Sling Raises $164.8 Million for Phase 3 Trial of Oral Tepezza Challenger

Sling Therapeutics raised $123 million (about 164.8 billion won) in a Series C financing to fund a Phase 3 trial of an oral treatment for thyroid eye disease (TED).

According to U.S. biotech publication Fierce Biotech on the 16th, Sling Therapeutics plans to use the proceeds to conduct a late-stage clinical trial of oral linsitinib and then pursue commercialization.

The financing was led by Forbion, with participation from existing investor TPG Life Sciences Innovations and new investor Sectoral Asset Management.

The Phase 3 trial of linsitinib will evaluate its effect on reducing proptosis (exophthalmos) over 24 weeks in 120 patients. The first patient has already been dosed.

Linsitinib is a tyrosine kinase inhibitor (TKI) that blocks insulin-like growth factor 1 receptor (IGF-1R). The receptor interacts with other receptors on the surface of cells behind the eye and with immune cells; when overexpressed or activated, it causes inflammation, swelling and tissue damage in TED.

Astellas originally developed the drug as a cancer treatment, but Sling Therapeutics licensed the technology in 2022. At the time, a $35 million Series A financing funded a Phase 2b trial in TED.

The U.S. Food and Drug Administration (FDA) has approved several IGF-1R inhibitors for TED, but they differ from linsitinib in their mechanisms of action and routes of administration. Amgen’s Tepezza and Viridian’s Lumbroa are monoclonal antibody treatments that bind directly to the IGF-1R and are administered intravenously.

By contrast, linsitinib is taken orally and acts on IGF-1R phosphorylation, with the goal of achieving safer and more durable clinical effects, Sling Therapeutics CEO Ryan Jaidan explained.

Sling Therapeutics reported positive results from a Phase 2b/3 trial in early 2025. In the trial, which enrolled 90 patients, high-dose linsitinib reduced proptosis enough to meet the response criteria in 52% of patients.

“Linsitinib will reach new patient populations, including patients who have refused monoclonal antibody treatment and those who prefer oral treatment,” CEO Jaidan said. “This is an opportunity for market growth and to provide a new treatment option.”

“IGF-1R is a mechanism with proven efficacy in these patients, and physicians are familiar with it,” he added. “It is a good opportunity to provide another attractive treatment option for patients and physicians.”