United States Patent 5,008,294: Scope, Claims, Expiration, and Patent Landscape for Catecholic Butane Tumor Treatments

U.S. Patent No. 5,008,294 covers topical or intratumoral treatment of tumors, skin tumors, keratoses, and actinic keratosis with catecholic butanes, particularly nordihydroguaiaretic acid, or NDGA. The patent issued April 16, 1991, and its 17-year pre-1995 patent term expired April 16, 2008, absent a terminal disclaimer or unusual term adjustment. The patent therefore does not create a current U.S. exclusivity barrier.

The commercial scope was broad in chemical structure but narrower in therapeutic use. The central claims required both a covered catecholic butane and administration at the tumor or lesion site. Systemic use, non-covered chemical structures, and unrelated indications were outside the literal scope.

What does U.S. Patent 5,008,294 protect?

The patent protects methods that combine four elements:

A mammalian patient.
A tumor, skin tumor, keratosis, or actinic keratosis.
Administration at the lesion site, generally through topical application or injection into or near the tumor.
A composition containing at least one catecholic butane within the claimed structural formulas.

The broadest tumor-treatment claim is claim 1. It covers topical administration of a composition containing at least one catecholic butane represented by the patent’s substituted butane-diphenyl structure. Claim 1 does not require NDGA specifically. It covers a genus that includes NDGA, ether derivatives, ester derivatives, and other substituted analogues.

The claims use “comprising,” making them open-ended. A product containing a claimed catecholic butane plus additional active or inactive ingredients can still fall within the claim if the other limitations are met.

Core claim architecture

Claim group	Subject matter	Principal limitations
Claims 1-15	Tumor inhibition and treatment	Catecholic butane; local administration; selected mammalian tumors
Claims 16-17	Skin tumors	Administration to the skin; catecholic butane; optional pharmaceutically acceptable carrier
Claims 18-27	Keratosis treatment	Local skin administration; catecholic butane; actinic keratosis in claim 27
Claims 28-30	Actinic keratosis	More specific structural genus or NDGA composition
Claims 31-34	Narrow skin-tumor methods	Restricted substitution patterns; actinic keratosis in claim 34

Which compounds fall within the patent claims?

NDGA is the most commercially important named compound in the claims. The patent also identifies multiple ether and ester derivatives.

Named chemical classes

Claim 7 and claim 25 expressly identify compounds including:

1,4-bis(3,4-dihydroxyphenyl)-2,3-dimethylbutane, corresponding to the NDGA core;
1,4-bis(3,4-dihydroxyphenyl)butane;
dimethoxy, diethoxy, and dipropoxy analogues;
tri- and tetrahydroxy analogues;
diacetoxy, dipropionyloxy, dibutyroyloxy, divaleroyloxy, and dipivaloyloxy derivatives;
dineopentylcarboxyl derivatives;
phenylbutane analogues containing one or more dihydroxyphenyl groups.

Claims 3, 11, 14, 19, 20, 29, and 30 narrow the subject matter to NDGA or specified NDGA derivatives. Claims 19 and 29 expressly include NDGA in racemic forms, tetrapivalate, tetrapropionate, and optical configurations.

Structural limitations

The claims generally permit:

hydrogen, lower alkyl, lower acyl, or alkylene at selected bridge positions;
hydrogen or lower alkyl at other positions;
hydroxy, lower alkoxy, or lower acyloxy substitution on the aromatic rings;
alkylene-dioxy groups formed by two adjacent substituents in certain claim sets.

Claims 6 and 24 define lower alkyl as C1-C6 alkyl, specify C1-C3 alkyl for selected positions, and define lower acyl as C1-C6 acyl.

The structural formulas are critical. A chemical compound must satisfy the relevant formula and substituent definitions. A compound that has antioxidant, cytotoxic, or antiproliferative activity but does not fit the claimed formula is not literally covered.

How broad are the tumor-treatment claims?

