More than 200,000 people in the United States live with thyroid eye disease (TED) — an autoimmune condition that inflames the tissue behind the eye, pushes the eyeball forward, and can damage the optic nerve. Every therapy approved for it so far reaches patients through an infusion or an injection. On September 16, 2026, Sling Therapeutics closed a $123 million Series C round and dosed the first patients in a Phase 3 trial of linsitinib, an oral pill aimed at the same disease.
The round is large for a company with one late-stage asset. The consequential detail is the route of administration.
The company is betting $123M that convenience, not potency, opens the thyroid eye disease market.
The Phase 3 readout is not due before 2028, so the commercial question stays open for at least two years.
IGF-1R is the validated target — and the only target behind today's approved TED drugs.
Financing led by Forbion, with TPG and Sectoral
Proceeds fund the Phase 3 ORBIT program for linsitinib. · Sling Therapeutics, 2026
High dose in the 90-patient LIDS trial
Reported in the 90-patient LIDS trial; ORBIT retests it in a placebo-controlled population. · BioSpace, 2026
Randomized 1:1, oral 150 mg or placebo
Twice-daily dosing for 24 weeks; primary endpoint at Week 24. · ClinicalTrials.gov NCT07753603
What is growing
Thyroid eye disease is a rare but expensive problem. It clusters around Graves' disease, hits women far more often than men, and moves in two phases: an active inflammatory stretch, then a fibrotic one where the tissue has already thickened. Once the eye bulges (proptosis), steroids help with inflammation but do little for the mechanical damage.
The approved antibody class changed that. It targets IGF-1R — a receptor that drives the inflammation and tissue expansion behind the eye. Amgen's Tepezza (teprotumumab) entered the market as an intravenous infusion. Viridian Therapeutics' Lumvoa (veligrotug-vvze) followed.
Those drugs validated the target and created a real market. They also created a logistics problem.
Infusion therapy means travel, a chair, a nurse, and hours. For a patient managing thyroid disease alongside it, that is a second treatment schedule. The pitch is blunt: an oral pill removes the infusion center from the equation.
What is under pressure
The efficacy bar is the first pressure point. Antibody therapies work, and clinicians already trust them. The claim is not that linsitinib beats that standard — the framing leans on tolerability and access instead.
BioWorld's read of the data is more cautious than the press release. Its September coverage noted that early results suggest linsitinib may not be as efficacious as the approved antibody treatments. That is the honest version of the bet: a slightly weaker or comparable efficacy signal, traded for a better safety profile and a pill.
The second pressure point is safety, and it is the reason the trade could work. IGF-1R inhibition has a class history — hearing impairment, glycemic shifts, menstrual-cycle changes. The company says its Phase 2b data showed a differentiated profile in exactly those areas. Reuters reported that hearing loss linked to Tepezza and Lumvoa is one reason patients decline antibody therapy, and Sling CEO Ryan Zeidan told the wire he expects linsitinib to reach patients who have already said no.
The third is competition moving under the antibody class itself. Amgen has a subcutaneous Tepezza trial running, which would cut infusion time without a new molecule. The convenience moat is not static.
What is new: the oral entrant
Sling Therapeutics is an Ann Arbor, Michigan company built around a single asset. Linsitinib started life as an oncology drug at Astellas. It licensed the molecule in 2022 and paired that licence with a $35 million Series A led by The Rise Fund, betting that an IGF-1R inhibitor could be reformulated into a chronic oral therapy for TED.
The safety database is the quiet argument for that bet. Linsitinib has been given to more than 900 patients across 15 clinical trials in multiple diseases — an unusually deep exposure record for a molecule that has not yet cleared Phase 3 in this indication.
The Phase 2b/3 LIDS trial met its primary endpoint of proptosis reduction, and the FDA granted Fast Track designation. ORBIT is the confirmatory step: roughly 130 adults, randomized 1:1 to 150 mg of oral linsitinib or placebo twice daily for 24 weeks. The primary endpoint is the share of patients whose proptosis drops by at least 2 mm in the study eye without worsening in the other.
