Abstract: Psoriatic arthritis (PsA) is a chronic, heterogeneous inflammatory joint disease that affects a significant proportion of patients with psoriasis. The interleukin (IL)-23/IL-17 signaling axis plays a central pathogenic role in this condition. BMS-986165, commonly known as deucravacitinib, is a first-in-class, highly selective, oral small-molecule inhibitor of tyrosine kinase 2 (TYK2). Unlike conventional Janus kinase (JAK) inhibitors that bind to the highly conserved active catalytic domain, deucravacitinib acts via a unique allosteric mechanism by binding to the regulatory pseudokinase (JH2) domain of TYK2. This distinct mechanism confers exceptional selectivity, effectively blocking IL-12, IL-23, and type I interferon signaling without the off-target toxicities typically associated with JAK1-3 inhibition. Clinical trials have demonstrated that deucravacitinib significantly improves PsA domains, including peripheral arthritis, enthesitis, dactylitis, and skin inflammation, while maintaining a favorable safety profile. This review summarizes the pharmacological activity, molecular mechanism, structure-activity relationship, current limitations, and future perspectives of deucravacitinib in the treatment of psoriatic arthritis.
1. Introduction
Psoriatic arthritis (PsA) is a chronic, immune-mediated inflammatory joint disease that affects approximately 30% of patients with psoriasis [7]. It is a heterogeneous disorder that primarily involves the peripheral joints but can also affect the axial skeleton, entheses, and nails, presenting with manifestations such as dactylitis and arthritis mutilans [7]. The pathogenesis of PsA involves a complex interplay of genetic and environmental factors that trigger immune activation, leading to the overproduction of proinflammatory cytokines. The IL-23/IL-17 signaling axis is recognized as a central pathogenic pathway shared between psoriasis and PsA [6][7].
While biologic therapies have revolutionized the management of PsA, there remains a significant unmet clinical need for highly effective, safe, and convenient oral therapies [2][6]. Conventional synthetic disease-modifying antirheumatic drugs (csDMARDs) and first-generation oral small molecules like apremilast are limited by suboptimal efficacy or tolerability issues [2][6]. Furthermore, while pan-JAK inhibitors are effective, they are associated with off-target systemic toxicities [2]. BMS-986165 (deucravacitinib) has emerged as a promising next-generation oral targeted therapy. As a highly selective TYK2 inhibitor, it bridges the therapeutic gap by providing an optimal balance of clinical efficacy and oral convenience for patients with psoriatic disease [3][6].
2. Pharmacological Activity
The pharmacological efficacy of deucravacitinib in active PsA has been robustly demonstrated in a Phase 2, randomized, double-blind, placebo-controlled clinical trial (NCT03881059) [1][2][3][4]. The study enrolled 203 adult patients with active joint disease (≥3 tender and ≥3 swollen joints) who had failed or were intolerant to at least one prior therapy [3]. Patients were randomized to receive placebo, deucravacitinib 6 mg once daily, or deucravacitinib 12 mg once daily [1].
At week 16, the primary endpoint—the American College of Rheumatology-20 (ACR20) response—was achieved by 52.9% of patients in the 6 mg group and 62.7% in the 12 mg group, both significantly higher than the 31.8% observed in the placebo group [1][2][3]. Improvements in ACR20 occurred early, becoming visible by week 8 [4]. Furthermore, deucravacitinib demonstrated a significantly higher rate of minimal disease activity (MDA) at week 16 compared to placebo (23.9% vs. 7.6%) [7]. The treatment also yielded significant improvements across multiple secondary endpoints, including the Health Assessment Questionnaire–Disability Index (HAQ-DI), Short Form-36 Physical Component Summary score, and PASI 75 response [3][7]. Higher numbers of patients treated with deucravacitinib also achieved resolution of enthesitis and dactylitis compared to placebo [2][4]. Pharmacodynamically, deucravacitinib treatment suppressed IL-23/IL-17 and interferon (IFN) pathway biomarkers in these patients [3].
