Resminostat clinical trial progress and patents: Drug pipeline profiles for drugs in development

Title	Sponsor	Phase
A Phase 1, Open-label Study of the Absorption, Metabolism, Excretion of [14C]-Resminostat	4SC AG	Phase 1
Resminostat for Maintenance Treatment of Patients With Advanced Stage Mycosis Fungoides (MF) or Sézary Syndrome (SS)	4SC AG	Phase 2
Resminostat (YHI-1001) in Combination With Sorafenib in Asian Patients With Advanced Hepatocellular Carcinoma (HCC)	Yakult Honsha Co., LTD	Phase 1/Phase 2

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Last updated: September 24, 2026

Resminostat is an investigational oral histone deacetylase inhibitor developed by 4SC AG, primarily for cutaneous T-cell lymphoma. Its lead Phase IIb RESMAIN trial failed to meet its primary progression-free-survival endpoint. 4SC subsequently discontinued further clinical development, leaving resminostat without an FDA or European marketing authorization, commercial revenue, Orange Book listing, or established generic-entry timeline. Near-term commercial value is therefore limited unless a new sponsor restarts development under a materially different clinical strategy.

What is the current development status of resminostat?

Resminostat, also known as 4SC-201, is an orally administered small-molecule HDAC inhibitor. The compound was evaluated in hematologic malignancies and selected solid tumors, with the most advanced program focused on relapsed or refractory cutaneous T-cell lymphoma, or CTCL.

Item	Current position
Active ingredient	Resminostat
Development code	4SC-201
Drug class	Oral histone deacetylase inhibitor
Primary developer	4SC AG
Lead indication	Cutaneous T-cell lymphoma
Most advanced study	Phase IIb RESMAIN
Regulatory status	No FDA, EMA, or other major-market approval
Commercial status	Not marketed
Orange Book status	No listed FDA-approved product
Development outcome	RESMAIN failed its primary endpoint
Current pipeline status	No active late-stage development publicly established through June 2024

The RESMAIN study evaluated resminostat as maintenance therapy in patients with advanced CTCL who had responded to prior systemic treatment. The clinical rationale was to delay disease progression after an earlier response. The trial did not establish the required efficacy benefit.

4SC reported that RESMAIN failed to demonstrate a statistically significant improvement in progression-free survival compared with placebo. The result removed the principal regulatory pathway for resminostat in CTCL and materially reduced the likelihood of a commercial launch.

What happened in the RESMAIN Phase IIb trial?

RESMAIN was a randomized, placebo-controlled Phase IIb study of maintenance resminostat in patients with advanced-stage CTCL. The study was designed to test whether maintenance treatment could prolong progression-free survival after prior systemic therapy.

The trial’s failure has three commercial consequences:

Resminostat did not generate a registrational efficacy package in CTCL.
4SC lost the most advanced route toward regulatory approval.
A future program would probably require a new protocol, new financing, and potentially a different patient population or combination strategy.

The failure was not equivalent to a safety-related withdrawal. The principal problem was the inability to establish the planned efficacy benefit. That distinction leaves a theoretical possibility of redevelopment, but a restart would require substantial new clinical investment.

Resminostat clinical development timeline

Period	Development event
Pre-2010s	Early clinical evaluation in cancer indications, including hematologic malignancies and solid tumors
2010s	CTCL became the main development focus
2017 onward	RESMAIN Phase IIb maintenance study advanced in CTCL
2021-2022	Top-line RESMAIN results became available
2022	4SC reported failure of the primary progression-free-survival endpoint
After RESMAIN	4SC discontinued further clinical development of resminostat
Through June 2024	No approved product or active pivotal program publicly established

When could resminostat lose exclusivity?

Resminostat has no marketed product and therefore has no practical commercial exclusivity date. Patent expiry dates may exist for individual composition, formulation, use, or manufacturing patent families, but they do not create market exclusivity without regulatory approval.

The commercial analysis is therefore different from an approved drug:

There is no FDA new drug application approval date.
There is no Orange Book-listed patent.
There is no Hatch-Waxman regulatory exclusivity period.
There is no approved-label use that a generic applicant can copy.
There is no known Paragraph IV litigation pathway tied to a marketed resminostat product.

Patent protection, where still active in a particular jurisdiction, could restrict independent development or manufacture. It would not by itself create an investable launch timeline.

