United States Drug Patent 6,844,013: Claim Scope, Expiration, Litigation Risk, and Patent Landscape

US 6,844,013 protects methods of stimulating the human immune system with isolated angeloyl-substituted ingenanes, their salts, and active derivatives obtained from Euphorbia sap. The patent is method-of-treatment focused. It does not claim a composition, extraction process, or specific product in isolation. Its commercial relevance is tied to ingenane compounds associated with Euphorbia peplus, including compounds related to ingenol 3-angelate and acetylated derivatives.

The patent’s practical blocking value is limited by its narrow therapeutic endpoint, source restrictions, functional language, likely expired term, and the distinction between its claimed compounds and FDA-approved ingenol mebutate products.

What does US Patent 6,844,013 claim?

US 6,844,013 contains one independent claim, claim 1. It requires all of the following:

A method for stimulating the immune system.
A human subject in need of treatment.
Administration of a therapeutically effective amount.
At least one isolated compound.
The compound must be an angeloyl-substituted ingenane, its salt, or an active derivative.
The compound must be obtained from the sap of a Euphorbia species.
An active derivative must exhibit the same activity as the relevant angeloyl-substituted ingenane.

The dependent claims narrow the genus by species, chemical structure, extraction method, biological activity, and dosage-form context.

Claim group	Subject matter	Main limitation
1	Immune-stimulation treatment	Isolated angeloyl-substituted ingenane or active derivative from Euphorbia sap
2	Euphorbia peplus	Species-specific source
3	Euphorbia drummondii	Species-specific source
4	Euphorbia hirta	Species-specific source
5-7	Acetylated derivatives	Species-linked acetylation
8	20-O-acetyl-ingenol-3-angelate and ester derivatives	Structural limitation
9	Salts	Pharmaceutically acceptable salt limitation
10	Ethanol extraction	95% v/v ethanol, discard solid, retain soluble fraction
11	T-cell proliferation	Specific immune response
12	G-CSF expression	Specific cytokine response
13	MHC expression	Specific immune response
14	Natural-killer-cell recruitment	Local immune-cell recruitment
15	Pharmaceutical or cosmetic composition	Carrier limitation in the administered formulation

Claims 2 through 15 depend on claims 1 through 4 and therefore retain the core requirements of claim 1.

What compounds fall within the patent?

The central chemical class is an angeloyl-substituted ingenane. The claim language covers:

Angeloyl-substituted ingenanes isolated from Euphorbia sap.
Salts of those compounds.
Active derivatives that exhibit the same immune-stimulating activity.
Acetylated derivatives.
20-O-acetyl-ingenol-3-angelate.
Ester derivatives of 20-O-acetyl-ingenol-3-angelate.

The patent is not limited to one named molecule. Claim 1 is a genus claim, while claim 8 identifies a narrower structural species.

Does the patent cover ingenol mebutate?

Ingenol mebutate is commonly identified as ingenol 3-angelate, the active ingredient historically marketed in Picato gel. The claim language supplied for US 6,844,013 specifically identifies 20-O-acetyl-ingenol-3-angelate and related ester derivatives in claim 8. That language does not automatically make every ingenol 3-angelate product fall within claim 8.

The broader issue is claim 1. A product containing isolated ingenol 3-angelate could potentially implicate claim 1 if the compound is:

Angeloyl-substituted;
Obtained from Euphorbia sap;
Used to stimulate the immune system in a human; and
Administered in a therapeutically effective amount.

A synthetically manufactured compound presents a stronger noninfringement position against the “obtained from the sap” limitation, although the analysis would depend on whether the accused compound is materially identical to a sap-derived compound and how the product-by-source language is construed.

Picato’s approved indication was treatment of actinic keratosis, not a standalone indication described as “stimulating the immune system.” A claim infringement analysis would therefore turn on the actual therapeutic purpose, label, promotional materials, mechanism, and evidence of the intended use.

How broad is independent claim 1?

Claim 1 is chemically broad but therapeutically and materially narrow.

Chemical breadth

The claim does not identify a single molecular formula. “Angeloyl-substituted ingenane” can encompass a class of diterpene esters and related derivatives. The active-derivative language expands the claim beyond the naturally occurring compound.

