Inhaled rentosertib

Insilico Medicine is developing a second version of rentosertib that is breathed in as a mist rather than swallowed. China’s regulator cleared it for a first-in-human trial in April 2026, but that trial has not started and has no registry entry.

What it is

The formulation is a nebulised inhalation solution. A nebuliser turns liquid medicine into a fine mist that is breathed in through a mask or mouthpiece, so the drug reaches the lungs directly instead of travelling there through the bloodstream.

On 28 April 2026 the Center for Drug Evaluation of China’s National Medical Products Administration cleared an investigational new drug application for it. Insilico describes this as the company’s 13th such clearance across all its programmes.

What is planned

Insilico has said the Phase 1 study will involve about 80 people. It is described as running in two parts: single and then repeated doses in healthy volunteers, followed by an open-label part in people with idiopathic pulmonary fibrosis (IPF). Doses have not been disclosed.

The reasoning behind it

The case for an inhaled version rests on animal work. In rats given bleomycin, a chemical used to produce lung scarring for research, inhaled rentosertib reached concentrations in lung tissue reported in a conference abstract as between 36.9 and 136.7 times those in the blood. Insilico’s own summary of the same work gives a figure of roughly 50-fold. The researchers also reported improvements in lung function and lung compliance in those animals.

If that ratio holds in people, the logic is that a dose reaching the lungs could be achieved with much less drug circulating elsewhere in the body. That is potentially relevant to the liver problems seen with the oral capsules in the Phase 2a trial, where 7 of the 12 people who stopped because of a side effect did so with liver injury or abnormal liver function. Whether an inhaled form actually reduces that risk is unknown, and animal data do not settle it.

Inhaled treatments for IPF have their own difficulties. Cough is the commonest side effect of inhaled treprostinil, another IPF candidate, and people with IPF often cough a great deal already.

Where it has been presented

Preclinical data on the inhaled formulation were presented as posters at the American Thoracic Society international conferences in 2025 and 2026, including poster 8945 at the 2026 meeting in Orlando. Conference posters are not peer-reviewed papers and the underlying data have not been published in full.