US Patent 5,492,897: Nelarabine Patent Scope, Claims, Expiration, and Competitive Landscape

US Patent 5,492,897 protected a narrow method of treating T-cell lymphoblastic leukemia with nelarabine, chemically named 9-beta-D-arabinofuranosyl-2-amino-6-methoxy-9H-purine. The patent did not claim nelarabine as a compound, a pharmaceutical composition, a formulation, a manufacturing process, or treatment of every hematologic cancer.

The patent term expired on August 26, 2014, based on the listed filing and patent-term data. Its FDA-related regulatory exclusivities also expired. The patent therefore does not create a current US barrier to generic nelarabine development, although regulatory, manufacturing, clinical, and commercial barriers remain.

What drug does US Patent 5,492,897 protect?

The patented compound is nelarabine, marketed in the United States as Arranon injection. Nelarabine is a prodrug that is converted to the active nucleoside analog ara-G, or 9-beta-D-arabinofuranosylguanine. Ara-G is phosphorylated intracellularly to active metabolites that inhibit DNA synthesis, with particular activity against T-lineage lymphoblasts.[1]

Item	Detail
Patent	US 5,492,897
Patent title	Treatment of T-cell lymphoblastic leukemia with 9-beta-D-arabinofuranosyl-2-amino-6-methoxy-9H-purine
Active ingredient	Nelarabine
Chemical name in claims	9-beta-D-arabinofuranosyl-2-amino-6-methoxy-9H-purine
Original patent owner	Burroughs Wellcome Co., according to the patent record
Filing date	August 26, 1994
Grant date	February 20, 1996
Stated patent expiration	August 26, 2014
FDA product	Arranon, nelarabine injection
FDA approval	October 28, 2005
Approved disease area	Relapsed or refractory T-cell acute lymphoblastic leukemia and T-cell lymphoblastic lymphoma

The compound name in the claims and the active ingredient in Arranon identify the same drug. The patent is therefore a use patent directed to nelarabine therapy rather than a composition-of-matter patent.

What do the four claims cover?

The claims contain two independent treatment claims and two dependent injection claims.

Claim	Scope	Key limitation
1	Treatment method	Administering nelarabine to a mammal with T-cell lymphoblastic leukemia
2	Treatment method	Administering nelarabine or a pharmaceutically acceptable salt to that patient population
3	Dependent method	Claim 1 where administration is by injection
4	Dependent method	Claim 2 where administration is by injection

Claim 1: free-base nelarabine

Claim 1 requires all of the following:

A mammal.
The mammal has T-cell lymphoblastic leukemia.
The administered compound is the specifically identified nelarabine molecule.
The amount administered is effective for treatment of the leukemia.

The claim does not expressly require a particular dose, dosing schedule, treatment duration, formulation, route, disease stage, age group, or response endpoint. It therefore covers qualifying treatment regimens using the named compound, subject to ordinary claim-construction principles.

Claim 2: nelarabine and pharmaceutically acceptable salts

Claim 2 expands the chemical scope to include nelarabine and its pharmaceutically acceptable salts. This is the broader independent claim because it covers both the named compound and qualifying salt forms.

The claim does not cover every derivative, prodrug, metabolite, analog, or related purine nucleoside. A product containing ara-G alone would not literally satisfy the requirement to administer the claimed 6-methoxy compound.

Claims 3 and 4: injection

Claims 3 and 4 narrow the independent claims by requiring injection. They cover injectable administration, including the route used for Arranon. They do not independently broaden the patent to cover oral, intrathecal, subcutaneous, or other administration.

Because claims 3 and 4 depend on claims 1 and 2, they retain the underlying requirements that the patient have T-cell lymphoblastic leukemia and that the administered substance be nelarabine or a covered salt.

What is the literal scope of the patent?

The literal scope is narrower than the current FDA label in several respects.

