IL-23 inhibitor development for axial spondyloarthritis — the investigation of risankizumab (Skyrizi), guselkumab (Tremfya), and other IL-23p19 selective inhibitors for axSpA following their success in psoriatic arthritis and psoriasis — represents the next pipeline wave for axSpA treatment, with the Axial Spondyloarthritis Market reflecting IL-23 inhibitors as an important pipeline development for the market.

Ustekinumab (Stelara) AS trial failure lesson — the Phase III TOPAS study showing ustekinumab (IL-12/23 combined inhibitor) failing to achieve primary endpoints in ankylosing spondylitis despite strong evidence for IL-23 pathway involvement in SpA pathogenesis — initially suggested that IL-23 pathway inhibition might not be effective in established AS. This finding generated the hypothesis that IL-23 pathway dependence may be different in early versus late/established axSpA.

Selective IL-23p19 inhibitors in early axSpA — the subsequent clinical development of selective IL-23p19 inhibitors (risankizumab, guselkumab) in nr-axSpA and early AS where IL-23-driven disease may be more active than established bone-dominant AS — represents the refined hypothesis that IL-23 pathway contributes to early disease where joint inflammation predominates over bone formation. Positive Phase II data for risankizumab and guselkumab in nr-axSpA have generated optimism about the potential for selective IL-23 inhibitors in earlier axSpA disease.

IL-23 pathway mechanisms in SpA — the research demonstrating that IL-23 activates IL-17-producing innate lymphoid cells (ILC3s) and Th17 cells in SpA pathogenesis connecting IL-23 upstream signaling to the established IL-17 pathway therapeutic target — provides the biological rationale for IL-23 inhibitor development in axSpA. Understanding IL-23's role in SpA enthesitis biology creates the scientific framework for enthesitis-predominant disease where IL-23 inhibitors may be particularly effective.

Do you think selective IL-23 inhibitors will eventually achieve clinical approval for axSpA based on positive nr-axSpA data, and will they differentiate from IL-17 inhibitors sufficiently to capture meaningful market share?

FAQ

Why did ustekinumab fail in ankylosing spondylitis? Ustekinumab (anti-IL-12/23) failed to achieve primary endpoints (ASAS40 at Week 24) in the Phase III TOPAS trial in established ankylosing spondylitis; leading hypothesis for failure: established AS may be driven more by IL-17 pathway already activated independently of ongoing IL-23 stimulation, TNF-driven bone formation pathways dominate in late disease, and late-stage AS may involve IL-23-independent IL-17 production via enteric bacterial stimulation; in contrast, selective IL-23p19 inhibitors show early Phase II signals in nr-axSpA and early AS where IL-23-dependent IL-17 production through ILC3s may be more prominent; disease stage and heterogeneity may explain differential IL-23 inhibitor responses.

What is the significance of enthesitis in SpA pathogenesis? Enthesitis (inflammation at tendon/ligament bone insertion sites) is a hallmark SpA pathological feature not seen in other inflammatory arthritides; the enthesis is considered the primary SpA target rather than the synovium; IL-23 is particularly important at enthesitis sites where resident innate T cells and ILC3s respond to mechanical stress and gut microbiome-derived IL-23 signals; entheseal IL-17 production from IL-23-dependent cells creates local bone-joint interface inflammation; IL-23 pathway therapies may be specifically effective for enthesitis-predominant SpA manifestations; the gut-enthesis-joint axis concept connects intestinal dysbiosis, mucosal IL-23 signals, and enthesitis-driven SpA pathogenesis.

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