NOF Corp v. Nektar Therapeutics

1. Case Identification

• Case #: Not Yet Assigned
• Patent #: 7,026,440
• Filed: July 25, 2019
• Petitioner(s): NOF Corp
• Patent Owner(s): Nektar Therapeutics
• Challenged Claims: 1-20 and 29-35

2. Patent Overview

• Title: Branched Reactive Water-Soluble Polymers
• Brief Description: The ’440 patent is directed to branched reactive water-soluble polymers, such as those with poly(ethylene glycol) (PEG) arms, attached to a central aliphatic hydrocarbon core via heteroatom linkages. These polymers are designed for PEGylation of biologically active molecules to improve properties like circulating half-life.

3. Grounds for Unpatentability

Ground 1: Obviousness over Bentley - Claims 1-16, 19-20, and 29-35 are obvious over Bentley.

• Prior Art Relied Upon: Bentley (5,990,237).
• Core Argument for this Ground:
  • Prior Art Mapping: Petitioner argued that Bentley discloses branched reactive polymers that meet the core structural limitations of the challenged claims. Specifically, Bentley teaches a branched polymer with two PEG arms (POLY) ether-linked (X') to a three-carbon aliphatic core (R), with a linker (X) and a reactive functional group (Y) in the form of an aldehyde hydrate. Petitioner asserted that the only remaining limitation of independent claim 1, a total molecular weight of at least 5,000 Da, was rendered obvious because Bentley teaches a broad, overlapping molecular weight range (up to 264,000 Da) and discloses that PEG properties vary with molecular weight.
  • Motivation to Combine (for §103 grounds): This is a single-reference ground. Petitioner contended that selecting a specific, narrow molecular weight range from a broader disclosed range to optimize a known property constitutes routine experimentation for a person of ordinary skill in the art (POSA).
  • Expectation of Success (for §103 grounds): A POSA would have had a reasonable expectation of success in preparing polymers with a total molecular weight above 5,000 Da by simply increasing the length of the PEG polymer arms, a well-known technique described by Bentley.

Ground 2: Obviousness and Anticipation over Harris - Claims 1-3, 5, 7-10, 12-16, 20, and 29-35 are obvious over Harris; Claims 29 and 31 are anticipated by Harris.

• Prior Art Relied Upon: Harris (5,932,462).
• Core Argument for this Ground:
  • Prior Art Mapping: Petitioner contended that Harris, which was of-record but not applied during prosecution, teaches multi-armed, hydrolytically stable polymers that anticipate or render obvious the challenged claims. An exemplary Harris polymer has two methoxy-capped PEG arms (POLY) linked to a lysine-derivative core (R) via stable thioether linkages (X'), with a carboxyl functional group (Y). Petitioner argued this structure anticipates claims 29 and 31, which require methoxy-capped arms and specific heteroatom linkages but lack a molecular weight limitation. For claim 1, Petitioner asserted that Harris renders the molecular weight limitation obvious by teaching the benefits of high molecular weight polymers (e.g., 40,000 Da) and explicitly disclosing ranges up to 100,000 Da.
  • Motivation to Combine (for §103 grounds): This ground primarily relies on a single reference. The motivation for achieving the claimed molecular weight was to obtain the known benefits of higher molecular weight PEG conjugates, such as increased in vivo half-life, a stated goal in Harris.
  • Expectation of Success (for §103 grounds): A POSA would have a high expectation of success because Harris explicitly teaches preparing polymers of 10,000 Da and 40,000 Da and provides methods for making even higher molecular weight versions by increasing the mPEG chain length.

Ground 3: Anticipation by JP-542 - Claims 1-15, 17, 19-20, 29, 31-33, and 35 are anticipated by JP-542.

• Prior Art Relied Upon: JP-542 (Japanese Application Publication No. P2000-1542A).

• Core Argument for this Ground:

  • Prior Art Mapping: Petitioner argued that JP-542 discloses branched reactive polymers that meet every limitation of the challenged claims. Specifically, formula (14) of JP-542 shows a polymer with a three-carbon core (R), two branched PEG arms (POLY), ether linkages (X'), a linker (X), and an N-hydroxysuccinimide (NHS) active ester functional group (Y). Critically, Petitioner asserted that an example in JP-542 describes a polymer with a calculated molecular weight of 5,162 Da, expressly anticipating the "at least about 5,000 Da" limitation of claim 1. Other disclosed polymer examples in JP-542 anticipate claims directed to specific functional groups (e.g., allyl ether) and the formation of biologically active conjugates.
  • Motivation to Combine (for §103 grounds): N/A (Anticipation ground).
  • Expectation of Success (for §103 grounds): N/A (Anticipation ground).

• Additional Grounds: Petitioner asserted additional challenges, including that claims 16-18 and 30 are obvious over Bentley in view of Liebigs (a 1983 chemistry article teaching the use of a benzyl protecting group for glycerol synthesis); that claims 1-15, 17, 19-20, 29 and 31-35 are obvious over JP-542 in view of MDD (a 2000 drug discovery article teaching optimization of polymer molecular weight); and that claims 16-18 and 30 are obvious over JP-542 in view of Bentley (combining JP-542's core structure with Bentley's activation chemistry).

4. Key Claim Construction Positions

• "Aliphatic Hydrocarbon": Petitioner argued this term should be construed as "a non-aromatic carbon chain analog, which may be linear or branched, and may include one or more heteroatoms in the chain." This construction, based on the patent's own specification, was critical to mapping prior art structures containing heteroatoms in their core (like glycerol) to the claims.
• "Functional group": Petitioner argued this term should be construed to mean "the portions of molecules that perform some function or activity and are reactive with other molecules, including protected functional groups." This construction was important for arguing that prior art disclosing protected groups (e.g., a protected hydroxyl) meets the "functional group" limitation.

5. Relief Requested

• Petitioner requested institution of an inter partes review and cancellation of claims 1-20 and 29-35 of Patent 7,026,440 as unpatentable.