United States Drug Patent 6,455,499: Claim Scope, Expiration, Litigation Risk, and LHRH Antagonist Patent Landscape

U.S. Patent No. 6,455,499 covers methods of treating LHRH-related disorders with broad classes of peptide LHRH antagonists, including the specific decapeptide abarelix. The patent is method-of-use focused. It does not independently claim a pharmaceutical composition, formulation, manufacturing process, delivery device, or nonpeptide LHRH antagonist.

The patent issued on September 24, 2002. Based on its earliest effective filing date, the ordinary patent term ended in 2017. The patent is therefore expired and does not currently block U.S. manufacture or sale of a product solely because it falls within the issued claims. Its historical commercial relevance was primarily tied to abarelix, marketed in the United States as Plenaxis.

What does U.S. Patent 6,455,499 cover?

The patent covers administering specified peptide compounds that inhibit luteinizing hormone-releasing hormone, also called gonadotropin-releasing hormone or GnRH, to treat disorders associated with LHRH activity.

The claims divide into four principal structural groups:

Claim group	Structural coverage	Primary legal function
Claims 1-4	Highly substituted peptide antagonists, including abarelix	Broad Markush genus and two named species
Claims 5-6	Peptides based on the natural LHRH sequence and analogues	Broad sequence and analogue coverage
Claims 7-12	Broader peptide antagonist classes with analogue language	Expanded genus coverage
Claims 13-23	Additional peptide structures and specified diseases	Species, disease, and treatment limitations

The claims require all of the following:

A subject with an LHRH-associated disorder.
Administration of an effective amount of the claimed peptide.
A peptide that inhibits LHRH activity.
A peptide sequence satisfying the claimed residue-by-residue limitations.
In most cases, a pharmaceutically acceptable salt is also covered.

The patent does not cover every GnRH antagonist. A product must satisfy the applicable amino-acid, stereochemical, terminal-group, and analogue limitations in at least one enforceable claim.

Which drug is specifically covered by claims 3 and 4?

Claims 3 and 4 specifically identify the following peptide structures:

Ac-D-Nal-4-Cl-D-Phe-D-Pal-Ser-N-Me-Tyr-D-Asn-Leu-Lys(iPr)-Pro-D-Ala-NH2
Ac-D-Nal-4-Cl-D-Phe-D-Pal-Ser-Tyr-D-Asn-Leu-Lys(iPr)-Pro-D-Ala-NH2

The first structure corresponds to abarelix, subject to the nomenclature used in the patent and product literature. Abarelix is a synthetic decapeptide GnRH antagonist formerly marketed by Praecis Pharmaceuticals as Plenaxis for advanced prostate cancer.

Claim 3 is narrower than claims 1 and 2 because it requires a defined N-methyltyrosine residue at position E and a defined D-asparagine residue at position F. Claim 4 replaces N-methyltyrosine with tyrosine.

Feature	Claim 3	Claim 4
N-terminal group	Ac-D-Nal	Ac-D-Nal
Position B	4-Cl-D-Phe	4-Cl-D-Phe
Position C	D-Pal	D-Pal
Position E	N-Me-Tyr	Tyr
Position F	D-Asn	D-Asn
Position H	Lys(iPr)	Lys(iPr)
C-terminus	Pro-D-Ala-NH2	Pro-D-Ala-NH2

A commercial product containing abarelix in the claimed sequence would have been directly exposed to these claims during the patent term, subject to formulation, salt, stereochemistry, and product-specific facts.

How broad are claims 1 and 2?

Claims 1 and 2 are broad Markush method claims. They define a ten-residue peptide, A-B-C-D-E-F-G-H-I-J, while allowing multiple alternatives at most positions.

Claim 1 permits:

Five alternatives at position A.
Two alternatives at position B.
Five alternatives at position C.
Fourteen alternatives at position E.
Two alternatives at position F.
Two alternatives at position G.
Four alternatives at position H.
Two alternatives at position J.

The theoretical number of expressly recited sequence combinations is approximately 10,080 before accounting for salts and other claim dependencies. That figure is a mathematical measure of the listed alternatives, not a conclusion that every combination is patentable or supported.

