Details for Patent: 6,537,579

Summary for Patent: 6,537,579

Title:	Compositions and methods for administration of pharmacologically active compounds
Abstract:	In accordance with the present invention, there are provided compositions and methods useful for the in vivo delivery of substantially water insoluble pharmacologically active agents (such as the anticancer drug paclitaxel) in which the pharmacologically active agent is delivered in the form of suspended particles coated with protein (which acts as a stabilizing agent). In particular, protein and pharmacologically active agent in a biocompatible dispersing medium are subjected to high shear, in the absence of any conventional surfactants, and also in the absence of any polymeric core material for the particles. The procedure yields particles with a diameter of less than about 1 micron. The use of specific composition and preparation conditions (e.g., addition of a polar solvent to the organic phase), and careful election of the proper organic phase and phase fraction, enables the reproducible production of unusually small nanoparticles of less than 200 nm diameter, which can be sterile-filtered. The particulate system produced according to the invention can be converted into a redispersible dry powder comprising nanoparticles of water-insoluble drug coated with a protein, and free protein to which molecules of the pharmacological agent are bound. This results in a unique delivery system, in which part of the pharmacologically active agent is readily bioavailable (in the form of molecules bound to the protein), and part of the agent is present within.
Inventor(s):	Neil P. Desai, Patrick Soon-Shiong
Assignee:	Abraxis Bioscience LLC
Application Number:	US09/574,763
Patent Litigation and PTAB cases:	See patent lawsuits and PTAB cases for patent 6,537,579
Patent Claim Types: see list of patent claims	Use; Composition; Formulation; Delivery;

US Patent 6,537,579: Claim Scope, Abraxane Relevance, Expiration, and Patent Landscape

US Patent 6,537,579 is a foundational nanoparticle drug-delivery patent associated with albumin-bound paclitaxel and the Abraxane platform. Its claims cover methods of preparing and administering submicron particles of substantially water-insoluble drugs, particularly paclitaxel, where the drug is coated with or associated with protein, especially albumin. The patent issued on March 25, 2003, and its core US patent term expired in December 2021. It is no longer an enforceable barrier to generic or competing products in the United States.[1]

The patent remains commercially important because its claim architecture established the technical framework later used for nab-paclitaxel: protein-associated drug particles, small particle size, Cremophor-free administration, higher-concentration dosing, and shorter infusion protocols.

What does US Patent 6,537,579 cover?

US 6,537,579 covers methods rather than a single branded product. The claims focus on five technical elements:

1. A substantially water-insoluble pharmacologically active agent.
2. A particle or dispersion generally no greater than about 1 micron.
3. A protein coating or protein-associated drug structure.
4. Free protein associated with the particle.
5. Administration to a patient for specified therapeutic or pharmacokinetic purposes.

The patent also covers high-pressure homogenization of an organic drug phase and an aqueous phase containing a biocompatible polymer. The claims extend beyond paclitaxel to taxanes generally, propofol, thyroid hormones, oil-soluble vitamins, anesthetics and other pharmacologically active agents.

The patent’s central technical concept is a protein-associated nanoparticle in which some drug is contained within the protein coating and some drug is associated with free protein. That limitation distinguishes the claimed system from a conventional coarse emulsion, a simple drug suspension, and some polymeric micelle formulations.

Core patent data

Item	Detail
Patent	US 6,537,579
Title	Methods for the preparation and use of compositions comprising nanoparticles
Issue date	March 25, 2003
Patent holder at issuance	American Bioscience, Inc.
Principal commercial relevance	Albumin-bound paclitaxel and related protein-bound nanoparticles
Technology	Protein-coated or protein-associated submicron particles
Key active ingredient	Paclitaxel
Key protein	Albumin
Key particle-size limitation	No greater than about 1 micron; dependent claims specify less than 200 nm
Key manufacturing limitation	High-pressure homogenization at approximately 100 to 100,000 psi
US term status	Expired in December 2021
Product associated with technology	Abraxane, marketed by Bristol Myers Squibb after Celgene’s acquisition of Abraxis

How are the claims organized?

The 53 claims contain multiple independent method claims. They are not a single narrow paclitaxel claim set. They create several overlapping enforcement theories.

