United States Patent 8,735,401 (Scope, Claims, and U.S. Landscape)
United States Patent 8,735,401 claims a method-of-treatment for sex-hormone-dependent prostate cancer using a single identified chemical entity: N-(4-(1-(2,6-difluorobenzyl)-5-((dimethylamino)methyl)-3-(6-methoxy-3-pyridazinyl)-2,4-dioxo-1,2,3,4-tetrahydrothieno[2,3-d]pyrimidin-6-yl)phenyl)-N′-methoxyurea (and salts). The only dependent limitations narrows to a dosing window and specifies a human subject.
What exactly does US 8,735,401 claim?
Claim 1 (core scope)
Claim type: Method of treating disease (active treatment in a mammalian subject)
Independent claim text (functional summary):
A method for treating sex-hormone-dependent prostate cancer by administering to a mammal in need thereof an effective amount of:
- N-(4-(1-(2,6-difluorobenzyl)-5-((dimethylamino)methyl)-3-(6-methoxy-3-pyridazinyl)-2,4-dioxo-1,2,3,4-tetrahydrothieno[2,3-d]pyrimidin-6-yl)phenyl)-N′-methoxyurea, or
- a salt of that compound.
Key scope properties:
- Single active ingredient: The claim is not “a compound of formula I”; it is anchored to a specific chemical name (plus salts).
- Salt coverage: “or a salt thereof” brings salt forms within the claim.
- Effective amount: Broad, covers any dosing regimen that a court finds “effective” for the recited indication.
- Disease limitation: “sex-hormone-dependent prostate cancer” narrows the patient population to hormone-driven disease states (typically androgen-driven prostate cancer, including castration-sensitive and/or castration-resistant forms depending on claim construction and the specification).
Claim 2 (dose limitation)
Dependent on claim 1: Adds a quantitative dosing range:
- 0.1 to 10 mg/kg weight/day of the same compound (or salt).
Key scope properties:
- Numerical constraint: Outside 0.1 to 10 mg/kg/day, literal infringement of claim 2 is harder, but claim 1 may still capture “effective amount” depending on how broadly “effective” is construed.
Claim 3 (patient limitation)
Dependent on claim 1: Specifies:
- The mammalian subject is a human.
Key scope properties:
- Narrows from “mammalian” to human for that dependent claim only. Claim 1 remains broader because it does not restrict to humans.
What is the claim coverage and what is it not?
Coverage: what is explicitly inside
- Use of the exact chemical entity named in claim 1.
- Salt forms of that chemical entity.
- Methods (administration) for sex-hormone-dependent prostate cancer.
- Any regimen that qualifies as an “effective amount” under claim construction.
- If dose is between 0.1 and 10 mg/kg/day, claim 2 is implicated.
What is not explicitly covered
- Other compounds that are not the named urea compound or its salts (even close analogs are outside the literal claim language).
- Alternative indications (the claim is tied to prostate cancer with the “sex-hormone-dependent” qualifier).
- Administration outside the dose window only blocks claim 2; claim 1 can still read on out-of-range dosing if it is deemed “effective.”
- Non-administration methods (the claims are methods “comprising administering,” so purely in vitro, formulation-only, or diagnostic steps are not targeted by these claims as written).
How broad is “sex-hormone-dependent prostate cancer”?
The phrase “sex-hormone-dependent” is a disease-state qualifier that typically maps to androgen dependence in prostate cancer. From a claim-coverage standpoint, it does two things:
- It narrows against generic “prostate cancer” claims, because not all prostate cancer is necessarily treated as “sex-hormone-dependent” in every clinical framing.
- It still allows substantial clinical scope because androgen-driven prostate cancer broadly includes many standard patient subsets and treatment contexts.
In practice, whether a defendant’s patient population falls within this qualifier is usually resolved by claim construction informed by the specification and prosecution history. The claims you provided do not include those details, so the analysis of the qualifier’s exact boundaries must be limited to the claim language itself.
Claim-to-product mapping: how infringement typically attaches
Literal infringement mechanics
A method claim generally requires:
- Proof that the defendant’s therapy involves administration.
- Proof the administered agent is the named compound or a salt.
- Proof the therapy is for sex-hormone-dependent prostate cancer.
- For claim 2, proof the dosing falls within 0.1 to 10 mg/kg/day.
- For claim 3, proof the subject is human.
Common defendant design-arounds (language-level)
Because claim 1 is tied to a specific chemical identity, typical design-around routes are:
- Substitute a different chemical entity (not “N-(4-(1-(2,6-difluorobenzyl)-…-N′-methoxyurea) …)”) even if mechanistically similar.
- Use a non-salt form if the defendant can argue non-salt status; but claim language includes “salt thereof,” so avoiding salt coverage requires both chemistry and labeling strategy.
- Treat a patient cohort and indication argued to be outside “sex-hormone-dependent prostate cancer.” This is fact-heavy.
What is the patent landscape around US 8,735,401 likely to look like (U.S.)?
