US Patent 6,123,916: Scope, Claims, Expiration, and Somatostatin Radiopharmaceutical Patent Landscape

US Patent 6,123,916 covers somatostatin peptide derivatives in which a terminal amino group is linked through an amide bond to a polyaminopolycarboxylic chelator. Its claims extend to therapeutic use, nuclear-medicine imaging, targeted radiotherapy, specific peptide structures, chelators, radionuclides, and disease indications.

The patent is historically relevant to radiolabeled somatostatin analogs, including compounds related to octreotide and later peptide-receptor radionuclide therapy products. Its core US patent term has expired, eliminating current US patent-exclusion rights from this patent. The claims remain relevant as prior art and as a technical foundation for analyzing later patents covering DOTATOC, DOTATATE, DOTANOC, and related somatostatin receptor-targeting agents.

What does US Patent 6,123,916 cover?

US Patent 6,123,916 is directed to somatostatin peptide derivatives modified with a metal-chelating group. The chelator is attached to a terminal amino group through an amide linkage. The resulting conjugate can be used either as an unlabeled therapeutic peptide or as a radiolabeled diagnostic or therapeutic agent.

The patent has three principal claim categories:

Claim category	Principal subject matter	Claims
Unlabeled therapy	Treatment of excess growth-hormone secretion, gastrointestinal disorders, epidermal-cell proliferation or keratinization, and degenerative senile dementia	1, 4-8
Diagnostic imaging	In vivo detection of specified diseases using gamma- or positron-emitting radionuclides	2, 9-20
Targeted radiotherapy	Treatment of malignant lymphoma, Merkel cell skin tumors, and osteosarcoma using alpha- or beta-emitting radionuclides	3, 21-23

The invention combines three technical elements:

A somatostatin peptide or analog.
A terminal polyaminopolycarboxylic chelator.
A therapeutic or diagnostic radionuclide, where applicable.

The claims are method claims rather than claims directed solely to a composition, commercial product, manufacturing process, or pharmaceutical formulation.

What are the key limitations in independent claims 1, 2, and 3?

Claim 1: Unlabeled somatostatin-peptide treatment

Claim 1 requires administration of a somatostatin peptide modified at its terminal amino group by a polyaminopolycarboxylic group. The modification must be through an amide bond.

The claimed indications are:

Disorders caused by or associated with excess growth-hormone secretion.
Gastrointestinal disorders.
Inhibition of epidermal-cell proliferation or keratinization.
Degenerative senile dementia.

The claim is broad as to the peptide structure, provided that the molecule is a qualifying somatostatin peptide and contains the specified terminal chelator conjugation.

A potential infringement analysis would therefore require proof of all of the following:

The administered compound is a somatostatin peptide.
The peptide has a terminal amino group.
A polyaminopolycarboxylic group is attached to that amino group.
The connection is an amide bond.
The compound is administered for one of the claimed indications.
The amount is effective for treating the indication.

The claim does not cover every somatostatin analog. A somatostatin analog lacking the terminal chelator, using a different attachment site, or using a non-amide linkage would fall outside the literal language of claim 1.

Claim 2: Diagnostic imaging

Claim 2 covers in vivo detection of:

Tuberculosis.
Sarcoidosis.
Malignant lymphoma.
Merkel cell tumor of the skin.
Osteosarcoma.
Focal lymphocytic reaction.
Localized autoimmune disease.
Organ rejection after transplantation.

The method requires administration of a labeled chelator-modified somatostatin peptide carrying either:

A gamma-emitting radionuclide; or
A positron-emitting radionuclide.

The second required step is recording the localization of receptors targeted by the labeled peptide.

Claim 2 is therefore narrower than a general claim to somatostatin-receptor imaging. It combines the compound architecture, radionuclide class, receptor-localization step, and an expressly listed disease or pathological condition.

Claim 3: Targeted radiotherapy

Claim 3 covers administration of a labeled chelator-modified somatostatin peptide carrying an alpha- or beta-emitting radionuclide for treatment of:

Malignant lymphoma.
Merkel cell tumor of the skin.
Osteosarcoma.

This claim does not expressly cover all neuroendocrine tumors or all somatostatin-receptor-positive cancers. Its disease scope is limited to the listed indications.