Claim 1: high-pressure homogenization

Claim 1 covers delivery of a substantially water-insoluble drug using a composition prepared from:

• an organic phase containing the drug;
• an aqueous medium containing a biocompatible polymer;
• optional absence of surfactant; and
• high-shear treatment in a high-pressure homogenizer.

The pressure range is unusually broad, extending from approximately 100 psi to 100,000 psi. The claim does not require albumin, paclitaxel, a specific particle size, or intravenous administration.

This claim is therefore broader in drug identity but narrower in manufacturing process. A competing product could potentially avoid claim 1 by using a different particle-generation method, even if the final product contains protein-associated nanoparticles.

Claims 2 through 9 narrow claim 1 by adding albumin, polyalkylene glycol, oil, oil-soluble vitamins, anti-neoplastics, taxanes, non-crystalline drugs, propofol and thyroid hormones.

Claims 10 through 15: Cremophor-free oncolytic particles

Claim 10 is directed to a method of eliminating cancer cells with a Cremophor-free oncolytic composition comprising:

• antineoplastic particles;
• a protein coating;
• free protein associated with the coating;
• drug both within the coating and associated with free protein; and
• average particle diameter of no greater than about 1 micron.

Claim 11 narrows the particle size to less than 200 nm. Claim 12 adds sterile filtration. Claims 13 and 14 address crystalline and substantially amorphous particles. Claim 15 specifically identifies paclitaxel and albumin.

This is the claim group most closely associated with Abraxane’s technical profile. Its practical significance comes from the combination of Cremophor-free formulation, albumin association, submicron particle size and paclitaxel.

Claims 16 through 21: reduced liver sequestration

Claim 16 covers administration intended to reduce liver sequestration of pharmaceutical agents. The delivery system again requires protein-coated particles no greater than about 1 micron, with free protein associated with the coating.

Claims 17 through 21 narrow the claim to paclitaxel, albumin, taxanes, propofol and thyroid hormone.

This claim group is vulnerable to evidentiary disputes because “reducing liver sequestration” is a functional therapeutic limitation. In an infringement case, the patentee would need to establish that the accused product and administration method satisfy the claimed pharmacokinetic or physiological result, not merely that the product contains small protein-associated particles.

Claims 22 through 24: paclitaxel concentration and infusion

Claims 22 through 24 target clinical administration of paclitaxel:

• Claim 22 requires a dosing solution containing more than 1 mg/mL paclitaxel.
• Claim 23 requires a total infusion volume of less than 300 mL per effective dose.
• Claim 24 covers rapid administration.

These claims are directed to clinical-use advantages associated with albumin-bound paclitaxel compared with conventional Cremophor-based paclitaxel, which historically required dilution and prolonged infusion with corticosteroid and antihistamine premedication.

The claims do not state a single fixed infusion duration in the supplied language. “Rapid administration” would require construction in the context of the specification and prosecution history.

Claims 25 through 31: reduced cycle time and toxicity

Claim 25 covers administering a multiply dosed drug over a reduced cycle time. Claims 26 through 29 identify drug classes, including taxanes, propofol and thyroid hormones.

Claims 30 and 31 claim methods of reducing myelosuppressive and neurotoxic effects by administering the drug in the claimed protein-associated particle system over a reduced cycle time.

These claims combine product characteristics with clinical outcomes. Their scope is narrower than a pure composition claim because infringement depends on both the delivery system and the claimed treatment result.

Claims 32 through 39: disease treatment and reduced premedication

Claim 32 covers administration of the particle system to treat a disease capable of treatment by the drug. The dependent claims add:

• proliferative disease;
• systemic cancer treatment;
• intravenous administration;
• intraarterial administration;
• administration without corticosteroid premedication;
• combination with biochemotherapy;
• administration without cytokines; and
• non-crystalline drug.

Claims 34 through 38 are particularly relevant to clinical differentiation from solvent-based paclitaxel. The absence of corticosteroid premedication and the absence of cytokines are treatment-protocol limitations, not simply formulation attributes.

Claims 40 through 44: localized sustained release

Claim 40 covers localized administration for sustained release where the particle composition is dispersed within a biocompatible matrix before administration.