Claim 2 narrows claim 1 by requiring D-Asn at position F. Its theoretical combination count is approximately 5,040.

The claimed architecture is more important than the raw number of combinations. The patent protects peptide antagonists having:

N-terminal acylated aromatic or constrained residues;
D-amino acids at key receptor-binding positions;
a central serine;
D-Asn or D-Gln;
Leu or Trp;
Lys(iPr), Gln, Met, or Arg;
Pro at the penultimate position; and
an amidated glycinamide or alaninamide terminus.

This design is directed to high-affinity, proteolytically stabilized GnRH antagonist peptides rather than conventional GnRH agonists such as leuprolide.

What do claims 5, 6, and 13 protect?

Claims 5 and 6 cover peptide sequences based on LHRH itself and broadly recite D- or L-amino acids and “analogues thereof.”

Claim 5 covers a ten-residue structure:

D/L-Glu - D/L-His - D/L-Trp - D/L-Ser - D/L-Tyr - D/L-Asn or Gln - D/L-Leu - D/L-Arg - D/L-Pro - D/L-Gly

Claim 6 covers a corresponding nine-residue structure ending at position I with Pro.

Claim 13 begins at residue B and covers a nine-residue structure ending at J. These claims are structurally distinct from claims 1-4 because they do not require the heavily substituted N-terminal Ac-D-Nal or Ac-D-Pal motif.

The principal limitation is the term “analogue thereof.” In litigation, that language would be evaluated against the specification’s disclosures, examples, definition of analogue, written-description support, enablement, and definiteness. A broad analogue limitation can increase coverage, but it also creates greater validity exposure if the specification does not teach the full claimed genus.

Which diseases are covered by the patent?

Claim 14 lists the principal disorders:

Precocious puberty
Prostate cancer
Ovarian cancer
Benign prostatic hypertrophy
Endometriosis
Uterine fibroids
Breast cancer
Premenstrual syndrome
Polycystic ovary syndrome

Claims 15-23 separately narrow treatment to individual indications. These dependent claims do not expand the peptide genus. They add disease-specific limitations to the preceding structural and treatment requirements.

The commercially important indication was prostate cancer. The patent’s disease claims could also have been relevant to clinical development programs in gynecology and reproductive endocrinology, but the issued claims do not cover all endocrine treatments involving suppression of gonadal hormones. The administered compound must remain within the claimed peptide classes.

When did U.S. Patent 6,455,499 expire?

Event	Date
U.S. patent issued	September 24, 2002
Ordinary 20-year term measured from earliest effective filing	2017
Current status	Expired

The ordinary term is calculated under 35 U.S.C. §154 from the relevant nonprovisional filing date, subject to patent-term adjustment, terminal disclaimers, patent-term extension, or other statutory modifications. The patent was not a currently enforceable U.S. patent as of the post-2017 period.

The practical result is that the patent no longer creates a current U.S. exclusionary right against generic or follow-on peptide products. Historical freedom-to-operate analyses still require review of related continuation, divisional, foreign, and formulation patents.

What was the FDA and Orange Book status of the related product?

Abarelix was approved by FDA under NDA 21-320 as Plenaxis. FDA approved it for advanced symptomatic prostate cancer in men for whom other hormonal therapies were not appropriate or were refused.

The product was subject to a risk-management program because of the risk of severe hypersensitivity reactions. FDA labeling required administration in a controlled setting with observation after injection. Praecis later discontinued commercial marketing in the United States.

Regulatory issue	Abarelix / Plenaxis
Active ingredient	Abarelix
Pharmacology	GnRH/LHRH antagonist
Dosage form	Injectable peptide
U.S. sponsor	Praecis Pharmaceuticals
FDA approval	2003
Main indication	Advanced prostate cancer
Risk control	Hypersensitivity monitoring and restricted use
Current commercial status	No active marketed U.S. product

The Orange Book is relevant to the listed NDA and any patents submitted for that product. Because U.S. Patent 6,455,499 has expired, it is not a current patent barrier. Orange Book listing history does not revive an expired patent and does not itself establish present enforceability. FDA discontinued-product records and the Orange Book must be read together because regulatory marketing status and patent status are separate issues. [2, 3]

Did the patent face Paragraph IV challenges?