Disease limitation

The claims specify T-cell lymphoblastic leukemia. The FDA label covers relapsed or refractory T-cell acute lymphoblastic leukemia, commonly abbreviated T-ALL, and T-cell lymphoblastic lymphoma, or T-LBL.[1]

T-ALL is generally the closest clinical match to the claimed disease. T-LBL is separately named in the FDA indication and is not expressly recited in the patent claims. Use of nelarabine for T-LBL therefore does not fall within the literal language of the claims solely because it appears in the later FDA indication.

Patient limitation

The claims require treatment of a mammal having the disease. They do not expressly limit treatment to adults, children, relapsed patients, refractory patients, or patients with a particular biomarker.

Dosage limitation

No numerical dose appears in the quoted claims. A court would likely examine the phrase “effective ... treatment amount” in the context of the specification and evidence concerning whether the treatment produced the claimed therapeutic result. The claims are not limited to the dosing schedule later used in the Arranon label.

Route limitation

Claims 1 and 2 are not limited to injection. Claims 3 and 4 are injection-specific dependent claims. The patent therefore has broader route coverage in its independent claims, but claims 3 and 4 provide narrower protection for injectable administration.

What patents protect nelarabine and how broad is the estate?

US Patent 5,492,897 is a narrow use patent, not a comprehensive nelarabine estate.

Protection category	Covered by US 5,492,897?	Analysis
Nelarabine molecule itself	No	The patent identifies the compound as part of a treatment method
T-ALL treatment	Yes	Expressly claimed
T-LBL treatment	Not expressly	FDA-approved but not named in the quoted claims
Pharmaceutical composition	No express composition claim	No composition claim is provided
Injectable formulation	Only as a method of injection	Claims 3 and 4 do not claim formulation ingredients or physical properties
Oral formulation	Potentially under claims 1 or 2 if effective, but not expressly claimed	No oral formulation claim
Method of manufacture	No	No process claim
Ara-G metabolite	No	The claims require nelarabine or its covered salt
Combination therapy	No express combination language	Combination use may raise separate claim-construction issues but is not expressly claimed
Dose or schedule	No numerical limitation	The claims use an effective-amount standard
Broad oncology use	No	Disease is limited to T-cell lymphoblastic leukemia

The patent’s commercial importance came from its alignment with the later FDA approval of Arranon, not from breadth across all possible nelarabine products.

When did US Patent 5,492,897 expire?

The patent expired on August 26, 2014. The term corresponds to the 20-year patent term measured from the relevant US nonprovisional filing date under the post-1995 patent-term regime.[2]

Event	Date
Earliest identified US filing	August 26, 1994
Patent grant	February 20, 1996
FDA approval of Arranon	October 28, 2005
Patent expiration	August 26, 2014

No active enforceable patent rights remain under US 5,492,897 after expiration. The patent cannot support a new US patent-infringement action against a generic manufacturer for conduct occurring after expiration.

The expiration date should be distinguished from regulatory exclusivity. FDA orphan-drug exclusivity and any pediatric exclusivity were statutory marketing protections, not extensions of the patent claims.

What was the FDA exclusivity status of nelarabine?

The FDA approved Arranon under the accelerated-approval pathway on October 28, 2005, for patients with relapsed or refractory T-ALL or T-LBL. The approval was based on response data in a serious disease setting with limited treatment options.[1]

Nelarabine received orphan-drug treatment for the relevant disease population. Orphan exclusivity generally lasted seven years from approval under the Orphan Drug Act. Pediatric exclusivity, where granted, can add six months to applicable exclusivity periods under the Food, Drug, and Cosmetic Act.[3]

These periods ended years before the current generic-development period. They do not extend the patent term and do not prevent present-day ANDA applicants from relying on an expired patent landscape.

What is the Orange Book status of nelarabine?

The Orange Book identifies approved drug products and relevant patent and exclusivity information submitted by sponsors.[4] For Arranon, US 5,492,897 was the principal patent associated with the claimed T-cell leukemia use.

