United States Patent 6,432,452 covers topical treatment of skin cancer with angeloyl-substituted ingenanes derived from Euphorbia peplus, including ingenol mebutate and specified derivatives. Its central method claims are broad, but the patent is expired under the ordinary 20-year term calculated from the U.S. filing date. It therefore presents no current U.S. blocking right. Later Picato patents focused on formulations, dosing regimens, and manufacturing rather than recreating the full scope of the original natural-product method claims.

United States Drug Patent 6,432,452: Scope, Claims, Expiration, and Patent Landscape

What does United States Patent 6,432,452 cover?

US 6,432,452 covers a method of treating skin cancer by topical administration of an angeloyl-substituted ingenane obtained from the sap of Euphorbia peplus, or an active derivative of that compound.[1]

The patent is associated with the natural-product technology that led to ingenol mebutate, also known as PEP005. Ingenol mebutate was later developed as Picato, a topical prescription product for actinic keratosis.[2]

The independent claim is claim 1. It requires four principal elements:

A subject with skin cancer.
Topical administration.
A therapeutically effective amount.
An angeloyl-substituted ingenane from Euphorbia peplus sap, or an active derivative with the same activity.

The claim does not require a particular concentration, dosing frequency, treatment duration, formulation vehicle, manufacturing process, or molecular structure beyond the defined compound category.

Patent element	Scope
Patent	US 6,432,452
Title	Treatment of skin cancer
Patent type	U.S. utility patent
Applicant/assignee history	Associated with Peplin Research Pty Ltd and the Euphorbia peplus technology
Core active	Angeloyl-substituted ingenane, including ingenol mebutate-related compounds
Route	Topical
Disease	Skin cancer and, under dependent claim 11, solar keratosis
Claimed subject	Any subject under claim 1; human subject under claim 12
U.S. filing date used for ordinary term analysis	March 16, 1998
Ordinary 20-year term	March 16, 2018, subject to any patent-term adjustment or extension recorded in the official patent file
Current status	Expired and not an enforceable U.S. blocking patent

How broad is claim 1 of US 6,432,452?

Claim 1 is broad in therapeutic and chemical scope but narrower than a generic claim to all topical ingenol compounds.

The claim is limited by the following language:

The compound must be an angeloyl-substituted ingenane.
The compound must be obtained from Euphorbia peplus sap, or be an active derivative of such a compound.
The administration must be topical.
The use must treat skin cancer.
The dose must be therapeutically effective.

The source limitation is important. A compound chemically identical to a natural Euphorbia peplus compound may not automatically satisfy the literal “obtained from the sap” language if it is manufactured entirely by chemical synthesis. Patent construction would depend on whether the phrase is treated as a product-source limitation, a process limitation, or a description of the claimed compound’s identity.

The claim also contains functional language: an active derivative must “exhibit the same activity” as the angeloyl-substituted ingenane. That language potentially expands coverage beyond a single named molecule, but it creates infringement and validity issues concerning:

The relevant biological activity.
The assay used to measure activity.
The degree of similarity required.
Whether an esterified or otherwise modified compound retains the claimed activity.
Whether the derivative is active as administered or only after conversion in skin.

Because claim 1 is a method claim, a potential infringer would generally need to practice the claimed therapeutic method. Mere manufacture or sale of a compound would not, by itself, necessarily infringe claim 1 unless the surrounding facts supported contributory or induced infringement.

What do claims 2 through 6 protect?

Claims 2 through 6 narrow the active compound or source process.

Claim	Subject matter	Practical effect
2	Acetylated derivative of an angeloyl-substituted ingenane	Covers a defined derivative class
3	20-O-acetyl-ingenol-3-angelate and ester derivatives	Identifies a more specific chemical genus
4	Pharmaceutically acceptable salt of the compound or ester derivative	Extends claim 3 to salt forms
5	Compound obtained by aqueous extraction of Euphorbia peplus sap and collection of the aqueous fraction	Adds an extraction-process limitation
6	Extraction with 95% v/v ethanol, discarding the soluble fraction and retaining the solid fraction	Adds a specific ethanol/solid-fraction process
1	Broad method using the compound class	Principal coverage

Claims 5 and 6 are particularly vulnerable to noninfringement arguments if a commercial process uses a materially different extraction scheme. They also raise enablement and claim-construction questions because the claims combine a therapeutic method with a source or preparation limitation.

