US Patent 7,608,280: Scope, Claim Construction, Expiration and Romidepsin Patent Landscape

US Patent 7,608,280 protects a specific crystalline polymorph of romidepsin, also known as FR901228 or depsipeptide. The patent does not claim romidepsin generally, a therapeutic use, a dosage regimen, or a finished formulation. Its operative scope is limited to Type B crystalline romidepsin and compositions identifiable by specified powder X-ray diffraction peaks.

The strongest commercial risk created by the patent is at the drug-substance level. A generic manufacturer that produces or purchases Type B romidepsin may face infringement exposure even if its finished dosage form, manufacturing process, and labeling differ from the branded product.

What drug does US Patent 7,608,280 protect?

US 7,608,280 concerns romidepsin, a cyclic depsipeptide histone deacetylase inhibitor. Romidepsin was marketed in the United States as Istodax by Celgene, later part of Bristol Myers Squibb, for relapsed or refractory cutaneous T-cell lymphoma and peripheral T-cell lymphoma.[1]

Item	Information
Active ingredient	Romidepsin
Alternative name	FR901228; depsipeptide
Drug class	Histone deacetylase inhibitor
Dosage form	Intravenous infusion product
Original U.S. sponsor	Gloucester Pharmaceuticals/Celgene
U.S. trade name	Istodax
Relevant patent	US 7,608,280
Patent subject	Type B crystalline romidepsin
Patent type	Composition-of-matter polymorph patent
FDA product category	Small-molecule drug
Biosimilar pathway	Not applicable

Romidepsin is a small molecule rather than a biologic. Biosimilar provisions under the Public Health Service Act therefore do not apply. Any competitor would ordinarily pursue an abbreviated new drug application, a 505(b)(2) application, or a full new drug application, depending on the proposed product and reliance strategy.

What are the claims of US 7,608,280?

The claims fall into three groups:

Claims 1 to 3 cover Type B crystalline romidepsin.
Claim 2 adds a preparation limitation involving hexanes.
Claims 4 to 7 cover compositions identified by selected PXRD peaks.

Claim	Claim category	Core limitation
1	Product claim	Type B crystalline form of FR901228
2	Product/process-related claim	Type B form obtained from hexanes
3	Product identification claim	Type B form having an PXRD pattern substantially similar to Figure 5
4	Composition claim	Composition containing Type B form and at least one specified PXRD peak
5	Composition claim	At least two specified peaks
6	Composition claim	At least three specified peaks
7	Composition claim	All four specified peaks

The patent therefore uses both a named polymorph and analytical fingerprinting to define the protected material. The PXRD limitations are central to infringement and validity analysis.

How should claim 1 be construed?

Claim 1 is a product claim directed to Type B crystalline romidepsin. It does not require:

a particular route of synthesis;
a particular solvent;
a particular particle size;
a particular purity;
a particular dosage form;
a pharmaceutical excipient;
a particular therapeutic use; or
a particular method of administration.

The central question is whether the accused romidepsin material is the Type B crystalline form described and enabled by the patent. A manufacturer cannot avoid claim 1 merely by using a different synthetic route if the resulting active ingredient is the same claimed polymorph.

The claim raises several construction issues:

Meaning of "Type B crystalline form"

"Type B" is a nomenclature term defined by the patent specification and its analytical data. The term should be read together with the disclosed PXRD pattern, crystallization procedures, and characterization data rather than as an independent trade name.

A court would likely examine:

the PXRD profile;
peak positions and relative intensities;
the crystallization solvent;
thermal analysis;
microscopy;
water or solvent content;
whether the material is a single polymorph or a mixture; and
the specification's distinction between Type A, Type B, and any amorphous form.

Analytical variability

PXRD peak positions can shift because of instrument calibration, sample preparation, crystallinity, hydration, preferred orientation, and impurities. The claim does not state exact numerical tolerances. The terms "about" and "substantially similar" therefore create a fact-intensive comparison.

A product may still fall within the claim even if its peaks are not numerically identical to the illustrated pattern. Conversely, a nominally similar pattern may not establish infringement if the differences reflect a different polymorph or a mixture lacking the claimed structure.

What does claim 2 protect?

Claim 2 covers Type B romidepsin "obtained from hexanes." The claim attempts to add a crystallization or isolation condition to the Type B product.

Its legal effect depends on claim construction:

If "obtained from hexanes" is treated as a product-by-process limitation, the claim may require the claimed crystalline product but not necessarily infringement by every material made through an unrelated process.
If the language is treated as a process limitation, the accused party may avoid claim 2 by using a process that does not involve hexanes, while remaining exposed under claim 1 or claim 3.
If the resulting Type B product is structurally indistinguishable regardless of process, the process language may have limited practical value in a product-infringement dispute.

