Sling Therapeutics raises $123M Series C to advance oral thyroid eye disease drug into Phase 3

Sling Therapeutics announced a $123 million Series C financing round aimed at moving its oral therapy for thyroid eye disease into a late‑stage trial and eventual market launch.

The company has begun dosing the first patients in a Phase 3 study that will enroll about 120 participants. The trial will evaluate the drug, linsitinib, for its ability to reduce proptosis, the bulging of the eyeball, over a 24‑week period.

Linsitinib, a tyrosine kinase inhibitor that blocks the IGF‑1 receptor, was originally created by Astellas for cancer treatment. Sling licensed the molecule in 2022 and previously raised $35 million in a Series A to conduct a Phase 2b trial in the same indication.

While the FDA has already approved other IGF‑1R inhibitors for thyroid eye disease, those agents differ in mechanism and delivery method, positioning Sling's oral candidate as a potentially distinct option for patients.