The claim reaches beyond intravenous oncology products. It potentially encompasses depot implants, injectable matrices and localized delivery systems containing protein-associated, water-insoluble drug particles. Claims 41 through 44 identify taxanes, propofol and thyroid hormone, although claim 43 appears internally inconsistent because it identifies propofol as an “anti-neoplastic” in the supplied text. Propofol is an anesthetic. The official issued patent and prosecution record should control any legal analysis of that wording.[1]

Claims 45 through 48: oral delivery with efflux inhibition

Claim 45 covers oral administration of the particle system in combination with intestinal cell efflux inhibitors. The dependent claims identify antineoplastics, taxanes and thyroid hormones.

This claim group is technically distinct from the intravenous Abraxane use case. It addresses oral bioavailability and intestinal transport rather than infusion speed or solvent avoidance.

Claims 49 through 53: combination therapy at reduced dose

Claim 49 covers administering multiple pharmacologically active agents at 25% to 75% of their generally accepted effective dosage levels, using the claimed particle system.

Claims 50 through 53 identify antineoplastics, taxanes, anesthetics and thyroid hormones.

This claim group could be relevant to combination oncology regimens, but it has several potential construction and proof issues. “Generally accepted effective dosage level” may require clinical and regulatory evidence. The accused regimen must also satisfy the 25% to 75% range for each active agent.

What are the principal claim limitations?

The following limitations define the practical center of gravity of the patent.

Limitation	Claims affected	Commercial importance
Substantially water-insoluble active agent	Most claims	Excludes many water-soluble drugs
Protein coating	Claims 10, 16, 22-25, 30-32, 40, 45, 49	Central structural limitation
Free protein associated with coating	Same claim groups	Important distinction from simple protein adsorption
Drug partly within coating and partly associated with free protein	Claims 10, 16 and descendants	Narrows particle architecture
Particle size no greater than about 1 micron	Claims 10 onward	Captures submicron formulations
Particle size less than 200 nm	Claim 11	Stronger but narrower size limitation
Albumin	Claims 2, 15, 17, 22 onward in relevant branches	Directly relevant to nab-paclitaxel
Paclitaxel	Claims 15, 17, 22-24	Core Abraxane relevance
Cremophor-free formulation	Claim 10 and related claims	Differentiates from Taxol
High-pressure homogenization	Claim 1	Process-specific coverage
Intravenous or intraarterial use	Claims 34 and 35	Limits treatment route
No corticosteroid premedication	Claim 36	Clinical protocol limitation
No cytokines	Claim 38	Clinical protocol limitation
Localized sustained release	Claim 40	Depot and matrix applications
Oral administration with efflux inhibitor	Claim 45	Separate oral-delivery pathway
Reduced-dose combination therapy	Claim 49	Combination-regimen coverage

What products could fall within the issued claims?

A product most closely aligned with the patent would have the following profile:

• paclitaxel as the active agent;
• albumin as the principal protein;
• particles below 1 micron;
• a fraction of paclitaxel associated with albumin and a fraction within the protein-associated particle structure;
• no Cremophor EL;
• sterile injectable presentation;
• intravenous administration;
• paclitaxel concentration above 1 mg/mL;
• infusion volume below 300 mL; and
• administration without routine corticosteroid premedication.

That profile describes the central technical and clinical attributes of Abraxane. The FDA label identifies Abraxane as paclitaxel protein-bound particles for injectable suspension, with albumin-bound particles and a recommended 30-minute intravenous infusion.[2]

A formulation can resemble Abraxane commercially without infringing every claim. For example, a competing formulation may contain paclitaxel and albumin but avoid a claim requiring the specific distribution of drug within the protein coating and with free protein. Conversely, a product made by a different manufacturing process could still implicate claims 10, 16, 22 or 32 if the final particle structure and administration method satisfy those claims.

When did US Patent 6,537,579 lose exclusivity?

The patent’s US term expired in December 2021. The expiration date is generally reported as December 4, 2021, based on the patent family’s effective filing chronology and statutory patent-term calculation.[1,3]

Event	Date or period
Earliest relevant priority	December 4, 1998
Patent issued	March 25, 2003
Abraxane US approval	October 2005
Core patent expiration	December 2021
Current enforceability	Expired
Current commercial effect	Historical foundation; no current blocking right from this patent alone

Patent expiration removes the enforceability of the patent claims. It does not eliminate later patents covering specific formulations, manufacturing controls, dosing regimens, combinations or methods of treating particular cancers.