What patents protect resminostat?

Public information identifies 4SC as the principal originator and rights holder associated with resminostat development. The patent estate has historically been directed at the compound class, pharmaceutical compositions, therapeutic use, and related chemical subject matter.

The relevant protection categories are:

Protection category	Commercial relevance
Composition-of-matter patents	Protect resminostat or related HDAC inhibitor chemical structures
Pharmaceutical composition patents	Cover drug-containing formulations and dosage forms
Method-of-use patents	Cover treatment of cancer or specified malignancies
Manufacturing patents	May restrict synthesis routes, intermediates, or process conditions
Regional continuation or divisional rights	Can extend or narrow protection in individual countries

The precise expiry position requires family-by-family review across the United States, Europe, Japan, China, and other markets. The public development record does not support treating the historical patent estate as a current market barrier equivalent to an approved-product portfolio.

How strong is the resminostat patent estate?

The estate has moderate theoretical value as a redevelopment asset but limited near-term blocking power.

Its strengths are:

An identified clinical compound with human safety exposure.
Potential composition and use claims.
Prior development in a rare oncology indication.
Possible know-how around oral dosing and HDAC inhibition.

Its weaknesses are:

Failure of the lead Phase IIb trial.
No approved label.
No current commercial product.
Unclear remaining term for individual patent families.
Potential prior-art pressure around HDAC inhibitors.
Limited value of narrow method-of-use claims without demonstrated efficacy.

A potential licensee would likely value the clinical database and development know-how more highly than the patent estate alone.

What is the FDA regulatory status of resminostat?

Resminostat is not FDA approved. The FDA has not granted it an approved indication, reference listed drug status, or market exclusivity.

The compound therefore has no:

New Drug Application approval.
FDA therapeutic equivalence listing.
Orange Book patent listing.
Five-year new chemical entity exclusivity.
Three-year clinical investigation exclusivity.
Orphan-drug approval exclusivity.
Pediatric exclusivity.

Resminostat could theoretically be redeveloped through the 505(b)(1) pathway or another applicable route, depending on the sponsor’s clinical and chemistry, manufacturing, and controls package. The failed Phase IIb study means that a new sponsor could not rely on a simple commercial filing based on the existing record.

What is the Orange Book status of resminostat?

Resminostat has no Orange Book listing because no resminostat product has received FDA approval.

That position removes the principal U.S. framework for generic substitution and Paragraph IV patent challenges. A future approved resminostat product could generate Orange Book-listed patents if the sponsor obtained claims covering the drug substance, formulation, method of use, or manufacturing process. No such approved-product framework currently exists.

Are there Paragraph IV challenges to resminostat?

No publicly established Paragraph IV challenge is associated with resminostat.

The reason is structural. Paragraph IV litigation generally follows submission of an abbreviated new drug application referencing an approved reference product and challenging Orange Book-listed patents. Resminostat has neither an approved reference product nor Orange Book-listed patents.

A future generic applicant could face ordinary patent infringement risk if it sought to manufacture or sell resminostat after approval of an innovator product. That scenario is remote unless clinical development restarts and a sponsor obtains marketing authorization.

What formulation and method-of-use patents could protect resminostat?

Potential formulation protection could cover:

Oral tablets or capsules.
Solid dosage forms with specified excipients.
Release profiles.
Particle size or salt forms.
Stability-enhancing compositions.
Dosing regimens for maintenance therapy.

Method-of-use protection could cover:

Treatment of CTCL.
Maintenance therapy after response to systemic treatment.
Combination use with other anticancer agents.
Treatment of selected hematologic or solid tumors.
Patient selection based on disease stage or prior therapy.

The failed RESMAIN result weakens the commercial value of maintenance-therapy claims in CTCL. A future sponsor would need clinical evidence supporting a narrower biomarker-defined population, a combination regimen, or a different disease setting before those claims could carry meaningful value.

What patent litigation affects resminostat?

No material public patent litigation involving resminostat had been established through June 2024.

The litigation risk profile is low because:

No approved product generates generic-entry disputes.
No Orange Book listing creates an automatic Paragraph IV pathway.
No commercial sales create an immediate infringement damages base.
Development was discontinued after the failed Phase IIb program.

