Spyre Therapeutics (Nasdaq: SYRE) reported that SPY001, its extended half-life anti-α4β7 antibody, met the primary endpoint in the open-label Part A of the Phase II SKYLINE trial, producing a 9.2-point reduction in Robarts Histopathology Index score from baseline at Week 12 (p<0.0001) in 43 patients with moderate-to-severe ulcerative colitis.
Trial specifics
The SKYLINE trial is a two-part induction and maintenance platform study in adults with moderately to severely active UC, evaluating SPY001 alongside SPY002 (anti-TL1A) and SPY003 (anti-IL-23), as well as pairwise combinations of all three agents. Part A is an open-label, single-dose-level monotherapy assessment; Part B is randomized and placebo-controlled.
At Week 12, 40% of patients achieved clinical remission by modified Mayo Score and 51% met the threshold for endoscopic improvement. The modified Mayo Score declined by 3.7 points from baseline. Because Part A carries no placebo arm, these figures reflect absolute response rates in an uncontrolled setting and cannot be interpreted as placebo-adjusted treatment effects. That context matters when comparing them to approved agents tested in randomized trials.
Six of 43 patients experienced treatment-emergent adverse events during induction (14%), with one serious adverse event — chest pain in a 68-year-old man with pre-existing coronary artery disease, type 2 diabetes, and hypertension. Cardiac enzymes and ECG did not indicate myocardial infarction, and the event was judged not drug-related. No drug-related adverse events, no discontinuations due to adverse events, and no deaths were recorded. The safety profile was consistent with the α4β7 class.
SPY001 aiming to challenge Takeda's Entyvio
SPY001 is engineered to replicate vedolizumab's binding epitope and potency while extending half-life to support less frequent dosing and higher induction exposure. Vedolizumab (Entyvio, Takeda) — the only approved α4β7 integrin inhibitor — requires intravenous infusions every eight weeks for maintenance or subcutaneous injections every two weeks, a schedule that imposes meaningful burden on patients and healthcare systems. Spyre's design thesis is that greater target coverage during induction, achieved through higher dosing enabled by the extended half-life, could translate to deeper and more durable mucosal healing. The Part A data offer preliminary support for that hypothesis, though cross-trial comparisons are limited by differences in study design, patient population, endpoints, and the absence of a concurrent control arm in the SKYLINE Part A dataset.
The UC biologic market has expanded considerably since vedolizumab's 2014 approval. Selective IL-23p19 inhibitors — mirikizumab (Omvoh, Lilly), risankizumab (Skyrizi, AbbVie), and guselkumab (Tremfya, Janssen) — have each received FDA approval for moderate-to-severe UC between 2023 and 2024, with clinical remission rates in randomized trials that have set a higher bar for new entrants. Oral JAK inhibitors, particularly upadacitinib (Rinvoq, AbbVie), have demonstrated high efficacy but carry class-wide boxed warnings for cardiovascular events, thrombosis, and malignancy that constrain their use in certain patient populations. SPY001's gut-selective mechanism avoids systemic immunosuppression and the safety concerns associated with JAK inhibition, positioning it alongside vedolizumab as a preferred option in patients where that profile is a priority.
What distinguishes Spyre's program from a straightforward vedolizumab follow-on is the combination strategy. The company is enrolling Part B cohorts that pair SPY001 with either SPY002 or SPY003 — combinations designated SPY120 and SPY130, respectively — alongside a three-agent combination (SPY230). No approved combination biologic regimen exists for UC, and the rationale for pairing a gut-selective integrin inhibitor with a cytokine-targeting agent draws on the complementary mechanisms: α4β7 blockade limits immune cell trafficking to the gut mucosa, while TL1A or IL-23 inhibition addresses the downstream inflammatory signaling that sustains mucosal damage. Proof-of-concept induction data from the SPY002 monotherapy cohort are expected mid-2026, with SPY003 monotherapy data targeted for Q3 2026. Part B induction data across all cohorts, including the combination arms, are expected in 2027.
The open-label design of Part A is a deliberate early-stage choice: it allows rapid assessment of whether SPY001 produces a meaningful signal before committing to the larger, placebo-controlled Part B. The 9.2-point RHI reduction and 51% endoscopic improvement rate in 43 patients are consistent with activity, but the absence of randomization and a control group means these numbers carry inherent uncertainty. The placebo-controlled Part B will be the more definitive test of whether SPY001's induction profile is meaningfully differentiated from vedolizumab and from the broader field.
For Spyre, the readout is strategically important beyond the molecule itself. The company's pipeline is built around the hypothesis that long-acting antibodies can reduce dosing frequency to a degree that changes the patient experience — potentially quarterly or semi-annual maintenance — while the combination platform addresses the subset of patients who fail or respond inadequately to monotherapy. Both claims require controlled data to substantiate, and the SKYLINE platform is designed to generate them in a single, efficient structure. Part B induction data in 2027 will determine whether the combination arms produce additive or synergistic effects that justify the complexity of dual-biologic therapy in UC.
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