Claim 1 is broad in chemical scope but has a use and route limitation. It requires a method for inhibiting tumor growth by topical administration to the tumor situs. “Topically” is expanded in dependent claims 9 and 13 to include:

administration to the surface of the skin at the tumor site; and
injection into the interior of or near the tumor.

Claims 10-14 focus on animal tumors, including:

equine sarcoid;
equine papilloma;
equine malignant melanoma;
equine squamous cell carcinoma;
canine perianal adenoma;
canine mast cell carcinoma;
canine breast adenocarcinoma; and
canine malignant melanoma.

Claim 15 adds human or mammalian tumor categories such as malignant melanoma, mammary tumor, basal cell carcinoma, squamous cell carcinoma, and epidermal skin tumors.

The claims do not require a particular mechanism of action. They do not require apoptosis, antioxidant inhibition, enzyme inhibition, immune activation, or a specified clinical response. The practical limitation is the requirement that the administration be directed to the tumor or lesion.

What formulations are protected?

The patent claims compositions primarily through the method claims rather than through standalone composition claims.

Claim 2 requires 0.1% to 10% by weight of catecholic butane. Claims 8, 17, and 26 require or permit a pharmaceutically acceptable carrier. The claims do not require a particular carrier, vehicle, dosage form, preservative, penetration enhancer, cream base, ointment base, gel, emulsion, or injectable excipient.

Potentially relevant formulations include:

creams;
ointments;
gels;
lotions;
solutions;
suspensions;
emulsions; and
injectable preparations for intratumoral or peritumoral use.

A formulation containing NDGA at 0.1% to 10% by weight and applied to an actinic keratosis would have matched the most commercially relevant claim pathway while the patent was in force. A formulation outside that concentration range could still implicate the broader claims if it satisfied all other limitations.

The carrier limitation is generally narrowing. A formulation without a pharmaceutically acceptable carrier would not infringe claims 8, 17, or 26 solely on that basis, but could still fall within the corresponding independent claim.

What does the patent claim for actinic keratosis?

Actinic keratosis is the clearest human dermatologic use in the patent.

Claim 18 covers treatment of a skin keratosis using the catecholic butane genus. Claim 27 narrows claim 18 to actinic keratosis. Claims 28 and 29 provide another actinic-keratosis pathway using a related structural genus and specified NDGA derivatives. Claim 30 is the most direct NDGA claim:

A method for treating actinic keratosis by administering a composition comprising nordihydroguaiaretic acid.

Claim 30 does not recite a concentration, carrier, dosage form, or specific ester derivative. It does require:

actinic keratosis;
administration to the skin at the lesion site; and
a composition comprising NDGA.

Claim 30 would have been commercially significant because it does not depend on the 0.1%-10% concentration limitation in claim 21 or the carrier limitation in claim 26.

What are the strongest and weakest claim features?

Strongest features

The strongest practical claim features were:

the express recitation of NDGA;
the specific actinic-keratosis claims;
the broad “comprising” language;
the absence of a required mechanism of action;
the absence of a required commercial formulation;
the inclusion of topical skin administration and local injection;
the express coverage of racemic and optical forms in claims 19 and 29.

Claims 27 and 30 were commercially easier to evaluate than the broad structural claims because they identified actinic keratosis and, in claim 30, NDGA directly.

Vulnerable features

The broad genus claims could have faced validity pressure based on:

written-description support for the full range of substituent combinations;
enablement across the entire chemical genus and multiple tumor types;
obviousness over known NDGA chemistry and known topical antitumor uses;
indefiniteness issues involving “effective amount,” “lower alkyl,” “situs,” and “near vicinity”;
proof that a particular compound satisfied the structural formula;
clinical or factual proof that the claimed administration inhibited tumor growth.

The phrase “effective amount” is a functional limitation. It requires that the administered amount achieve the claimed therapeutic result, not merely that a product contain a listed compound.

When did U.S. Patent 5,008,294 lose exclusivity?

