By admin 
Ann Arbor, Michigan – Biotechnology innovator Sling Therapeutics announced on Wednesday the successful closure of a $123 million Series C financing round, a pivotal moment that will propel its investigational oral drug, linsitinib, into a global Phase 3 clinical trial for Thyroid Eye Disease (TED). This substantial capital infusion underscores investor confidence in Sling’s differentiated approach to addressing a debilitating autoimmune condition and positions the company to potentially disrupt the burgeoning TED treatment market with a more convenient therapeutic option.
The Unmet Need in Thyroid Eye Disease (TED)
Thyroid Eye Disease, also known as Graves’ ophthalmopathy, is a chronic, progressive autoimmune disorder that affects approximately 10 to 20 per 100,000 individuals annually, with a significantly higher incidence in women. It is closely associated with Graves’ disease, an autoimmune condition causing hyperthyroidism, though TED can occur independently. The disease is characterized by an immune attack on the tissues surrounding the eyes, including muscles, fat, and connective tissue. This inflammatory response leads to a cascade of debilitating symptoms such as proptosis (eye bulging), diplopia (double vision), pain, redness, swelling, impaired vision, and in severe cases, optic nerve compression leading to permanent vision loss. Beyond the physical manifestations, TED carries a significant psychosocial burden, severely impacting patients’ quality of life, self-esteem, and daily functioning.
For decades, treatment options for TED were largely symptomatic and palliative, relying on corticosteroids to reduce inflammation, orbital decompression surgery to alleviate proptosis, or radiation therapy. While these interventions offered some relief, they often came with significant side effects or were invasive, failing to address the underlying autoimmune pathology comprehensively. The landscape began to shift dramatically with the advent of targeted biologics.
In 2020, Amgen’s (formerly Horizon Therapeutics) Tepezza (teprotumumab-trbw) marked a watershed moment, becoming the first and only FDA-approved drug specifically for TED. Tepezza is a monoclonal antibody that inhibits the Insulin-like Growth Factor-1 Receptor (IGF-1R), a critical pathway implicated in the pathogenesis of TED. Administered via intravenous (IV) infusion, Tepezza has demonstrated remarkable efficacy in reducing proptosis and improving other symptoms. However, its IV administration schedule can be burdensome for patients, requiring regular visits to infusion centers. Furthermore, Tepezza is associated with side effects such as hearing impairment, muscle spasms, and hyperglycemia, necessitating careful patient monitoring. More recently, Viridian Therapeutics’ Lumvoa (lonigutamab), another IGF-1R inhibitor, received approval, offering a subcutaneous injection option, which provides a degree of convenience over IV infusions but still involves a biologic injection.
Despite these advancements, a significant unmet need persists for oral, well-tolerated, and highly effective therapies that can offer patients greater convenience, accessibility, and potentially a more favorable side-effect profile, particularly for chronic management.
Sling Therapeutics’ Strategic Advancement with Linsitinib
Sling Therapeutics aims to fill this critical gap with linsitinib, an oral small molecule inhibitor of IGF-1R. The $123 million Series C funding round, led by Forbion, with participation from TPG Life Sciences Innovations and Sectoral Asset Management, provides Sling with the financial runway to execute its ambitious development plan. This investment brings Sling’s total capital raised since its inception in 2022 to $200 million, signaling robust investor confidence in both the company’s leadership and the therapeutic potential of linsitinib.
Ryan Zeidan, President and CEO of Sling Therapeutics, articulated the strategic vision behind linsitinib’s development: "Our goal is to provide a more convenient and potentially safer alternative for TED patients. While existing treatments have been transformative, an oral drug like linsitinib, taken twice daily, could significantly enhance patient adherence and quality of life by eliminating the need for infusions or injections." Zeidan emphasizes that the company’s focus is on delivering a therapy that not only works but also integrates seamlessly into patients’ lives.
The newly secured capital will primarily support the global Phase 3 "Orbit" study for linsitinib. This pivotal trial is designed to confirm the promising results observed in earlier clinical development and build a robust dataset for regulatory submissions worldwide. While the company has not disclosed a specific timeline for topline data from "Orbit," its initiation marks a significant milestone in the journey toward bringing linsitinib to patients.
Linsitinib: A Differentiated Approach to IGF-1R Inhibition
Like Tepezza and Lumvoa, linsitinib targets the IGF-1R pathway, a well-validated mechanism in TED. However, linsitinib distinguishes itself as an oral small molecule, a stark contrast to the monoclonal antibody biologics currently on the market. This fundamental difference in molecular structure and administration route is central to Sling’s strategy.
