Sling Therapeutics Raises $123M for Oral TED Therapy

Sling Therapeutics has closed a $123M Series C to carry oral thyroid eye disease candidate linsitinib through a global Phase 3 trial and toward commercialization. Forbion led the financing, with existing investor TPG Life Sciences Innovations and new investor Sectoral Asset Management participating. The Ann Arbor biotech announced the round on September 16, 2026, the same day it reported that the first patients had been dosed in the ORBIT pivotal study.

The transaction puts a large late-stage check behind a specific clinical and commercial argument. IGF-1R is already a validated target in thyroid eye disease, and the U.S. market now includes approved infused biologics from Amgen and Viridian Therapeutics. Sling must show that an oral small molecule can match enough of the clinical value while reducing the scheduling, site-of-care, and treatment burden built into an infusion regimen.

What Sling Therapeutics Announced

The $123M Series C was led by Forbion, a global life-sciences investor managing more than EUR5B across multiple strategies. TPG Life Sciences Innovations returned as an existing investor, while healthcare-focused Sectoral Asset Management joined as a new backer. Regina Salvat of Forbion and Francois Beaubien of Sectoral were appointed to Sling's board in connection with the financing.

Sling said the proceeds will support continued clinical development of linsitinib and work toward commercialization. The company did not disclose valuation, ownership, investor allocations, financing terms, runway, or a line-item budget. Those omissions matter in a late-stage biotechnology round because clinical execution, manufacturing readiness, regulatory work, and commercial preparation can all consume the same capital while producing very different kinds of proof.

Sling launched publicly in 2022 with a $35M Series A led by TPG's The Rise Fund and an in-license for linsitinib from Astellas Pharma. A company investor presentation says a Series B was completed in January 2024 but does not disclose its size or participants. The public record therefore supports at least $158M across the disclosed Series A and C, not a precise total-funding figure.

Why an Oral IGF-1R Drug Matters

Thyroid eye disease is a rare autoimmune condition that causes inflammation and tissue remodeling around and behind the eyes. Patients can experience pain, swelling, eye bulging known as proptosis, double vision, and impaired vision. The disease often appears alongside Graves' disease, but the practical burden extends beyond the underlying thyroid condition into ophthalmology visits, specialist coordination, treatment logistics, and sometimes surgery.

Linsitinib inhibits insulin-like growth factor 1 receptor, or IGF-1R, the same pathway targeted by approved TED biologics. Sling's differentiation begins with dosage form: linsitinib is a pill taken twice daily rather than an antibody delivered at an infusion center. Oral delivery does not establish efficacy, safety, adherence, reimbursement, or access by itself, but it changes the operating question for patients and physicians if a Phase 3 program can support the clinical profile.

That distinction is commercially relevant because the market is no longer waiting for evidence that IGF-1R can work. Amgen's Tepezza established the target, and Viridian's Lumvoa received FDA approval in June 2026 with a five-infusion course across 12 weeks. Viridian is also developing a subcutaneous option. Sling is entering a field where convenience, site of care, benefit-risk profile, and prescriber reach are becoming part of the competitive design.

The Evidence Behind the Phase 3 Handoff

Sling's earlier LIDS study enrolled 90 adults with active, moderate to severe TED at 35 sites across five countries. Participants received linsitinib 150 mg twice daily, 75 mg twice daily, or placebo for 24 weeks. In sponsor-reported topline results, the company said the 150 mg arm produced a 52% proptosis responder rate at Week 24 and met the primary endpoint with p=0.01.

Sling also reported a favorable profile in adverse-event categories associated with IGF-1R treatment, including hearing impairment, glycemic change, menstrual-cycle change, and QTc prolongation. The company says more than 900 people have received linsitinib across 15 trials in multiple diseases, reflecting the compound's earlier oncology development. These data provide useful clinical history, but they remain sponsor-reported and do not turn an investigational drug into an approved treatment.

The FDA has granted linsitinib Fast Track designation for TED, according to Sling. Fast Track can increase interaction with the agency and create eligibility for review mechanisms when their criteria are met; it is not approval or a shortcut around a successful registrational program. The financing gives Sling resources to produce that program's evidence rather than treating the designation as the finish line.

How the ORBIT Trial Is Designed

The ORBIT study, NCT07753603, is recruiting adults with moderate to severe active TED. The randomized, double-masked, placebo-controlled Phase 3 trial expects to enroll about 130 participants. They will receive linsitinib 150 mg twice daily or placebo for 24 weeks, and eligible participants may enter a 24-week open-label extension.

The primary endpoint is the proportion of proptosis responders at Week 24, defined as at least a 2 mm reduction in the study eye without corresponding deterioration in the other eye. Secondary measures include change in proptosis, overall response, Clinical Activity Score, and Graves' Ophthalmopathy Quality of Life. The design moves the oral thesis into the measurements regulators, clinicians, and payers will use to judge whether a new option belongs in practice.

Sling reported the first ORBIT patients dosed on the financing date. That timing makes the Series C more than runway for a future plan. Capital and execution have met at the point where enrollment pace, site performance, adherence, safety monitoring, manufacturing, and data quality begin to shape the regulatory record.

What the $123M Must Prove

Founder and director Gary D. Hammer and president and CEO Ryan Zeidan have built Sling around one lead clinical program. Current management includes commercial, clinical-operations, development-operations, and manufacturing leadership, signaling the shift from a development story toward a potential launch organization. The company does not list a current CTO, and no technology-stack claim belongs in this biotechnology record.

Forbion, TPG, and Sectoral are financing a narrower proposition than the size of the round might suggest. Sling does not need to rediscover the target. It needs to show that twice-daily oral dosing can produce a credible efficacy and safety profile, survive a blinded pivotal trial, fit real patient routines, and support the access and manufacturing work required after approval.

The unanswered questions now sit inside ORBIT rather than the financing announcement. A pill may remove infusion appointments, but it introduces its own adherence, monitoring, reimbursement, and prescribing considerations. Over the coming trial, Sling's oral argument will be measured patient by patient, visit by visit, and millimeter by millimeter before it can move from convenient idea to available medicine.