Thin Disclosure but "Bulletproof" Protection: How a Salt Form Patent was Upheld in China Despite Minimal Data
In China, innovative drug companies typically rely on their initial composition of matter patents to block out competitors. Other “follow-on” IP, such as those directed towards formulations, polymorphs, and salt forms, are often regarded as less likely to survive invalidation challenges, especially in China where the standard of “person skilled in the art” is so high.
Having said that, we share below today a positive counter example case in which a salt form of a JAK inhibitor survived invalidation. This case is one of CNIPA’s Top Ten Patent Re-examination and Invalidation Cases for 2024 (published in the 2025 list). These cases are meant to be guiding cases, showcasing exemplary real-world decisions that clarify certain aspects of the law.
Background
Incyte Corporation is owner of Chinese patent ZL200880102903.3 (‘033 patent) which claims three salt forms of Ruxolitinib ((R)-3-(4-(7H-pyrrolo[2,3-d]pyrimidin-4-yl)-lH-pyrazol-l- yl)-3-cyclopentylpropanenitrile). Ruxolitinib is a Janus Kinase (JAK) inhibitor used to treat certain blood cancers and was disclosed in an earlier Incyte patent application (US 11/637,545, hereinafter the ‘545 application).
Petitioner Chongqing Pharscin filed an invalidation request based on Articles 26.3, 26.4, (29) and 22.3 of the Chinese Patent Law. The petitioner argued that the ‘033 patent was invalid for lack of inventiveness and insufficient disclosure, alleging that the patent had an invalid priority claim and thus was not inventive in view of its own earlier Ruxolitinib prior art. If Incyte could not establish a valid claim to priority, its earlier US application directed towards Ruxolitinib would become the closest (and likely destructive) prior art.
After detailed analysis of a variety of issues, the CNIPA Patent Reexamination and Invalidation Department (PRD) upheld all claims as valid (Decision No. 4W117594).
What happened? How did this patent survive the allegations of insufficient disclosure?
This case highlights how invention patents in the chemical and pharmaceutical arts are examined in three key aspects:
- Priority entitlement and “same subject matter” in highly unpredictable fields
- Cited foreign documents “incorporated” into a priority application’s specification
- Sufficiency of disclosure for salt-form inventions
A Seemingly Faulty Specification
At first glance, the ‘033 specification appeared to be missing a lot of important details, such as the compounds’ abilities to inhibit JAK activity and treat JAK-related diseases. For example, when describing the results of Example A (an in vitro JAK kinase inhibition assay), the specification only stated “[b]oth the phosphoric acid[(phosphate)] salt of the invention, and the corresponding free base compound, were found to have IC50 values of less than 50 nM for each of JAKl, JAK2, and JAK3.” However, the specification failed to explain what technical effects were associated with IC50 values of less than 50 nM. Furthermore, out of the three salt forms (maleic acid, sulfuric acid and phosphate salts), only the phosphate salt had associated data. There were also no clinical data regarding the diseases that could be treated.
The priority document US 60/943,705 (filed on 13 Jun 2007) did not recite Example A either, making it questionable whether the priority claim was valid.
In short, this ‘033 Chinese patent appeared to be missing a lot of key information:
- Only the phosphate salt’s JAK1/2/3 IC₅₀ values (<50 nM) were reported (Example A)
- No IC₅₀ data for maleate or sulfate salts
- No in vivo or clinical data
- Example A was absent from the earliest US provisional priority document (60/943,705, filed 13 June 2007)
Priority Claiming in China
In order to properly claim priority in China, inventions need to have the “same subject matter of invention” as those in the priority application. The definition of the “same subject matter of invention” is similar to the standard for novelty: the same technical field, the same technical solution, the same technical problem to be solved, and the same expected technical effect.
As Example A was not present in the priority document, one could not directly determine whether the priority document shared the same expected technical effect with the ‘033 patent. At the same time, the advantageous properties of the salt forms over the free base form were clearly stated in the specification.
What ultimately saved the priority claim was a statement in the priority application’s background section that cited an even earlier patent US 11/637,545. This, together with the common knowledge in field of JAK research, made it such that the priority document included the same subject matter as the invention.
Cited Foreign Document Treated as Part of the Priority Document
This decision recognizes that an earlier foreign patent application (US 11/637,54) merely cited in the priority application’s specification is treated as part of the priority document itself, sort of as if it were incorporated by reference. Despite earlier Examination Guidelines requiring cited documents to be published before the priority date, the PRD applied the 2023 Guidelines retroactively in light of legislative intent and interest balancing, holding that the cited US application forms part of the priority document itself for assessing technical effects (despite the US application publishing after the Chinese application was filed).
