Rezubio has dosed the first cohort of patients in a Phase I trial of RZ-520, an inhaled therapeutic drug for chronic respiratory diseases.

The study follows investigational new drug clearances (IND) from China's National Medical Products Administration (NMPA) and the US Food and Drug Administration (FDA).

It is assessing the pharmacodynamics (PD), pharmacokinetics (PK), safety and tolerability in healthy volunteers.

RZ-520 is the second candidate to reach clinical testing from Rezubio's Membrane-Anchored Drug Design (MADD) platform, which the company uses to engineer tissue-targeted treatments intended to remain locally active for longer periods.

According to Rezubio, the platform can be applied to cell surface proteins in the gastrointestinal (GI) and the respiratory tracts.

RZ-520 is designed to maintain drug exposure within the lung while restricting systemic distribution, with the stated aim of improving efficacy, safety and dosing convenience.

In preclinical work, the inhaled drug candidate showed therapeutic activity across several disease models, alongside limited systemic exposure. Such findings are early-stage and have not been confirmed in humans.

Rezubio CEO Yusheng Xiong said: “The dual IND clearances from the FDA and NMPA and first cohort dosing of RZ-520 mark a pivotal milestone for both this programme and our MADD platform.

“Advancing our second MADD-derived drug candidate into clinical development further validates the power of our platform to design tissue-targeted therapies that address a broad spectrum of challenging diseases.

“We look forward to advancing these clinical studies and evaluating RZ-520's potential to deliver a transformative, highly differentiated treatment option for patients living with chronic respiratory diseases.”

In December 2025, Rezubio secured $20m in a Series A financing round led by Lapam Capital, with participation from Riverhead Capital and Frees Fund, to advance its lead programme into Phase II clinical development for diabetes and obesity.