Claim 6 is unusual from a commercial manufacturing perspective. It does not simply claim an active ingredient. It ties the claimed material to extraction with 95% ethanol, disposal of the soluble fraction, and retention of the solid fraction. A manufacturer using a purified synthetic route, supercritical-fluid extraction, a different solvent concentration, or a different fractionation sequence could have a stronger noninfringement position under that dependent claim.

Which cancers and conditions are covered by the claims?

Claims 7 through 11 identify specific skin conditions:

Malignant melanoma.
Merkel cell carcinoma.
Squamous cell carcinoma.
Basal cell carcinoma.
Solar keratosis, commonly referred to as actinic keratosis.

Claim 12 limits the subject to a human.

The approved Picato indication was actinic keratosis, not melanoma, Merkel cell carcinoma, basal cell carcinoma, or squamous cell carcinoma.[2] The broader cancer indications in the patent therefore exceed the approved U.S. label.

Claimed condition	Covered by patent?	Picato U.S. label
Actinic/solar keratosis	Yes	Yes
Squamous cell carcinoma	Yes	No
Basal cell carcinoma	Yes	No
Merkel cell carcinoma	Yes	No
Malignant melanoma	Yes	No

The patent’s inclusion of melanoma and Merkel cell carcinoma does not establish clinical efficacy or FDA approval for those diseases. Those claim categories would have required supporting disclosure and evidence sufficient to satisfy patentability standards at filing and, separately, regulatory evidence for marketing approval.

When did US 6,432,452 expire?

The ordinary patent term is 20 years from the earliest effective U.S. nonprovisional filing date, subject to patent-term adjustment, patent-term extension, terminal disclaimers, and other statutory adjustments.[3]

For US 6,432,452, the ordinary term calculated from the March 16, 1998 U.S. filing date ended March 16, 2018. The patent is now expired under the U.S. patent records used for commercial freedom-to-operate analysis.

Event	Date
Earliest priority associated with the invention	March 14, 1997
U.S. filing	March 16, 1998
Patent grant	August 13, 2002
Ordinary 20-year term endpoint	March 16, 2018
Current enforceability	Expired

The patent grant date does not control the modern U.S. patent term for this application. The relevant calculation is generally based on the U.S. filing date, not the August 13, 2002 issue date.

What is the Orange Book status of the Picato patents?

Picato was approved by FDA in January 2012 for topical treatment of actinic keratosis.[2] The product’s Orange Book protection historically included patent information associated with ingenol mebutate and its use or formulation.

The Orange Book does not itself create patent rights. It records patents submitted by an NDA holder that are asserted to cover the approved drug, its formulation, or an approved method of use.[4]

The commercial significance of US 6,432,452 is now historical:

It supported the original natural-product therapeutic concept.
It may have been relevant to the early Picato patent position.
Its method claims are no longer enforceable because the patent term has ended.
A generic applicant cannot receive a current market-exclusivity advantage merely by challenging an expired patent.
The product’s present patent risk must be evaluated against later patents, if any remain enforceable, rather than against 6,432,452 alone.

Were there Paragraph IV challenges to Picato?

A Paragraph IV certification is used when a generic applicant asserts that a listed patent is invalid, unenforceable, or not infringed.[5]

For an expired patent such as US 6,432,452, a new Paragraph IV challenge would have little practical value. The applicant would ordinarily certify that the patent has expired rather than mount a conventional litigation challenge seeking early entry.

Historical generic litigation involving Picato would have been directed to unexpired Orange Book-listed patents, if any, including later formulation, dosage, or use patents. The business impact of a Paragraph IV filing would have depended on:

The exact patent numbers listed at the time.
Whether the generic product used the same strength and dosage form.
Whether the generic applicant carved out patented indications.
Whether the NDA holder filed suit within the statutory period.
Whether 180-day generic exclusivity was triggered.

There is no current Paragraph IV barrier created by US 6,432,452 itself.