Claim 2 is narrower than claim 1 and is less likely to be the sole basis for a generic challenge. Its commercial importance depends on whether hexanes were used in the branded active pharmaceutical ingredient process and whether the patent treats hexane-mediated crystallization as necessary to obtain the claimed form.

What does claim 3 protect?

Claim 3 covers Type B crystalline romidepsin characterized by an PXRD pattern substantially similar to Figure 5.

This claim is directed to the analytical identity of the polymorph. It is potentially broader than a claim listing fixed peak positions because it incorporates the complete pattern shown in the figure rather than only selected peaks.

The principal infringement test would compare the accused material's PXRD pattern against Figure 5. Relevant evidence would include:

peak locations;
relative intensities;
baseline and background;
peak broadening;
sample orientation;
instrumental resolution;
solvent or hydrate content; and
reproducibility across multiple lots.

Claim 3 also creates a validity issue. If Figure 5 lacks sufficient detail to distinguish Type B from other forms, an accused infringer could argue indefiniteness or inadequate written description. The strength of that argument would depend on the specification's full characterization data and the level of ordinary skill in pharmaceutical solid-state analysis at the relevant filing date.

What do claims 4 through 7 protect?

Claims 4 through 7 cover compositions containing Type B crystalline romidepsin and defined PXRD peaks.

The peak set is:

about 7.1 degrees 2-theta;
about 11.7 degrees 2-theta;
about 11.9 degrees 2-theta; and
about 15.1 degrees 2-theta.

The claims form a nested structure:

Claim	Required peaks
4	At least one of the four peaks
5	At least two of the four peaks
6	At least three of the four peaks
7	All four peaks

Claim 4 is the broadest of the composition claims. It can potentially read on a composition having only one of the listed peaks, provided the composition also comprises Type B crystalline romidepsin. Claim 7 is the narrowest and most analytically specific.

Composition scope

"Composition" is broader than a finished vial or injectable formulation. Depending on the specification and claim construction, it may include:

bulk active pharmaceutical ingredient;
an intermediate solid;
a formulation containing excipients;
a sample or mixture containing Type B crystals;
a pharmaceutical composition prepared for administration; or
a mixture containing Type B and another polymorph.

The claim does not expressly require a particular excipient, concentration, dosage, or route of administration. It also does not expressly require that Type B be the only crystalline form present.

Mixed-polymorph risk

Claims 4 to 7 may create exposure for mixtures of polymorphs. A batch containing Type B romidepsin together with another solid form could potentially satisfy the "comprising" transition, subject to the required PXRD peaks and the construction of "Type B crystalline form."

This matters for:

polymorph conversion during storage;
spray-drying or lyophilization;
milling;
reprocessing;
formulation manufacture; and
drug-substance release testing.

A generic applicant should test the final active ingredient and finished product, not only the initial crystallization batch.

How strong is the patent estate for romidepsin?

US 7,608,280 is technically focused but commercially meaningful. Its strength comes from claiming the physical form of the active ingredient rather than a narrow formulation or treatment method.

Strength factor	Assessment
Product coverage	Strong if the accused API is Type B
Process independence	Strong under claims 1 and 3
Formulation dependence	Low; claims do not require a specific formulation
Analytical enforceability	Moderate to strong, depending on PXRD reproducibility
Claim breadth	Claims 1 and 3 are broader; claim 7 is narrower
Design-around potential	Possible through a different stable polymorph or amorphous form
Validity exposure	Prior-art polymorph disclosures, obviousness, enablement, and definiteness
Biosimilar relevance	None
Generic relevance	High

The patent is more important for API manufacturers than for companies that merely formulate romidepsin sourced from an independent supplier. However, sourcing a non-infringing API is not sufficient if the material converts into Type B during downstream processing or storage.

When does US 7,608,280 lose exclusivity?

The patent issued on October 6, 2009. Its expiration date depends on the effective nonprovisional filing date, patent-term adjustment, terminal disclaimers, and any patent-term extension or regulatory adjustment recorded in the official USPTO file.