The claim also requires a radiotherapeutic radionuclide. Diagnostic isotopes such as indium-111 or gallium-68 would not satisfy the alpha- or beta-emission limitation in claim 3.

What structures and chemical classes are protected by claims 4 through 8?

Claims 4 and 5 define a large peptide genus through Markush language. The disclosed structural variables cover modified analogs containing residues corresponding to:

Phenylalanine or substituted phenylalanine.
Tryptophan, including D-tryptophan and N-methylated variants.
Lysine and lysine analogs.
Threonine, serine, valine, phenylalanine, isoleucine, aminobutyric acid, and related residues.
Beta-naphthylalanine.
4-aminocyclohexylalanine and 4-aminocyclohexylglycine.
D- and L-configured amino-acid residues.
Substituted terminal groups and peptide extensions.

Claim 4 also permits several chelator-compatible terminal configurations. The claim requires selection of A and A' such that the compound contains a terminal NH group capable of linkage to the polyaminopolycarboxylic group.

Claim 5 narrows the peptide to a more specific series in which:

B is phenylalanine or tyrosine.
C is D-tryptophan.
D is lysine.
E is valine or threonine.
G is a specified amide-containing group.

Claim 6 identifies four chelator classes:

Chelator	Common abbreviation or description
Ethylenediaminetetraacetic acid	EDTA
Diethylenetriaminepentaacetic acid	DTPA
1,4,7,10-tetraazacyclododecanetetraacetic acid	DOTA
1,4,8,11-tetraazacyclotetradecanetetraacetic acid	Cyclam-derived tetraacetic acid

Claim 7 narrows the structure to a formula Ia compound containing a DTPA residue. Claims 8 and 9 appear to identify specific structures reproduced as patent drawings. Because the structures are supplied in the question only as image placeholders, the exact chemical names of those compounds cannot be determined from the text alone.

Which radionuclides are covered by US 6,123,916?

The patent claims broad radionuclide categories and then lists specific isotopes.

Diagnostic radionuclides

Claim 10 lists gamma-emitting radionuclides:

Gallium-67.
Indium-111.
Technetium-99m.
Ytterbium-169.
Rhenium-186.

Claim 11 separately identifies positron-emitting gallium-68.

Claim 12 narrows the diagnostic method to a specific chelator-modified peptide labeled with indium-111.

Therapeutic radionuclides

Claim 22 lists beta-emitting radionuclides, including:

Yttrium-90.
Copper-67.
Rhenium-186.
Rhenium-188.
Erbium-169.
Tin-121.
Tellurium-127.
Praseodymium-143.
Gold-198.
Palladium-109.
Dysprosium-165.
Phosphorus-32.
Praseodymium-142.

Claim 23 identifies alpha-emitting astatine-211 and bismuth-212.

The radionuclide claims are important because they distinguish diagnostic imaging from therapeutic irradiation. Modern peptide-receptor radionuclide therapy generally relies on beta-emitting lutetium-177 or yttrium-90, while the issued claims specifically list yttrium-90 but do not list lutetium-177.

When did US Patent 6,123,916 expire?

Event	Date or status
US patent number	6,123,916
Issue date	September 26, 2000
Earliest priority date generally associated with the patent family	August 19, 1994
Core US patent term	Expired in 2015, subject to any applicable term adjustment
Current enforceability	No ordinary enforceable US patent term remains

The relevant term analysis depends on the patent family’s priority and US national-stage filing history. For a PCT-derived application filed after June 8, 1995, the effective term generally runs 20 years from the applicable international filing date, rather than 20 years from the earliest foreign priority date. The patent’s commercial exclusion period nevertheless ended years ago under the ordinary US patent-term framework. The patent should not be treated as a live blocking patent for current US development or commercialization.

No current patent-term extension appears to be the basis for continuing enforceability of US 6,123,916. A patent-term extension under 35 U.S.C. § 156 would also require a qualifying regulatory product and an eligible patent-product relationship. The claimed diagnostic and therapeutic methods do not establish such an extension by themselves.

What is the Orange Book status of US Patent 6,123,916?

US Patent 6,123,916 is not a current Orange Book exclusion right for Lutathera or other modern somatostatin-receptor radiopharmaceuticals.