What later patents protected ingenol mebutate and Picato?

The later patent landscape generally separated into four categories:

Formulation patents

These patents addressed topical compositions containing ingenol mebutate or related compounds. Typical limitations included:

Concentration ranges.
Gel, cream, or solution vehicles.
Stabilizers and preservatives.
pH.
Packaging.
Single-use dosing units.
Storage stability.

A formulation claim can remain relevant even after an earlier active-ingredient or treatment-method patent expires if the marketed product practices the later formulation claims.

Method-of-use patents

Later patents may have addressed:

Treatment of actinic keratosis.
Specific body sites, including the face, scalp, trunk, or extremities.
One-day, two-day, or three-day regimens.
Specific concentration schedules.
Sequential or field-directed treatment.
Reduced-irritation dosing.

A generic applicant can sometimes avoid method-of-use infringement through a “skinny label” that excludes patented indications or regimens. That strategy does not eliminate all risk if the generic product is actively marketed for the patented use.

Manufacturing patents

Manufacturing protection could cover:

Isolation of ingenol mebutate from Euphorbia peplus.
Purification and crystallization.
Removal of co-extracted diterpenes.
Control of impurities.
Conversion of precursor compounds.
Synthetic or semisynthetic production.
Batch consistency and pharmaceutical-grade specifications.

These patents are commercially more important where natural sap extraction produces variable composition or where the active ingredient requires a controlled impurity profile.

Composition and derivative patents

Additional patents could cover:

Specific esters.
Acetylated derivatives.
Prodrugs.
Salt forms.
Polymorphs.
Solid forms.
Combination products.

The claims supplied for US 6,432,452 already address acetylated derivatives and salts, but the patent’s expiration prevents those claims from blocking current U.S. development.

How strong was the patent estate for ingenol mebutate?

US 6,432,452 had strong historical breadth at the concept level because it connected a natural product to topical treatment of multiple skin cancers. Its principal weaknesses were technical and legal:

Source ambiguity: “obtained from the sap” could create disputes for purified or synthetic material.
Functional uncertainty: “same activity” is broad but potentially difficult to apply.
Therapeutic breadth: the claims covered cancers beyond the later FDA-approved indication.
Natural-product disclosure: the scope depended on sufficient identification and reproducibility of the active compounds.
Method-claim dependence: infringement required practice of the treatment method.
Expiration: the patent no longer has exclusionary value.

The later Picato estate was likely more commercially targeted because formulation and regimen claims can map directly to the marketed product. Those claims are generally narrower than the original concept claim but can be more useful in litigation because they identify concrete product characteristics.

Are biosimilar risks relevant to ingenol mebutate?

No. Ingenol mebutate is a small molecule, not a biologic. A competing product would follow the generic drug framework, generally under an abbreviated new drug application under section 505(j) of the Federal Food, Drug, and Cosmetic Act, rather than the biosimilar pathway under section 351(k) of the Public Health Service Act.[6]

Relevant competitive pathways include:

Generic topical ingenol mebutate.
A new drug application for a reformulated product.
A different topical natural-product extract.
A synthetic or semisynthetic analog.
A noninfringing formulation.
A product using a different treatment regimen.

Bioequivalence for topical products can be more complex than for conventional oral generics. FDA may evaluate formulation composition, pharmacokinetics, pharmacodynamics, comparative clinical endpoint data, or other product-specific evidence.

What generic launch risks exist?

A generic launch based solely on the expiration of US 6,432,452 faces no remaining patent barrier from that patent. Commercial risks may still include:

FDA safety concerns regarding ingenol mebutate.
Product withdrawal or discontinuation.
Difficulty reproducing the reference formulation.
Limited market size.
Generic development cost.
Manufacturing complexity.
Residual later patents.
Product liability exposure.
Physician and patient adoption concerns.

FDA warned about an increased risk of skin cancer with Picato and concluded that the risks outweighed the benefits in the United States. The manufacturer subsequently discontinued U.S. marketing.[7] That regulatory history materially reduces the attractiveness of a conventional generic launch even though the foundational patent has expired.

What is the current competitive landscape?