The patent's nominal term is generally 20 years from the earliest effective nonprovisional filing date under 35 U.S.C. §154. A precise expiration calculation must account for the patent's prosecution history and any adjustment recorded by the USPTO.[2]

The relevant exclusivity layers are separate:

Exclusivity layer	Relevance to romidepsin
US 7,608,280 patent	Protects Type B crystalline material
FDA chemical exclusivity	Applied when the product received approval under the NCE framework
Orphan-drug exclusivity	May apply to the approved lymphoma indication and approval date
Formulation or method patents	Must be evaluated separately from US 7,608,280
Patent-term extension	Requires separate USPTO/FDA confirmation
Regulatory exclusivity after marketing discontinuation	Depends on FDA action and product status

Patent expiration does not automatically remove regulatory exclusivity, and regulatory exclusivity does not extend a patent. A generic launch analysis must compare both dates.

What is the Orange Book status of US 7,608,280?

The Orange Book identifies patents submitted by sponsors for approved drug products and may include drug-substance, drug-product, method-of-use, and formulation patents.[3]

For romidepsin, the relevant Orange Book questions are:

whether US 7,608,280 was submitted for Istodax;
whether it was listed against the drug product or a specific indication;
whether the listing remained active;
whether any delisting request was filed;
whether the patent had expired;
whether an ANDA applicant made a Paragraph IV certification; and
whether the reference product was still eligible for ANDA reliance.

An Orange Book listing does not itself establish patent validity or infringement. It affects the FDA review process and the timing of a Paragraph IV dispute.

If an ANDA applicant certifies that the patent is invalid, unenforceable, or will not be infringed, the applicant may trigger the Hatch-Waxman litigation framework. A timely patent-infringement action can create a statutory stay of FDA approval, subject to the requirements of the Hatch-Waxman Act.[4]

Were there Paragraph IV challenges to romidepsin?

A Paragraph IV assessment requires a complete review of FDA ANDA records, Orange Book patent listings, court dockets, and any notices of Paragraph IV certification. The supplied claim set does not identify an ANDA applicant, litigation docket, or certification date.

The most relevant potential challenge theories against US 7,608,280 would be:

The accused material is not Type B.
The PXRD pattern does not satisfy Figure 5 or the listed peak limitations.
The claims are anticipated by an earlier disclosure of the same crystalline form.
The Type B form was obvious in view of known crystallization screening and prior art.
The terms "about" and "substantially similar" are indefinite.
The specification does not adequately describe or enable the full scope of the claims.
Claim 2 does not cover a Type B form made without hexanes.

The most commercially effective noninfringement route would be a reproducible polymorph design-around. A generic applicant could seek to use a different crystalline form or amorphous romidepsin, but that approach would require proof that the alternative form remains stable, manufacturable, bioequivalent, and acceptable under the applicable FDA pathway.

What manufacturing and intellectual-property barriers remain?

The patent creates several manufacturing barriers even if a competitor avoids the exact claimed crystallization procedure.

Polymorph control

Romidepsin solid-form manufacture requires control of:

solvent composition;
cooling rate;
seeding;
agitation;
water activity;
drying conditions;
milling energy; and
storage temperature and humidity.

A process designed to produce a non-Type B form could still generate Type B as a minor phase. Claims 4 to 7 increase the risk because they use peak-based definitions that may capture compositions containing detectable quantities of the claimed form.

Analytical release testing

A competitor would need validated solid-state methods capable of distinguishing:

Type B from other polymorphs;
a polymorph from an amorphous material;
a pure form from a mixed phase; and
a genuine PXRD peak from an artifact caused by sample preparation.

PXRD alone may not resolve every issue. Differential scanning calorimetry, thermogravimetric analysis, infrared spectroscopy, solid-state NMR, microscopy, and dynamic vapor sorption may be needed to support a noninfringement position.

API supply agreements

A drug-product company that purchases romidepsin from a third-party API supplier may still face commercial exposure if the supplied material is Type B. Supply contracts should address:

polymorph identity;
infringement indemnity;
batch testing;
change control;
crystallization conditions;
conversion during formulation; and
regulatory notification obligations.

How does US 7,608,280 compare with formulation and method-of-use patents?

US 7,608,280 is materially different from a formulation patent or method-of-use patent.

Patent category	Typical protected subject matter	Relevance to US 7,608,280
Polymorph patent	Crystal form of the API	Directly relevant
Formulation patent	Excipients, concentration, stability, container, or dosage form	Not claimed expressly
Method-of-use patent	Treatment of lymphoma or another disease	Not claimed
Process patent	Synthesis, purification, or crystallization route	Only indirectly implicated by claim 2
Combination patent	Romidepsin with another agent	Not claimed
Manufacturing patent	Solid-state conversion or isolation process	May operate alongside US 7,608,280

A competitor could avoid a formulation patent while still infringing the polymorph patent. The reverse is also possible. Freedom to operate therefore requires a family-level review covering the API, formulation, manufacturing process, therapeutic indication, and labeling.

