United States Patent 5,041,424: Scope, Claims, and US Patent Landscape (Etoposide 4’-Phosphate Disodium)
What does US 5,041,424 claim, in enforceable terms?
US 5,041,424 is directed to a method of treating mammalian tumors that are sensitive to etoposide or teniposide by administering an antitumor-effective dose of a specific etoposide-class phosphate prodrug (or a salt). The claims are narrow in claim language because they require (i) the tumor sensitivity predicate and (ii) the exact structural constraints on the administered compound.
Claim 1 (core claim scope)
“A method for inhibiting mammalian tumor… sensitive to etoposide or teniposide” by:
- administering to a mammal in need thereof an antitumor effective amount of a compound of formula (as shown in the patent) where:
- R1 is methyl or 2-thienyl
- R6 is H
- including use of a pharmaceutically acceptable salt of that compound
Scope takeaways for claim 1
- It is a method-of-treatment claim, not a compound claim.
- Liability turns on use: administering a covered compound to inhibit a covered tumor type (sensitive to etoposide or teniposide).
- The chemical scope is constrained by R-group definitions (R1 and R6) and by the requirement that the administered entity fits the specified formula.
Claim 2 (limiting dependent claim)
Claim 2 narrows claim 1 to a single identified compound:
- “wherein said compound is etoposide 4’-phosphate disodium salt.”
Scope takeaways for claim 2
- If a product is etoposide 4’-phosphate disodium salt, it is explicitly within the claim 2 framing.
- The method predicate still matters: the tumor must be etoposide/teniposide-sensitive as stated in the claim.
What are the enforceable claim elements that define infringement?
For US 5,041,424, the claim grammar creates four infringement-relevant elements.
| Element |
Claim language anchor |
Practical proof point in a dispute |
| Treatment type |
“method for inhibiting mammalian tumor” |
Patient is treated with intent to inhibit tumor growth |
| Sensitivity predicate |
tumor “being sensitive to etoposide or teniposide” |
Clinical rationale, biomarker/test outcome, or established sensitivity profile for regimen choice |
| Administered entity |
“antitumour effective amount of a compound of the formula” with R1 and R6 constraints |
Chemical identity of administered API (and whether it is a pharmaceutically acceptable salt form) |
| Identified example (claim 2) |
“etoposide 4’-phosphate disodium salt” |
Product labeling/COA, formulation documentation, or manufacturing release specs |
How broad is the chemical coverage in claim 1?
Claim 1 does not name a single drug. It covers a family of compounds defined by substituents in a formula block:
- R1 = methyl or 2-thienyl
- R6 = H
and requires the compound be administered as an antitumor effective dose.
What that means
- Competitors using different prodrugs or different phosphate placement or different leaving-group variants can avoid claim 1 unless they still fall within the defined formula limits.
- The claim language leaves room for salts (“pharmaceutically acceptable salt thereof”), which expands form-factor coverage without changing core structure.
What does the “etoposide or teniposide-sensitive tumor” limitation do to scope?
This is a functional/diagnostic predicate embedded in the method claim. It narrows the claim to uses where the tumor is expected to respond to either:
Business impact
- It reduces the risk that a generic “etoposide prodrug” use automatically infringes if the regimen targets tumor types without established etoposide/teniposide sensitivity.
- It can also create litigation focus on whether the treated tumor met the claim predicate in practice, depending on how the regimen was justified and how tumors are categorized clinically.
Claim 2 makes the patent product-specific: etoposide 4’-phosphate disodium salt
Claim 2 is explicit: etoposide 4’-phosphate disodium salt.
Practical read-through
- Any US launch, marketing authorization, or compendial regimen for this exact active salt form that is used to inhibit an eligible tumor would map directly onto claim 2’s compound element.
- The remaining gating issue is the method-use predicate (tumor sensitivity to etoposide/teniposide) and the “antitumor effective amount” dosing requirement.
Where does US 5,041,424 sit in the patent landscape for etoposide phosphate prodrugs?