U.S. Patent No. 5,008,294 issued April 16, 1991. For a patent issued from an application subject to the pre-Uruguay Round Agreements Act term regime, the ordinary term was 17 years from issuance. On that basis, the patent expired April 16, 2008. The patent is therefore expired and cannot presently block U.S. commercialization under ordinary patent rights. (U.S. Patent No. 5,008,294, 1991; 35 U.S.C. § 154.)

Event	Date or status
Patent issued	April 16, 1991
Ordinary statutory term	17 years from issue
Expected expiration	April 16, 2008
Current enforceability	Expired
Patent-term extension relevance	No current term identified
Current U.S. patent barrier from this patent	None

Patent expiration does not eliminate other possible rights, including later patents on formulations, synthetic processes, delivery systems, combinations, or newly developed uses.

Is U.S. Patent 5,008,294 listed in the Orange Book?

The patent is not an Orange Book drug patent for an FDA-approved NDGA product. The Orange Book lists patents and exclusivity associated with approved prescription drug products, not every patent that claims a pharmaceutical method. (U.S. Food and Drug Administration, n.d.-a.)

NDGA is not an FDA-approved active ingredient for treatment of actinic keratosis or cancer based on the patent’s claimed uses. The patent itself did not establish FDA approval, clinical efficacy, or marketing authorization.

Approved actinic-keratosis therapies have included fluorouracil, imiquimod, diclofenac, photodynamic therapy products, and tirbanibulin. Those products occupy separate regulatory and patent estates. Their approval does not validate or revive the expired NDGA patent.

Were Paragraph IV challenges or patent settlements relevant?

Paragraph IV litigation generally applies when a generic applicant files an abbreviated new drug application that references an approved listed drug and certifies that an Orange Book patent is invalid, unenforceable, or will not be infringed. Because U.S. Patent 5,008,294 is not an Orange Book-listed patent for an approved NDGA product, it does not present a conventional Paragraph IV barrier. (21 U.S.C. § 355; FDA, n.d.-a.)

No widely recognized FDA-linked Paragraph IV dispute or settlement is associated with this patent. The absence of a Paragraph IV case is consistent with the absence of an approved NDGA reference product and the patent’s expiration in 2008.

What is the current patent landscape for NDGA and catecholic butanes?

The current landscape is better characterized as an expired foundational-use patent surrounded by potential later rights in adjacent areas.

Technology area	Relevance to U.S. Patent 5,008,294	Current commercial risk
NDGA topical treatment for actinic keratosis	Directly claimed in claims 27-30	No risk from the expired patent
NDGA treatment of skin tumors	Directly claimed in claims 15-17 and 31-34	No risk from the expired patent
NDGA ester or ether derivatives	Covered in genus and dependent claims	Later derivative patents may matter
Intratumoral NDGA use	Covered by dependent claims 9 and 13	No risk from the expired patent
NDGA manufacturing process	Not the principal subject of the claims provided	Process patents require separate review
NDGA cream or gel formulation	Carrier permitted, but no detailed formulation claim	Later formulation patents may matter
Combination therapy	Not expressly required by the claims	Combination patents may create separate risk
FDA-approved actinic-keratosis products	Separate active ingredients and regulatory records	Competitive and patent review required
Veterinary oncology use	Expressly covered for listed animal tumors	No risk from the expired patent

The most important freedom-to-operate issue is not the expired patent. It is whether a later patent covers a particular NDGA formulation, salt, derivative, manufacturing process, delivery system, combination, or newly defined clinical use.

What generic launch scenarios exist?

A company could now evaluate several development paths without infringement exposure from Patent 5,008,294 itself:

An NDGA topical product for actinic keratosis.
An NDGA cream, gel, or ointment for localized skin lesions.
A veterinary topical or intratumoral product.
An NDGA derivative with improved stability, penetration, or tolerability.
A combination product with another dermatologic or antineoplastic agent.
A locally delivered formulation designed to limit systemic exposure.

