Sling Therapeutics Raises $123M for Thyroid Eye Disease Drug

Sling Therapeutics has secured $123 million in Series C financing to advance its oral thyroid eye disease treatment, linsitinib, into a pivotal Phase 3 trial as a potential alternative to existing injectables, according to a Business Wire report.

The financing round was led by Forbion, with participation from TPG Life Sciences Innovations and Sectoral Asset Management, according to the Business Wire report.

Advancing the Phase 3 ORBIT Trial

The capital will directly fund the Phase 3 ORBIT trial for linsitinib, an investigational oral small-molecule blocker targeting the insulin-like growth factor 1 receptor (IGF-1R) for thyroid eye disease, according to a BioSpace report.

The ORBIT trial is designed to evaluate a 150-milligram twice-daily dose of linsitinib against a placebo, targeting an enrollment goal of 130 patients, with initial data expected in mid-2028, according to the BioSpace report.

Understanding the Drug Mechanism

Thyroid eye disease is an autoimmune condition where the immune system attacks the tissues surrounding the eyes, leading to inflammation, swelling, and exophthalmos, or bulging eyes. Linsitinib acts as an oral small-molecule inhibitor of IGF-1R, a receptor heavily implicated in the inflammatory and fibrotic processes driving the disease.

Traditional therapeutic approaches often rely on systemic corticosteroids or surgical interventions for severe cases. By targeting the IGF-1R pathway directly via a small molecule, linsitinib aims to disrupt the signaling cascade responsible for orbital fibroblast activation without requiring intravenous administration.

The Competitive Market for Thyroid Eye Disease

If approved, linsitinib is positioned as potentially the first oral alternative to approved injectables, according to a BioPharma Dive report.

The current market for IGF-1R inhibition is dominated by intravenous treatments such as Amgen's Tepezza and emerging candidates like Viridian's Lumvoa, according to the BioPharma Dive report. While these injectable biologics have established clinical efficacy, their administration schedules often require frequent clinic visits for infusions.

What Is at Stake for Patients and Developers

The transition from intravenous infusions to an oral pill could lower the logistical burden for patients managing chronic, disfiguring orbital inflammation. Securing $123 million in private financing provides Sling Therapeutics with the runway required to complete the ORBIT trial and test whether an oral small molecule can match the clinical outcomes of established biologic therapies.