First-in-class nitric oxide prodrug demonstrates favorable safety, tolerability, and dose-proportional pharmacokinetics in healthy volunteers

Vast Therapeutics, a clinical-stage life science company developing nitric oxide-based medicines for serious lung diseases, today announced late-breaking Phase 1 data for its inhaled drug candidate ALX1, presented at the American Thoracic Society (ATS) 2026 International Conference in Orlando, Florida.

The data demonstrates that ALX1, a first-in-class nitric oxide prodrug designed for targeted delivery to the lungs, was well tolerated without safety concerns across all dose levels evaluated, with no dose-limiting toxicities observed and successful escalation above the calculated human effective dose. The study also showed systemic dose-proportional pharmacokinetics, supporting further clinical development in muco-obstructive airway diseases such as bronchiectasis and COPD.

"What stood out in the data is what we didn't see,” said Paul Bruinenberg, MD, MBA, Chief Medical Officer of Vast Therapeutics. “No bronchospasm, no methemoglobinemia, no dose-limiting toxicities, even as we escalated past the calculated human effective dose. Those fundamental challenges have held back inhaled nitric oxide gas for decades. We're very encouraged by what our delivery technology can provide for patients with bronchiectasis and other muco-obstructive airway diseases who have limited options today."

Key study findings include:

• ALX1 was well tolerated without safety concerns at doses up to 172 mg/day in healthy volunteers
• No bronchospasm, wheezing, or meaningful reductions in lung function were observed
• No clinically significant methemoglobinemia detected at any dose level
• No serious adverse events reported
• Transient decreases in blood pressure were observed, consistent with nitric oxide pharmacology, and returned to baseline within 24 hours
• Pharmacokinetics demonstrated dose-proportional increases in systemic exposure (C_max and AUC_last) across all dose levels

The Phase 1 study evaluated 48 healthy volunteers across single ascending dose and multiple ascending dose cohorts using a nebulized formulation of ALX1. The therapy is designed to release nitric oxide locally in the airways over time, enabling dual anti-inflammatory and antimicrobial activity while minimizing systemic exposure.

“Nitric oxide's potential as treatment for airway diseases has been known for a long time,” said Nate Stasko, PhD, Chief Executive Officer of Vast Therapeutics. “The problem has always been getting enough of it, in the right place, at the right time without creating new problems in the process. We believe these data represent a gateway for nitric oxide in respiratory medicine.”

About Vast Therapeutics

Vast Therapeutics is a clinical-stage life science company developing nitric oxide-based medicines for serious lung diseases. The company’s novel technology delivers sustained release nitric oxide in the lungs to address both inflammatory and microbial drivers of disease progression without toxicity. Our goal is to give patients life-changing therapies that restore lung function and quality of life without the limitations of current treatments.
www.VastTherapeutics.com

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