Ascendis Pharma v. BioMarin: TransCon CNP Safe Harbor Battle Moves to the ITC
Ascendis Pharma A/S filed a declaratory judgment action in the Northern District of California seeking safe harbor protection for its TransCon CNP (navepegritide) program against BioMarin’s USRE048267 patent. After 88 days, Ascendis voluntarily dismissed without prejudice — deliberately re-routing the dispute to the ITC where parallel proceedings are already underway.
A tactical forum pivot: Ascendis redirects TransCon CNP safe harbor fight to the ITC
On April 11, 2025, Ascendis Pharma A/S filed a declaratory judgment complaint against BioMarin Pharmaceutical in the U.S. District Court for the Northern District of California (Case No. 4:25-cv-03302), before Judge Yvonne Gonzalez Rogers. The action sought a declaration that Ascendis’s pre-approval activities relating to TransCon CNP (navepegritide) — its investigational C-type natriuretic peptide conjugate therapy — fall within the safe harbor of 35 U.S.C. § 271(e)(1), insulating them from infringement liability under BioMarin’s U.S. Reissue Patent No. RE48,267.
The procedural catalyst was a BioMarin complaint filed at the U.S. International Trade Commission alleging patent infringement by Ascendis. Rather than await that forum, Ascendis moved pre-emptively to secure a safe harbor declaration in district court. BioMarin responded by moving to dismiss or stay the district court action, arguing the ITC was the proper venue. Ascendis ultimately agreed, voluntarily dismissing the action without prejudice on July 8, 2025 under Fed. R. Civ. P. 41(a)(1)(A)(i) — a mechanism available because BioMarin had not yet answered or filed a summary judgment motion.
The 88-day duration reflects a purely procedural skirmish rather than substantive adjudication. Notably, Ascendis announced plans to file a new declaratory judgment action for non-infringement of USRE048267, which it intends to stay immediately under 28 U.S.C. § 1659 — the mandatory stay provision for cases with parallel ITC proceedings. The deliberate refiling strategy, rather than amending the existing complaint, suggests Ascendis’s counsel sought to avoid any argument that § 1659’s mandatory stay did not apply to the older action, which had already been pending over 30 days.
Filing to Voluntary dismissal in 88 days
88-day lifespan — resolved before any answer or summary judgment motion was filed
Voluntarily dismissed: what the Rule 41 notice means for both parties
Rule 41(a)(1)(A)(i): self-executing dismissal before answer
Under Fed. R. Civ. P. 41(a)(1)(A)(i), a plaintiff may dismiss an action without a court order by filing a notice of dismissal before the opposing party serves an answer or a motion for summary judgment. Because BioMarin had done neither, Ascendis’s notice was self-executing — the court had no discretion to refuse it. The dismissal took immediate effect upon filing.
No court approval requiredRecord confirms ‘without prejudice’ — but conditions are unspecified
Ascendis expressly stated the dismissal is without prejudice, meaning it retains the right to re-litigate the same claims. Critically, the public record does not disclose any negotiated conditions, cost-sharing terms, or side agreements between the parties. The distinction matters commercially: a with-prejudice dismissal would bar re-filing; without prejudice keeps all options open. Here, Ascendis immediately signalled its intent to re-file a broader declaratory judgment action.
Re-filing rights preservedAscendis pivots to ITC and a fresh DJ action under § 1659 stay
Rather than litigating the safe harbor issue in district court, Ascendis is pursuing the defense at the ITC — the forum BioMarin chose. Simultaneously, Ascendis plans to file a new district court declaratory judgment action for non-infringement of USRE048267 and immediately seek a § 1659 mandatory stay, preserving its ability to return to federal court once ITC proceedings conclude. The deliberate refiling avoids any dispute about whether the mandatory stay covers a case pending more than 30 days.
ITC + district court dual trackTransCon CNP’s regulatory path remains the core battleground
The safe harbor under § 271(e)(1) protects activities ‘reasonably related’ to obtaining FDA approval. If Ascendis’s TransCon CNP activities qualify, BioMarin cannot obtain injunctive relief or damages for the pre-approval period. The outcome at the ITC — and eventually in district court — will determine whether Ascendis can advance its CNP therapy to market without a licensing agreement, making this a high-stakes commercial dispute for the rare disease growth hormone deficiency sector.