3. Molecular Mechanism of Action
TYK2 is a member of the JAK family that mediates the intracellular signaling of cytokines involved in adaptive (IL-12, IL-23) and innate (type I IFNs) immune responses [3][7]. Upon cytokine binding, TYK2 forms receptor complexes that phosphorylate cytokine receptors, creating docking sites for signal transducers and activators of transcription (STAT) proteins, which then translocate to the nucleus to regulate inflammatory responses [7].
Deucravacitinib acts via a unique allosteric mechanism. Instead of binding to the highly conserved active catalytic domain (JH1) where adenosine triphosphate (ATP) binds—the target of traditional orthosteric JAK inhibitors—deucravacitinib specifically binds to the regulatory pseudokinase domain (JH2) of TYK2 [1][2][6]. This allosteric binding induces a conformational change that stabilizes an inhibitory interaction between the regulatory JH2 domain and the catalytic JH1 domain, effectively locking TYK2 in an inactive state [3][7]. Consequently, deucravacitinib blocks downstream signaling of IL-12, IL-23, and type I IFNs, thereby suppressing the inflammatory cascades responsible for PsA and psoriasis [2][7].
4. Structure-Activity Relationship (SAR)
The structural design of deucravacitinib is fundamental to its exceptional selectivity profile. Because the JH1 catalytic domain is highly conserved across all Janus kinases, orthosteric inhibitors targeting this site often exhibit cross-reactivity with JAK1, JAK2, and JAK3, leading to off-target effects [1][2]. By targeting the less conserved JH2 pseudokinase domain, deucravacitinib achieves high functional selectivity [3].
In vitro studies demonstrate that deucravacitinib has a 100- to 200-fold greater selectivity for TYK2 over JAK1 and JAK3, and a 2000- to 3000-fold greater selectivity for TYK2 over JAK2 [4][7][8]. At clinically relevant doses, deucravacitinib does not interfere with JAK1-3 biomarkers [2]. This high selectivity is crucial because it allows the drug to inhibit the pathogenic IL-23/Th17 axis without disrupting JAK2-dependent hematopoietic functions or other JAK1/3-mediated physiological processes, thereby mitigating the systemic toxicities (such as cytopenias and lipid abnormalities) typically seen with nonselective JAK inhibitors [1][2][6].
5. Current Limitations
While deucravacitinib exhibits a favorable safety profile compared to pan-JAK inhibitors, it is not without limitations and adverse events. In the Phase 2 PsA trial, adverse events were more frequently reported in the deucravacitinib groups (65.7%) compared to placebo (42.4%) [2]. The most common adverse events include nasopharyngitis, upper respiratory tract infections, sinusitis, bronchitis, rash, headache, diarrhea, and nausea [1][2][7]. Additionally, acne and dermatitis acneiform were reported exclusively in the active treatment groups (up to 3.0% in the PsA trial), which has been hypothesized to result from commensal bacteria proliferation secondary to cytokine inhibition [2].
Another limitation is the current lack of long-term Phase 3 data specifically for PsA. While the drug has been approved for moderate-to-severe plaque psoriasis based on extensive Phase 3 data, its definitive role, long-term radiographic progression prevention, and comparative efficacy against established biologic agents in PsA remain to be fully elucidated [1][2].
6. Future Perspectives
The future of deucravacitinib in the treatment of PsA is highly promising. To confirm the efficacy and safety observed in Phase 2, two large multinational Phase 3 clinical trials—POETYK PsA-1 (NCT04908202) and POETYK PsA-2 (NCT04908189)—are currently recruiting patients with active PsA [1][2][3]. These trials will evaluate the drug in both biologic-naïve patients and those who have previously failed TNFα inhibitors [7]. Furthermore, a Phase 3 trial (NCT06869551) is planned for children and adolescents with active PsA [7].
If the Phase 3 trials replicate the success of earlier studies, deucravacitinib is poised to become a first-line oral systemic therapy for PsA, offering an alternative to currently available JAK inhibitors with a potentially superior safety profile [1][6]. Ongoing research into predictive biomarkers may also enable personalized medicine approaches, identifying PsA patients most likely to achieve durable responses to TYK2 inhibition [6].
