IP Law Daily, PATENT—N.D. Ill.: Ingenus Pharmaceuticals’ patent claims describing stable liquid formulation of cyclophosphamide invalid for indefiniteness, (May 13, 2025)

By Carolin Dennis, B.Sc., LL.B., LL.M.

Claims directed to stable ready to use cyclophosphamide liquid formulations were invalid because the term “stable” as used in the ’952 patent was indefinite to provide a POSA notice of what is claimed.

The U.S. District Court for the Northern District of Illinois granted Nexus’s motion for summary judgment based on invalidity because the term “stable” as used in the ’952 patent is indefinite. The district court found that the term “stable” as used in the ’952 patent could be ascertained by different measures, those measures could yield different results, and neither intrinsic nor extrinsic evidence indicates which to use. Additionally, a person of ordinary skill in the art (POSA) could not be reasonably certain under which test or what conditions the claimed formulations are stable (Ingenus Pharmaceuticals, LLC v. Nexus Pharmaceuticals, Inc., No. 1:22-cv-02868 (N.D. Ill. May. 9, 2025)).

Background. Ingenus Pharmaceuticals, LLC (Ingenus) was the owner of U.S. Patent No. 10,993,952, (the ’952 patent) titled “Stable ready to Use Cyclophosphamide Liquid Formulations.” The ’952 patent contained four claims directed to formulations of cyclophosphamide all of which require a stable liquid parenteral formulation. Ingenus brought suit for infringement against Nexus Pharmaceuticals, Inc. (Nexus). Nexus moved for summary judgment of invalidity, arguing that the ’952 patent is invalid.

Invalidity. Nexus argued that the ’952 patent is invalid because the term “stable” is indefinite. The district court found that the ’952 patent uses the word “stable” in several different ways. In the specification, the patent states that the “inventive compositions of Cyclophosphamide were found to be stable when stored at 2 C°. to 8 C°. temperature.” The parties and their experts refer to this as “Refrigerated Conditions.” Separately, the patent explains that its formulations were “tested for stability under accelerated condition for a period of 1 week at 40 C°. and 75% RH,” referring to room humidity. The patent then summarizes the “stability data” of the invention when tested under these conditions. Additionally, all four claims in the patent require a stable liquid parenteral formulation of cyclophosphamide.

Nexus primarily relied on Ingenus’s experts, Dr. Rabinow and Dr. Yaman, to argue that the term stable is indefinite and thus does not provide a POSA with reasonable certainty of the scope of the invention claimed. Both experts agreed that there is no single definition of “stable” but generally claim that a POSA would understand the term in reference to cyclophosphamide in terms of the following “aspects”: degradation, impurity formation, decomposition, solution stability, and storage stability. However, the district court noted that the question is not whether “stable” has a singular definition; the question is whether the patent provides a POSA notice of what is claimed by the word “stable” such that a POSA can know when they risk infringement. The district court found that Nexus has established by clear and convincing evidence that an impermissible “zone of uncertainty” exists. A POSA could not be reasonably certain under which test or what conditions the claimed formulations are stable, and thus under which test or conditions a similar invention could be said to infringe on the patent’s claims.

Ingenus also argued that because Nexus appeared to understand and apply a rigorous definition of the word “stable” in its own Abbreviated New Drug Application, the word cannot be indefinite. However, the district court determined whether Nexus was able to put forth a definitive meaning of the word “stable” is irrelevant to whether “stable,” as used in the ’952 patent, is indefinite to a POSA. The district court did not hold that the word stable can never be definite as applied to formulations of cyclophosphamide or any other pharmaceutical. Rather, the district court found the term “stable” as used in the ’952 patent is too indefinite to provide a POSA notice of what is claimed.

The term “stable” as used in the ’952 patent could be ascertained by different measures, those measures could yield different results, and neither intrinsic nor extrinsic evidence indicates which to use. Therefore, “stable,” as used in the ’952 patent, is indefinite. Accordingly, Nexus’s motion for summary judgment on the basis that the ’952 patent is invalid was granted.

Infringement. Ingenus argued that infringement and invalidity are separate questions and that the district court could find Nexus has infringed on the ’952 patent without regard to its validity. The district court noted that literal infringement first requires the trial court to interpret the claims to determine their scope and meaning. This approach is also reflected in the plain text of the Patent Act, which lists “invalidity of the patent or any claim in suit” as a defense in any action involving the validity or infringement of a patent. In short, because an “invalid claim cannot be infringed,” and because all the claims in the ’952 patent either implicitly or explicitly contain the indefinite term “stable,” Ingenus’s motion for summary judgment was denied.

Accordingly, the district court granted Nexus’s motion for summary judgment based on invalidity and denied Ingenus’s motion for summary judgment.

The Case is No. 1:22-cv-02868.

Judge: Rowland, M.

Attorneys: John T. Callahan (Sughrue Mion, PLLC) for Ingenus Pharmaceuticals, LLC. Imron T. Aly (ArentFox Schiff LLP) for Nexus Pharmaceuticals, Inc.

Companies: Ingenus Pharmaceuticals, LLC; Nexus Pharmaceuticals, Inc.

Cases: Patent IllinoisNews