Within the etoposide prodrug landscape, patents often split into different layers:
- Base cytotoxic agents and intermediates (etoposide/teniposide core scaffold)
- Prodrug/polar derivative inventions (e.g., phosphate forms)
- Formulation and administration (parenteral stability, vehicles, infusion regimens)
- Use claims (tumor types or sensitivity-based treatment methods)
- Salt/solid form variations
US 5,041,424 is best characterized as layer (4) with a defined compound scope, and layer (2) through the prodrug structure definition. Claim 2 anchors the prodrug identity.
Landscape implications for R&D decisions
- If you are developing a different phosphate salt, a different salt counterion set, or a different prodrug placement, claim 2 may fall away and claim 1 coverage will hinge on whether your structure meets the R-group constraints in the formula and whether your product still qualifies as the same structural category.
- If you are developing the same salt identity, the strongest remaining design-around target is typically the method-of-use predicate (tumor sensitivity framing) and, in some strategies, the compound identity itself. The claim 2 text is unforgiving on the compound identity.
Typical US claim interactions for this area
For method claims in oncology, US litigation often turns on:
- whether the asserted drug matches the claimed formula/salt identity
- whether the clinical use matches the claimed tumor sensitivity predicate
- whether the dosing regimen supports “antitumor effective amount”
US 5,041,424’s claim set concentrates on those factors.
What claims exist beyond 1 and 2?
Only claims 1 and 2 were provided in the prompt. The analysis above is limited to those claims, and the enforceable scope discussed flows only from the two provided claim texts.
How to map US 5,041,424 to competitor design-around options
The claim structure creates a small set of viable design-around axes:
-
Compound identity axis
- Avoid being a “compound of the formula” with R1 = methyl or 2-thienyl and R6 = H
- Avoid specifically being etoposide 4’-phosphate disodium salt (claim 2)
-
Salt form axis
- Claim 1 includes “pharmaceutically acceptable salt thereof,” so changing to another acceptable salt will not necessarily avoid claim 1 if the parent compound still matches the formula definition.
- Claim 2 is specific: changing disodium to another counterion set can avoid exact coverage if the product is not “disodium.”
-
Method-use axis
- The claim requires tumors “sensitive to etoposide or teniposide.” A competitor can attempt to avoid infringement by targeting clinical contexts where the tumor sensitivity predicate does not apply.
- This axis is risky because clinical practice can still support that sensitivity for many tumor categories.
Key takeaways on scope
- Claim 2 is compound-explicit: etoposide 4’-phosphate disodium salt.
- Claim 1 covers a narrow formula subset: R1 is methyl or 2-thienyl, R6 is H, plus pharmaceutically acceptable salts.
- Both claims require a method of inhibiting a mammalian tumor that is sensitive to etoposide or teniposide and administering an antitumor effective amount.
Key Takeaways
- US 5,041,424 is a method-of-treatment patent with enforceability tied to the administration of a specific etoposide phosphate prodrug family to etoposide/teniposide-sensitive tumors.
- Claim 2 provides the most direct coverage for etoposide 4’-phosphate disodium salt as the administered compound.
- Design-around is structurally driven for the compound identity (R1/R6 limits and disodium specificity) and method-use driven for the sensitivity predicate.
- The patent landscape for this subject matter is layered; US 5,041,424 sits primarily in use-plus-defined-compound territory, making clinical and formulation identity documentation central in any infringement analysis.
FAQs
1) Is US 5,041,424 a compound patent or a method patent?
It is a method claim: it requires administering an antitumor-effective amount of a claimed compound to inhibit tumors.
2) What is the single compound explicitly covered by claim 2?
Etoposide 4’-phosphate disodium salt.
3) Does claim 1 cover salts?
Yes. Claim 1 includes “pharmaceutically acceptable salt thereof.”
4) What tumor criterion must be met for claim coverage?
The tumor must be “sensitive to etoposide or teniposide.”
5) Where do design-arounds most plausibly succeed?
On the compound identity axis (R1/R6 formula constraints and disodium counterion specificity) and, secondarily, on the method-use predicate involving tumor sensitivity.
References
[1] US Patent 5,041,424 (claims 1-2 as provided in prompt).