The phrase “same activity” creates a functional boundary. It may cover derivatives that are structurally modified but retain the claimed immune-stimulating effect. That language also creates enforcement and validity issues because the patent must provide sufficient guidance to identify which derivatives qualify.

Source limitation

The compound must be “obtained from the sap of a Euphorbia species.” This is a meaningful limitation. A competitor using a fully synthetic route, a recombinant route, or a non-sap botanical fraction may argue that the claim does not reach its product.

The source limitation is strongest against products using direct sap extraction or a compound isolated from sap. It is less certain for semisynthetic products made by modifying a sap-derived intermediate.

Therapeutic limitation

The accused administration must stimulate the immune system. A method directed solely to keratinocyte destruction, lesion clearance, cytotoxicity, or another nonimmune endpoint may create a claim-construction dispute. Claims 11 through 14 provide narrower examples of immune activity but do not necessarily limit claim 1 to those mechanisms.

What do claims 2 through 15 add?

Species claims

Claims 2, 3, and 4 identify Euphorbia peplus, Euphorbia drummondii, and Euphorbia hirta. These claims are narrower than claim 1 and may be easier to defend against prior art that discloses a different Euphorbia species.

Acetylated derivatives

Claims 5 through 7 specify acetylated derivatives associated with the three named species. These claims focus on chemical modification after isolation or on naturally occurring acetylated constituents, depending on the evidence supporting the claim construction.

20-O-acetyl-ingenol-3-angelate

Claim 8 is the principal narrow chemical claim. It identifies 20-O-acetyl-ingenol-3-angelate and ester derivatives. Claim 9 adds pharmaceutically acceptable salts.

A competitor that uses a different ester, a nonacetylated compound, or a structurally unrelated ingenane may avoid claims 8 and 9 while still facing an argument under claim 1.

Extraction process

Claim 10 requires extraction with 95% v/v ethanol, discarding a solid fraction, and retaining a soluble fraction. This is not a standalone process claim. The extraction must produce a compound used in the claimed immune-stimulation method.

The claim is therefore vulnerable to factual distinctions involving:

Ethanol concentration;
Extraction sequence;
Solid-fraction handling;
Solvent replacement;
Purification;
Use of a synthetic or semisynthetic compound;
Use of a different botanical fraction.

Biological activity claims

Claims 11 through 14 identify measurable or observable biological outcomes:

T-cell proliferation;
G-CSF expression;
MHC expression;
Natural-killer-cell recruitment.

These limitations may assist infringement proof when a product has the same pharmacology. They also create prior-art and enablement questions because the scope depends on assay design, dose, tissue, timing, and the meaning of “induces” or “recruits.”

Composition claim

Claim 15 requires a pharmaceutical or cosmetic carrier, but it remains a method claim. It does not independently protect a cream, gel, ointment, solution, or other composition when sold without the claimed use.

When did US 6,844,013 lose exclusivity?

US 6,844,013 was issued on January 18, 2005. Its enforceable term would generally be determined under the 20-year patent-term rules applicable to the relevant application and priority chain, subject to patent-term adjustment, terminal disclaimers, and maintenance-fee events.[1][2]

Public patent records identify US 6,844,013 as an older Peplin-related patent, and the patent is generally treated as expired rather than an active blocking patent. A current freedom-to-operate analysis should therefore distinguish:

Historical infringement exposure during the patent term;
Any patent-term adjustment;
Patent-term extension;
Continuation or divisional patents;
Foreign counterparts;
Later patents covering formulations, dosing regimens, manufacturing, or approved products.

Expiration of US 6,844,013 would not eliminate separate rights in later patents covering ingenol mebutate formulations or clinical uses.

What is the Orange Book status of US 6,844,013?

US 6,844,013 is not, on the claim language supplied, a conventional Orange Book product patent. It claims a method of immune stimulation rather than a defined FDA-approved drug composition.

The FDA Orange Book lists patents submitted by an NDA holder for an approved drug product. Listing depends on the approved product, the NDA submission, and the sponsor’s patent certification position. A patent may be relevant to an active ingredient or use without being listed for every product containing that ingredient.[3]

Picato, the former ingenol mebutate product, was approved by the FDA under NDA 202833 in 2012 for actinic keratosis. The FDA later approved withdrawal of Picato at the sponsor’s request. The withdrawal was separate from ordinary patent expiration analysis.[4]

The relevant Orange Book questions are therefore product-specific:

Whether US 6,844,013 was ever submitted for Picato;
Whether it was listed for the approved strength or indication;
Whether any listing was removed or delisted;
Whether later formulation or method patents remained listed.