The Orange Book lists patents submitted by an NDA holder for an approved drug product. A historical method patent may be absent because:

It expired before the relevant product approval.
It was not submitted by the NDA holder.
Its claims did not correspond to the approved drug’s labeling.
The patent covered research compounds or indications different from the approved indication.
The product approval involved a later compound and a separate patent estate.

The FDA approved Lutathera, lutetium Lu 177 dotatate, in 2018 for adults with somatostatin receptor-positive gastroenteropancreatic neuroendocrine tumors, including foregut, midgut, and hindgut neuroendocrine tumors. Lutathera is associated with later patents and regulatory exclusivities, not with an unexpired exclusion right under US 6,123,916 (FDA, 2018).

How does this patent compare with Lutathera and modern DOTATATE patents?

US 6,123,916 is an early platform patent. It claims the general concept of attaching a metal chelator to a somatostatin peptide and using the conjugate for imaging or radionuclide therapy.

Lutathera uses lutetium-177 dotatate, a DOTA-conjugated somatostatin analog. The product’s commercial and regulatory position depends on later patents directed to the specific peptide, radiolabeled complex, formulation, manufacturing process, dosing regimen, and clinical use.

Issue	US 6,123,916	Modern Lutathera estate
Core peptide concept	Broad chelator-modified somatostatin peptides	Specific DOTATATE and related compounds
Principal chelator scope	EDTA, DTPA, DOTA, cyclam derivatives	Primarily DOTA-based chemistry
Listed therapeutic isotope	Y-90 and many others	Lu-177
Principal claimed indications	GH disorders, gastrointestinal disease, selected tumors, immune and inflammatory conditions	SSTR-positive gastroenteropancreatic neuroendocrine tumors
Claim type	Primarily method claims	Compound, composition, use, formulation, manufacturing, and dosing claims
US status	Expired	Later patents may have expired or remain active depending on patent number and claim
Orange Book relevance	No current blocking position	Product-specific listings may be relevant

The absence of lutetium-177 from claim 22 is significant. A product using Lu-177 would require a separate infringement analysis under the patent’s broader claim 3, if the isotope were interpreted to fall within the claim’s generic “beta-emitting radionuclide” language. Claims 21 and 22 together may raise that issue, but the patent’s expiration makes it commercially immaterial in the United States.

What patent litigation and Paragraph IV risks affect this patent?

No current Paragraph IV challenge can create a live market-exclusion dispute for US 6,123,916 because the patent has expired. A Paragraph IV certification applies to a listed patent in the Orange Book for an abbreviated new drug application. It does not revive an expired patent or create a new enforceable term.

The practical litigation relevance is historical and analytical:

The patent could have been asserted against products using covered chelator-peptide combinations during its term.
A defendant could have challenged written description, enablement, anticipation, obviousness, claim construction, or method-of-use infringement.
Claims 4 and 5 would have been vulnerable to written-description and enablement scrutiny because of their extensive Markush variables.
Claims 2 and 3 could have raised divided-infringement issues where imaging, radiolabeling, administration, and receptor localization were performed by different actors.
Disease-specific method claims would have required evidence that the accused product was used for the claimed indication.

There is no current commercial Paragraph IV risk based solely on this patent.

How strong was the patent estate?

The patent was strongest as an early platform patent covering the general architecture of chelator-linked somatostatin peptides. Its broadest practical value came from the combination of:

A somatostatin-receptor targeting peptide.
A chelator capable of binding diagnostic or therapeutic metals.
A radionuclide-linked imaging or treatment method.

Its limitations were material:

The claims were method claims, making proof of the treatment or diagnostic use necessary.
The listed diseases did not map cleanly onto the later commercial use of Lutathera in gastroenteropancreatic neuroendocrine tumors.
The claims did not expressly identify every later commercial peptide, radionuclide, or formulation.
The Markush genus created potential validity disputes concerning written description and enablement.
The patent expired before the major commercial expansion of peptide-receptor radionuclide therapy.

The estate is therefore historically important but has no remaining US blocking strength.

What generic and biosimilar entry risks exist?

Biosimilar risk is not the relevant framework because the covered products are synthetic peptides and radiolabeled small-molecule-peptide complexes, not biologics regulated through the biosimilar pathway under section 351(k) of the Public Health Service Act.

