Drug candidate CS1

Targeting the underlying pathophysiology of PAH

CS1 is a novel, oral, controlled-release formulation of the Class I HDACi valproic acid (VPA). By targeting key disease-driving processes such as pathological vascular remodeling, CS1 has the potential to be an effective disease-modifying therapy for PAH patients also due to the favorable safety and tolerability profile. Furthermore, CS1 may be an effective treatment option providing an alternative that may alleviate patients from side effects affecting their everyday life.

In preclinical cardiovascular disease models, VPA has shown potential disease-modifying effects. including reverse pathological remodeling, as well as anti-fibrotic, anti-inflammatory, pulmonary pressure-reducing, anti-proliferative and anti-thrombotic effects.

The main objectives of the CS1 treatment are to enhance quality of life and extend life for patients with PAH. CS1’s unique efficacy profile aligns closely with the underlying mechanisms that drives the progression of PAH. This further position CS1 as a uniquely differentiated and highly promising treatment option.

The disease-modifying effects of CS1 has the potential to stop, halt or reverse the PAH disease progression

PAH is characterized by thickening and narrowing of the small arteries in the lungs, including the development of characteristic plexiform lesions, which restrict blood flow from the right side of the heart to the lungs. Over time, these changes, combined with increased tissue scarring (fibrosis), reduce the elasticity of the blood vessels and increase resistance to blood flow. This process, known as vascular remodeling, raises the pressure in the pulmonary arteries and impairs circulation. Epigenetic modulation through the effect of HDAC inhibition with CS1 has the potential to reverse the disease progression by reverse vascular remodeling.

Strengthened protection in patents and orphan designations

CS1 has a comprehensive patent portfolio comprising three patent families in key global markets. The development of CS1 in PAH is further supported by Orphan Drug Designation (ODD) from the U.S. Food and Drug Administration (FDA), granted in March 2020, and Orphan Medicinal Product Designation (OMPD) from the European Commission (based on EMA's recommendation) in August 2024. These designations recognize CS1's potential therapeutic benefit for a rare, life-threatening disease and confer important regulatory and commercial advantages, including:

• 7 years of market exclusivity post-approval in the US
• 10 years of market exclusivity in the EU
• Assistance with regulatory processes and potential financial incentives

CS1 Phase IIa trial in PAH

A Phase IIa trial evaluating the safety, tolerability pharmacokinetics, and exploratory efficacy of CS1 on top of standard therapy in patients with PAH was completed in 2024. The Phase IIa trial was conducted at 10 US clinics over 12 weeks with a total of 25 patients of which 21 were evaluated for efficacy parameters. The trial successfully met its primary endpoint of safety and tolerability, with no drug-related serious adverse events.

The exploratory Phase IIa trial of CS1 identified efficacy signals suggesting reversal of pathological remodeling of pulmonary vessels. This was observed through:

• Signals of improved right ventricular function, which is the most significant predictor of mortality in PAH was observed through improvement of right ventricular global longitudinal strain (RV GLS) and reduced tricuspid regurgitation (TR)
• Signals of improved overall cardiac function was observed through improved NYHA/WHO functional class and Quality of Life (QoL)
• Signals of disease modification and prognosis was observed through improved REVEAL 2.0 risk score

Fast Track designation for CS1 in PAH

CS1 has been granted Fast Track designation by the FDA. The Fast Track designation enables closer and more frequent interaction with the FDA, eligibility for rolling review of submissions, and potential priority review. These advantages can help shorten timelines and strengthen the development pathway for CS1. For patients, it means that promising new therapies may become accessible more quickly.

Expanded Access Program for CS1 in PAH

Upon request from patients and physicians, CS1 was made available to eligible patients as an extension of the Phase IIa trial in pulmonary arterial hypertension (PAH) through an Expanded Access Program (EAP). Conducted under an FDA-approved protocol, the EAP enabled the collection of longer-term safety and tolerability data in patients treated with CS1. The program has now been completed, and initial 12-month data confirmed that CS1 met the primary endpoint of safety and tolerability, consistent with findings from the Phase IIa study. Together, the Phase IIa study and the EAP provide up to 15 months of treatment data, representing an important addition to the clinical package for CS1.

Beyond enabling continued treatment access, the EAP plays an important strategic role in the development of CS1. The longer-term dataset strengthens the overall clinical understanding of CS1 and supports ongoing preparations for the planned Phase IIb study. It also contributes supportive data for regulatory interactions and ongoing partnering discussions.

As part of the EAP, a sub-study was initiated in February 2025 using Functional Respiratory Imaging (FRI), an advanced imaging technology developed by Fluidda, to provide patient-specific insights into pulmonary vascular changes. Further analyses from the EAP, including the Fluidda imaging sub-study, are expected during Q2 2026 and are intended to provide insights into how long-term treatment with CS1, on top of standard therapy, impacts key parameters in PAH, including REVEAL risk score, overall function, right heart function, and quality of life.

Read our policy further down the page.

Preparations for further clinical development

The clinical development plan for CS1 is focused on continuing to evaluate it as a well-tolerated, orally administered therapy with a favorable safety profile and robust disease-modifying effects in PAH.

Following the promising Phase IIa results, a larger, placebo-controlled Phase IIb trial is planned to start in June 2026.

The FDA has endorsed the Phase IIb trial plans through a Type C meeting and a global top-tier CRO has been selected to lead the trial execution.

Updated April 2026.

At Cereno Scientific, our mission is to develop pioneering treatments to enhance and extend life for people living with rare cardiovascular and pulmonary diseases. We recognize the urgent needs faced by patients and their families, and we are committed to bring safer and more effective treatments to patients with high unmet needs.

We understand that there are times when an individual is unable to participate in a clinical trial, and other treatment options have been exhausted. In those cases, the individual's physician may choose to request access to an investigational drug outside of a clinical trial via what is often termed “Expanded Access” in the United States.

Expanded access, sometimes called “compassionate use” in the US, allows patients with serious or life-threatening conditions to gain access to investigational treatments outside of clinical trials, when no comparable alternatives exist. While participation in clinical trials remains the preferred path to access, we understand that this may not always be possible. If you are interested to learn more about expanded access, please visit the US FDA’s website.

Cereno Scientific does not have any active Expanded Access Programs at this time.

In line with the 21st Century Cures Act, Cereno Scientific may revise this policy at any time.