What is the Orange Book status of US 6,537,579?

US 6,537,579 was listed in FDA’s Approved Drug Products with Therapeutic Equivalence Evaluations for Abraxane and was associated with the albumin-bound paclitaxel product.[3] Its expiration has passed.

Orange Book listing does not itself determine validity or infringement. It identifies patents that the sponsor submitted as relevant to the approved drug. A later patent may remain listed even when the foundational platform patent has expired.

The relevant regulatory distinction is:

• US 6,537,579: foundational, now expired platform patent.
• Later Abraxane patents: potentially relevant to formulation, manufacturing, dosing or use, depending on their individual term and listing status.
• FDA approval: independent of patent validity, although an ANDA applicant must address listed patents through the Hatch-Waxman process.

Which companies challenged the Abraxane patent estate?

The principal generic challenge came from Actavis, which sought approval for a generic version of Abraxane and litigated patents in the Abraxane estate. Abraxis and later Celgene asserted later patents covering albumin-bound paclitaxel and its use in cancer treatment.

The litigation strategy generally moved beyond US 6,537,579 because the core patent had already approached or reached expiration. Later disputes focused on patents such as US 7,820,788 and other Abraxane-related patents directed to treatment methods and product characteristics.[4,5]

The most relevant legal point is that a Paragraph IV challenge to a later-listed Abraxane patent would not revive or extend the expired rights under US 6,537,579. A generic applicant must analyze each unexpired listed patent separately.

What later patents protect Abraxane?

The later patent estate has included patents directed to:

• albumin-bound paclitaxel treatment;
• treatment of specific cancers;
• dosing schedules;
• combination therapy;
• formulation and particle characteristics;
• manufacturing and process controls; and
• product-by-process or quality attributes.

Representative later US patents associated with the Abraxane estate include US 7,820,788 and US 8,802,100. Their enforceability, expiration dates and relevance depend on claim scope, terminal disclaimers, patent-term adjustment and Orange Book status.[3-5]

The later estate is commercially more important than US 6,537,579 for current launch analysis. A generic applicant could freely practice the expired platform claims but still face a Paragraph IV dispute involving unexpired method-of-use or formulation claims.

How strong was the patent estate?

Strengths

The patent had substantial historical strength because it combined a broad platform concept with commercially specific embodiments:

• water-insoluble drug particles;
• albumin or other protein association;
• submicron size;
• Cremophor-free delivery;
• paclitaxel;
• sterile filtration;
• high-concentration dosing;
• reduced infusion volume; and
• reduced premedication requirements.

The patent also included multiple independent claims, creating several potential infringement theories.

Weaknesses

The claim set had material limitations:

• Most commercially important claims require particular particle architecture.
• Several claims depend on functional treatment outcomes.
• Some claims require clinical administration parameters.
• Claim 1 depends on a particular high-pressure homogenization process.
• The broad drug-class language may face written-description, enablement or obviousness challenges when applied to compounds not specifically exemplified.
• The patent does not provide continuing protection after expiration.

The issued claims are strongest against products that copy the complete albumin-bound nanoparticle architecture and the associated clinical administration protocol. They are weaker against products using liposomes, polymeric micelles, nanocrystals, emulsions or alternative protein-free delivery systems.

How does Abraxane compare with competing paclitaxel formulations?

Product or platform	Delivery technology	Cremophor-free	Relationship to US 6,537,579
Taxol	Cremophor-based solution	No	Generally outside the protein-coated nanoparticle claims
Generic paclitaxel injection	Cremophor-based solution	No	Usually outside the core claim structure
Abraxane	Albumin-bound paclitaxel particles	Yes	Closest commercial embodiment
Liposomal paclitaxel	Liposome	Usually yes	Depends on whether protein-coating limitations are met
Polymeric micelle paclitaxel	Polymer-based micelle	Yes	Usually differentiated by particle architecture
Paclitaxel nanocrystal	Crystalline nanoparticle	Yes	May avoid albumin and free-protein limitations
Oral paclitaxel systems	Oral absorption-enhanced formulation	Product-specific	Relevant mainly to claims 45-48 if protein particles and efflux inhibitor are used

The expired patent does not block current development of alternative paclitaxel delivery systems. It remains relevant as prior art and as a technical map of the albumin-bound nanoparticle approach.

