The Pill That Wants to Kill a $2 Billion Needle

Sling's founders, including Gary D. Hammer, MD, PhD, licensed the drug from Astellas in 2022 after watching Tepezza's commercial success. They launched the company publicly in 2022 with a $35 million Series A and got to work.

Phase 2 Data That Turned Heads

In January 2025, Sling reported results from its Phase 2b/3 LIDS trial, and the numbers were compelling. The study hit its primary endpoint (the main thing the trial was designed to prove) at the 150 mg twice-daily dose.

52% of patients in the treatment group were proptosis responders at Week 24, meaning their eyes measurably receded back toward normal position. The result was statistically significant, with a p-value of 0.01; in plain English, there's only a 1% chance this was a fluke.

Perhaps more importantly, the safety profile looked encouraging. Sling has been tracking the side effects that plague existing TED therapies: hearing problems, blood sugar spikes, and menstrual cycle disruptions. Early indications suggest linsitinib may have a more favorable profile on these fronts, though Phase 3 data will be the real test.

$123 Million Says the Investors Believe It

The Series C round, announced September 16, was led by Forbion and joined by TPG Life Sciences Innovations and Sectoral Asset Management. It's a meaningful step up from Sling's earlier fundraising, and it signals something important: these aren't speculators chasing a hot sector. They're backing a company heading into a global Phase 3 trial called ORBIT.

TPG has been with Sling since the beginning (its Rise Fund led the Series A), and their continued investment speaks volumes. As part of the deal, Regina Salvat of Forbion and François Beaubien of Sectoral Asset Management joined Sling's board.

Sling CEO Ryan Zeidan framed the opportunity around the limitations of current therapy, noting that an oral option could be used earlier and more broadly in the treatment journey. That's a subtle but important point: if patients don't have to schedule IV infusions, doctors might start treatment sooner, potentially expanding the overall market.

The Billion-Dollar Question

Can a pill really compete with billion-dollar biologics? The TED treatment market is large and growing. Tepezza owns the lion's share, though Lumvoa is now nipping at its heels with a shorter infusion schedule and approval for both active and chronic disease.

Sling doesn't need to wipe out either competitor to win. It just needs to carve out a meaningful slice of patients who prefer the convenience of an oral option, or who can't tolerate the side effects of infused therapies. In a disease where treatment today means repeated clinic visits, that's potentially a large group.

The bear case is straightforward: Phase 3 trials are where good Phase 2 data goes to die. The ORBIT trial will need to confirm that linsitinib works in a larger, more diverse patient population. Plenty of drugs have stumbled at this stage, and a 52% responder rate, while solid, leaves room for the confidence interval to narrow in an unfavorable direction.

Why This One Matters

The TED market is a fascinating microcosm of a broader trend in biotech: the race to turn injected biologics into oral pills. We've seen it in obesity (GLP-1 pills), autoimmune disease, and now ophthalmology. Every time a company cracks the oral code for a disease dominated by needles, it reshapes how patients access care.

Sling is still a clinical-stage company with no revenue and a long road ahead. But with $123 million in fresh funding, positive Phase 2 data, and a clear convenience advantage over every approved competitor, it's the most interesting underdog in the TED space right now.

Amgen and Viridian should be paying attention. Their patients certainly will be.

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