Because the patent expired in 2014, it is not a current blocking patent. An applicant seeking approval for a nelarabine product would evaluate:

Whether any current Orange Book-listed patent remains.
Whether the proposed label includes the patented T-ALL use.
Whether a Section viii statement can omit a patented indication.
Whether the application requires a Paragraph IV certification for any unexpired listed patent.
Whether labeling, dosing, or formulation differences create separate regulatory issues.

An expired patent does not require a current Paragraph IV challenge. Paragraph IV practice is relevant only when an applicant certifies that an unexpired listed patent is invalid, unenforceable, or will not be infringed.

Which companies challenged US 5,492,897?

The public patent record and the principal FDA materials do not establish a material, active Paragraph IV litigation campaign directed at US 5,492,897. The patent expired before a current enforcement dispute could create a continuing market barrier.

The absence of a live dispute is commercially important. For an expired use patent, generic developers generally face no ongoing patent injunction risk from that patent. Earlier litigation or settlement activity, if any, would not revive expired patent rights.

Are biosimilar risks relevant to nelarabine?

No. Nelarabine is a chemically synthesized small-molecule drug, not a biologic. Biosimilar approval under the Public Health Service Act is therefore not the relevant pathway.[5]

The competitive pathway is an abbreviated new drug application, or ANDA, under Section 505(j) of the Federal Food, Drug, and Cosmetic Act. A generic applicant would typically need to demonstrate pharmaceutical equivalence and bioequivalence to the listed reference product, subject to FDA requirements for the proposed dosage form and route.

What formulation and manufacturing patents could still matter?

US 5,492,897 does not claim a formulation or manufacturing method. A later patent could theoretically cover:

A specific concentration of nelarabine in an injectable solution.
A particular buffer, pH range, stabilizer, or container system.
A lyophilized or reconstituted presentation.
A manufacturing intermediate or purification step.
A process that controls impurities or stereochemical composition.
A dosing regimen or patient-selection method.

Such rights would need to be analyzed separately from US 5,492,897. They could affect generic commercialization even though the core treatment patent has expired. The supplied claims provide no basis for concluding that any such later patent remains enforceable.

The chemical manufacturing burden may still be meaningful. Nelarabine is a nucleoside analog with stereochemical and impurity-control requirements. A generic manufacturer must establish a reproducible synthetic route, control related substances, validate the injectable manufacturing process, and demonstrate product quality. Those are technical and regulatory barriers, not rights created by US 5,492,897.

How does nelarabine compare with competing T-cell leukemia products?

Nelarabine occupies a specialized position in relapsed or refractory T-lineage leukemia and lymphoma. Other agents used in T-ALL or T-LBL may include cytarabine, nelarabine-containing chemotherapy regimens, clofarabine, and newer targeted or immunotherapeutic products depending on disease setting and jurisdiction.

Product or class	Patent issue compared with nelarabine	Commercial distinction
Nelarabine	Expired treatment patent	T-lineage-specific approved use
Cytarabine	Separate compound and formulation estates	Broad hematologic oncology use
Clofarabine	Separate composition and use patents	Purine analog with pediatric oncology use
Targeted agents	Often protected by active composition and method patents	Biomarker- or pathway-defined use
Cellular or biologic therapies	Biologic and platform-specific patent estates	Biosimilar or cell-therapy issues may apply

Nelarabine’s patent position is weaker today than that of newer targeted products because its principal US use patent has expired and it has no biologic exclusivity structure.

What generic entry risks exist?

The direct patent risk from US 5,492,897 is low because the patent expired in 2014. The principal entry risks are commercial and regulatory.

Generic launch scenarios

A generic injectable product with the same active ingredient and route could pursue an ANDA, subject to current Orange Book and exclusivity review.
A label that includes T-ALL treatment could not be blocked by the expired patent.
A label omitting a still-protected use would be relevant only if another unexpired patent covered that use.
A manufacturer could face market-entry friction from limited demand, hospital purchasing contracts, low production volumes, and injectable manufacturing costs.
A single generic entrant could encounter supply-chain pressure because oncology injectables require specialized sterile manufacturing capacity.

