85% of Biologic-Eligible AD Patients Left Behind — Can KT-621 Reach Them?

The IL-4/IL-13 signaling pathway has become one of the most therapeutically validated targets in atopic dermatitis (AD), largely on the back of dupilumab's clinical success. Yet biologics require subcutaneous injection, and the only approved oral alternatives — JAK inhibitors — carry meaningful safety concerns that limit their use in routine practice. KT-621, a selective STAT6 protein degrader developed by Kymera Therapeutics, is emerging as a candidate that may bridge this gap.¹

In an interview with Dermatology Times, Jared Gollob, MD, chief medical officer at Kymera Therapeutics, outlined the rationale and early clinical data behind the program. "If you want to develop an oral therapy that can reach more patients, you probably have to target something which is inside the cell," he explained. "And so STAT6 has been the target that everybody's been interested in."

STAT6 is the intracellular transcription factor downstream of both IL-4 and IL-13 receptor signaling. Unlike receptor-level blockade with an antibody, targeting STAT6 directly offers a path to an orally bioavailable therapy. What makes degrader technology distinct from conventional small molecule inhibition is its catalytic mechanism — rather than occupying an active site, the drug marks STAT6 for proteasomal destruction, enabling sustained, deep target suppression. As Gollob put it, the drug's mechanism "allows us to potently and completely degrade the target 24/7."

In a phase 1b study enrolling 22 patients with moderate to severe AD, once-daily KT-621 at 100 mg or 200 mg produced 98% reduction in circulating STAT6, sometimes within 4 to 8 hours of the first dose, with levels remaining suppressed throughout 28 days of dosing and recovering within 3 to 4 days of discontinuation. Skin biopsies from eczema lesions confirmed greater than 94% STAT6 degradation, closely mirroring pharmacodynamic effects seen in the healthy volunteer cohort — what Gollob described as "really nice translation from healthy volunteers into patients."

Beyond the pharmacodynamic readouts, the study demonstrated meaningful downstream pathway suppression. Type 2 inflammatory biomarkers including TARC, Eotaxin-3, and IL-31 — the cytokine most directly linked to itch — fell by approximately 55% on average. Patient-reported disease burden, measured by POEM, also improved across the spectrum of disease severity, with biological and clinical endpoints tracking consistently together.

Safety data have been encouraging. No treatment-related adverse events or serious adverse events were observed during the 28-day study period, and chronic toxicology studies in nonhuman primates and rats out to 9 months have not identified concerning signals.

The drug is now being evaluated in BROADEN-2, a 200-patient, dose-ranging phase 2b study with 16 weeks of treatment and a 52-week open-label extension. A parallel 260-patient phase 2b study in moderate to severe eosinophilic asthma is expected to read out in 2027.

The commercial imperative is clear. As Gollob noted, despite the availability of therapeutics, "only about 15% percent of those patients are actually getting" biologic therapy among those who are eligible. If the phase 2b data confirm what the phase 1b signal suggests, KT-621 could represent a meaningful advance for the estimated 85% of biologic-eligible patients currently not receiving systemic treatment.