The claim language alone does not establish an Orange Book listing.

Were Paragraph IV challenges available?

A Paragraph IV certification could have been relevant to any abbreviated new drug application referencing an approved ingenol mebutate product if a listed patent covered the referenced product, formulation, or method of use.[5]

US 6,844,013 would present a difficult Paragraph IV target if it were not listed for the referenced product. A generic applicant could not create Paragraph IV litigation merely because a patent broadly relates to the active ingredient.

Potential Paragraph IV positions against this patent would include:

Challenge	Argument
Noninfringement	The generic compound is synthetic or not obtained from Euphorbia sap
Noninfringement	The proposed label does not direct immune-system stimulation
Noninfringement	The product does not contain a claimed acetylated derivative
Invalidity	Prior art discloses the compound, sap extract, or immune activity
Invalidity	“Same activity” is indefinite or insufficiently objective
Invalidity	The genus exceeds the written description or enabling disclosure
Invalidity	The method would have been obvious from known ingenane pharmacology

A section viii statement could be relevant where only method claims are listed and the generic label omits the protected use. That route would depend on the patent’s actual listing and the scope of the approved indication.

What patent litigation affects this estate?

The supplied claim set does not establish a current infringement case, settlement, or Paragraph IV judgment involving US 6,844,013. The patent’s commercial history is more closely associated with the broader Euphorbia peplus/ingenol compound program and the later Picato product estate.

The principal litigation risks historically would have involved:

Competing suppliers of ingenol compounds;
Sap extraction and purification methods;
Semisynthetic conversion of sap-derived intermediates;
Formulated topical products;
Actinic-keratosis treatment methods;
Patent ownership and licensing rights arising from Peplin’s development program.

No settlement agreement should be attributed to US 6,844,013 without a docket-specific record identifying the patent.

Which companies and products were associated with the compound estate?

Peplin developed ingenol mebutate from Euphorbia peplus. LEO Pharma acquired Peplin and commercialized Picato in multiple markets. The principal commercial product was topical ingenol mebutate gel in different strengths for actinic keratosis.

The relevant competitive groups included:

Originator companies developing ingenol-based topical therapies;
Generic manufacturers evaluating abbreviated applications;
Specialty pharmaceutical companies acquiring dermatology assets;
Botanical-extract suppliers;
Manufacturers of synthetic or semisynthetic ingenane compounds;
Developers of alternative actinic-keratosis treatments.

The patent does not create biosimilar risk. Ingenol mebutate is a small molecule, not a biologic. Any follow-on product would ordinarily proceed through a small-molecule generic or hybrid regulatory pathway rather than a biosimilar application under the Biologics Price Competition and Innovation Act.

How strong is the patent estate for US 6,844,013?

The estate is strongest against a company that:

Uses Euphorbia sap as the source material;
Isolates an angeloyl-substituted ingenane;
Uses an acetylated or salt form;
Administers the compound to humans;
Promotes immune stimulation or an immune-mediated therapeutic effect.

The estate is weaker against:

Fully synthetic ingenane compounds;
Products using a different active chemical class;
Products labeled only for a nonimmune endpoint;
Formulations that do not use a sap-derived compound;
Compounds not covered by the acetylated-derivative language;
Manufacturing processes that do not meet claim 10.

Validity risk is material. The claim uses broad genus and functional language, while the dependent claims identify particular species and biological assays. An invalidity challenge would likely focus on written description, enablement, anticipation, obviousness, and definiteness under 35 U.S.C. §§ 102, 103, and 112.[1]

What manufacturing and geographic barriers remain?

The patent’s source limitation can create operational barriers even where patent term has ended. Commercial production may still require:

Controlled cultivation or harvesting of Euphorbia species;
Botanical authentication;
Standardized sap collection;
Solvent extraction and impurity control;
Batch-to-batch chemical characterization;
Supply-chain controls for plant material;
Good Manufacturing Practice compliance;
Protection of downstream purification and formulation know-how.