What generic launch scenarios exist?

Scenario 1: Same Type B API

A generic applicant uses Type B romidepsin supplied by its API manufacturer. This creates the highest risk under claims 1, 3, and 4 to 7.

Scenario 2: Different crystalline form

A competitor develops a distinct, stable polymorph with a materially different PXRD pattern. This offers the clearest design-around, but the alternative form must pass pharmaceutical development, stability, bioequivalence, and regulatory requirements.

Scenario 3: Amorphous romidepsin

An amorphous API may avoid a crystalline-form claim if it does not contain Type B crystals. Manufacturing and storage conversion would require close monitoring.

Scenario 4: Mixed or partially converted material

This is a high-risk scenario. Detectable Type B peaks may support infringement allegations under the composition claims, particularly claims 4 and 5.

Scenario 5: 505(b)(2) product

A 505(b)(2) applicant could pursue a materially different formulation or route of administration, but this pathway would not automatically avoid infringement of API polymorph claims.

What litigation and settlement issues matter?

The critical litigation record would include:

ANDA notices containing Paragraph IV certifications;
district-court complaints under 35 U.S.C. §271(e)(2);
claim-construction rulings;
Markman opinions addressing "Type B," "about," and "substantially similar";
expert PXRD testimony;
laboratory testing of the proposed generic API;
preliminary-injunction proceedings;
settlements involving launch dates or licenses; and
Federal Circuit decisions affecting polymorph claim construction.

A settlement could permit an authorized generic, a delayed generic launch, or entry upon patent expiration. Without a confirmed docket and settlement document, no reliable conclusion can be drawn about a particular challenger's launch date or license status.

Key Takeaways

US 7,608,280 is a romidepsin polymorph patent covering Type B crystalline FR901228.
Claims 1 and 3 are the principal product claims.
Claim 2 adds a hexane-related limitation and is narrower.
Claims 4 to 7 cover compositions identified by one or more specified PXRD peaks.
The patent does not claim romidepsin generally, a therapeutic method, a dosage regimen, or a specific finished formulation.
The principal generic risk is use of Type B romidepsin as the active pharmaceutical ingredient.
A different crystalline form or amorphous material may provide a design-around, but phase conversion can recreate infringement risk.
Romidepsin is a small molecule, so biosimilar competition is not relevant.
Orange Book status, Paragraph IV activity, patent-term adjustment, patent-term extension, and litigation outcomes require confirmation from the current FDA, USPTO, and court records.
A complete freedom-to-operate analysis must review related formulation, process, method-of-use, and regulatory-exclusivity rights, not US 7,608,280 alone.

FAQs About US Patent 7,608,280 and Romidepsin

Does US 7,608,280 cover all forms of romidepsin?

No. The claims are directed to Type B crystalline romidepsin and compositions exhibiting specified analytical characteristics.

Can a generic manufacturer use romidepsin made by a different synthesis route?

Yes, a different synthesis route may avoid claim 2's hexane limitation. It does not necessarily avoid claims 1, 3, or 4 to 7 if the resulting material is Type B.

Can a different polymorph avoid this patent?

Potentially. A distinct polymorph with a materially different PXRD pattern may avoid the asserted claims, but the alternative must be stable and pharmaceutically suitable.

Does a detectable Type B peak automatically prove infringement?

No. Infringement would depend on the full claim language, the meaning of "about," the presence and identity of Type B, analytical reliability, and the applicable claim construction.

Is romidepsin subject to biosimilar competition?

No. Romidepsin is a chemically synthesized small molecule. Competitors would generally use an ANDA, 505(b)(2), or full NDA pathway rather than the biosimilar pathway.

References

U.S. Food and Drug Administration. (2009). FDA approves Istodax for cutaneous T-cell lymphoma. FDA.
United States Patent and Trademark Office. (2009). U.S. Patent No. 7,608,280, Crystalline forms of FR901228. USPTO.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations. FDA.
United States Congress. (1984). Drug Price Competition and Patent Term Restoration Act of 1984, 21 U.S.C. §§355 and 35 U.S.C. §§156, 271, 282.

Foriegn Application Priority Data
Foreign Country	Foreign Patent Number	Foreign Patent Date
Japan	2000-265414	Sep 01, 2000

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Argentina	030714	⤷ Start Trial
Australia	8010901	⤷ Start Trial
European Patent Office	1313872	⤷ Start Trial
Japan	2004508049	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Summary for Patent: 7,608,280