FDA safe harbor at stakeFull party and counsel information
| Role | Name | Type | Detail |
|---|---|---|---|
| Plaintiff | Ascendis Pharma A/S | Individual | Danish biopharmaceutical company — holder of the safe harbor defense position on USRE048267Search in Eureka ↗ |
| Defendant | BioMarin Pharmaceutical | Individual | BioMarin Pharmaceutical — rare disease biotech and asserting party of USRE048267 at the ITCSearch in Eureka ↗ |
| Plaintiff counsel | Deirdre Marie Wells | Attorney | Counsel for Ascendis Pharma A/SSearch in Eureka ↗ |
| Plaintiff counsel | Gabriel S. Gross | Attorney | Counsel for Ascendis Pharma A/SSearch in Eureka ↗ |
| Plaintiff counsel | Gabrielle Lahatte | Attorney | Counsel for Ascendis Pharma A/SSearch in Eureka ↗ |
| Plaintiff counsel | Jamie Underwood | Attorney | Counsel for Ascendis Pharma A/SSearch in Eureka ↗ |
| Plaintiff counsel | John Christopher Rozendaal | Attorney | Counsel for Ascendis Pharma A/SSearch in Eureka ↗ |
| Plaintiff counsel | Kristina Caggiano Kelly | Attorney | Counsel for Ascendis Pharma A/SSearch in Eureka ↗ |
| Plaintiff counsel | Michael A David | Attorney | Counsel for Ascendis Pharma A/SSearch in Eureka ↗ |
| Plaintiff counsel | Michael E. Joffre | Attorney | Counsel for Ascendis Pharma A/SSearch in Eureka ↗ |
| Plaintiff law firm | Latham & Watkins LLP | Law Firm | Representing Ascendis Pharma A/SSearch in Eureka ↗ |
| Plaintiff law firm | Sterne, Kessler, Goldstein & Fox PLLC | Law Firm | Representing Ascendis Pharma A/SSearch in Eureka ↗ |
| Defendant counsel | Edward Robert Reines | Attorney | Counsel for BioMarin PharmaceuticalSearch in Eureka ↗ |
| Defendant counsel | Miguel Alejandro Alvarez | Attorney | Counsel for BioMarin PharmaceuticalSearch in Eureka ↗ |
| Defendant counsel | Sean Christian Platt | Attorney | Counsel for BioMarin PharmaceuticalSearch in Eureka ↗ |
| Defendant law firm | Jones Day | Law Firm | Representing BioMarin PharmaceuticalSearch in Eureka ↗ |
| Presiding judge | Judge Yvonne Gonzalez Rogers | Judge | California Northern District CourtSearch in Eureka ↗ |
Official order — verbatim text
The dismissal notice confirms Ascendis invoked Rule 41(a)(1)(A)(i) — a self-executing procedural right triggered by BioMarin’s failure to answer or file a summary judgment motion. The phrasing ‘without prejudice’ is legally significant: it extinguishes no claim and imposes no res judicata bar. Ascendis’s contemporaneous announcement of a planned refiling for non-infringement of USRE048267, combined with its intent to invoke § 1659’s mandatory stay, suggests the dismissal was a calculated realignment rather than a retreat — the substantive safe harbor and non-infringement disputes remain fully live.
USRE048267 — C-type natriuretic peptide conjugate therapy for skeletal dysplasia
U.S. Reissue Patent No. RE48,267 (application no. US15/646822) is a reissued patent, meaning it was granted to correct or broaden the original grant after post-issuance review by the USPTO. Reissue patents carry the same legal force as original patents but may contain revised or expanded claims. The patent relates to C-type natriuretic peptide (CNP) conjugate technology — the mechanistic basis of BioMarin’s vosoritide program and the platform Ascendis seeks to leverage with navepegritide (TransCon CNP) for conditions including achondroplasia and related skeletal dysplasias.
The strategic significance of USRE048267 lies in its potential to cover the CNP conjugate and delivery methods that are central to the next generation of achondroplasia treatments. Ascendis’s TransCon CNP uses its proprietary TransCon linker technology to extend the half-life of CNP — a differentiated approach that BioMarin alleges reads on this reissued patent. For companies in the CNP therapeutics space, the reissue’s claim scope is the critical question: if the reissued claims are interpreted broadly, they could block multiple competing CNP conjugate programs currently in development.
