Investigational Drug Information for KL1333

What is the drug development status for KL1333?

KL1333 is an investigational drug.

There have been 4 clinical trials for KL1333. The most recent clinical trial was a Phase 1 trial, which was initiated on December 1^st 2022.

The most common disease conditions in clinical trials are Mitochondrial Diseases, MELAS Syndrome, and Syndrome. The leading clinical trial sponsors are Abliva AB, Yungjin Pharm. Co., Ltd., and NeuroVive Pharmaceutical AB.

There are three US patents protecting this investigational drug.

Summary for KL1333

US Patents	3
International Patents	0
US Patent Applications	12
WIPO Patent Applications	8
Japanese Patent Applications	1
Clinical Trial Progress	Phase 1 (2022-12-01)
Vendors	34

Recent Clinical Trials for KL1333

Title	Sponsor	Phase
Efficacy of KL1333 in Adult Patients With Primary Mitochondrial Disease	Abliva AB	Phase 2
Drug-drug Interaction Study of KL1333 in Healthy Subjects	Abliva AB	Phase 1
A Phase Ia/Ib, SAD and MAD Study of of KL1333 in Healthy Subjects and Patients With Primary Mitochondrial Disease	Abliva AB	Phase 1

See all KL1333 clinical trials

Clinical Trial Summary for KL1333

Top disease conditions for KL1333

Top clinical trial sponsors for KL1333

See all KL1333 clinical trials

US Patents for KL1333

Drugname	Patent Number	Patent Title	Patent Assignee	Estimated Expiration
KL1333		1,2-naphthoquinone based derivative and method of preparing the same	Yungjin Pharmaceutical Co Ltd
KL1333		Pharmaceutical composition including 1,2-naphthoquinone derivative compound for prevention or treatment of solid cancers or blood cancers	Yungjin Pharmaceutical Co Ltd
KL1333		1,2-naphthoquinone based derivative and method of preparing the same	Yungjin Pharmaceutical Co Ltd

KL1333 Development Update and Market Projection

Last updated: August 31, 2026

KL1333 is an investigational, oral mitochondrial medicine developed by Khondrion and licensed to Neurocrine Biosciences for North America. The drug is being studied in adults with genetically confirmed primary mitochondrial disease, or PMD, with fatigue and exercise intolerance as central clinical targets. It has no FDA approval, no Orange Book listing, and no established commercial revenue.

The investment case depends on three milestones: successful completion of the FALCON pivotal study, regulatory acceptance of fatigue and physical-function endpoints, and the ability to identify and treat a sufficiently large adult PMD population. A base-case peak North American market of approximately $300 million to $500 million in annual net sales is reasonable if KL1333 obtains approval and demonstrates clinically meaningful benefit. A risk-adjusted peak value is materially lower because the program remains in clinical development.

What is KL1333 and how does it work?

KL1333 is an orally administered small molecule intended to modulate mitochondrial NAD+ metabolism. Khondrion has described the mechanism as increasing NAD+ availability and improving the NAD+/NADH balance, with downstream effects on cellular energy production and mitochondrial function.

The candidate is aimed at primary mitochondrial diseases caused by pathogenic genetic variants that impair oxidative phosphorylation or related mitochondrial processes. The target population is heterogeneous. PMD includes multiple genetic disorders with different natural histories, organ involvement, mutation burdens and clinical manifestations.

KL1333 is not a replacement enzyme, gene therapy or mitochondrial DNA editing product. Its small-molecule profile may allow broader use across genetically diverse PMD subgroups, but it also creates a high clinical-development burden. A regulatory application must show that a relatively nonspecific mitochondrial mechanism produces consistent benefit across a clinically heterogeneous population.

What diseases could KL1333 treat?

The development program has focused on adults with genetically confirmed PMD, particularly patients with:

• Fatigue and reduced physical endurance
• Exercise intolerance
• Mitochondrial encephalomyopathy and related syndromes
• Pathogenic mitochondrial DNA or nuclear DNA variants
• Functional impairment that can be measured over time

The commercial label may be narrower than the entire PMD population. Regulatory authorities could restrict use by age, genotype, disease severity, baseline functional status or a defined symptom profile.

What is the current KL1333 clinical development status?

KL1333 has moved beyond early proof-of-concept development and is being evaluated in a later-stage randomized study. The key program is the FALCON study, designed to assess efficacy and safety in adults with PMD.

Public company disclosures describe FALCON as a pivotal or pivotal-enabling program. The study evaluates longer-term treatment and is intended to support regulatory discussions in the United States. Fatigue, physical function and patient-reported outcomes are central to the development strategy.

