Sling raises $123M to push oral thyroid-eye-disease drug into Phase 3

Sling Therapeutics has raised a $123 million Series C to advance linsitinib, an oral small-molecule IGF-1R inhibitor for thyroid eye disease (TED), through a pivotal Phase 3 program.

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

Sling has begun dosing patients in the global, randomized, double-masked, placebo-controlled ORBIT trial in adults with moderate-to-severe active TED. The study is designed to evaluate efficacy and safety over 24 weeks, with reduction in proptosis—eye bulging—a central measure.

Linsitinib is being positioned as a potentially more convenient oral alternative to injectable IGF-1R therapies, including Amgen’s IV Tepezza and Viridian’s Lumvoa. It works by inhibiting IGF-1R signaling rather than directly binding the receptor as an antibody.

The Phase 3 effort follows Sling’s 90-patient Phase 2b/3 LIDS trial:
the high-dose arm achieved the primary endpoint, with 52% of patients meeting the proptosis-response criterion at 24 weeks. The company also reported a potentially differentiated safety profile, though this will need confirmation in the larger trial.