Should your CNP therapy program run an FTO against USRE048267?
Any company developing CNP conjugate, CNP fusion, or extended-release CNP therapies for achondroplasia or related skeletal conditions should treat USRE048267 as a priority FTO target. The fact that BioMarin has already asserted this patent at the ITC against a well-resourced competitor — and that the patent is a reissue, potentially with broadened claims — materially elevates infringement risk for programs using CNP-based active pharmaceutical ingredients with modified delivery or half-life extension strategies.
PatSnap Eureka’s FTO Search Agent can map your CNP program’s technical features against the claim landscape of USRE048267 and its reissue history, identifying both literal and doctrine-of-equivalents risk. Eureka can also surface related BioMarin patent families, ITC general exclusion order precedents in the pharmaceutical space, and comparable safe harbor case outcomes — giving your IP and R&D teams a defensible FTO position before IND or NDA filing.
Run a freedom-to-operate analysis on USRE048267E to assess your product’s exposure
Run FTO in Eureka →Similar pharmaceutical safe harbor and ITC declaratory judgment cases
Cases involving § 271(e)(1) safe harbor disputes and parallel ITC proceedings in the pharmaceutical biologics sector before Northern District of California courts.
What this case signals for the rare disease biopharmaceutical IP landscape
The Ascendis–BioMarin dispute illustrates how pre-approval pharmaceutical IP battles increasingly span the ITC and federal courts simultaneously.
The § 271(e)(1) safe harbor is a primary litigation shield for pre-approval drug programs
Competitors developing drugs that potentially read on a rival’s patents increasingly invoke the safe harbor as a first-line defense. This case confirms that district courts are a viable forum to seek a pre-emptive safe harbor declaration, even if the ultimate battleground shifts to the ITC.
ITC proceedings now drive forum selection for pharmaceutical patent disputes
BioMarin’s decision to file first at the ITC effectively forced Ascendis to redirect its declaratory judgment strategy. Companies holding key reissue patents in the pharmaceutical space should assess whether ITC filings can shape the litigation landscape to their advantage before a competitor seeks a district court declaration.
A/S v BioMarin — key questions answered
35 U.S.C. § 271(e)(1) exempts from patent infringement any use of a patented invention ‘solely for uses reasonably related to the development and submission of information’ to the FDA. Ascendis invoked it to argue that its TransCon CNP (navepegritide) activities before FDA approval cannot constitute actionable infringement of BioMarin’s USRE048267, even if those activities would otherwise read on the patent’s claims.
Ascendis dismissed under Fed. R. Civ. P. 41(a)(1)(A)(i) after deciding to litigate the safe harbor defense at the ITC — the forum BioMarin had already chosen. The ‘without prejudice’ designation preserves Ascendis’s right to refile. Ascendis simultaneously announced plans to file a new DJ action for non-infringement of USRE048267 to be stayed under 28 U.S.C. § 1659 pending ITC resolution.
Section 1659 requires a district court to stay proceedings on any claim that involves the same issues as a parallel ITC investigation, upon timely motion by the respondent. The stay is mandatory, not discretionary. Ascendis’s deliberate refiling — rather than amending the existing complaint — was designed to ensure the new action qualifies for the mandatory stay without dispute over whether the 30-day filing window had already lapsed.
USRE048267 is a reissued U.S. patent (application no. US15/646822) held by BioMarin Pharmaceutical relating to C-type natriuretic peptide (CNP) conjugate technology. Reissue patents are granted to correct or broaden the original patent claims. BioMarin has asserted this patent both at the ITC and, through the ITC complaint, effectively triggered the district court dispute with Ascendis over its TransCon CNP (navepegritide) program.
The substantive disputes — safe harbor applicability and non-infringement of USRE048267 — will be litigated at the ITC in the parallel proceeding BioMarin initiated. Ascendis has stated it will file a new district court declaratory judgment action for non-infringement, to be stayed under § 1659 pending the ITC outcome. The ITC proceedings will likely determine the commercial fate of Ascendis’s TransCon CNP program in the near term.
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