Sling Therapeutics secures $123m to advance oral thyroid eye disease drug

Sling Therapeutics has completed a Series C financing round raising $123m to support the development of linsitinib, an oral treatment for thyroid eye disease. The capital will be utilised to evaluate the drug in an ongoing Phase III clinical trial. In a concurrent announcement, the biotechnology firm confirmed that the first patients have already been dosed in the ORBIT study, which is currently enrolling participants.

Thyroid eye disease is an autoimmune condition characterised by inflammation, swelling and a bulging appearance of the eyes. Although the condition is frequently associated with Graves’ disease and overactive thyroids, patients can also develop it while maintaining healthy thyroid function. Sling’s linsitinib operates as an insulin-like growth factor-1 receptor inhibitor, a mechanism shared by several other approved therapies for the condition. By blocking these receptors, the drug aims to reduce swelling and inflammation. If approved, linsitinib would become the first oral inhibitor of this specific receptor class to reach the market.

The ORBIT trial is designed to enrol 130 patients, with half receiving the study drug and the other half taking a placebo twice daily for a period of six months. The primary endpoint for the study is defined as patients achieving a reduction of at least 2mm in eye bulging in the treated eye, without a corresponding worsening in the fellow eye. Linsitinib has previously demonstrated strong results in this specific measure during a Phase IIb/III trial, where it met its endpoint for reducing eye bulging in patients with moderate-to-severe thyroid eye disease. Following this data, the US Food and Drug Administration granted the drug fast track designation, recognising its potential to provide patients with an alternative administration option.

Ryan Zeidan, chief executive officer of Sling Therapeutics, stated that the financing reinforces the company’s conviction in the drug’s potential to transform the treatment landscape. He noted that the data generated to date provides confidence in linsitinib’s ability to address the limitations of current therapies, offering an effective and convenient oral option that could be used earlier and more broadly in the treatment journey. Sling is one of a limited number of biotechs targeting safer and more efficacious treatments for the condition. While targeted biologic drugs such as Amgen’s Tepezza and Viridian Therapeutics’ Lumvoa are approved, they carry safety trade-offs including severe hearing issues and spikes in blood sugar.

The competitive landscape remains active, with Khartis Therapeutics emerging from stealth in August 2026 with $95m to develop its own oral inhibitor, although it has not yet started clinical trials. Additionally, Eli Lilly is expanding its presence in the space after acquiring Merida Biosciences for $2.875bn earlier this month. Merida’s lead programme, MER511, is currently in Phase I development for Graves’ disease and thyroid eye disease.