Sling Therapeutics has raised $123m to propel its thyroid eye disease (TED) pill through a pivotal clinical trial.
The funds, which were raised in a Series C round, will help the biotech evaluate linsitinib in an ongoing Phase III trial. In a separate announcement alongside the financing, Sling said that the first patients have already been dosed in the ORBIT study (NCT07753603).
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TED is an autoimmune condition that causes inflammation, swelling, and a bulging appearance of the eyes. While closely linked to Graves’ disease and overactive thyroids, patients can still develop the disease with healthy thyroids.
Sling’s linsitinib is an insulin-like growth factor-1 receptor (IGF-1R) inhibitor, the same class as several other approved therapies for the disease. Blocking these receptors helps reduce swelling and inflammation. Linsitinib would be the first oral IGF-1R blocker, if approved.
Eyes will therefore be on ORBIT to observe pivotal clinical data. Sling plans to enrol 130 patients in the trial, with half receiving the study drug and half taking placebo twice daily for six months. The primary endpoint is defined as patients achieving a reduction of at least 2mm in eye bulging in the study eye without a corresponding worsening in the fellow eye.
Linsitinib has already demonstrated strong results in this measure. In a Phase IIb/III trial (NCT05276063), the small molecule hit its endpoint of eye bulging reduction in patients with moderate-to-severe TED. Following this data and its potential to provide patients with an alternative administration option, the US Food and Drug Administration (FDA) granted the drug fast track designation.
Sling’s CEO, Ryan Zeidan, said: “This financing reinforces our conviction in linsitinib’s potential to transform the treatment landscape for people living with TED as the first and only oral IGF-1R inhibitor in late-stage development.
“The data generated to date give us confidence in linsitinib’s potential to meaningfully address important limitations of current TED therapies and offer patients an effective, convenient oral treatment option that could be used earlier and more broadly in the treatment journey.”
Sling is one of a handful of biotechs targeting safer and more efficacious TED treatments. Corticosteroids and immunomodulators are common options for moderate-to-severe TED. While targeted biologic drugs are approved to treat TED, including Amgen’s blockbuster Tepezza (teprotumumab) and Viridian Therapeutics’ Lumvoa (veligrotug), these do come with safety trade-offs. For example, both drugs can cause severe hearing issues and spikes in blood sugar.
Immunology biotech Khartis Therapeutics is one of those aiming to improve upon the safety of therapies for TED patients. The company emerged from stealth with $95m in August 2026, unveiling its lead programme, which is also an oral IGF-1R inhibitor. Khartis has not yet started clinical trials for its asset, meaning Sling is the only biotech with an oral IGF-1R inhibitor in late-stage clinical trials.
Eli Lilly is also eyeing the TED treatment space. Earlier this month, the big pharma company outlaid $2.875bn to acquire Merida Biosciences. Merida’s lead programme, MER511, is in Phase I development for Graves’ disease and TED. MER511 is a fusion protein containing a portion of the thyroid-stimulating hormone receptor (TSHR) ectodomain.
