United States Patent 5,508,020: Scope, Claims, Expiration, and Technetium-99m Peptide Patent Landscape

U.S. Patent No. 5,508,020 covers multivalent technetium-99m imaging reagents in which multiple short specific-binding peptides are attached to a polyvalent linker and associated with a technetium-99m binding moiety. The patent is directed to composition-of-matter protection, not merely a diagnostic-use method. Its central commercial concept is a multivalent peptide imaging precursor capable of generating a scintigraphic agent for targeting sites in a mammalian body.

The patent’s enforceable term has expired under the U.S. patent-term rules applicable to its filing period. It therefore does not present a current U.S. blocking right, although its claim structure remains relevant for freedom-to-operate analysis, validity review, and identification of later patent families.

What does U.S. Patent 5,508,020 cover?

The patent covers a reagent containing three functional elements:

Multiple specific-binding peptides.
A polyvalent linking moiety.
A technetium-99m binding moiety.

The claimed peptides contain 3 to 100 amino acids and specifically bind to a site in a mammalian body. The peptides are covalently attached to the polyvalent linker. The technetium-binding component is covalently linked to multiple peptides, the linker, or both.

The principal claim concept can be represented as:

Claimed element	Required characteristic
Specific-binding peptides	Multiple peptides, each 3-100 amino acids
Biological function	Specific binding to a mammalian target site
Linker	Polyvalent and covalently connected to peptide components
Radionuclide-binding unit	Technetium-99m binding moiety
Product type	Reagent for preparing a scintigraphic imaging agent
Claim category	Composition of matter

This architecture differs from a conventional monovalent radiolabeled peptide. The invention requires a multivalent structure, meaning that several targeting peptides are presented through a common molecular framework.

How broad is claim 1 of U.S. Patent 5,508,020?

Claim 1 is broad in its biological and structural definitions but limited by the requirement that the reagent conform to the specific formula identified in the patent as Formula 8.

The broadest functional language covers any reagent having:

A multiplicity of specific-binding peptides;
Peptides within the stated 3-100 amino-acid range;
Covalent attachment to a polyvalent linker;
A technetium-99m binding group attached to the peptides, linker, or both; and
The prescribed Formula 8 structure.

The phrase "specific-binding peptide" is central. A molecule would not fall within the claim merely because it contains several peptides. Each peptide must specifically bind to a site in a mammalian body. A generic spacer peptide, solubilizing peptide, or nonbinding sequence would not satisfy that limitation unless it independently performs the claimed binding function.

The claim also requires covalent linkage. Noncovalent association, physical admixture, ionic interaction, or simple co-formulation would not ordinarily satisfy the express covalent-linkage limitations.

The "multiplicity" requirement creates another boundary. A single targeting peptide attached to a technetium chelator would generally fall outside the multivalent limitation, assuming no other part of the molecule supplies the required multiple specific-binding peptides.

What do claims 2 and 3 protect?

Claims 2 and 3 are narrower composition claims directed to the individual structures shown in Formulas 9 and 10.

These claims are likely species claims within the broader generic structure of claim 1. Their legal scope depends on the exact chemical structures, substituent definitions, stereochemistry, linker identities, and technetium-binding group shown in the patent drawings.

Claim	Scope type	Practical significance
Claim 1	Generic composition and Markush-style structure	Broadest coverage of the multivalent reagent concept
Claim 2	Defined chemical composition shown in Formula 9	Narrower species protection
Claim 3	Defined chemical composition shown in Formula 10	Narrower species protection

Because the supplied claim text represents the chemical drawings only as <STR9> and <STR10>, the substituent-level scope of claims 2 and 3 cannot be determined from the text alone. The claims should therefore be read against the issued patent’s structural drawings and any incorporated definitions before conducting a molecule-by-molecule infringement analysis.

What technical invention does the patent claim?

The patent claims a multivalent targeting platform for nuclear imaging. Its technical objective is to increase the effective interaction between the imaging reagent and a biological target by presenting several binding peptides on one molecular scaffold.

The structure has four functional design requirements:

Multivalent targeting

Multiple targeting peptides are attached to a single scaffold. This can increase avidity when the target site has suitable spatial arrangement or repeated binding sites.

Short peptide ligands

The claim does not require antibodies or intact proteins. It expressly encompasses peptides from 3 to 100 amino acids. This places the invention within the early peptide-radiopharmaceutical field rather than the larger antibody imaging field.

Polyvalent linker chemistry

The linker must provide multiple attachment points or otherwise support the required multivalent arrangement. Linker chemistry is therefore a claim-critical feature, not merely a formulation excipient.

Technetium-99m coordination

The reagent includes a technetium-binding moiety. The patent is directed to preparation of a scintigraphic imaging agent, so the technetium-binding chemistry is part of the composition architecture.

What patents protect related technetium-99m peptide imaging agents?

The relevant patent landscape includes several overlapping technology groups rather than a single patent family.

