Swiss biotech company, Oculis Holding, achieves significant regulatory milestone following successful Phase 2 ACUITY trial results; global pivotal trials underway for first-in-class therapy addressing critical unmet medical need

Oculis Holding AG announced that the Food and Drug Administration (FDA) has granted Breakthrough Therapy Designation to PRIVOSEGTOR (formerly OCS-05) for the treatment of acute optic neuritis, marking a significant regulatory milestone in the development of novel therapies for a rare but sight-threatening neuro-ophthalmic condition with profound clinical implications, particularly for multiple sclerosis patients.

The FDA’s decision is supported by robust clinical data from the Phase 2 ACUITY trial, wherein PRIVOSEGTOR demonstrated substantial improvements in visual function alongside consistent anatomical and biological neuroprotective benefits compared with placebo. This designation positions PRIVOSEGTOR as a potential first-in-class neuroprotective therapy for optic neuropathies, addressing a critical gap in the treatment landscape where no FDA-approved neuroprotective agents currently exist.

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Acute Optic Neuritis Unmet Medical Need

Optic neuritis represents a rare yet significant cause of acute vision loss, often serving as the first clinical manifestation of multiple sclerosis. According to the recent optic neuritis epidemiological data, approximately 23,000 incident cases of optic neuritis were reported in the United States alone in 2024, with the broader seven-major-markets region (7MM), comprising the US, EU4 countries, the United Kingdom, and Japan, recording more than 40K total incident cases. The 7MM optic neuritis market was valued at approximately USD 3 million in 2024 and is projected to grow at a significant compound annual growth rate (CAGR), underscoring the expanding clinical and commercial importance of emerging therapeutic interventions.

The condition disproportionately affects young women, with data indicating that in the US, females represented nearly 15,000 of the approximately 23,000 incident cases in 2024—almost double the 8,000 cases reported in males. Despite the availability of corticosteroid therapy, which accelerates visual recovery, a critical unmet need persists for treatments that preserve vision through neuroprotective mechanisms and prevent disease recurrence. Current treatment options remain largely supportive, with corticosteroids serving as the only established therapy, while no medications specifically target the underlying neuroinflammation and demyelination driving vision loss.

Phase 2 ACUITY Trial Results: Groundbreaking Clinical Evidence

The Breakthrough Therapy Designation was anchored by compelling efficacy data from the ACUITY (Acute OptiC NeUrITis of DemYelinating Origin) Phase 2 trial, which enrolled 36 patients aged 18 to 60 with recent-onset unilateral acute optic neuritis of demyelinating origin. The trial evaluated PRIVOSEGTOR as a neuroprotective adjunct to intravenous methylprednisolone, the standard-of-care corticosteroid therapy.

PRIVOSEGTOR demonstrated a clinically meaningful improvement in low-contrast letter acuity (LCVA), a sensitive functional vision measure that evaluates the ability to read faint gray letters—a critical metric for assessing visual resolution relevant to daily functioning. Patients receiving the highest dose of PRIVOSEGTOR (2-3 mg/kg/day) exhibited a mean improvement of 18 letters compared with placebo three months after treatment completion, representing approximately a two-fold improvement in visual resolution. At six months, this advantage persisted with approximately 15 additional letters compared with placebo, demonstrating sustained functional benefit.

Beyond functional vision gains, PRIVOSEGTOR delivered consistent anatomical preservation of critical optic nerve and retinal structures, which are typically damaged during acute optic neuritis. Advanced biomarker analyses revealed reduced neurofilament release, a molecular marker associated with decreased neuroaxonal injury documented in neurological disorders, including multiple sclerosis, providing mechanistic evidence supporting neuroprotection.

The safety profile was favorable, with the most common drug-related adverse events being headache and acne, each occurring in 10.5% of participants (two patients). Critically, no drug-related serious adverse events or treatment discontinuations were reported, establishing an acceptable safety window for pivotal development.

Breakthrough Therapy Designation: Regulatory Acceleration and Strategic Implications

The FDA’s Breakthrough Therapy Designation conveys significant regulatory advantages, accelerating the development pathway and facilitating more frequent regulatory communication during clinical program design and execution. This designation, combined with PRIVOSEGTOR’s previously secured Orphan Drug designations from both the FDA and the European Medicines Agency for acute optic neuritis, provides substantial development incentives and market exclusivity considerations for addressing this rare disease.