1) Foreground: this patent is a method claim tethered to a single drug
Given the claim drafting style, US 8,735,401’s core position in the U.S. landscape is not as a composition-of-matter patent but as an indication/usage lock on a specific drug in sex-hormone-dependent prostate cancer.
2) Adjacent “cliffs” risk: composition patents vs. method patents
In the U.S., the typical landscape around a specific small-molecule cancer drug is structured as:
- Earlier composition-of-matter patents covering the molecule (broadest scope).
- Later formulation, salt, polymorph, intermediate, and method-of-treatment patents narrowing by use, dose, or regimen.
Without the rest of the family documents, what matters for business planning is that:
- If a composition patent still exists, method-only patents are often less strategically important.
- If composition rights have expired or are weak, method patents like 8,735,401 can provide a sharper enforcement handle for ongoing clinical use.
3) U.S. enforcement leverage
Method claims can be enforced by:
- asserting against manufacturers who induce performance of the method (depending on the defendant’s role),
- asserting against providers when the evidence supports direct performance,
- and using label/dosing instructions as evidence of intended use (especially when the prescribed indication aligns tightly with claim language).
For this patent, enforcement leverage is higher where:
- the drug’s U.S. label or clinical protocols clearly match “sex-hormone-dependent prostate cancer,” and
- dosing aligns with recognized regimens (potentially overlapping the 0.1 to 10 mg/kg/day range).
How to interpret the claims for freedom-to-operate (FTO) decisions
FTO trigger test (language-based)
A product or program is most likely to trigger this patent if all are true:
- The active agent is the exact named urea (or a salt).
- The therapy is for sex-hormone-dependent prostate cancer.
- The administered dose is within 0.1 to 10 mg/kg/day (for claim 2 issues).
If the dose is outside claim 2, claim 1 can still be a risk if the dose remains an “effective amount.”
What FTO teams often do with these claims
- Compare the candidate drug substance and salt forms to the claim’s identity requirement.
- Compare the intended patient indication to “sex-hormone-dependent prostate cancer.”
- Compare dosing to the numeric window for a claim 2 assessment.
What are the enforceability and validity pressure points (claim-structure level)?
Even without written description details, the claim structure suggests pressure points that typically arise in U.S. litigation:
- Indefiniteness and scope clarity tied to “effective amount,” which courts often treat as reasonably definite when supported by specification.
- Enablement/adequacy for the “method” claim, particularly if the specification does not support the breadth of “effective amount” across patient subpopulations.
- Written description for the disease qualifier “sex-hormone-dependent,” depending on what the intrinsic record supports.
These are litigation issues driven by the specification and prosecution history, which are not included in the claim excerpt you provided. The claim language alone shows that the only hard constraints are the active ingredient identity, disease qualifier, and dose window (for claim 2).
Landscape summary table (US 8,735,401 only, from provided claims)
| Item |
Claim 1 |
Claim 2 |
Claim 3 |
| Claim type |
Method of treating |
Same method, dose-limited |
Same method, human-limited |
| Active ingredient |
Named N′-methoxyurea (or salt) |
Same |
Same |
| Indication |
Sex-hormone-dependent prostate cancer |
Same |
Same |
| Dose constraint |
“Effective amount” |
0.1 to 10 mg/kg/day |
No additional dose limit |
| Patient constraint |
Mammalian subject |
Mammalian subject |
Human |
| Litigation hook |
Any effective administration matching indication |
Dosing falls in the numeric window |
Human-treatment scenario |
Key Takeaways
- US 8,735,401 is a narrow, drug-identity-tethered method patent: it covers administration of a specific urea compound (or its salts) to treat sex-hormone-dependent prostate cancer.
- Claim 2 adds a dosing window (0.1 to 10 mg/kg/day), which can materially affect infringement analysis if dosing strays outside the range.
- Claim 3 restricts to humans, but claim 1 remains broader because it covers any mammalian subject.
- In a U.S. landscape review, this patent functions as an indication-use constraint on the specific compound rather than a broad “class of compounds” right.
FAQs
1) Is this patent a composition-of-matter or a method-of-treatment patent?
It is a method-of-treatment patent. The claim language requires administering the named compound (or salt) to treat the specified prostate cancer condition.
2) Does “salt thereof” expand the claim beyond the free base/parent compound?
Yes. Claim 1 expressly includes salts of the named compound, so salt forms are within literal scope.
3) What dose range is protected by the dependent claim?
0.1 to 10 mg/kg weight/day under claim 2.
4) If dosing is outside 0.1 to 10 mg/kg/day, is the patent irrelevant?
No. Claim 2 would be avoided on dose-literal grounds, but claim 1 can still apply because it covers administration of an “effective amount.”
5) Does claim 1 limit treatment to humans?
No. Claim 1 covers a mammalian subject. Only claim 3 specifies the subject is human.
References
[1] United States Patent 8,735,401 (claims as provided by user).