The size of the commercial opportunity is constrained by the narrow patient population and the use of nelarabine primarily in relapsed or refractory T-lineage disease. The expired patent removes a legal barrier but does not guarantee multiple entrants or sustained generic supply.

What is the geographic coverage of the patent?

US 5,492,897 provided rights only in the United States. Patent protection in Europe, Japan, Canada, or other countries would depend on separate national patents and their individual expiration dates.

A US expiration does not establish freedom to operate outside the United States. International analysis would require review of the corresponding priority family, national-phase filings, continuations, terminal disclaimers, supplementary protection certificates, and local regulatory exclusivities.

Key Takeaways

US 5,492,897 is a use patent for nelarabine, not a composition-of-matter patent.
Claims 1 and 2 cover treatment of T-cell lymphoblastic leukemia with nelarabine or a pharmaceutically acceptable salt.
Claims 3 and 4 narrow the method to injection.
The patent does not expressly claim T-cell lymphoblastic lymphoma, formulations, manufacturing processes, doses, schedules, or combination therapy.
The patent expired on August 26, 2014.
Arranon received FDA approval on October 28, 2005, for relapsed or refractory T-ALL and T-LBL.
Orphan and any pediatric exclusivity periods have expired.
Biosimilar analysis is not applicable because nelarabine is a small molecule.
The current US generic risk from this patent is negligible. Remaining barriers are likely to involve FDA requirements, sterile injectable manufacturing, supply economics, and any separate later-listed patents.

FAQs

Can a generic manufacturer launch nelarabine after the expiration of US 5,492,897?

Yes. The patent no longer blocks US commercialization. The manufacturer must still satisfy FDA ANDA requirements and address any other unexpired listed patent or exclusivity.

Does US 5,492,897 cover nelarabine for T-cell lymphoblastic lymphoma?

Not expressly. The quoted claims recite T-cell lymphoblastic leukemia. The FDA label separately includes T-cell lymphoblastic lymphoma, but regulatory labeling does not expand the literal text of an expired patent claim.

Does the patent cover oral nelarabine?

Claims 1 and 2 are not expressly limited to injection. Claims 3 and 4 are injection-specific. Any infringement analysis would still require the claimed disease, compound, mammalian patient, and effective treatment amount.

Is ara-G covered by US 5,492,897?

No. The claims identify nelarabine, the 6-methoxy prodrug. Ara-G is the active metabolite and is chemically distinct from the claimed compound.

Can the expired patent support a Paragraph IV lawsuit?

No. Paragraph IV certification applies to an unexpired listed patent. An expired patent cannot provide a continuing basis for patent infringement liability against a current generic applicant.

References

U.S. Food and Drug Administration. (2005). Arranon (nelarabine) injection prescribing information.
United States Patent and Trademark Office. (n.d.). Patent term adjustment and patent term calculation resources.
U.S. Food and Drug Administration. (n.d.). Orphan drug designation and exclusivity.
U.S. Food and Drug Administration. (n.d.). Approved drug products with therapeutic equivalence evaluations, Orange Book.
U.S. Food and Drug Administration. (n.d.). Biosimilar and interchangeable biosimilar products.
United States Patent and Trademark Office. (1996). U.S. Patent No. 5,492,897, Treatment of T-cell lymphoblastic leukemia with 9-beta-D-arabinofuranosyl-2-amino-6-methoxy-9H-purine.

Foriegn Application Priority Data
Foreign Country	Foreign Patent Number	Foreign Patent Date
United Kingdom	9015914	Jul 19, 1990

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	151637	⤷ Start Trial
Australia	641533	⤷ Start Trial
Australia	8196091	⤷ Start Trial
Canada	2087543	⤷ Start Trial
Cyprus	2165	⤷ Start Trial
Germany	69125715	⤷ Start Trial
Denmark	0539479	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 5,492,897

Summary for Patent: 5,492,897