Mark Kupersmith, MD, Chief Medical Advisor of Neuro-Ophthalmology at Oculis, emphasized the significance of the ACUITY findings: “The ACUITY trial delivered truly groundbreaking results, demonstrating for the first time in a single study that a drug candidate consistently improves visual function alongside anatomical and biological evidence of neuroprotective benefit. Significant unmet medical needs remain, as patients with optic neuritis—more often young women and frequently experiencing the first sign of multiple sclerosis—are still at high risk of permanent visual loss.”

Riad Sherif, MD, Chief Executive Officer of Oculis, underscored the company’s strategic positioning: “Today’s Breakthrough Therapy Designation underscores PRIVOSEGTOR’s significant potential as a first-of-its-kind neuroprotective therapy for people living with optic neuritis. With the ACUITY results and PRIVOSEGTOR now progressing as a neuroprotective platform across key neuro-ophthalmic diseases, Oculis is uniquely positioned to reshape the treatment landscape in areas with substantial unmet needs. We believe 2026 will be a milestone-rich year across our late-stage portfolio.”

PIONEER Registrational Program: Advancing Toward Clinical Approval

Following positive regulatory feedback from FDA meetings conducted in 2025, Oculis initiated the PIONEER (PRIVOSEGTOR Investigation in Optic Neuropathies Efficacy Evaluation Research) program, a comprehensive registrational initiative comprising three pivotal global trials designed to support marketing approval of PRIVOSEGTOR in optic neuritis and an additional indication—nonarteritic anterior ischemic optic neuropathy (NAION), a non-inflammatory optic nerve condition associated with ischemic damage.

PIONEER-1, the first trial evaluating PRIVOSEGTOR in acute optic neuritis, commenced site activation in the fourth quarter of 2025, with patient enrollment anticipated to begin in the near term. This global trial spans three continents and will evaluate PRIVOSEGTOR in a broader population, including both patients with multiple sclerosis and those without MS. The second trial, PIONEER-2, is planned to initiate enrollment in the first half of 2026, following the FDA-approved development strategy established through formal regulatory interactions.

Optic Neuritis Market and Competitive Landscape

The competitive landscape for optic neuritis therapeutics remains nascent, with Oculis’ PRIVOSEGTOR advancing as the leading candidate in this therapeutic category. According to optic neuritis market intelligence, several companies, including Trethera Corporation (developing TRE-515) and Noveome Biotherapeutics (advancing ST266), are pursuing alternative therapeutic approaches. However, PRIVOSEGTOR’s demonstrated functional and structural efficacy, combined with its favorable safety profile and neuroprotective mechanism of action, positions it as a first-mover advantage in addressing this critical unmet medical need.

The broader market trajectory reflects growing industry recognition of optic neuritis’ clinical significance. Diagnostic advancements, including optical coherence tomography (OCT) and high-resolution MRI, have enhanced early detection and disease characterization, facilitating more rapid treatment initiation and supporting the clinical rationale for emerging neuroprotective interventions.

PRIVOSEGTOR Mechanism of Action and Therapeutic Potential

PRIVOSEGTOR is a novel peptoid small-molecule candidate designed to penetrate both the blood-brain barrier and retinal barrier—a critical pharmacological property enabling therapeutic intervention in the central and peripheral nervous system compartments. The compound activates serum/glucocorticoid-regulated serum kinase 2 (SGK-2), a signaling pathway that elicits multiple mechanisms supporting nerve cell development, survival, and repair. This mechanism distinguishes PRIVOSEGTOR from conventional corticosteroid therapy, which provides symptomatic benefit through immunosuppression but lacks direct neuroprotective properties.

Conclusion

Oculis’ achievement of FDA Breakthrough Therapy Designation for PRIVOSEGTOR marks a pivotal advancement in neuro-ophthalmic therapeutics, representing the culmination of rigorous preclinical research and disciplined clinical development. With Phase 2 data demonstrating meaningful functional and structural benefits, combined with an acceptable safety profile, PRIVOSEGTOR stands positioned to potentially become the first neuroprotective therapy approved for acute optic neuritis, addressing a critical therapeutic void that has persisted despite the high burden of vision-threatening disease. The initiation of the global PIONEER registrational program signals Oculis’ commitment to advancing this innovative therapy toward patient access, with regulatory milestones anticipated throughout 2026.

For patients affected by optic neuritis and the clinicians managing this complex condition, this regulatory milestone offers meaningful hope for vision preservation and disease modification, potentially transforming clinical outcomes in one of ophthalmology’s most challenging acute neuro-inflammatory conditions.

About Oculis Holding AG

Oculis is a clinical-stage biopharmaceutical company focused on developing transformative therapies for ophthalmic and neuro-ophthalmic diseases with significant unmet medical needs.