The principal barriers would be regulatory development, clinical evidence, manufacturing quality, dermal penetration, irritation, stability, toxicology, and later patent rights. A generic drug pathway would not automatically apply because the patent does not identify an approved reference product. A new drug application or another applicable FDA pathway could be required depending on the product, indication, route, and regulatory classification. (FDA, n.d.-b.)

How does this patent compare with modern actinic-keratosis patents?

Patent 5,008,294 is an early use patent. Its claims are relatively broad regarding formulation and mechanism but relatively narrow regarding the requirement for a catecholic butane and local lesion treatment.

Modern actinic-keratosis patent estates commonly focus on:

defined active ingredients;
treatment schedules;
concentration ranges;
vehicle composition;
penetration enhancers;
combination regimens;
specific lesion-response endpoints;
reduced irritation;
photodynamic systems; and
manufacturing and stability specifications.

That structure can produce stronger product-level exclusivity than the older patent, particularly where the formulation and regimen are difficult to design around.

Key Takeaways

U.S. Patent 5,008,294 covers local treatment of tumors, skin tumors, keratoses, and actinic keratosis with catecholic butanes.
NDGA is the principal named compound and is directly recited in claims 3, 11, 14, 20, 29, and 30.
Claims 27-30 are the most relevant to actinic keratosis.
The patent also covers selected NDGA ether and ester derivatives, including tetrapivalate and tetrapropionate forms.
Topical skin application and local injection are covered through the claim structure.
The patent issued April 16, 1991, and its ordinary 17-year term expired April 16, 2008.
The patent is not an Orange Book barrier for an approved NDGA product.
No conventional Paragraph IV pathway is implicated by this expired, non-Orange-Book patent.
Current diligence should focus on later formulation, process, derivative, delivery, combination, and regulatory rights.
Biosimilar risk is not relevant because NDGA is a small molecule, not a biologic.

FAQs

Does patent 5,008,294 cover oral NDGA treatment?

No. The claims are directed to administration at the tumor, skin lesion, or keratosis site. Oral or systemic administration without local application would generally fall outside the express administration limitations.

Does the patent cover an NDGA product for ordinary cosmetic skin use?

Not automatically. The claims require treatment of a tumor, skin tumor, keratosis, or actinic keratosis. A purely cosmetic product without the claimed therapeutic purpose would not satisfy the method-of-treatment limitations.

Does patent 5,008,294 cover every NDGA formulation?

No. The patent covers methods using compositions comprising NDGA or a covered catecholic butane. It does not establish ownership of every formulation, manufacturing process, salt, derivative, delivery system, or later combination involving NDGA.

Are veterinary uses covered by the patent?

Yes. Claims 10-14 expressly identify multiple equine and canine tumors. Those claims were part of the original patent scope, but the patent expired in 2008.

Is NDGA a biosimilar or generic biologic issue?

No. NDGA is a small molecule. Biosimilar statutes and biologic exclusivity concepts do not apply. Any current development issue would involve small-molecule drug regulation, a new drug pathway, or another applicable product classification.

References

U.S. Patent No. 5,008,294. (1991). Treatment of tumors with catecholic butanes. U.S. Patent and Trademark Office.
21 U.S.C. § 355. (2023). New drugs. United States Code.
35 U.S.C. § 154. (2023). Contents and term of patent; provisional rights. United States Code.
U.S. Food and Drug Administration. (n.d.-a). Approved drug products with therapeutic equivalence evaluations. FDA.
U.S. Food and Drug Administration. (n.d.-b). New drug application (NDA). FDA.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	70449	⤷ Start Trial
Australia	1736088	⤷ Start Trial
Australia	2099092	⤷ Start Trial
Australia	616641	⤷ Start Trial
Australia	8172487	⤷ Start Trial
Canada	1334170	⤷ Start Trial
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Details for Patent: 5,008,294

Summary for Patent: 5,008,294