Sling Therapeutics
An Ann Arbor-based clinical-stage biotech challenging the injectable standard of care in thyroid eye disease with the first late-stage oral IGF-1R inhibitor
Sling Therapeutics is a clinical-stage biopharmaceutical company co-founded by University of Michigan endocrinologist Gary D. Hammer, M.D., Ph.D., with Ryan Zeidan, Ph.D. joining as CEO in April 2021 to lead the company’s formal build-out. Sling came out of stealth with its Series A in June 2022 and is headquartered in Ann Arbor, Michigan. We note that the company has concentrated its entire clinical effort on a single indication, thyroid eye disease (TED) — a capital-efficient strategy in our view, but one that also concentrates single-asset risk in a way investors should weigh explicitly.
B.S. in Chemistry and Chemical Engineering, MIT; Ph.D. in Chemistry, Caltech. Previously Chief Development Officer and SVP of Development at Millendo Therapeutics; held program and portfolio leadership roles at Celgene, Novartis Oncology, and Novartis Vaccines. Joined Sling as CEO in April 2021.
Holds the Millie Schembechler Professorship of Adrenal Cancer at the University of Michigan, where he has directed endocrine oncology for 22 years. Immediate past President of the Endocrine Society (2020–2021). Co-founder of Millendo Therapeutics. Ph.D. in neuroendocrinology from Tufts; endocrinology training at UCSF.
The board is chaired by Faheem Hasnain and includes Peter Bojo and Lucian Iancovici, M.D. of TPG Life Sciences, alongside Andrew Guggenhime, who joined in January 2025. Forbion’s Regina Salvat, Ph.D. and Sectoral Asset Management’s François Beaubien, Ph.D., CFA were added to the board concurrent with the Series C close. Clinical development is led by Chief Scientific Officer Raymond Douglas, M.D., Ph.D., an oculoplastic specialist at Cedars-Sinai Medical Center and a recognized key opinion leader in TED trial design.
Sling’s sole clinical asset is linsitinib, an oral small-molecule tyrosine kinase inhibitor of insulin-like growth factor-1 receptor (IGF-1R) — the only validated target underlying every currently approved TED therapy, and the one for which linsitinib is the sole oral candidate. The molecule was in-licensed from Astellas Pharma in 2022 and carries an existing oncology safety database of more than 900 patients across 15 clinical trials, which we view as the primary driver behind the compressed timeline from IND clearance to a positive Phase 2b/3 readout.
| Candidate | Indication | Stage | Notes |
|---|---|---|---|
| Linsitinib | Thyroid Eye Disease — ORBIT pivotal | Phase 3 | First patients dosed September 2026 (NCT07753603). Primary endpoint is proptosis reduction at Week 24. Design aligned with FDA at an End-of-Phase 2 meeting |
| Linsitinib | Thyroid Eye Disease — LIDS registrational | Phase 2b/3 | Positive topline reported January 2025; 150mg BID arm reached statistical significance on the primary endpoint and underpins the Fast Track designation |
| Undisclosed | Rare / autoimmune endocrine disease | Exploratory | Directional language from the 2022 launch release; we find no subsequent disclosure of a specific candidate or preclinical program — pipeline diversification remains effectively nonexistent |
At its 2022 launch, Sling signaled an intent to expand into “rare and autoimmune diseases” beyond TED. We find no subsequent public disclosure of a specific candidate or preclinical program supporting that intent. We treat Sling as effectively a single-asset company built around linsitinib and assign no incremental value to the stated diversification ambition.
On regulatory pathway: Unlike a 505(b)(2) reformulation strategy built around a previously approved active ingredient, linsitinib is a new molecular entity that has never been approved for any indication. Its oncology database substantially de-risks toxicology, but approval in TED will still require a standard NDA pathway rather than the abbreviated review associated with 505(b)(2) filings.
Sling has financed itself through just two disclosed rounds across roughly four years since its June 2022 Series A. We read the low frequency of disclosed rounds paired with large, milestone-linked round sizes as typical of a late-stage, single-asset clinical biotech, and we view TPG Life Sciences Innovations’ participation across every disclosed round — Series A through Series C — as a continuity signal from a sophisticated life-sciences investor.
Ryan Zeidan joined as President and CEO in April 2021 to build out the company around Gary Hammer’s founding concept. We understand licensing negotiations for linsitinib and IND preparation took place during this period, though funding details from this phase were not disclosed.
Led by TPG’s The Rise Fund. The round accompanied Sling’s public launch and disclosure of the linsitinib license from Astellas, funding the FDA IND clearance and the initiation of the Phase 2b LIDS trial.
The 150mg BID arm achieved a 52% PRR (p=0.01) at Week 24, meeting the primary endpoint with statistical significance. Andrew Guggenhime joined the board the same month. Not a financing event, but in our assessment the data point that underwrote the subsequent Series C valuation.