Technology group	Typical protected subject matter	Relationship to U.S. 5,508,020
Technetium-99m chelators	HYNIC, MAG3, N2S2, triamide, and related coordination systems	May overlap at the radionuclide-binding component
Radiolabeled peptides	Specific peptide sequences labeled with technetium	May overlap in the targeting ligand but not necessarily the multivalent linker
Multivalent peptide constructs	Multiple copies of a ligand attached to one scaffold	Most directly related
Kit formulations	Freeze-dried reagents, reducing agents, buffers, and reconstitution systems	Usually separate from the composition claim
Methods of imaging	Administering and detecting a radiolabeled agent	Separate method-of-use protection
Manufacturing processes	Conjugation, purification, technetium loading, and quality-control steps	Can create manufacturing barriers independent of composition claims
Indications	Imaging tumors, infection, thrombosis, inflammation, or receptors	May produce separate method-of-use rights

The key freedom-to-operate question is whether a later product uses the patented combination of multivalent peptide presentation, polyvalent linker, and technetium-binding unit. A product that uses a monovalent peptide, a noncovalent mixture, or a different structural arrangement may avoid the core composition limitations even if it performs a similar imaging function.

When did U.S. Patent 5,508,020 lose exclusivity?

U.S. Patent 5,508,020 is expired. The patent issued on April 16, 1996. Under the modern U.S. patent-term framework, patents based on applications filed after June 8, 1995 generally receive a term measured from the earliest effective nonprovisional filing date. Older applications were subject to a 17-year term from issuance, subject to transitional rules and any patent-term adjustment.

The relevant term analysis is:

Event	Date or status
Patent issuance	April 16, 1996
Original statutory framework	Transitional pre-1995 filing rules may apply
U.S. enforceable term	Expired
Current blocking effect	None from the expired patent
Continuing relevance	Prior art, claim construction, validity, and family analysis

The exact expiration date should be confirmed against the USPTO Patent Center file history, priority chain, terminal-disclaimer data, and any patent-term adjustment or extension records. Patent expiration does not eliminate the possibility that related continuation, divisional, foreign, or improvement patents had different terms.

What is the Orange Book status of U.S. Patent 5,508,020?

U.S. Patent 5,508,020 is not itself an Orange Book patent listing for a currently protected drug product.

The Orange Book lists patents submitted for approved drug products under Section 505 of the Federal Food, Drug, and Cosmetic Act. A patent directed to a research reagent or broad radiopharmaceutical platform does not automatically receive Orange Book protection. Listing depends on an approved product, the relevant NDA, and FDA acceptance of the submitted patent information.

The patent should therefore be distinguished from:

An NDA product patent;
A drug-substance patent listed for an approved radiopharmaceutical;
A drug-product or formulation patent;
A method-of-use patent with a corresponding FDA use code.

No Orange Book listing can be inferred solely from the patent’s composition claims. [FDA, 2024]

Are there Paragraph IV challenges to this patent?

No current Paragraph IV challenge can create a live dispute over U.S. Patent 5,508,020 because the patent has expired.

Paragraph IV certifications apply when an ANDA applicant challenges a patent listed for an approved drug product. The patent’s expired status removes the practical need for an ANDA applicant to make a Paragraph IV certification directed to this patent.

A historical Paragraph IV record would require review of FDA patent-listing records, ANDA litigation dockets, and district-court complaints. The patent number alone does not establish that an ANDA challenge occurred.

Does biosimilar risk apply to this patent?

Biosimilar risk is not the appropriate framework for this patent.

The claimed subject matter is a peptide-based technetium-99m reagent. It is not an antibody, recombinant protein, or other reference biological product governed by the principal biosimilar pathway under the Public Health Service Act. A later competitor would more likely pursue a drug application, abbreviated pathway where available, or a product-specific radiopharmaceutical approval route.

The relevant competitive risks are:

Generic or follow-on radiopharmaceutical development;
Alternative peptide sequences;
Different technetium chelators;
Nonradioactive imaging agents;
PET agents using fluorine-18, gallium-68, or copper-64;
Products using monovalent rather than multivalent targeting.

What formulation patents and manufacturing patents matter?

The patent’s composition claims do not appear, from the supplied claim text, to provide broad protection for every final dosage form or kit presentation. Later patent families may separately protect:

Lyophilized kit compositions;
Reducing agents used to reduce pertechnetate;
Stabilizers and antioxidants;
Buffer systems;
Reconstitution conditions;
Peptide-chelator purification;
Sterile manufacturing;
Radiolabeling temperature and reaction time;
Quality-control specifications;
Shelf-life and storage conditions.

A competitor could avoid the expired composition patent yet encounter later rights covering a specific kit, manufacturing sequence, or approved indication. This is particularly relevant for technetium-99m products, where commercial performance depends on radiochemical purity, labeling yield, sterility, stability, and kit logistics.

Which companies and technology platforms are relevant competitors?