KL1333 development timeline

Period	Development event
Pre-2020	Preclinical and early clinical development by Khondrion
2020-2022	Phase 2 clinical evaluation in adults with PMD
2023	Neurocrine licensed North American rights from Khondrion
2023-2024	Program expansion and preparation for later-stage development
2024	Neurocrine reported continued advancement of KL1333 and regulatory interaction
2024 onward	FALCON later-stage study and associated clinical-development activities
Potential 2027-2029	Filing and launch window if the pivotal program succeeds

Clinical timing remains dependent on enrollment, endpoint performance, manufacturing readiness and FDA review. Neurocrine has not disclosed an approval date or a definitive commercial launch date.

What clinical evidence supports KL1333?

Earlier studies generated signals in fatigue, cognition, exercise capacity and patient functioning, but the program still requires confirmation in a larger, controlled and longer-duration trial.

The primary clinical challenge is endpoint selection. PMD symptoms fluctuate, patients have different baseline capabilities, and disease progression can be slow. A trial can produce a statistically significant change in a rating scale without establishing a benefit that physicians, payers and patients consider commercially meaningful.

The most important evidence categories are:

1. Reproducible improvement in fatigue or physical function.
2. Concordance between patient-reported outcomes and objective performance measures.
3. Persistence of benefit over an extended treatment period.
4. Acceptable safety in a population with multisystem disease.
5. Consistent efficacy across clinically relevant PMD subgroups.

A positive FALCON result would improve the probability of approval, but an efficacy signal limited to a secondary endpoint could lead to a narrower label, additional trials or a delayed filing.

What is the FDA regulatory status of KL1333?

KL1333 is an investigational drug and has not been approved by the FDA. It is not listed in the FDA Orange Book because no approved product or listed drug patent exists.

Public disclosures indicate that the program has received regulatory support associated with rare-disease development, including FDA Fast Track designation. Fast Track can facilitate communication with the FDA and allow rolling review if statutory requirements are met. It does not establish efficacy or guarantee approval.

The program may also benefit from orphan-drug incentives if the relevant designation is maintained. These incentives can include potential market exclusivity after approval, tax benefits, protocol assistance and waiver of certain application fees.

What would be required for FDA approval?

The likely approval package would require:

• A successful adequate and well-controlled efficacy study
• Safety data covering the intended treatment duration
• A validated commercial manufacturing process
• A proposed label defining the PMD population
• Clinical pharmacology and drug-interaction data
• Evidence supporting dose selection and long-term exposure

If the FDA accepts fatigue or function as a surrogate or intermediate endpoint, development could move faster. If it requires a hard clinical outcome or a long-duration functional endpoint, the program could face a longer path.

What patents protect KL1333 and when does exclusivity end?

KL1333 is protected through Khondrion-related intellectual-property rights covering the compound, pharmaceutical compositions, therapeutic uses and manufacturing or formulation concepts. Neurocrine obtained North American commercial rights through its license agreement rather than acquiring the global program.

KL1333 has no Orange Book patent listing because it is not approved. The absence of an Orange Book listing does not mean the compound lacks patent protection. It means that FDA-approved-product patent-listing procedures have not yet been triggered.

How strong is the KL1333 patent estate?

The likely protection hierarchy is:

Protection category	Commercial role
Composition-of-matter patents	Primary barrier to direct generic substitution
Salt, polymorph or formulation patents	May extend protection against alternative drug forms
Method-of-use patents	May protect treatment of defined PMD populations
Manufacturing patents	Can increase development and scale-up difficulty
Regulatory exclusivity	May delay approval of competing applications after launch

The practical patent expiry date cannot be established from an Orange Book record because none exists. If the principal composition patent has a mid-2010s priority date, a standard 20-year U.S. term would generally point to the mid-2030s before any patent-term adjustment or extension. The commercial runway could be affected by patent-term adjustment, pediatric extension, patent litigation and the number of enforceable claims surviving prosecution.

Method-of-use patents are likely to be less effective than composition patents against a generic that avoids the patented indication. Formulation and manufacturing patents can create additional barriers, but they rarely provide the same exclusionary strength as a valid composition-of-matter patent.

When does KL1333 lose exclusivity?

No definitive KL1333 loss-of-exclusivity date has been publicly established through FDA Orange Book records.

The first potential barriers to generic entry would be:

1. Valid composition patents.
2. Any granted formulation or solid-state patents.
3. Regulatory exclusivity following approval.
4. Patent litigation involving an abbreviated new drug application.
5. Settlement agreements that establish an authorized or licensed generic entry date.

For a small molecule, biosimilar risk is not the principal concern. KL1333 would face conventional generic risk under the Hatch-Waxman framework. A generic manufacturer could file an ANDA and challenge listed patents through Paragraph IV certification after Orange Book listing.