Led by Forbion, with continued participation from existing investor TPG Life Sciences Innovations and new investor Sectoral Asset Management. Announced the same day as first patients dosed in the ORBIT Phase 3 trial — a sequencing choice we read as a deliberate pairing of a capital event with a clinical milestone for maximum market signal.
CEO Ryan Zeidan told BioPharma Dive that Sling has raised $200 million in total since its 2022 launch. Summing disclosed rounds — the $35M Series A and $123M Series C — yields $158M, a roughly $42M gap. We do not rule out an undisclosed bridge round, debt financing, or an unannounced Series B accounting for the difference, but we flag this figure as management-stated and outside the scope of independently verifiable disclosure. We would treat the $158M disclosed-round total as the verifiable floor for underwriting purposes.
The TED treatment landscape shifted from a single-approved-therapy market under Amgen’s teprotumumab (Tepezza, approved 2020) to a multi-competitor market with Viridian’s veligrotug (Lumvoa) approval in June 2026. We frame this as a market where the validated target (IGF-1R) is now contested primarily on route of administration, safety differentiation, and convenience — and we see Sling’s competitive positioning as resting on structural product-design factors rather than target novelty.
Tepezza (8 IV infusions) and Lumvoa (5 IV infusions) both carry infusion-center dependency and patient time burden. Linsitinib, if approved, would be the only infrastructure-free oral option — and sits at least two years ahead of the nearest oral IGF-1R competitor, Khartis Therapeutics, founded in 2024.
Tepezza carries known IGF-1R-class risks including hearing impairment and hyperglycemia. In the LIDS trial, the 150mg arm reported zero drug-related hearing events and no significant hyperglycemia or menstrual-cycle signal — though we note this comparison is cross-trial, not head-to-head against Tepezza or Lumvoa.
The existing 15-trial, 900-plus-patient exposure base substantially de-risked toxicology and allowed the TED program to reach Phase 2b/3 on a compressed timeline. We address the asset’s prior lack of oncology commercialization separately under Risks.
Fast Track designation combined with pivotal-trial design agreement at an End-of-Phase 2 meeting structurally lowers regulatory uncertainty and preserves optionality for Rolling Review, Accelerated Approval, or Priority Review if criteria are met.
Hammer and Zeidan’s shared Millendo track record, combined with CSO Raymond Douglas’ standing as a Cedars-Sinai oculoplastic KOL, provides structural advantages in trial execution, patient recruitment, and eventual prescriber adoption.
Tepezza alone generated roughly $1.9B in 2025 revenue against an estimated 190,000 moderate-to-severe U.S. TED patients — implying only single-digit percentage penetration. We see room for a third or fourth entrant to capture share even without displacing incumbents, given the ~$2.3B (2023, 7MM) addressable market’s growth trajectory.
M&A precedent worth noting: Amgen paid approximately $27.8 billion to acquire Horizon Therapeutics in 2023, primarily to secure Tepezza. We read this as evidence that large pharma will pay significant premiums for a single-indication TED asset, and we believe Sling would be a plausible strategic acquisition target should linsitinib generate positive Phase 3 data.
Sling remains a private, clinical-stage company with no commercial revenue and no audited financial statements in the public domain. The assessment below draws on company disclosures, management interviews, and third-party clinical trial registries (NCT records); where figures could not be independently verified, we flag them explicitly per the Data Integrity Flags above.
Opportunities we would highlight: Fast Track designation and pre-agreed FDA trial design reduce regulatory uncertainty; oral dosing carries genuine potential to capture patients who have declined antibody-based therapy; continued participation from Forbion, TPG, and Sectoral signals institutional conviction from specialist healthcare investors; the addressable market remains under-penetrated even with Tepezza generating roughly $1.9B in annual revenue; and the Amgen-Horizon precedent points to real strategic exit optionality if Phase 3 succeeds.
Risks we would flag: the Phase 2b/3 sample was modest (roughly 29–30 patients in the 150mg arm), and we would caution against over-weighting a 52% PRR (p=0.01) ahead of a larger confirmatory readout; competitive intensity is rising quickly, with Lumvoa’s broad label and Amgen’s subcutaneous 76.7% PRR data point (not head-to-head, and thus only a directional cross-trial comparison) both landing shortly before Sling’s pivotal program; Immunovant’s Phase 3 failure underscores that TED itself carries meaningful late-stage clinical risk as a category; twice-daily oral dosing’s long-term adherence advantage over infrequent injectables remains unproven; Sling has no commercial infrastructure and will require substantial additional capital beyond the Series C to fund launch preparation; and as a private company, disclosed financial figures rely on management statements with limited independent verification — see the $42M cumulative-funding gap flagged above.