No material public Paragraph IV litigation against U.S. Patent 6,455,499 is generally associated with an active generic abarelix market. The commercial product was discontinued, and no established U.S. generic market developed around Plenaxis.

A Paragraph IV challenge would have required an ANDA applicant to certify that the listed patent was invalid, unenforceable, or would not be infringed. The principal commercial barriers were likely greater than the patent alone:

Limited market size.
Injectable peptide manufacturing.
Product-specific clinical and safety requirements.
The restricted-use program.
The absence of a sustained commercial market after Plenaxis discontinuation.

The lack of a prominent Paragraph IV dispute should not be interpreted as proof that the patent was strong. It more likely reflects limited generic-commercial incentives.

What formulation and manufacturing protection existed?

U.S. Patent 6,455,499 is not principally a formulation or manufacturing patent. Its claims focus on treatment methods and peptide identity.

The claims do not expressly require:

A particular vehicle or excipient.
A depot formulation.
A sustained-release microsphere.
A specific injection volume.
A particular concentration.
A lyophilized cake.
A defined reconstitution method.
A peptide synthesis route.
A purification specification.
A manufacturing host or recombinant process.

For a follow-on product, the more important IP questions would have involved related patents covering:

Solid-state forms or salts.
Injectable compositions.
Depot delivery.
Stabilization during storage.
Sterile manufacturing.
Purification and impurity control.
Device or administration systems.

These categories can create commercial friction after a core sequence patent expires, but they are not established by the claims supplied for Patent 6,455,499.

How does this patent compare with competing GnRH antagonist patents?

Product	Type	Peptide or small molecule	Relationship to Patent 6,455,499
Abarelix	GnRH antagonist	Peptide	Directly exemplified by claims 3 and 4
Degarelix	GnRH antagonist	Peptide	Different peptide sequence and commercial patent estate
Cetrorelix	GnRH antagonist	Peptide	Different sequence and earlier development history
Ganirelix	GnRH antagonist	Peptide	Different sequence and separate patent family
Relugolix	GnRH antagonist	Small molecule	Outside the peptide sequence claims
Elagolix	GnRH antagonist	Small molecule	Outside the peptide sequence claims
Leuprolide	GnRH agonist	Peptide	Pharmacologically distinct and outside the antagonist claims

The patent has little direct relevance to modern oral GnRH antagonists such as relugolix and elagolix because those products are nonpeptide small molecules. Their patent estates focus on chemical compounds, salts, formulations, methods of treatment, and crystalline forms rather than the peptide sequences claimed here.

Degarelix, cetrorelix, and ganirelix require separate sequence-by-sequence analysis. A peptide can have GnRH antagonist activity without infringing Patent 6,455,499 if it lacks the claimed residue pattern or falls outside the applicable analogue construction.

How strong is the patent estate?

Strengths

The patent’s strongest historical features were:

Broad Markush coverage across multiple peptide positions.
Separate coverage for N-terminally modified antagonist peptides.
Species claims directed to abarelix-like sequences.
Disease-specific dependent claims covering prostate cancer and other hormone-dependent disorders.
Salt coverage that could capture commercially usable pharmaceutical forms.

Weaknesses

The principal weaknesses were:

The claims are method claims, not direct composition claims.
Infringement requires administration, not merely making or possessing the peptide.
“Analogue thereof” language creates construction and validity questions.
The claims contain apparent drafting inconsistencies, including nomenclature changes between D- and non-D residues.
Claims 7-10 and related claims use broad analogue language that may invite written-description and enablement attacks.
The patent did not cover oral nonpeptide GnRH antagonists.
The commercial product was injectable and subject to significant safety controls.

Claims 3 and 4 were likely more defensible than the broad analogue claims because they identify precise peptide structures. The broad genus claims had greater potential market coverage but also presented more substantial validity and claim-construction risk.

What generic launch scenarios exist after expiration?

A generic or follow-on entrant would face three principal scenarios.

