 16, 18): Petitioner proposed this means using acetone as a conventional solvent to wash the surface of the crystallized STS product to remove filtrate or other impurities. This distinguished the "washing" step from the "crystallizing" step and allowed Petitioner to map the combination of Sherman (washing) and Edwards (acetone as a suitable solvent) to the claims.

5. Relief Requested

  • Petitioner requested institution of an inter partes review (IPR) and cancellation of claims 1-27 of the ’363 patent as unpatentable.