A future dispute could involve ownership of clinical data, licensing rights, compound patents, or manufacturing know-how rather than routine innovator-generic litigation.

Which companies are challenging resminostat?

No company was publicly identified as pursuing a commercial or generic challenge to resminostat through June 2024.

The relevant competitive pressure came from other approved or clinically established CTCL treatments rather than direct resminostat challengers. These included:

Vorinostat, an oral HDAC inhibitor marketed in the United States for CTCL.
Romidepsin, an intravenous HDAC inhibitor used in CTCL.
Mogamulizumab, an anti-CCR4 monoclonal antibody.
Brentuximab vedotin, used in selected CD30-positive disease.
Conventional systemic and skin-directed therapies.

How does resminostat compare with competing CTCL drugs?

Drug	Class	Administration	Regulatory position	Competitive implication
Resminostat	Oral HDAC inhibitor	Oral	Investigational; discontinued development	No current commercial presence
Vorinostat	HDAC inhibitor	Oral	FDA approved for CTCL	Closest commercial comparator
Romidepsin	HDAC inhibitor	Intravenous	FDA approved for CTCL historically	Established efficacy and safety database
Mogamulizumab	Anti-CCR4 antibody	Intravenous	FDA approved for relapsed/refractory CTCL	Competes in systemic treatment
Brentuximab vedotin	Antibody-drug conjugate	Intravenous	Approved in selected CD30-positive lymphoma settings	Competes in biomarker-selected patients

Resminostat’s proposed advantage was oral administration and a maintenance-treatment strategy. Its clinical disadvantage was the failure to show a progression-free-survival benefit in the target population.

What is the market projection for resminostat?

The near-term market projection is effectively zero because resminostat is not approved, not marketed, and has no active late-stage program.

Scenario	Probability-adjusted commercial outlook
No redevelopment	No product revenue
Licensing and Phase II restart	Limited value; development-stage asset
Successful new pivotal program	Potential niche CTCL revenue
Approval in a broader oncology indication	Higher upside but low visibility and high clinical risk

A successful future CTCL product would address a specialty market rather than a mass-market opportunity. CTCL is rare, treatment is concentrated among oncology specialists, and competition includes approved targeted therapies and established HDAC inhibitors. Pricing could be high on a per-patient basis, but total annual revenue would depend on:

Approved disease stage.
Duration of maintenance treatment.
Position in the treatment sequence.
Payer restrictions.
Differentiation from vorinostat and romidepsin.
Evidence in combination therapy.
Geographic launch scope.

No defensible revenue forecast should be assigned to resminostat without a new sponsor, active clinical program, regulatory designation, and a demonstrated efficacy signal.

What revenue exposure does 4SC have to resminostat?

Resminostat does not provide current commercial revenue exposure because it is not marketed. Its value to 4SC is primarily an asset value, licensing value, or optionality value.

The failed RESMAIN trial sharply reduced the asset’s net present value. Any residual value would likely depend on:

Acquisition of the program by a specialty oncology company.
A new indication with stronger biological rationale.
A combination study.
Biomarker-based patient selection.
Access to existing clinical and regulatory data.
Remaining patent term in major markets.

What biosimilar or generic risks exist for resminostat?

Biosimilar risk is not relevant because resminostat is a small molecule, not a biologic. Generic risk is also not commercially active because there is no approved reference product.

If resminostat were eventually approved, generic competition could arise through an abbreviated application after applicable regulatory exclusivity and patent barriers expired. The principal long-term risks would be:

Loss of composition-of-matter protection.
Narrow or expired method-of-use claims.
Generic oral HDAC inhibitor competition.
Therapeutic substitution by other CTCL agents.
Limited market size reducing commercial incentive for a branded relaunch.

What licensing deals involve resminostat?

4SC was the principal developer associated with resminostat. No major current global licensing transaction establishing a new commercial owner or active late-stage development program was publicly established through June 2024.

The absence of a visible licensing deal is commercially relevant. A transaction would likely require a low upfront payment, milestone-heavy economics, and substantial sponsor control over redevelopment. A partner would also need to absorb the cost of a new clinical program after the RESMAIN failure.

What generic launch scenarios exist for resminostat?

There is no credible near-term generic launch scenario.

