Details for Patent: 6,241,999

Summary for Patent: 6,241,999

Title:	Method for producing liposomes with increased percent of compound encapsulated
Abstract:	The efficiency of encapsulating a drug into a liposomal formulation is increased by use of a lipid having a carbon chain containing from about 13 to about 28 carbons during preparation of the liposomes. Preferably the liposomes are multivesicular liposomes.
Inventor(s):	Qiang Ye, Mantripragada Bhima Sankaram
Assignee:	Pacira Pharmaceuticals Inc
Application Number:	US09/454,521
Patent Claim Types: see list of patent claims	Use; Formulation; Dosage form;

US Patent 6,241,999: What Is Claimed, What It Covers, and How It Sits in the US Liposome Encapsulation Landscape

United States Patent 6,241,999 claims a method to increase the percent encapsulation efficiency of at least one compound in a liposome by substituting a defined “first” amphipathic lipid (with a defined fatty acyl chain length range) with a “second” amphipathic lipid that has a substantially similar chemical structure but a longer fatty acyl chain. The core lever is increasing the number of carbons in the fatty acyl chain of the lipid component to drive higher encapsulated content.

The claims are method claims with layered limitations on:

• lipid chain length ranges (first vs second),
• structural similarity requirement (same headgroup class and “substantially similar” structure),
• specific endpoint encapsulation ranges (some dependent claims),
• specific phospholipid identities (dependent claims),
• and specifics about which acyl chain is increased (SN1/SN2, and “by X carbons”).

This defines a fairly crisp infringement and license map for anyone designing liposomal formulations for improved encapsulation efficiency.

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What is the independent claim 1 actually requiring?

Claim 1 is the only independent claim provided. It requires, in sequence (or at least as a defined method workflow):

A. Liposome formation with a defined first lipid class

• Form a liposome by conventional means
• The liposome has:
  • at least one encapsulated compound
  • at least one first amphipathic lipid
• First amphipathic lipid carbon chain length: about 1 to about 12 carbons in the lipid component of the formulation.

B. Determine percent encapsulated compound

• Determine the percent amount of encapsulated compound (encapsulation efficiency expressed as percent encapsulated content).

C. Substitute first lipid with second lipid of substantially similar structure and longer fatty acyl chain

• Replace the first amphipathic lipid(s) with at least one second amphipathic lipid:
  • substantially similar chemical structure
  • fatty acyl chain carbon count: from 1 to 16 more carbons in the second lipid versus the first lipid.

D. Link between chain-length increase and percent encapsulation

• The claim recites that the increased carbons in the fatty acyl chain results in an increase in percent encapsulated compound.

Claim 1 summary in one line

Switch from a short-chain (1 to 12 carbons) amphipathic lipid to a structurally similar longer-chain lipid (+1 to +16 carbons) and thereby increase encapsulation percent.

This is the basis for both literal infringement analysis (does the accused method include the substitution with the recited chain-length shift?) and for design-around analysis (alter lipid class, alter structural similarity requirement, avoid the “carbon chain length” relationship, or decouple the method such that substitution is not used as the asserted mechanism).

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How broad is the claim set beyond claim 1?

Dependent claims tighten the claim to specific outcomes, phospholipid types, chain-length deltas, and procedural staging.

Encapsulation-efficiency numeric ranges

• Claim 2: percent encapsulated increased to about 7.5 to 50%
• Claim 6: percent encapsulated increased to about 30 to 85%

These create two different “target windows” that can matter for validity and for infringement if a product team can demonstrate encapsulation is outside either window for the relevant lipid substitutions.

Specific chain-length ranges

• Claim 3: carbon number increased from 12 or less to 13 to about 22
• Claim 8: if first acyl chain contains 14 carbons, increase by minimum 2 carbons
• Claim 9: if first contains 16 carbons, increase by minimum 2 carbons
• Claim 10: if first contains 18 carbons, increase by 2 carbons
• Claim 11: increase by 4 carbons
• Claim 12: increase by 6 carbons or more

These dependent claims create discrete “anchor points” that a competitor can hit or avoid. In practice, many liposomal formulation teams use common phospholipid species with predictable acyl chain lengths; these dependent claim steps can map to those choices.

Phospholipid-only narrowing

• Claim 4: amphipathic lipid is a phospholipid
• Claim 5: phospholipid is a saturated phospholipid

This can be used as a validity and scope lever because many formulation efforts rely on unsaturated lipids to tune membrane properties and fusion/clearance behavior.