That trial started dosing on the same day the financing closed. Estimated primary completion is 2028.
As we wrote in September, the first AI-engineered antibody reached Phase 3 — a useful contrast. Platform stories and single-molecule stories rarely move on the same clock. Generate Biomedicines is selling a discovery engine. The bet here is narrower: one drug, one disease, and a dosing format.
The $123M buys three years of runway to a 2028 readout; the financing risk now sits with the trial, not the science.
If linsitinib clears ORBIT, the competitive question flips from "is it better?" to "who will prescribe a pill first?"
Oral versus injectable IGF-1R therapy
| Parameter | Linsitinib (Sling) | Tepezza (Amgen) | Lumvoa (Viridian) |
|---|---|---|---|
| Route | Oral, self-administered | Intravenous infusion | Intravenous infusion |
| Stage | Phase 3 (ORBIT), data ~2028 | Approved and marketed | Approved and marketed |
| Efficacy signal | 52% proptosis response (Phase 2b, high dose, n=90) | Established in pivotal trials | Established in pivotal trials |
| Stated differentiation | Convenience plus differentiated tolerability | Subcutaneous Phase 3 running | Infused biologic |
Sources: Sling Therapeutics, FierceBiotech, Reuters, BioWorld (September 2026).
Why an oral drug changes the addressable market
The prevalence number — more than 200,000 people in the United States — describes the pool, not the market. Diagnosis is uneven, and many patients with mild disease never enter the treated population. The ones who do tend to be moderate-to-severe, and that is where the infusion barrier bites hardest.
The argument rests on a simple filter: how many patients declined treatment because it required a chair, a nurse, and a drive. Reuters put the point directly — hearing-loss concerns and the impracticality of intravenous therapy keep some patients away. An oral option does not need to be more effective to win those patients. It needs to be available.
That is the addressable-market expansion thesis, and it is testable in one direction: enrolment. ORBIT is aiming for roughly 130 participants across a global footprint. A fast-accruing trial is evidence that patients and investigators want the option. A trial that stalls past 2027 is evidence that the convenience argument is weaker in practice than on a slide.
The economics of a rare-disease oral asset sit in a different part of the reimbursement system than a hospital-administered biologic. That difference shapes access, and it is one of the commercial problems to solve alongside the clinical readout.
There is a second-order effect worth watching. If an oral IGF-1R inhibitor works, it does not stay a TED-only story. The same mechanism has been explored across autoimmune and oncology settings — linsitinib's own history began in cancer. A clean Phase 3 in TED would hand any winning sponsor a safety database and a regulatory pathway it could point at adjacent indications. That optionality is part of what a $123M Series C is buying.
The swing factor is safety. Antibody efficacy is a known quantity; the linsitinib case leans on a differentiated profile in the IGF-1R areas clinicians worry about — hearing, glucose, menstrual cycles. If ORBIT confirms that profile, there is a pill physicians can reach for earlier. If it does not, convenience has to carry the entire story on its own.
Compare the two commercial paths. An infused biologic sells into a concentrated set of treatment centres, where a handful of specialists control the decision. A primary-care-adjacent oral therapy can travel further into the referral chain, reaching endocrinologists and ophthalmologists who would never set up an infusion suite. That is both the promise and the execution risk: broader reach demands a commercial infrastructure that does not yet exist, which is what the Series C is meant to fund between now and 2028.
None of this resolves in 2026. The financing closed on the same day the trial started. The next hard information is an enrolment update and, eventually, a Week 24 proptosis number. Everything between now and then is a probability distribution.
Signals to track
ORBIT enrolment pace — a 130-patient trial that slips past 2027 pushes revenue past 2029.
The Week 24 proptosis response rate — anything below the Phase 2b 52% reframes the asset as a convenience play only.
Amgen's subcutaneous Tepezza readout — it competes for the same "no infusion chair" patient.
Hearing and glycemic safety data — the differentiation claim lives or dies here.
A second raise at this scale would signal private investors see a path to approval; a down round or a licensing deal would signal the opposite.