The competitive field has included radiopharmaceutical companies, peptide developers, diagnostic imaging companies, and academic institutions. Relevant platform categories include:

Competitor type	Relevant activity
Radiopharmaceutical developers	Technetium-99m kits and diagnostic agents
Peptide therapeutics companies	Targeting ligands and peptide conjugates
Nuclear medicine companies	Imaging agents and hospital supply chains
Antibody imaging developers	Larger targeting molecules with different clearance profiles
PET developers	Fluorine-18, gallium-68, and copper-64 alternatives
Contract manufacturers	Peptide synthesis, conjugation, radiolabeling, and sterile fill-finish

The strongest commercial substitutes are not limited to products with the same patent architecture. A PET agent directed to the same biological target may compete clinically even if its chemistry does not resemble the claimed technetium reagent.

How strong is the patent estate for U.S. Patent 5,508,020?

As a current U.S. exclusion right, the estate is weak because the patent has expired. As a historical platform patent, its claim structure was potentially significant because claim 1 combines:

Multivalency;
Specific-binding peptides;
A defined peptide-length range;
Covalent attachment;
A polyvalent linker; and
Technetium-binding functionality.

The strongest infringement case would involve a product reproducing the entire architecture, including the required structural formula. The weakest case would involve a monovalent agent, a different linker topology, a different radionuclide, or a noncovalently assembled formulation.

The claim is also vulnerable to conventional validity challenges based on:

Earlier technetium-99m chelator disclosures;
Prior peptide imaging agents;
Known multivalent ligand constructs;
Obvious combinations of chelator and targeting peptide technology;
Written-description and enablement issues across a broad peptide sequence range.

Because the patent is expired, those validity questions have greater value for historical patent analysis and interpretation of later patent families than for current enforcement.

What generic launch scenarios existed for products related to this patent?

A competitor could have pursued several design-around routes:

Use one targeting peptide instead of multiple peptides.
Use a multivalent scaffold without the claimed polyvalent linker architecture.
Attach the technetium-binding group only through a different structural arrangement.
Replace the claimed peptide sequence with a different ligand.
Use a non-technetium radionuclide.
Use a different chelator or coordination geometry.
Supply the peptide-chelator conjugate separately from the radiolabeling reagent.
Develop a PET imaging agent for the same target.

These routes would require separate analysis of later patents, regulatory requirements, and clinical comparability. Avoiding U.S. Patent 5,508,020 would not establish freedom to operate against the broader radiopharmaceutical patent landscape.

Key Takeaways

U.S. Patent 5,508,020 covers multivalent peptide-based technetium-99m imaging reagents.
Claim 1 requires multiple specific-binding peptides, a polyvalent linker, covalent attachment, and a technetium-binding moiety.
Claims 2 and 3 are narrower species claims directed to the structures shown in Formulas 9 and 10.
The patent is expired and does not create a current U.S. blocking right.
The patent is not, by itself, an Orange Book listing or a biosimilar-relevant patent.
Later patents covering chelators, kits, formulations, manufacturing methods, indications, and alternative radionuclides may remain commercially important.
The most credible design-arounds use monovalent ligands, different linkers, different chelators, or non-technetium imaging platforms.
Exact scope analysis for claims 2 and 3 requires the structural drawings for Formulas 9 and 10, which are not reproduced in the supplied text.

FAQs About U.S. Patent 5,508,020

Does U.S. Patent 5,508,020 cover all technetium-99m peptide imaging agents?

No. The claims require a multivalent arrangement with multiple specific-binding peptides and the specified linker and technetium-binding architecture.

Does the patent cover a single peptide linked to a technetium chelator?

Generally, no. A single-targeting-peptide construct would not satisfy the express multiplicity and multivalency limitations of claim 1.

Can an expired patent still affect a new radiopharmaceutical launch?

It cannot block commercialization through current patent enforcement, but it can remain relevant as prior art and as a source for interpreting related continuation, foreign, or improvement patents.

Are the Formula 9 and Formula 10 structures important for infringement?

Yes. Claims 2 and 3 are structure-specific. The exact linker, chelator, peptide attachment points, substituents, and stereochemistry may determine whether a later compound falls within either claim.

Is a technetium-99m imaging kit automatically covered by this patent?

No. A kit must satisfy the claimed molecular composition. Separate kit, formulation, manufacturing, and regulatory patents may apply even when the kit falls outside this patent.

References

U.S. Patent No. 5,508,020. United States Patent and Trademark Office. Issued April 16, 1996.
United States Patent and Trademark Office. (2024). Patent Center and patent term adjustment records. https://patentcenter.uspto.gov/
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations: Orange Book. https://www.fda.gov/drugs/drug-approvals-and-databases/approved-drug-products-therapeutic-equivalence-evaluations-orange-book
U.S. Food and Drug Administration. (2024). Patent listing and certification requirements under the Hatch-Waxman amendments. https://www.fda.gov/drugs/fdas-regulations-and-guidance-industry/patent-and-exclusivity-information
U.S. Food and Drug Administration. (2024). Biosimilar and interchangeable biosimilar products. https://www.fda.gov/drugs/biosimilars/bsu.fa

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	152918	⤷ Start Trial
Austria	222264	⤷ Start Trial
Australia	4528793	⤷ Start Trial
Australia	5402694	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 5,508,020

Summary for Patent: 5,508,020