Specific named phospholipids

• Claim 7 recites a group including (verbatim list condensed for readability):
  • 1,2-dioleoyl-sn-glycero-3-phosphocholine (unsaturated)
  • 1,2-dilauroyl (C12:0)
  • 1,2-dimyristoyl (C14:0)
  • 1,2-dipalmitoyl (C16:0)
  • 1,2-distearoyl (C18:0)
  • 1,2-diarachidoyl (C20:0)
  • 1,2-dibehenoyl (C22:0)
  • 1,2-dipalmitoleoyl (mixed unsat)
  • 1,2-dieicosenoyl (unsat)
  • 1,2-dierucoyl (unsat)
  • 1,2-dipalmitoyl-sn-glycero-3-phosphoglycerol
  • 1,2-dioleoyl-sn-glycero-3-phosphoglycerol

The claim language also says “selected from the group consisting of …” meaning infringement of claim 7 requires selection of one of these defined phospholipids as the relevant lipid.

SN1/SN2 acyl-chain-specific increases

• Claim 13: acyl chain is an SN1 or SN2 chain, or both
• Claim 14: increase is in SN1
• Claim 15: increase is in SN2
• Claim 16: increase is in both SN1 and SN2

This matters because many phospholipids used in formulations are symmetrical (same acyl chain on both positions), but asymmetric species can exist and be used to tune properties. These dependent claims can force an assessment of how many carbons are increased at each acyl position.

Method sequencing constraints

• Claim 17: steps (a) and (b) are performed only until desired encapsulation efficiency is determined
• Claim 18: only step (c) is performed once the desired formulation is determined

These are drafting features that can limit the method pattern to a formulation optimization routine rather than an open-ended process.

Multi-lipid substitution

• Claim 19: 2 or more first amphipathic lipids (1 to 12 carbons) substituted with second amphipathic lipids with substantially similar structures but with 1 to 16 more carbons

This broadens beyond a single lipid substitution to multi-component systems, but still keeps the chain-length rule.

More than one encapsulated compound

• Claim 20: 2 or more compounds encapsulated

This broadens target scope for combination cargo.

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Scope map: what the patent covers vs what it narrows

What it covers (high-confidence based on the claim text)

• Liposomal formulations where optimization proceeds by: 1) making a liposome with a short-chain amphipathic lipid, 2) measuring encapsulation percent, 3) substituting that lipid with structurally similar longer-chain lipid, 4) achieving higher encapsulation percent.
• Substitution can be:
  • one lipid or multiple lipids,
  • on SN1, SN2, or both,
  • with specified chain-length deltas (dependent claims),
  • for one or multiple cargo compounds.

What it narrows (where it is easier to argue non-infringement/design-around)

• The “lever” is fatty acyl chain carbon count and “substantially similar chemical structure.” If a formulation changes other determinants (headgroup class entirely, amphipathic class, or introduces different chemistry) without satisfying “substantially similar chemical structure,” scope narrows.
• Independent claim 1 requires the first lipid has about 1 to about 12 carbons and the second lipid is +1 to +16 carbons relative to that first lipid.

This makes it harder to reach if the baseline formulation uses already-long acyl chains above the claimed “first lipid” range, or if the substitution is not within the claimed carbon delta relationship.

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Patent landscape positioning (US liposome encapsulation efficiency via lipid composition)

Below is a practical landscape view: where this patent’s claim theme fits relative to typical US liposome IP families.

1) Liposome composition and encapsulation optimization claims

This patent sits inside a subcategory: claims that use membrane lipid composition modifications to alter encapsulation efficiency (percent encapsulated). Many competitors protect:

• lipid composition,
• manufacturing/process steps (e.g., hydration, remote loading),
• and analytical/assay methods.

6,241,999’s differentiator is the specific optimization mechanism: swap short-chain amphipathic lipids with substantially similar longer-chain amphipathic lipids and tie the chain-length increase to percent encapsulated.

2) Remote loading and active loading families

A large portion of liposome efficiency IP centers on active loading (pH gradient, ion gradients, drug-to-lipid ratio optimization, etc.). Those may improve encapsulation without necessarily mapping to the specific acyl chain substitution rule.

The key for infringement landscape is whether accused methods:

• rely on active loading mechanics alone, or
• still include the claimed substitution rule (first lipid 1 to 12 carbons, then structurally similar second lipid with +1 to +16 carbons).

3) Lipid type families (phospholipid vs non-phospholipid)

Because dependent claims include phospholipid and even saturated phospholipid limitations, the independent claim is broader in principle, but still anchored in the “amphipathic lipid” substitution concept.