“Same Subject Matter” Established via Common General Knowledge
In order to determine whether a priority claim is valid, the priority document and the present application must share “the same subject matter,” and “the same subject matter” is defined by having the same technical field, the same technical problem to be solved, the same technical solution and the same technical effects. As summarized in the invalidation decision:
In the field of chemistry and pharmaceuticals, due to the high degree of unpredictability of technical effects, it is generally necessary to include in the specification sufficient qualitative or quantitative experimental data to demonstrate the achievement of the stated purpose and/or expected effect, so as to assure those skilled in the art that the invention can achieve the stated purpose or effect. Accordingly, in the determination of “the same subject matter” in the field and possess the same technical effect [for determining whether priority claim is valid], there is a high degree of reliance on experimental data.
With the high standard on experimental data, even without Example A in the priority document, a person skilled in the art could reproduce the JAK assay from the cited US 11/637,545 and would immediately recognize that the phosphate (and other) salts retain the same potent JAK-inhibitory profile as the free base. Therefore, a person skilled in the art would understand that the priority document and the present application have the same technical effects and share “the same subject matter,” making the priority claim valid.
Sufficiency of Disclosure Upheld
The PRD rejected the insufficiency attack on three independent grounds, all rooted in the low predictability threshold required when the invention is a pharmaceutically acceptable salt of a well-characterized active compound.
First, salt formation and characterization are routine operations. As no special conditions or unexpected difficulties were provided as evidence by the petitioner, the preparation methods and structural confirmation of the salts were deemed sufficiently enabled by a person skilled in the art.
Regarding the point that only the phosphate salt’s result was disclosed: Because the three claimed salts share the same cationic core, the activity of the other two salts is predictable to a person skilled in the art and can be tested by the experimental methods cited in the specification. Therefore, the disclosure of only the phosphate salt’s result was sufficient to enable the others without undue experimentation.
Most importantly, regarding the claimed therapeutic use/use in manufacture of therapeutic drugs: The specification and the priority document cited multiple references in the background to show that researchers in this art have long focused on and studied the relationship between JAK and various diseases. Although the ‘033 patent discloses no experimental data or clinical results specifically linking the three salts to disease treatment, a person skilled in the art would still understand that the claimed salts, which possess the similar JAK-inhibitory activity, have potential therapeutic use for those diseases.
EIP Thoughts
Being the first ever JAK inhibitor approved, Ruxolitinib remains highly significant in the pharmaceutical market due to its inhibition of a fundamental pathway. Numerous clinical trials are ongoing to expand its indications. Several other companies have petitioned to invalidate this salt form patent, and one of the petitions challenging disclosure sufficiency was rejected under the "一事不再理原则" (ne bis in idem principle).
This patent remains robust in China, likely due to its narrow scope limited to the specific salt form compounds, which have different structures than the prior art compounds at that time. Furthermore, the surprising technical effects of the salts are clearly stated in the specification. While the specific patent strategy used to protect these Ruxolitinib salt forms might not be 100% applicable in other cases, this invalidation decision still provides some useful insights regarding priority entitlement, the determination of “the same subject matter,” the role of cited foreign documents, and sufficient disclosure. It provides a positive example of how technical effects can still be fully considered even when the priority document and the later application are not identical.
Further, as seen in this decision, the determination of whether two applications include the same subject matter in this particular field involves more common knowledge in the art, including the effect of Ruxolitinib itself and importantly, the common knowledge that salt formation does not change the property or effect of the drug. A person skilled in the art would recognize the claimed salt as a direct, foreseeable improvement derived from the parent compound.
Our general practice is not to leave out certain disclosures and rely solely on incorporation by reference. While the Examination Guidelines permit examiners to consult cited documents when necessary, Part II, Chapter 2, Section 2.2.6 also explicitly cautions that content essential for meeting Article 26(3) (sufficiency/enablement) “should not be written by citing other documents, but should be specifically included in the specification.” Omitting comparative examples, characterization data, or key technical effects and expecting examiners to retrieve them from prior applications or literature carries unnecessary risk of rejection for insufficient disclosure.
Therefore, the safest and most examiner-friendly approach is to incorporate all enabling and distinguishing technical information directly into the Chinese specification itself.
This article is for general informational purposes only and should not be considered legal advice or a legal opinion on a specific set of facts.
