US Patent 6,132,766 (Multivesicular Liposomes with Acidified Release Chambers): Scope, Claim Map, and US Patent Landscape

US Patent 6,132,766 covers multivesicular liposomes made by a water-in-oil emulsion that contains a non-hydrohalic acid at a specified concentration range, followed by formation of solvent spherules and organic solvent removal to generate multivesicular structures with non-concentric internal chambers and internal membranes distributed as a network. The claims are drafted to read broadly across (i) liposome compositions (solvent, amphipathic and neutral lipids, optional lipid charge types), (ii) acid identity (selected non-hydrohalic acids), (iii) payload classes (broad therapeutic categories and explicit examples), and (iv) manufacturing modalities (emulsification, spherule formation, solvent removal).

US Patent 6,132,766: What is the core invention and what is the claim scope?

Is the claim centered on the liposome structure or the manufacturing method?

The independent claim is method-defined but still structural on the product. It requires a multivesicular liposome having:

multiple non-concentric chambers
internal membranes distributed as a network throughout

…and it requires that the liposome is produced by a specific process that includes:

forming a water-in-oil emulsion from two immiscible components where the lipid component comprises:
- at least one organic solvent
- at least one amphipathic lipid
- at least one neutral lipid lacking a hydrophilic head group
adding a first aqueous component such that the emulsion further contains:
- non-hydrohalic acid at 0.1 mM to 0.5 M
- at least one biologically active substance
- the acid and payload are independently incorporated into the lipid component, the first aqueous component, or both
mixing the water-in-oil emulsion with a second aqueous component to form solvent spherules
removing the organic solvent from the solvent spherules to form multivesicular liposomes

This drafting creates a hybrid claim: the result must be a multivesicular liposome with defined internal architecture, and the route to make it is constrained by the emulsion/solvent-spherule/solvent-removal sequence.

What is the “release” element that ties acid to function?

The acid concentration is stated to be “selected to provide controlled release” of the biologically active substance “in” the liposome. Dependent claims then sharpen the acid scope and add a physiologic condition qualifier and disease-recovery language.

What specific limitations appear in claim 1 (scope gates that limit design-arounds)?

A. Structural limits on internal chamber topology

multiple non-concentric chambers
internal membranes distributed as a network throughout

These are product architecture constraints that are not satisfied by generic multivesicular formulations that have concentric lamellae or a different chamber arrangement.

B. Process limits that likely drive invalidity risk and infringement proof

Key process constraints in claim 1:

Water-in-oil emulsion from immiscible components (lipid component + first aqueous component)
lipid component must include:
- organic solvent
- amphipathic lipid
- neutral lipid lacking hydrophilic head group
emulsion contains:
- non-hydrohalic acid at 0.1 mM to 0.5 M
- biologically active substance
- acid and payload are in lipid phase, aqueous phase, or both
mixing with a second aqueous component to form solvent spherules
removing the organic solvent to form multivesicular liposomes

Infringement implication: If accused products are not made by the solvent-spherule route, claim 1 can be harder to prove, even if the final internal architecture matches.

C. Controlled release language

Claim 1’s release is functionally tied to acid concentration. Dependent claim 2 adds controlled release at physiologic conditions; claim 18 adds an “ameliorate a disease” outcome tied to dosing.

Which acid types are claimed, and how narrow is the acid limitation?

Non-hydrohalic acid requirement in claim 1

Claim 1 recites a non-hydrohalic acid at 0.1 mM to 0.5 M.

Dependent claims enumerate acid identities.

Dependent claim 2: specific acid set and physiologic-controlled release

acid selected from: sulfuric, phosphoric, acetic, and combinations
controlled release at physiologic conditions

Dependent claim 3: broader acid set

acid selected from: nitric, formic, sulfuric, phosphoric, acetic, glucuronic, citric, and combinations

Dependent claim 35

repeats selected non-hydrohalic acids including: nitric, glucuronic, citric, formic, acetic, sulfuric, phosphoric, combinations

Scope outcome: The acid carve-outs are explicit for multiple commonly used organic/inorganic acids. A design-around would likely require changing the acid class outside the enumerated list while still satisfying “non-hydrohalic acid” in claim 1, which remains broad.

What payloads are covered: broad categories and explicit named actives?

Broad payload class (claim 4)

Biologically active substance includes:

antitumor, anesthetic, analgesic, antimicrobial
hormone, antiasthmatic
cardiac glycoside, antihypertensive
vaccine, antiarrhythmic
immunomodulator, steroid
monoclonal antibody
neurotransmitter, radionuclide, radio contrast agent
nucleic acid, protein, plus herbicide/pesticide

Explicit examples for litigation leverage (claims 5-17)

Named actives include:

cytarabine (5)
amikacin (6)
hydromorphone (7)
leuprolide (8)
insulin (9)
interleukin-2 (10)
insulin-like growth factor-1 (11)
interferon (12)
G-CSF (13)
tumor necrosis factor (14)
tumor growth factor alpha (15)
tumor growth factor beta (16)
morphine (17)

Scope outcome: The payload portion is not narrow by indication. It is broad enough to read on many marketed and pipeline programs if the formulation architecture and acid-driven solvent-removal process are present.