A landscape risk rises if competitors remain within:

• phospholipid headgroups, and
• saturated chain-length stepping.

Risk can fall if competitors move to:

• different amphipathic lipid classes that do not satisfy “substantially similar chemical structure,” or
• baseline systems outside the “first lipid” chain-length range.

4) Known phospholipid selection (anchor species)

Claim 7 names a set of common phospholipids across multiple acyl chain lengths:

• C12 (dilauroyl)
• C14 (dimyristoyl)
• C16 (dipalmitoyl)
• C18 (distearoyl)
• C20 (diarachidoyl)
• C22 (dibehenoyl) plus unsaturated analogs (oleoyl, palmitoleoyl, etc.) and phosphoglycerols.

That ties the patent to widely used materials. In a landscape review, this tends to increase “obviousness pressure” in prosecution and increases the likelihood that downstream formulation teams already considered chain-length impacts.

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Claim-by-claim scope leverage for freedom-to-operate

If you are assessing infringement risk

The operative infringement question for claim 1 is: did the accused method

• start with liposomes using at least one first amphipathic lipid with 1 to 12 carbons,
• substitute it with a second amphipathic lipid that has substantially similar chemical structure and +1 to +16 carbons,
• and measure encapsulation percent that increases as a result?

Dependent claim exposure then turns on:

• measured encapsulation percent hitting the ranges in claims 2 and/or 6,
• whether baseline and replacement chain lengths fall into claims 3, 8-12,
• whether phospholipid and saturated phospholipid limitations are met (claims 4, 5),
• whether one of the enumerated lipids appears (claim 7),
• whether changes were specifically located in SN1/SN2 chains (claims 13-16),
• and whether the method is structured as a formulation determination workflow (claims 17-18).

If you are assessing design-around options

The clearest structural/design avoidance axes implied by the claim text are:

• Avoid the claimed “first lipid” baseline: do not use an amphipathic lipid whose fatty acyl chain falls in the claimed 1 to 12 carbon range in the relevant substitution step.
• Avoid “substantially similar chemical structure”: switch to a different amphipathic lipid class/headgroup that does not preserve the required similarity.
• Avoid the required carbon delta relationship: ensure the replacement is not “from 1 to 16 more carbons” versus the first lipid used in the relevant step.
• Decouple the method from percent encapsulation increase by that mechanism: if the method improvement is achieved by steps not tied to the claimed lipid chain-length substitution, the chain-length substitution might not be used “wherein the increased number of carbons … results in an increase” in the method’s operative logic.

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Key Takeaways

• US 6,241,999 is a liposome formulation method patent focused on increasing encapsulation percent by substituting a short-chain amphipathic lipid (1 to 12 carbons) with a structurally similar longer-chain lipid (+1 to +16 carbons).
• Claim coverage is broad at the independent level but narrowed through dependent claims to:
  • specific encapsulation efficiency windows (about 7.5 to 50% and about 30 to 85%),
  • specific chain-length ranges and deltas (including 13 to about 22 and deltas of 2, 4, and 6+ carbons),
  • phospholipid and saturated phospholipid use,
  • enumerated phospholipid species,
  • and SN1/SN2-specific increases.
• The landscape positioning is strongest against competitors who improve encapsulation by systematically stepping acyl chain length within structurally similar phospholipid families.

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FAQs

1) Does the patent claim only phospholipids?

No. Claim 1 requires an “amphipathic lipid.” Claims 4-7 narrow to phospholipids, saturated phospholipids, and then specific named phospholipids.

2) Is the encapsulated cargo limited to a specific drug class?

No. Claim 1 is tied to “at least one encapsulated compound” and Claim 20 covers multiple compounds. The claim text does not restrict compound identity.

3) What is the central variable that drives scope?

The number of carbons in the fatty acyl chain of the amphipathic lipid used in the liposome, specifically moving from 1-12 carbons in the first lipid to +1 to +16 carbons in the second lipid while retaining “substantially similar chemical structure.”

4) Can the lipid chain increase occur only on one acyl position?

Yes. Claims 13-16 cover increases on SN1, SN2, or both.

5) What method steps are required in claim 1?

Form the liposome with the first lipid, determine encapsulation percent, then substitute the first lipid with the second longer-chain lipid so the chain-length increase results in increased encapsulation percent.

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References

1. United States Patent 6,241,999. Claims as provided in the prompt.

Drugs Protected by US Patent 6,241,999

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 6,241,999

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Australia	4657997
Australia	738020
Canada	2267416
European Patent Office	1005326
Israel	129145