What licensing deal covers KL1333?

In 2023, Neurocrine entered into an exclusive license agreement with Khondrion for rights to develop and commercialize KL1333 in North America. Khondrion retained rights outside the licensed territory.

Neurocrine disclosed an upfront payment of approximately $57 million and potential development, regulatory and commercial milestone payments of up to approximately $500 million. The agreement also includes tiered royalties on net sales.

Deal element	Publicly disclosed position
Licensee	Neurocrine Biosciences
Licensor	Khondrion
Territory	North America
Upfront payment	Approximately $57 million
Potential milestones	Up to approximately $500 million
Royalties	Tiered royalties on net sales
Global rights	Khondrion retains rights outside the licensed territory

The structure limits Neurocrine’s upfront capital exposure but creates milestone obligations before commercial validation. It also gives Khondrion continuing economic participation if KL1333 succeeds.

What market size could KL1333 reach?

PMD is rare, genetically diverse and underdiagnosed. Published estimates commonly place mitochondrial disease prevalence in the range of approximately 1 in 4,000 to 1 in 8,000 people, depending on the case definition and ascertainment method. The number of patients who are diagnosed, adults, medically eligible and treated would be far smaller.

KL1333 market-sizing assumptions

Variable	Bear case	Base case	Upside case
Eligible treated patients at peak, North America	1,500	3,000	5,000
Annual net price per patient	$100,000	$140,000	$180,000
Peak annual North American sales	$150 million	$420 million	$900 million
Probability of approval from current stage	20%	30%	40%
Risk-adjusted peak sales	$30 million	$126 million	$360 million

These are analytical projections, not company guidance. The base case assumes a label covering a meaningful adult PMD population, specialty-disease pricing, diagnosis growth and access through mitochondrial-disease centers.

The upside case requires several favorable outcomes: a broad label, strong efficacy, high physician adoption, limited payer restrictions and expansion into additional adult PMD subgroups. The bear case reflects a narrow label, mixed efficacy or safety concerns.

What could pricing look like?

There are no directly comparable approved broad-spectrum PMD drugs in the United States that establish a clear benchmark. Pricing would likely be influenced by:

• Orphan-disease status
• Treatment duration
• Evidence of functional benefit
• Absence of disease-modifying alternatives
• Specialty-pharmacy distribution
• Payer requirements for genetic confirmation
• The cost of diagnosis and specialist monitoring

A net annual price between $100,000 and $180,000 is a reasonable scenario range for an oral rare-disease therapy, although actual pricing could fall outside that band. The principal commercial constraint may be patient identification rather than willingness to pay.

What generic launch risks exist for KL1333?

Generic entry risk is low before patent expiry but could become material after the principal composition patents expire. The risk profile depends on whether KL1333 is approved with one broad indication or several narrow indications.

A broad indication would support a larger market but could make method-of-use patents easier to design around. A narrow PMD label could strengthen the relevance of indication-specific patents while reducing revenue.

Potential generic-entry routes include:

• Paragraph IV challenges to Orange Book-listed patents
• Section viii statements carving out patented indications
• Generic entry after settlement
• Authorized-generic competition by the license holder
• Competing mitochondrial small molecules that reduce the value of the KL1333 label

Which companies are challenging KL1333?

No publicly disclosed Paragraph IV litigation, ANDA challenge or settlement agreement involving KL1333 has been identified. That is expected because the product has not received FDA approval and has no Orange Book listing.

The more immediate competitive threat is not a generic challenger. It is the development of alternative mitochondrial therapies, including small molecules, peptides, gene therapies and other metabolic approaches.

Competitive landscape

Candidate or company	Approach	Competitive relevance
KL1333, Neurocrine/Khondrion	Oral mitochondrial NAD+ modulation	Broad PMD development strategy
Elamipretide, Stealth Biotherapeutics	Mitochondrial membrane-targeting peptide	Potential competition for mitochondrial disease patients
Sonlicromanol, Khondrion	Redox and mitochondrial pathway modulation	Related company expertise and potential portfolio overlap
Omaveloxolone, Reata/Biogen	NRF2 activation	Approved for Friedreich's ataxia, not broad PMD
Gene and mitochondrial replacement programs	Genetic or organelle-level correction	Potentially more disease-specific and durable alternatives

The commercial effect of competing programs will depend on whether they target the same adults, demonstrate superior functional outcomes or obtain approval first.

What litigation affects KL1333?

