Cereno's CS1 Gets FDA Nod, Targeting Pulmonary Hypertension's Root Cause

GOTHENBURG, Sweden – December 08, 2025 – In a move that could reshape the treatment paradigm for a rare and fatal lung disease, Swedish biotech firm Cereno Scientific announced it has received clearance from the U.S. Food and Drug Administration (FDA) to initiate a pivotal Phase IIb clinical trial for its lead drug candidate, CS1. The study will evaluate CS1's efficacy in patients with pulmonary arterial hypertension (PAH), a progressive condition characterized by dangerously high blood pressure in the arteries of the lungs.

This regulatory green light is more than a procedural step; it’s a validation of a novel therapeutic strategy. Unlike current standard-of-care treatments that primarily manage symptoms by dilating blood vessels, CS1 is designed to address the underlying pathology of the disease. The FDA’s decision, which follows a favorable Phase IIa study, allows Cereno to advance toward enrolling its first patient in the second quarter of 2026, setting the stage for a potential breakthrough in a field with significant unmet medical needs.

The Epigenetic Edge: Rewriting the Rules of PAH

At the heart of CS1's potential is its innovative mechanism of action: epigenetic modulation. CS1 is a histone deacetylase inhibitor (HDACi), a class of drugs that can alter gene expression without changing the DNA sequence itself. In PAH, the disease progresses through a destructive process called vascular remodeling, where the walls of the pulmonary arteries thicken and stiffen due to abnormal cell growth, inflammation, and fibrosis. This remodeling restricts blood flow, forcing the right side of the heart to work harder, which eventually leads to heart failure.

"Our goal with CS1 is to address the underlying mechanisms that drive PAH, not simply manage symptoms," said Rahul Agrawal, CMO and Head of R&D at Cereno Scientific. By inhibiting HDAC enzymes, CS1 aims to reactivate protective genes that can halt and potentially reverse this pathological remodeling. Preclinical studies and encouraging signals from the Phase IIa trial suggest CS1 has anti-inflammatory, anti-fibrotic, and anti-proliferative properties, directly targeting the root causes of the disease's progression.

This approach represents a significant departure from the current treatment landscape, which is dominated by vasodilators like endothelin receptor antagonists (ERAs) and PDE5 inhibitors. While these drugs provide critical symptomatic relief, they do not stop the underlying disease from advancing. CS1, being developed as an add-on therapy, holds the promise of not just improving quality of life but fundamentally altering the long-term course of PAH for patients who currently have a median survival of about seven years post-diagnosis.

De-Risking the Path to Market

The FDA’s clearance is a major catalyst for Cereno, significantly bolstering the commercial prospects of CS1. This milestone is amplified by two key regulatory advantages the drug has already secured: Orphan Drug Designation (ODD) and Fast Track designation. These designations are reserved for therapies addressing rare or serious conditions with high unmet needs and are designed to accelerate the journey from lab to clinic.

Orphan Drug Designation, granted in both the U.S. and Europe, provides powerful incentives, including seven years of market exclusivity upon approval in the U.S., tax credits for clinical development, and waived regulatory fees. This exclusivity is crucial in the rare disease space, protecting a company's investment from competition. Fast Track designation, awarded in August 2025, ensures more frequent communication with the FDA and enables a 'rolling review' of the marketing application, which can substantially shorten the time to a final approval decision.

"Receiving FDA clearance to proceed with our Phase IIb study is a significant catalyst for Cereno," stated Sten R. Sörensen, the company's CEO. "This milestone strengthens the commercial potential of CS1, supports our positioning as a leader in epigenetic modulation for rare cardiovascular diseases, and creates additional momentum in our partnering discussions." These regulatory tailwinds make CS1 a more attractive asset for potential pharmaceutical partners, who could provide the substantial capital and infrastructure needed for late-stage development and global commercialization.

A Rigorous Trial for a Devastating Disease

The upcoming Phase IIb study is a robust, global, and multicenter trial designed to provide definitive answers about CS1's efficacy and safety. Approximately 126 PAH patients, who are already stable on existing therapies, will be enrolled across 65 sites in the U.S., Europe, and South America. The study's design is both rigorous and patient-centric.

For the first 36 weeks, participants will be randomized to receive one of two doses of CS1 or a placebo. The primary goals are to measure the change in pulmonary vascular resistance (PVR)—a direct measure of pressure in the lungs assessed via right-heart catheterization—and the change in the 6-minute walk distance (6MWD), a key indicator of functional capacity and exercise tolerance. Following this period, the trial incorporates a clever re-randomization. This ensures all participants will receive the active drug at some point, allowing for longer-term evaluation of CS1's disease-modifying effects while providing ethical access to the promising therapy for all trial volunteers. The total study duration will be 60 weeks.

This dose-finding study is critical for planning a subsequent Phase III trial. As Dr. Agrawal noted, it is "designed to determine the optimal dose for a Phase III trial and to assess CS1's potential to meaningfully reduce pulmonary vascular resistance and improve functional capacity when added to today's standard therapies."

A New Horizon for Patients and the Market

For the thousands of people living with PAH, this development offers a tangible glimmer of hope. The daily burden of the disease—breathlessness, fatigue, and reduced ability to perform simple tasks—is immense. The prospect of a therapy that could potentially halt or reverse the disease's course is transformative. The positive signals from the Phase IIa study, including improved right heart function and enhanced quality of life, provide a strong foundation for this optimism.

Cereno is entering a competitive but dynamic market. Recent approvals, such as Merck’s sotatercept, have already begun to shift the focus toward disease modification. However, CS1’s unique epigenetic mechanism as an oral, well-tolerated therapy could carve out a distinct and valuable position. As Cereno advances its global study-start activities, including site selection and regulatory submissions in participating countries, the biotech and patient communities will be watching closely. With top-line data anticipated around the fourth quarter of 2028, the journey is still long, but the path toward a new era in PAH treatment has never been clearer.