Sling Therapeutics Raises $123M Series C+ for Late-Stage Thyroid Eye Disease Therapy

Sling Therapeutics Secures $123M Series C+ Round

Ann Arbor, Michigan-based clinical-stage biopharmaceutical company Sling Therapeutics has raised $123 million in a Series C+ financing, announced on September 16, 2026. The round was led by Forbion, with participation from TPG Life Sciences Innovations and Sectoral Asset Management.

What Sling Therapeutics Does

Sling Therapeutics is developing linsitinib, an oral small-molecule IGF-1R inhibitor. According to the company, linsitinib is the first and only late-stage oral therapy in development for thyroid eye disease (TED), a rare autoimmune condition affecting more than 200,000 people in the United States.

Clinical Progress

Linsitinib has an established safety profile across more than 900 patients in 15 clinical trials. The therapy met its primary endpoint in the Phase 2b/3 LIDS trial and holds U.S. FDA Fast Track designation. Sling Therapeutics is currently advancing linsitinib through the global Phase 3 ORBIT pivotal trial.

Funding Details

Item	Detail
Round type	Series C+
Amount	$123,000,000
Date	September 16, 2026
Lead investor	Forbion
Additional investors	TPG Life Sciences Innovations, Sectoral Asset Management

Why This Matters for the Biopharma Market

Thyroid eye disease is a rare autoimmune condition with limited treatment options, particularly oral therapies. Linsitinib's late-stage development status and Fast Track designation position it as a potentially differentiated option if approved. The Phase 3 ORBIT trial is the key near-term catalyst for the program.

The Series C+ round provides capital to support the ongoing global Phase 3 trial and related activities. The participation of specialist life sciences investors—Forbion, TPG Life Sciences Innovations, and Sectoral Asset Management—reflects continued institutional interest in late-stage rare disease assets.

Acquisition Perspective

For acquirers and strategic partners, Sling Therapeutics offers a late-stage clinical asset in a rare autoimmune indication with an oral route of administration. The company's established safety database across more than 900 patients and its Phase 2b/3 primary endpoint success provide a clinical foundation that could be attractive to larger biopharma companies seeking to expand in immunology or ophthalmology.

Key milestones to watch include the progress and readout of the global Phase 3 ORBIT pivotal trial, as well as any regulatory developments related to the existing FDA Fast Track designation. As a clinical-stage company, Sling Therapeutics remains focused on advancing linsitinib toward potential approval and commercialization.