How broad are the lipid composition limitations (solvent, amphipathic, neutral)?

Claim 20: amphipathic lipid admixture with cholesterol/plant sterols

amphipathic lipid can be provided with cholesterol or plant sterols

Amphipathic lipid head group types

zwitterionic (21)
anionic (22)
mixtures of zwitterionic + anionic (23)
mixtures of zwitterionic + cationic (24)

Zwitterionic examples (claim 25)

phosphatidylcholines, phosphatidylethanolamines, sphingomyelins
lysophosphatidylcholines, lysophosphatidylethanolamines

Anionic examples (claim 26)

phosphatidylglycerols, phosphatidylserines, phosphatidylinositols
phosphatidic acids, cardiolipins

Cationic examples (claim 27)

diacyl trimethylammonium propanes
diacyl dimethylammonium propanes
stearylamine

Neutral lipid requirement and examples

Neutral lipid must lack a hydrophilic head group (claim 1)
claim 28 examples: triglycerides, diglycerides, ethylene glycols (and combinations)

Organic solvent in lipid component (claim 29)

Examples:

ethers
hydrocarbons
halogenated hydrocarbons
halogenated ethers
esters

Design-arounds: Replacing the specific solvent class is not guaranteed to avoid infringement because claim 1 only demands “organic solvent.” Claim 29 narrows examples but does not define the only permissible solvents unless those are used as limiting in the asserted dependent claim set.

What manufacturing parameters are claimed (emulsification, spherule formation, solvent removal)?

Emulsification and spherule formation (claims 30-31)

Either can be:

mechanical agitation
ultrasonic energy agitation
nozzle atomization

This is broad and likely covers most microfluidics-adjacent and conventional emulsification methods.

Organic solvent removal methods (claim 32)

Either can be:

sparging
rotary evaporation
passing gas over solvent spherule suspension
solvent selective filtration

This set includes many common solvent-extraction/stripping operations.

How tight are the numeric composition ranges (claim 33-34)?

Claim 33: numeric concentration windows

organic solvent: ~3.98 mM to ~15 mM
amphipathic lipid: ~3.2 mM to ~47.77 mM
neutral lipid: ~0.5 mM to ~7.3 mM

Claim 34: example amphipathic lipid split

DOPC: ~2.64 mM to ~39.44 mM
DPPG: ~0.56 to ~8.33 mM

Scope outcome: Numeric limits can become major infringement and validity focal points in litigation. If accused formulations operate outside these ranges, dependent claims 33-34 could be avoided while independent claim 1 may still capture if the acid/process/architecture elements are met.

What is the likely claim hierarchy and infringement strategy by claim bundling?

Broadest to narrowest (typical reading)

Claim 1 sets the platform: multivesicular network membranes + acidified solvent-spherule process.
Claims 2-3 narrow acids and add physiologic-controlled release.
Claims 4 and 5-17 define payload scope.
Claims 20-28 define lipid classes and charge compositions.
Claims 29-32 define solvent, emulsification, spherule formation, and removal operations.
Claims 33-34 provide numeric formulation windows.
Claim 18 ties to disease amelioration outcome.

Practical implication

For licensing or freedom-to-operate (FTO) work, the highest-risk design parameters are:

inclusion of a non-hydrohalic acid in the stated range
use of the water-in-oil emulsion + second aqueous component to form solvent spherules + organic solvent removal sequence
achievement of the non-concentric multivesicular architecture with network internal membranes
presence of an organic solvent + amphipathic lipid + neutral non-headgroup lipid system

How strong is the patent estate likely to be based on claim drafting (scope strength vs. prior-art susceptibility)?

Strong scope signals

Broad lipid and solvent language (multiple classes)
Broad payload categories and many named actives
Broad manufacturing method options
Explicit internal membrane topology language increases product specificity but can also be used to argue non-obviousness if supported by structure characterization in the specification.

Potential vulnerabilities (claim language driven)

Functional “controlled release” tied to acid concentration can invite arguments that the feature is inherent or obvious, depending on prior art teaching acidified lipid microemulsions or multivesicular liposomes.
The process framing is detailed but includes generic operations (emulsify, mix aqueous, remove solvent) that may be anticipated if the record shows prior multivesicular liposome methods with similar steps but different functional elements.