The relevant competitive pathways are:

Generic or hybrid drug applications for non-radioactive peptide products.
NDA-based competition for radiopharmaceuticals.
505(b)(2) applications for products relying partly on published literature or an existing reference product.
Compounded or hospital-prepared radiolabeled products, subject to applicable FDA and radiation-regulatory requirements.
New proprietary radioligands using different peptides, chelators, isotopes, or targeting ligands.

For products such as Lutathera, commercial barriers are more likely to arise from manufacturing controls, radionuclide supply, peptide synthesis, radiolabeling facilities, quality systems, dosimetry, logistics, and clinical evidence than from US 6,123,916.

What manufacturing and geographic barriers remain?

The patent’s geographic coverage was limited to the jurisdictions in which corresponding applications were filed and granted. US 6,123,916 cannot block activity in Europe, Japan, China, or other jurisdictions after its US expiry. Each foreign family member requires separate status review.

The technical barriers to entry include:

Production of high-purity peptide intermediates.
Site-specific chelator conjugation.
Control of radiochemical purity and specific activity.
Reliable access to radionuclides.
Aseptic manufacture and sterile filtration.
Short shelf life and radiopharmacy distribution.
Patient-specific dosing and radiation protection.
Validation of receptor affinity and tumor uptake.
Regulatory controls for radioactive medicinal products.

These barriers can preserve commercial concentration even after platform patents expire.

Key Takeaways

US Patent 6,123,916 claims chelator-modified somatostatin peptides for treatment, diagnostic imaging, and targeted radiotherapy.
Independent claims 1, 2, and 3 are limited by the terminal amide-linked polyaminopolycarboxylic group and by specified disease and radionuclide categories.
Claim 6 identifies EDTA, DTPA, DOTA, and a cyclam-derived tetraacetic acid as chelator classes.
The patent issued on September 26, 2000, and its ordinary US patent term expired in 2015.
The patent is not a current US Orange Book blocking patent for Lutathera.
Lutathera and later DOTATATE products depend on later product, formulation, manufacturing, dosing, and method-of-use patents.
Biosimilar analysis is generally inapplicable because the relevant products are synthetic peptide radiopharmaceuticals rather than biologics.
Current entry barriers are more likely to involve radionuclide supply, radiopharmacy infrastructure, manufacturing validation, regulatory approval, and later product-specific patent rights.

FAQs

Does US 6,123,916 cover Lutathera?

It may describe an early technical platform relevant to Lutathera, but it does not provide a current enforceable US patent barrier. Lutathera depends primarily on later patents and regulatory approvals directed to lutetium Lu 177 dotatate and its commercial use.

Does claim 22 expressly list lutetium-177?

No. Claim 22 lists several beta-emitting radionuclides, including yttrium-90 and rhenium isotopes, but does not expressly list lutetium-177.

Can an expired patent still be cited against a new radioligand patent?

Yes. The patent can be used as prior art in novelty, obviousness, written-description, and enablement analyses. Expiration removes enforcement rights but does not remove prior-art significance.

Are DOTA and DTPA both covered?

Yes. Claim 6 expressly identifies DOTA and DTPA, along with EDTA and a cyclam-derived tetraacetic acid, as covered polyaminopolycarboxylic groups.

Is a new somatostatin radiopharmaceutical automatically free to operate because this patent expired?

No. Expiration of US 6,123,916 removes one patent risk only. A freedom-to-operate review must assess later patents covering the specific peptide, chelator, radionuclide, formulation, manufacturing method, dosing regimen, indication, and radiolabeling process.

References

United States Patent and Trademark Office. (2000). Somatostatin peptide derivatives (U.S. Patent No. 6,123,916).
U.S. Food and Drug Administration. (2018). FDA approves new treatment for certain digestive tract cancers.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations.
United States Code, 35 U.S.C. §§ 154, 156, 271, and 282.
United States Code, 21 U.S.C. § 355(j).

Foriegn Application Priority Data
Foreign Country	Foreign Patent Number	Foreign Patent Date
United Kingdom	9004017	Feb 22, 1990

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Belgium	1004645	⤷ Start Trial
Switzerland	683318	⤷ Start Trial
Germany	4104308	⤷ Start Trial
France	2658421	⤷ Start Trial
United Kingdom	2241167	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 6,123,916

Summary for Patent: 6,123,916