US 6,844,013 has no continuing US patent exclusivity if its term has expired. Geographic risk must be assessed separately because foreign counterparts may have different filing dates, term adjustments, opposition outcomes, and national-phase status. A US expiration does not establish freedom to operate in Europe, Australia, Japan, Canada, or other markets.

What is the generic launch risk?

For the expired patent itself, the current US launch risk is low. The more relevant barriers are regulatory and commercial:

Whether an approved reference product remains available;
Whether the FDA accepts a generic or hybrid application;
Whether other patents cover the formulation or approved use;
Whether the applicant can demonstrate pharmaceutical equivalence;
Whether the product’s safety profile supports development;
Whether the market is commercially attractive after Picato withdrawal.

A generic using a sap-derived angeloyl ingenane for immune stimulation could have faced infringement exposure during the patent term. After expiration, the principal risks shift to other patents, regulatory exclusivity, trade secrets, manufacturing controls, and product liability.

Key Takeaways

US 6,844,013 is a method-of-treatment patent, not a standalone composition or extraction patent.
Claim 1 covers human immune stimulation using isolated angeloyl-substituted ingenanes, salts, or active derivatives obtained from Euphorbia sap.
Euphorbia peplus, Euphorbia drummondii, and Euphorbia hirta are expressly covered in dependent claims.
Claim 8 narrows the estate to 20-O-acetyl-ingenol-3-angelate and ester derivatives.
Claim 10 requires a specific 95% ethanol extraction sequence but only as part of the claimed treatment method.
Claim 15 covers administration in a pharmaceutical or cosmetic carrier, not the carrier composition by itself.
Ingenol mebutate must be analyzed separately from the claimed 20-O-acetyl derivative.
The patent is generally treated as expired, subject to confirmation of the complete priority and patent-term-adjustment record.
The patent does not create biosimilar risk because ingenol compounds are small molecules.
Current commercial exposure is more likely to arise from later formulation, use, manufacturing, or product-specific patents than from US 6,844,013.

FAQs About US Patent 6,844,013

Does US 6,844,013 claim a cream or gel?

No. Claim 15 requires a pharmaceutical or cosmetic carrier, but the patent claims a method of administering the composition. It does not independently claim the cream or gel as a composition.

Can a synthetic version of the compound avoid US 6,844,013?

Potentially. The claim requires a compound obtained from Euphorbia sap. A fully synthetic compound may avoid that limitation, although the complete manufacturing history and infringement theory would control.

Does the patent cover all uses of Euphorbia peplus sap?

No. The claims require administration of an isolated qualifying compound for immune stimulation. They do not broadly claim every use of the plant, every sap extract, or every dermatological application.

Is claim 10 an independent extraction patent?

No. Claim 10 is dependent on the treatment claims. The ethanol extraction steps matter only when the resulting compound is used in the claimed human treatment.

Does patent expiration eliminate FDA exclusivity?

No. Patent expiration and FDA regulatory exclusivity are separate rights. FDA exclusivity depends on the approved product and applicable statutory exclusivity period, while patent rights depend on the patent term and related patent family.

References

United States Patent No. 6,844,013, Methods for stimulating the immune system using compounds from Euphorbia species (2005). United States Patent and Trademark Office.
United States Patent and Trademark Office. (2024). Patent term adjustment and patent term calculation. https://www.uspto.gov/patents/laws/patent-term-calculator
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. (2020). FDA approves withdrawal of Picato (ingenol mebutate) gel from the market. https://www.fda.gov
U.S. Food and Drug Administration. (2024). Abbreviated new drug application submissions: Patent certifications and section viii statements. https://www.fda.gov/drugs/abbreviated-new-drug-application-anda/anda-submissions-patent-certifications-and-section-8-statements

Foriegn Application Priority Data
Foreign Country	Foreign Patent Number	Foreign Patent Date
Australia	PO 8640	Aug 19, 1997

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
European Patent Office	1015413	⤷ Start Trial	C300592	Netherlands	⤷ Start Trial
European Patent Office	1015413	⤷ Start Trial	CA 2013 00024	Denmark	⤷ Start Trial
European Patent Office	1015413	⤷ Start Trial	92185	Luxembourg	⤷ Start Trial
European Patent Office	1015413	⤷ Start Trial	C01015413/01	Switzerland	⤷ Start Trial
European Patent Office	1015413	⤷ Start Trial	505	Finland	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 6,844,013

Summary for Patent: 6,844,013