What generic launch risks remain after expiration?

Generic entry risk for the expired patent is zero as a matter of patent enforcement. The commercial risk shifts to:

1. Later unexpired Abraxane patents.
2. FDA requirements for demonstrating therapeutic equivalence.
3. Manufacturing reproducibility and particle-size control.
4. Sterility and injectable product quality.
5. Clinical labeling and substitution mechanics.
6. Potential formulation differences that prevent automatic substitution.
7. Trade secrets involving manufacturing parameters and release specifications.

For an ANDA applicant, the main legal task is not to challenge US 6,537,579. It is to address any remaining Orange Book-listed patents and assess non-listed patents that could support separate infringement litigation.

What manufacturing and IP barriers remain?

The patent’s expired process claims do not eliminate manufacturing barriers. Albumin-bound nanoparticle products require control of:

• drug loading;
• particle-size distribution;
• aggregation;
• residual solvent;
• protein association;
• sterile filtration;
• concentration;
• reconstitution behavior;
• stability; and
• batch-to-batch release specifications.

These parameters can be protected through later patents, regulatory filings and trade secrets. A competitor can avoid the expired patent while still facing technical difficulty reproducing the product’s performance and obtaining FDA approval.

Key Takeaways

• US 6,537,579 is a foundational patent for protein-associated, submicron delivery of water-insoluble drugs.
• Its most important embodiment is albumin-bound paclitaxel, commercially represented by Abraxane.
• The principal claim limitations are protein coating, free protein association, drug distribution within and around the coating, and particle size of no greater than about 1 micron.
• Claim 1 separately covers high-pressure homogenization of organic and aqueous phases.
• Claims 22 through 24 target high-concentration, low-volume and rapid paclitaxel administration.
• Claims 36 and 38 address administration without corticosteroid premedication or cytokines.
• Claims 40 through 48 extend the patent to localized sustained release and oral delivery with efflux inhibitors.
• The patent expired in December 2021 and cannot independently block current US generic entry.
• Later Abraxane patents, not US 6,537,579, determine most current Paragraph IV and Orange Book risk.
• Alternative liposomal, polymeric, micellar and nanocrystal paclitaxel systems are structurally differentiated from the patent’s albumin-particle claims.

FAQs

Does US 6,537,579 still block generic Abraxane?

No. The patent expired in December 2021. Generic Abraxane applicants must instead analyze any later unexpired patents listed for the product and any separately enforceable patents.

Is a paclitaxel formulation infringing if its particles are below 200 nm?

Not necessarily. Particle size alone is insufficient. The relevant claims also require protein coating, free protein association and a specified relationship between the drug and protein.

Does the patent cover all Cremophor-free paclitaxel products?

No. The claims are directed to particular protein-associated particle systems. Liposomal, polymeric micelle and nanocrystal products may avoid the claims if they do not contain the required protein architecture.

Can a company use albumin-bound paclitaxel after the patent expired?

Yes, subject to other applicable patents, FDA approval requirements, regulatory exclusivities and non-patent manufacturing constraints.

Was US 6,537,579 a composition patent?

The supplied claim set is composed primarily of method claims. It does not operate like a simple composition claim covering every albumin-bound paclitaxel particle. Infringement depends on the claimed method, product characteristics and administration conditions.

References

1. United States Patent and Trademark Office. (2003). US Patent No. 6,537,579, Methods for the preparation and use of compositions comprising nanoparticles.
2. U.S. Food and Drug Administration. (2023). Abraxane prescribing information. Bristol Myers Squibb.
3. U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations.
4. United States Patent and Trademark Office. (2010). US Patent No. 7,820,788.
5. United States Patent and Trademark Office. (2014). US Patent No. 8,802,100.

Drugs Protected by US Patent 6,537,579

Applicant	Tradename	Generic Name	Dosage	NDA	Approval Date	TE	Type	RLD	RS	Patent No.	Patent Expiration	Product	Substance	Delist Req.	Patented / Exclusive Use	Submissiondate

International Family Members for US Patent 6,537,579

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
European Patent Office	0961612		CA 2009 00036	Denmark
European Patent Office	0961612		91613	Luxembourg
European Patent Office	0961612		09C0050	France
European Patent Office	0961612		C00961612/01	Switzerland