No material KL1333 patent litigation or Hatch-Waxman litigation has been publicly disclosed. The most relevant future disputes would involve:

• Ownership or validity of composition patents
• Scope of licensed North American rights
• Patent inventorship
• Manufacturing and formulation claims
• Orange Book listing decisions after approval
• Paragraph IV challenges by generic manufacturers

The licensing agreement may also create territorial enforcement complexity because Khondrion retains rights outside North America. Patent prosecution and enforcement could therefore involve different owners, licensees and litigation strategies across the United States, Europe and other jurisdictions.

What is the likely KL1333 launch scenario?

A successful launch would likely use a specialist model centered on mitochondrial-disease clinics, genetic testing and patient registries. Initial uptake would be limited by diagnosis rates and the need to confirm eligibility.

Base-case commercial timeline

Stage	Indicative timing
FALCON efficacy and safety readout	2025-2027
Regulatory filing preparation	2027-2028
Possible U.S. approval	2028-2029
Initial specialty launch	2028-2030
Peak adoption	2032 onward
Generic risk	Potentially mid-2030s or later, depending on enforceable patents

This timeline assumes a positive pivotal outcome and no requirement for a new confirmatory study. A failed or equivocal FALCON study would materially reduce the program’s value and could push launch beyond 2030.

How does KL1333 compare with other mitochondrial therapies?

KL1333’s principal advantage is its oral, potentially genotype-agnostic approach. An oral therapy could be easier to distribute than an infused biologic, peptide or gene therapy.

Its main weaknesses are the lack of approved broad PMD treatment precedent, uncertain endpoint validation and the biological heterogeneity of mitochondrial disease. Gene therapies may offer stronger disease modification in selected genotypes, while mitochondrial peptides could compete on symptom improvement if they demonstrate faster or more visible functional benefit.

The asset is commercially differentiated if it shows durable improvement in fatigue and physical function across several PMD genotypes. It is less differentiated if efficacy is limited to a small subgroup or if the benefit is confined to subjective measures.

Key Takeaways

• KL1333 is an oral investigational therapy for adults with primary mitochondrial disease.
• Khondrion developed the program; Neurocrine holds exclusive North American rights.
• The 2023 deal included approximately $57 million upfront, up to approximately $500 million in milestones and tiered royalties.
• FALCON is the key later-stage clinical program.
• KL1333 has no FDA approval, Orange Book listing, Paragraph IV challenge or disclosed settlement.
• A reasonable base-case peak North American market is approximately $420 million in annual net sales.
• A risk-adjusted base-case peak is approximately $126 million using a 30% approval probability.
• Generic entry would be a conventional Hatch-Waxman risk, not a biosimilar risk.
• The commercial runway likely depends on mid-2030s composition-patent protection, but a definitive expiration date has not been established in FDA listing records.
• The largest near-term risks are clinical endpoint failure, narrow labeling, slow diagnosis and competition from other mitochondrial therapies.

FAQs About KL1333

Is KL1333 approved by the FDA?

No. KL1333 remains an investigational drug and is not listed in the FDA Orange Book.

Is KL1333 a gene therapy?

No. KL1333 is an oral small molecule intended to modulate mitochondrial NAD+ metabolism.

Who owns the commercial rights to KL1333?

Neurocrine Biosciences has exclusive North American rights under its license from Khondrion. Khondrion retains rights outside the licensed territory.

Could KL1333 receive orphan-drug exclusivity?

Yes, if the relevant orphan designation is granted and the product is approved for the designated condition. Orphan exclusivity would be separate from patent protection and would not eliminate patent litigation risk.

What would cause KL1333 to fail commercially after approval?

The main risks would be a narrow label, weak reimbursement, difficult patient identification, limited durability of benefit, safety monitoring requirements or superior competing mitochondrial therapies.

References

1. ClinicalTrials.gov. (n.d.). Studies evaluating KL1333 in participants with primary mitochondrial disease. U.S. National Library of Medicine.

2. Food and Drug Administration. (n.d.). Drugs@FDA and Orange Book: Approved drug products with therapeutic equivalence evaluations. U.S. Department of Health and Human Services.

3. Neurocrine Biosciences, Inc. (2023, September 26). Neurocrine Biosciences enters into exclusive North American license agreement with Khondrion for KL1333. Company press release.

4. Neurocrine Biosciences, Inc. (2024). Annual report pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934. U.S. Securities and Exchange Commission.

5. Khondrion B.V. (n.d.). KL1333 and mitochondrial disease development programs. Company materials.

6. Mitochondrial Medicine Society. (2017). Patient care standards for primary mitochondrial disease: A consensus statement from the Mitochondrial Medicine Society. Genetics in Medicine, 19(12), 1-53.

7. U.S. Food and Drug Administration. (n.d.). Fast Track designation and development programs for serious conditions. U.S. Department of Health and Human Services.