Janus kinase (JAK) enzymes are involved in cell signaling pathways activated by various cytokines dysregulated in allergy. The objective of this study was to determine whether the novel JAK inhibitor oclacitinib could reduce the activity of cytokines implicated in canine allergic skin disease. Using isolated enzyme systems and in vitro human or canine cell models, potency and selectivity of oclacitinib was determined against JAK family members and cytokines that trigger JAK activation in cells. Oclacitinib inhibited JAK family members by 50% at concentrations (IC₅₀'s) ranging from 10 to 99 nm and did not inhibit a panel of 38 non‐JAK kinases (IC₅₀'s > 1000 nm). Oclacitinib was most potent at inhibiting JAK1 (IC₅₀ = 10 nm). Oclacitinib also inhibited the function of JAK1‐dependent cytokines involved in allergy and inflammation (IL‐2, IL‐4, IL‐6, and IL‐13) as well as pruritus (IL‐31) at IC₅₀'s ranging from 36 to 249 nm. Oclacitinib had minimal effects on cytokines that did not activate the JAK1 enzyme in cells (erythropoietin, granulocyte/macrophage colony‐stimulating factor, IL‐12, IL‐23; IC₅₀'s > 1000 nm). These results demonstrate that oclacitinib is a targeted therapy that selectively inhibits JAK1‐dependent cytokines involved in allergy, inflammation, and pruritus and suggests these are the mechanisms by which oclacitinib effectively controls clinical signs associated with allergic skin disease in dogs.

Background: Pruritus is a characteristic clinical sign of allergic skin conditions including atopic dermatitis (AD) in the dog. IL‐31 is a cytokine found in the serum of some dogs with AD and can induce pruritic behaviours in laboratory beagle dogs.Hypothesis/Objectives: The objectives were to characterize an IL‐31‐induced pruritus model by evaluating the efficacy of prednisolone, dexamethasone and oclacitinib, and to compare the speed of anti‐pruritic effects of oclacitinib against those of prednisolone and dexamethasone.Animals: Purpose‐bred beagle dogs were used in all studies.Methods: Randomized, blinded, placebo‐controlled studies were designed to evaluate and compare the anti‐pruritic properties of prednisolone, dexamethasone and oclacitinib following a single intravenous injection of recombinant canine IL‐31. Video surveillance was used to monitor and score pruritic behaviours in study animals.Results: Prednisolone [0.5 mg/kg, per os (p.o.)] reduced IL‐31‐induced pruritus when given 10 h prior to observation. When the time interval between drug treatment and observation was shortened to 1 h, dexamethasone (0.2 mg/kg, intramuscular) but not prednisolone (0.25 or 0.5 mg/kg, p.o.) reduced IL‐31‐induced pruritus. Oclacitinib (0.4 mg/kg, p.o.) reduced pruritus when given 1, 6, 11 and 16 h prior to the observation period, and the anti‐pruritic activity of oclacitinib was greater when compared to prednisolone and dexamethasone at all time points assessed.Conclusion and clinical importance: The efficacy of prednisolone, dexamethasone and oclacitinib in the IL‐31‐induced pruritus model gives confidence that this may be a relevant model for acute pruritus associated with allergic dermatitis including AD and can be used to evaluate novel compounds or formulations.

The canine cytokine IL-31 induces pruritus in dogs and can be detected in dogs with atopic dermatitis; however very little is understood around its interactions with specific canine cells. We hypothesize that IL-31 is involved in the progression of allergic skin disease by coordinating the interaction between the immune system with skin and neuronal systems. The goal of the following work was to identify cells that produce IL-31 as well as cells that may respond to this cytokine. Peripheral blood mononuclear cells (PBMCs) were collected from naïve and house dust mite (HDM) allergen-sensitized beagle dogs and used for ex vivo characterization of cytokine production assessed using ELISpot and quantitative immunoassay. Sensitization to HDM allergen induced a T-helper type 2 (Th2) cell phenotype characterized by an increase in the production of IL-4 protein. Interestingly, repeated allergen challenge over time also resulted in an increase in IFN-γ. Further evaluation showed that co-stimulation of Th2 polarized cells with antigen and the bacterial component Staphylococcus enterotoxin B (SEB) produced higher levels of IL-31 compared to either stimulant alone. Production of IL-31 when PBMCs were stimulated by T cell mitogens suggests T cells as a source of IL-31. Quantitative real-time PCR was utilized to determine expression of the IL-31 receptor alpha chain in canine cell lines and tissue. Canine monocytic cells, keratinocytes, and dorsal root ganglia were shown to express the IL-31 receptor alpha chain mRNA. In a multifaceted disease such as canine atopic dermatitis, the combination of Th2 polarization and microbial presence may lead to IL-31 mediated effects driving inflammation and pruritus by immune cells, keratinocytes, and direct neuronal stimulation.

Background: Interleukin (IL)‐31 is a cytokine involved in allergic inflammation which induces pruritus across species including dogs. Using recombinant canine IL‐31 we have developed a model of pruritus in the dog to evaluate onset of action and duration of effect of therapeutic drugs.Objective: To assess the onset of action and duration of effect of lokivetmab (Cytopoint) in the IL‐31‐induced pruritus model.Animals: Twenty‐four purpose‐bred beagle dogs (neutered males, spayed and intact females) 1.5–4.7 years old and weighing between 6 and14 kg.Methods and materials: Randomized, blinded, placebo‐controlled studies were designed to evaluate the antipruritic properties of lokivetmab. Laboratory beagle dogs were given either placebo, 0.125, 0.5 or 2.0 mg/kg lokivetmab, subcutaneously. IL‐31 then was administered to evaluate pruritus 3–5 h post‐placebo or ‐lokivetmab administration as well as one, seven, 14, 28, 42 and 56 days post‐dosing. Pruritus was evaluated over a 2 h window in animals by video monitoring and scored using a categorical scoring system.Results: When animals were given 2.0 mg/kg lokivetmab, a significant reduction in pruritus was observed at 3–4, 4–5 and 3–5 h post‐treatment (P ≤ 0.0001). When animals were given either 0.125, 0.5 or 2 mg/kg lokivetmab, the duration of effect was dose‐dependent and statistically significant for 14, 28 and 42 days, respectively (P ≤ 0.0288).Conclusion: These data indicate that a single subcutaneous injection of 2 mg/kg lokivetmab produces a significant suppression of pruritus starting 3 h post‐treatment that can be sustained for 42 days.