Sequence-identical injectable product

A sequence-identical abarelix product would not face Patent 6,455,499 after expiration. The remaining issues would be FDA approval, bioequivalence or clinical bridging, injectable manufacturing, sterility, immunogenicity, hypersensitivity risk, and commercial demand.

Nonidentical peptide antagonist

A different peptide could avoid the patent if its sequence falls outside the literal limitations and is not captured under a valid doctrine-of-equivalents theory. The risk would depend on the extent of sequence similarity, stereochemical substitutions, terminal modifications, and the patent’s specification.

Nonpeptide GnRH antagonist

A small-molecule antagonist such as relugolix or elagolix is outside the literal scope of these peptide claims. Its freedom-to-operate analysis would center on its own compound and formulation patents.

What licensing deals affected commercialization?

Praecis Pharmaceuticals commercialized abarelix and held the principal U.S. commercial interest in Plenaxis. The patent record and product history indicate that commercialization involved licensed or acquired peptide antagonist technology associated with academic and biotechnology research programs, including work originating from LHRH antagonist researchers.

The supplied claim text alone does not establish the complete chain of title, license scope, royalty terms, or whether every related patent was owned by the same entity. Patent ownership, regulatory sponsorship, and commercialization rights should be separated in any transaction analysis.

What patent litigation affects Patent 6,455,499?

The supplied information identifies no active litigation affecting the patent. Because the patent expired in 2017, current litigation risk under this patent is effectively limited to historical disputes, accrued claims, ownership issues, or related patents that remain unexpired.

The principal present-day risk is therefore not enforcement of Patent 6,455,499 itself. It is the possibility that a related continuation, formulation patent, process patent, or foreign counterpart has a different term or claim scope.

Key Takeaways

U.S. Patent 6,455,499 is a peptide GnRH/LHRH antagonist method-of-use patent.
Claims 3 and 4 specifically cover abarelix-like decapeptides.
Claims 1, 2, 7, 8, 9, 10, 11, and 12 use broad Markush structures.
Claims 5, 6, and 13 cover natural-LHRH-derived structures and analogues.
Claim 14 lists nine LHRH-related disorders, including prostate cancer and endometriosis.
The ordinary U.S. patent term ended in 2017.
The patent does not claim formulations, manufacturing methods, devices, or nonpeptide GnRH antagonists.
No significant Paragraph IV generic litigation is associated with the patent’s commercial product.
Plenaxis was FDA-approved for advanced prostate cancer but was later discontinued in the United States.
Current freedom to operate depends on related patents, not on the expired claims of Patent 6,455,499.

FAQs About U.S. Patent 6,455,499

Does Patent 6,455,499 cover degarelix?

Not on the supplied claims alone. Degarelix has a different peptide structure and must be compared residue by residue against the relevant Markush and analogue limitations.

Is abarelix generic now that Patent 6,455,499 expired?

The patent no longer blocks a generic abarelix product. FDA approval, injectable manufacturing, sterility, hypersensitivity risk, and commercial-market considerations remain separate issues.

Does the patent cover oral GnRH antagonists?

No. The issued claims require peptide compounds. Oral small-molecule antagonists are outside the literal sequence claims.

Can a salt of a covered peptide fall within the patent?

Yes. The claims expressly include pharmaceutically acceptable salts of the claimed peptide compounds.

Does the patent cover treatment of infertility?

The listed disease claims do not expressly identify infertility. A treatment would need to satisfy an applicable LHRH-associated-disorder claim and all structural limitations, including the peptide and activity requirements.

References

U.S. Patent No. 6,455,499. (2002). Peptide compounds having LHRH antagonist activity. United States Patent and Trademark Office.
U.S. Food and Drug Administration. (2003). Plenaxis (abarelix for injectable suspension) prescribing information. FDA.
U.S. Food and Drug Administration. (n.d.). Approved drug products with therapeutic equivalence evaluations: Orange Book. FDA.
U.S. Food and Drug Administration. (n.d.). Discontinued drug product listings and drug approval history. FDA.
35 U.S.C. § 154. (2024). Contents and term of patent; provisional rights. United States Code.

Details for Patent: 6,455,499

Summary for Patent: 6,455,499