Zeidan elaborated on linsitinib’s unique attributes, highlighting its precision: "It’s a tricky target to hit. Similar oral IGF-1R inhibitors have been explored in oncology, where they largely struggled due to off-target effects and a broader impact on multiple pathways. However, linsitinib is more targeted and impacts IGF-1R with greater precision than those earlier cancer-focused molecules, and even compared to its antibody-drug counterparts approved for TED. This precision is expected to yield a different, and potentially more favorable, clinical profile." He added that the IGF-1R inhibitors previously studied in cancer hit multiple other pathways, making them unsuitable for development in TED. Linsitinib’s design is specifically optimized for TED, aiming to maximize efficacy while minimizing unwanted systemic effects.
A key differentiator for linsitinib, as suggested by early data, lies in its potential to mitigate some of the challenging side effects associated with approved TED medicines. Sling believes linsitinib’s design should help it dodge many of the adverse events, such as hearing loss, hyperglycemia, and fertility issues, that have been observed with existing treatments. Furthermore, testing to date has suggested that the drug could prove to be more durable than biologics, offering sustained benefit to patients. The convenience of an oral formulation, coupled with a potentially improved safety and durability profile, could represent a significant leap forward in TED management.
Clinical Evidence and Development Chronology
Sling Therapeutics’ rapid progress with linsitinib is built upon a foundation of prior clinical investigation. The company strategically licensed linsitinib from Astellas Pharma in a 2022 deal. Crucially, linsitinib had already undergone extensive testing in over a dozen cancer indications. While its oncology development did not proceed, this prior research provided a wealth of safety and pharmacokinetic data, significantly de-risking and accelerating its development pathway for TED. As Zeidan noted, this allowed Sling to quickly move the drug into mid-stage testing, bypassing much of the preclinical and early-phase clinical work typically required for a novel compound.
The strength of linsitinib’s potential was further solidified by positive topline results from an earlier Phase 2b/3 trial, known as "LIDS." This study demonstrated that treatment with linsitinib was associated with a statistically significant 52% response rate after 24 weeks. Critically, the trial reported no drug-related cases of hearing loss or tinnitus, addressing a key concern with current treatments. These compelling results paved the way for the initiation of the global Phase 3 "Orbit" study, which aims to validate these findings in a larger, more diverse patient population.
Sling Therapeutics was launched in June 2022 with a $35 million Series A financing round, also led by Forbion. The company’s vision from the outset was to leverage existing clinical assets with proven safety profiles to address high-unmet-need conditions. The success in securing subsequent financing rounds, culminating in the $123 million Series C, reflects a consistent belief from investors in the company’s strategy and execution.
The Competitive Landscape and Broader Market Implications
The TED treatment market is dynamic and increasingly competitive. Beyond Amgen and Viridian, other companies like Ethyreal Bio and Khartis have emerged in recent months, also pursuing novel therapies for TED. Conversely, some drugmakers, such as Immunovant and Argenx, have seen their prospective treatments for the inflammatory eye condition fall short in testing, highlighting the inherent challenges and scientific rigor required in drug development for complex autoimmune diseases.
Sling’s entry with an oral small molecule could introduce a paradigm shift. For patients, the ability to manage their condition with a pill at home, rather than frequent clinic visits for injections or infusions, offers unparalleled convenience and potentially improved quality of life. This convenience factor could also translate into broader accessibility, especially in regions with limited healthcare infrastructure or for patients facing mobility challenges.
From a market perspective, an effective and well-tolerated oral treatment could capture a significant share of the TED market, particularly if it demonstrates a superior safety profile or greater durability. The global market for TED treatments is projected to grow substantially in the coming years, driven by increasing awareness, improved diagnostic capabilities, and the availability of targeted therapies. An oral option could expand the patient population willing to seek and adhere to treatment, further fueling market expansion.
Future Outlook and Investor Confidence
Looking ahead, Zeidan indicated that Sling Therapeutics is exploring additional opportunities for linsitinib. The company is considering testing the drug in earlier stages of the disease or against the chronic form of TED, which could broaden its utility and address a wider spectrum of patient needs. "We have some really interesting commercial expansion opportunities and new patient indications that would benefit from this drug, that are unique to a small molecule oral therapeutic," he noted, hinting at a broader strategic roadmap beyond the immediate acute TED indication.
Investor enthusiasm remains high. Peter Bojo, a Principal at TPG Life Sciences, affirmed this sentiment in a statement: "Our continued investment into Sling reflects our confidence in the team’s execution and in linsitinib’s potential to meaningfully improve the treatment paradigm for TED patients. We believe that an oral, targeted therapy with a favorable safety profile has the potential to become a cornerstone treatment for this debilitating disease."
Sling Therapeutics, based in Ann Arbor, Michigan, is positioned at the forefront of innovation in autoimmune disease treatment. The successful Series C funding and the imminent launch of the global Phase 3 "Orbit" study represent crucial steps toward realizing the full potential of linsitinib. If successful, this oral small molecule could not only offer a much-needed convenient alternative but also set a new standard of care for the thousands of individuals worldwide living with the challenging realities of Thyroid Eye Disease. The coming years will be critical as Sling navigates the rigorous path to regulatory approval and, ultimately, to delivering a transformative therapy to patients.