A generic launch would require:

An innovator or other sponsor to obtain approval.
A reference product to become available.
An abbreviated application pathway to open.
Patent and regulatory exclusivity barriers to expire or be overcome.
Sufficient market size to justify commercial entry.

None of those conditions currently applies. The realistic near-term scenario is continued absence from the market, not generic substitution.

What geographic coverage does resminostat have?

Resminostat was developed for international oncology use, with clinical activity associated with Europe and other major research markets. Development exposure does not equal commercial coverage.

There is no current approved market in:

The United States.
The European Union.
The United Kingdom.
Japan.
China.
Major Latin American markets.

Patent rights may vary by jurisdiction and may have different expiry dates, claim scope, maintenance status, and enforceability. Any transaction would require a live patent-family review rather than reliance on the historical development footprint.

What manufacturing and intellectual-property barriers remain?

Manufacturing barriers are likely manageable for an experienced small-molecule oncology manufacturer because resminostat is an oral chemical drug rather than a biologic. The main barriers are more likely to involve:

Reconstructing validated manufacturing processes.
Confirming impurity controls.
Establishing long-term stability.
Requalifying active pharmaceutical ingredient suppliers.
Rebuilding clinical and regulatory documentation.
Confirming freedom to operate around synthesis routes.
Preserving access to proprietary development data.

The failed clinical result, rather than manufacturing complexity, is the principal barrier to commercialization.

Key Takeaways

Resminostat is an investigational oral HDAC inhibitor developed by 4SC AG.
Its lead RESMAIN Phase IIb trial in CTCL failed its primary progression-free-survival endpoint.
4SC discontinued further clinical development after the failure.
Resminostat has no FDA approval, Orange Book listing, commercial sales, or regulatory exclusivity.
No publicly established Paragraph IV challenge, generic launch, or material patent litigation affects the compound.
CTCL competitors include vorinostat, romidepsin, mogamulizumab, and brentuximab vedotin.
Near-term revenue is effectively zero without a new sponsor and a successful redevelopment program.
Residual asset value lies in the clinical database, prior human exposure, formulation know-how, and any surviving patent rights.
The patent estate should be treated as a redevelopment and freedom-to-operate issue, not as an active branded-product exclusivity platform.

FAQs About Resminostat

Is resminostat approved for cutaneous T-cell lymphoma?

No. Resminostat has not received FDA, EMA, or other major-market approval for CTCL or another cancer indication.

Is resminostat still being developed?

No active late-stage development program was publicly established through June 2024. Development was discontinued after the Phase IIb RESMAIN study failed its primary endpoint.

Can patients currently obtain resminostat commercially?

No. Resminostat is not marketed as an approved prescription medicine.

Is resminostat a competitor to vorinostat?

It was intended to compete in the oral HDAC inhibitor segment, particularly for CTCL maintenance therapy. Vorinostat is approved and commercially established, while resminostat remains unapproved.

Could resminostat return to clinical development?

A return is theoretically possible through licensing, acquisition, or a new sponsor-led program. Such a restart would require new financing and clinical evidence after the failed CTCL Phase IIb study.

References

4SC AG. (2022). Annual report 2021. Martinsried, Germany: 4SC AG.
4SC AG. (2022). 4SC announces results from the RESMAIN Phase IIb study of resminostat in cutaneous T-cell lymphoma. Martinsried, Germany: 4SC AG.
ClinicalTrials.gov. (n.d.). RESMAIN: A randomized, double-blind, placebo-controlled Phase IIb study of resminostat maintenance treatment in patients with cutaneous T-cell lymphoma. U.S. National Library of Medicine.
U.S. Food and Drug Administration. (2023). Drugs@FDA: FDA-approved drugs. Silver Spring, MD: FDA.
U.S. Food and Drug Administration. (2023). Approved drug products with therapeutic equivalence evaluations. Silver Spring, MD: FDA.
U.S. Food and Drug Administration. (2023). Zolinza (vorinostat) prescribing information. Silver Spring, MD: FDA.
European Medicines Agency. (n.d.). Medicines and regulatory information database. Amsterdam, Netherlands: EMA.

US Patents	0
International Patents	0
US Patent Applications	1,001
WIPO Patent Applications	283
Japanese Patent Applications	82
Clinical Trial Progress	Phase 2 (2009-07-01)
Vendors	42

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