What patent landscape issues arise for multivesicular liposomes with acidified release?

Because you supplied only the claims (not the full patent text, prosecution history, priority dates, continuation status, or citation sets), a complete, defensible “US patent landscape” with specific neighboring patents, litigation, Orange Book status, or expiration timelines cannot be produced here without risking fabrication.

What generic entry risks exist under US patent 6,132,766 (product categories, not brands)?

Small molecule generics

If a drug substance is a small molecule loaded into such a liposome system, the risk is that the formulation patent blocks generic equivalents unless they:

avoid the acid/process architecture in claim 1, or
demonstrate non-infringement by testing of internal chamber topology and/or manufacturing route.

Biologics (proteins, nucleic acids)

For protein/nucleic acid payloads, the risk is typically higher for formulation-level patents because generics or biosimilar developers often change manufacturing and payload incorporation. Claim 4 plus claims 5-17 show explicit coverage of multiple biologic-relevant actives, so formulation replication without the same acidified solvent-spherule approach is the key non-infringement route.

Key claim-to-design-parameter map (fast infringement screening)

Claim element	What it captures	Common design deviations
Multivesicular liposome with multiple non-concentric chambers	Internal topology	Use concentric vesicles, different chamber architecture, or single-compartment systems
Internal membranes distributed as a network	Membrane distribution across internal compartments	Build compartmentalization without networked membrane arrangement
Water-in-oil emulsion with lipid component containing organic solvent + amphipathic lipid + neutral non-headgroup lipid	Composition platform	Change solvent class/phase role; remove organic solvent from lipid component
Non-hydrohalic acid at 0.1 mM to 0.5 M	Acidified controlled-release mechanism	Use no acid; use different acid family outside “non-hydrohalic acid” requirement; alter concentration outside window
Acid and payload can be in lipid phase or aqueous phase	Loading flexibility	Change incorporation location and loading mechanism (may still not avoid if still satisfies claim element)
Mix with second aqueous component to form solvent spherules	Intermediate formation	Avoid solvent-spherule intermediate route
Remove organic solvent to form multivesicular liposomes	Solvent-removal process	Use alternative encapsulation/coacervation methods without organic solvent removal step
Broad emulsification/spherule formation options	Manufacturing broad coverage	Hard to design around since it includes multiple mainstream processes
Broad solvent removal options	Post-processing coverage	Also broad; avoid by different manufacturing method class
Dependent lipid charge composition (zwitterionic/anionic/cationic mixtures)	Charged lipid variants	Exclude specific lipid head groups in dependent claim assertions
Numeric concentration windows	Tightens specific embodiments	Operate outside claim 33-34 ranges

Key Takeaways

US 6,132,766 is dominated by a multivesicular liposome architecture requirement plus a specific solvent-spherule emulsion manufacturing sequence.
The patent’s central functional hook is controlled release driven by incorporation of a non-hydrohalic acid at 0.1 mM to 0.5 M, with dependent claims enumerating multiple acids and adding physiologic-controlled release language.
Payload scope is broad by class and explicit by example, including multiple oncology and biologic-relevant actives.
The lipid system is flexible (amphipathic charge types, cholesterol/sterols admixture, multiple organic solvent classes), while dependent numeric claims (33-34) can create tighter infringement boundaries.
A defensible clearance analysis must treat acid identity/concentration, solvent-spherule route, and multivesicular internal membrane topology as the highest-risk elements.

FAQs

Does US 6,132,766 require that the acid and payload be in the same phase?
No. Claim 1 states the non-hydrohalic acid and biologically active substance are independently incorporated into the lipid component, the first aqueous component, or both.
Can a formulation avoid the patent by using a different emulsification technique than mechanical agitation/ultrasonic/nozzle atomization?
Claims 30 and 31 already cover those three methods, but the independent claim does not limit to them if the asserted claim set stays at claim 1; avoidance depends on which dependent claims are asserted.
Is the patent limited to anticancer drugs?
No. Claim 4 covers broad therapeutic categories, and claims 5-17 list multiple named actives across oncology, analgesia, infection, endocrine, cytokines, and growth factors.
Do numeric concentration ranges in claim 33-34 determine infringement for all claim sets?
No. Those ranges appear in dependent claims (33 and 34). If only claim 1 is asserted, infringement can still be possible without meeting the specific numeric windows.
Is the “controlled release” requirement structural or purely functional?
It is functional in claim language, tied to acid concentration and, in dependent claim 2, to controlled release at physiologic conditions. The underlying structural requirements (non-concentric multivesicular chambers and networked internal membranes) still constrain the product.

References

United States Patent No. 6,132,766.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
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Australia	1053595	⤷ Start Trial
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Bulgaria	100596	⤷ Start Trial
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Summary for Patent: 6,132,766