The principal competition is no longer limited to patent-cleared ingenol mebutate. Actinic keratosis treatment includes cryotherapy, photodynamic therapy, topical 5-fluorouracil, imiquimod, diclofenac, tirbanibulin, and procedural approaches.[8]

Product or approach	Active treatment	Competitive relevance
Picato	Ingenol mebutate	Historical reference product; U.S. marketing discontinued
Efudex and generic 5-FU	Fluorouracil	Established topical competitor
Aldara/Zyclara	Imiquimod	Immune-response modifier
Solaraze and generic products	Diclofenac	Topical anti-inflammatory treatment
Klisyri	Tirbanibulin	Newer short-course topical treatment
Photodynamic therapy	Aminolevulinate or methyl aminolevulinate-based protocols	Office-based field treatment
Cryotherapy	Physical lesion destruction	Common procedural alternative

Key Takeaways

US 6,432,452 claims topical treatment of skin cancer with angeloyl-substituted ingenanes from Euphorbia peplus, including ingenol mebutate-related compounds.
Claim 1 is broad but depends on topical administration, therapeutic use, skin cancer treatment, and the compound’s natural-product identity or active derivative status.
Claims 2 through 6 narrow the invention to acetylated derivatives, ester and salt forms, and specified extraction procedures.
Claims 7 through 11 cover melanoma, Merkel cell carcinoma, squamous cell carcinoma, basal cell carcinoma, and solar keratosis.
Claim 12 limits the subject to humans.
The ordinary U.S. patent term ended in 2018. The patent is no longer enforceable.
Picato was FDA-approved for actinic keratosis, not the full range of cancers recited in the patent.
Ingenol mebutate is a small molecule, so biosimilar analysis is not applicable.
Current commercial risk depends on FDA safety history, later patents, manufacturing capability, and competition from other actinic keratosis therapies.
The largest residual risk is regulatory and commercial rather than infringement risk under US 6,432,452.

FAQs about US 6,432,452 and ingenol mebutate

Does US 6,432,452 cover synthetic ingenol mebutate?

Not necessarily. The claims refer to an angeloyl-substituted ingenane obtained from Euphorbia peplus sap or an active derivative of that material. A fully synthetic product would require a claim-construction analysis under the patent’s source and identity limitations. In any event, the patent is expired.

Does US 6,432,452 cover Picato?

Historically, the patent was relevant to the technology underlying Picato. It is not a current enforceable patent blocking Picato or a generic ingenol mebutate product.

Can a generic company file a Paragraph IV certification against US 6,432,452 today?

A generic applicant would not ordinarily challenge an already expired patent under Paragraph IV. The practical certification would reflect expiration rather than a conventional invalidity or noninfringement challenge.

Does the patent cover treatment of nonhuman animals?

Claim 1 is not limited to humans, while claim 12 expressly limits the method to a human subject. The broader claim could raise nonhuman-subject coverage questions, subject to claim construction and statutory patent requirements.

Is a new Euphorbia peplus extract automatically covered by the patent?

No. The extract would need to satisfy the relevant compound, activity, topical-use, and skin-cancer limitations. The patent’s expiration also eliminates current U.S. infringement risk under these claims.

References

United States Patent No. 6,432,452. (2002). Treatment of skin cancer. U.S. Patent and Trademark Office.
U.S. Food and Drug Administration. (2012). Picato (ingenol mebutate) prescribing information.
U.S. Patent and Trademark Office. (2024). Patent term calculator and patent term adjustment guidance.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations.
U.S. Food and Drug Administration. (2024). Hatch-Waxman amendments and abbreviated new drug application patent certifications.
U.S. Food and Drug Administration. (2024). Abbreviated new drug application pathway and biosimilar product pathway.
U.S. Food and Drug Administration. (2020). FDA approves label changes for Picato due to skin cancer risk.
U.S. Food and Drug Administration. (2024). Actinic keratosis treatment products and regulatory information.

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

PCT Information
PCT Filed	August 19, 1998	PCT Application Number:	PCT/AU98/00656
PCT Publication Date:	February 25, 1999	PCT Publication Number:	WO99/08994

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
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 6,432,452

Summary for Patent: 6,432,452