The anti-inflammatory effect of topical tofacitinib on immediate and late-phase cutaneous allergic reactions in dogs: a placebo-controlled pilot study Amanda Blubaugh*, Daniel Rissi†, Deborah Elder‡, Tara Denley*, Sitka Eguiluz-Hernandez§ and Frane Banovic* *Department of Small Animal Medicine and Surgery, †Department of Pathology, College of Veterinary Medicine, University of Georgia, 501 D.W. Brooks Drive, Athens, GA 30602, USA ‡Department of Pharmaceutical and Biomedical Sciences, College of Pharmacy, University of Georgia, 250 W. Green Street, Athens, GA 30602, USA §Department of Population Health and Pathobiology, and the NCSU Comparative Medicine Insti- tute, College of Veterinary Medicine, North Carolina State University, 1060 William Moore Drive, Raleigh, NC 27607, USA Correspondence: Frane Banovic, University of Georgia, College of Veterinary Medicine, 2200 College Station Road, Athens, GA 30602, USA. Email: fbanovic@uga.edu Background – Topical Janus kinase (JAK) inhibition is a promising therapeutic target for several inflammatory skin diseases of humans. Objectives – To evaluate the anti-inflammatory effect of tofacitinib, a JAK 1/3 inhibitor, on immediate and late- phase skin reactions in dogs. Animals – Five healthy laboratory beagle dogs. Methods – Topical tofacitinib (total daily dosage: 0.5 mg/cm 2 ) or its gel vehicle were applied on either the left or right lateral thorax of each dog for eight days. Three days before application and after eight days of topical treat- ment, intradermal injections of histamine and anticanine-IgE antibodies were performed on both sides; they were evaluated by an investigator blinded to the interventions. Results – The tofacitinib gel was well-tolerated; one dog developed mild erythema at Day 5 that resolved by the next application. Treatment with tofacitinib reduced histamine and anticanine-IgE global wheal scores (one-way ANOVA, P ≤ 0.005 for both) compared to baseline; there was no significant difference for the vehicle placebo (histamine; P = 0.163; IgE, P = 0.223). Late-phase reactions (LPRs) were markedly, but not significantly reduced after tofacitinib treatment (P = 0.071). A blinded histological evaluation of 6 h-anti-IgE-associated LPRs revealed a significant reduction in the total leucocyte superficial dermal cellularity (P = 0.022), as well as eosinophil (P = 0.022) and mast cell (P = 0.022) counts at tofacitinib-treated sides compared with pretreatment values. Post-treatment complete blood counts and serum chemistry profiles did not show relevant tofacitinib-induced changes. Conclusions – Our observations suggest that topical tofacitinib exerts an inhibitory effect on activated canine skin-emigrating immune cells; this drug should be investigated further as a topical immunosuppressive drug in dogs. Introduction Canine atopic dermatitis (cAD) is a highly pruritic and inflammatory skin disease; it is estimated that that atopic dermatitis (AD) affects 10% of the canine population with a majority of cases demonstrating IgE antibodies directed at environmental allergens. 1 Treatment of severe and chronic cAD cases can be challenging; topical agents, including emollients and glucocorticoids, are the mainstay of AD therapy. 1 Systemic immunosuppressants such as glucocorticoids, ciclosporin and oclacitinib are used for long-term control of refractory cases with recurrent flares. 1 The discovery of the Janus kinase (JAK)-signal transducer and activator of transcription (STAT) sig- nalling pathway opened a new window of opportunity for the treatment of inflammatory skin diseases in humans. The JAK-STAT pathway is an important sig- nalling mechanism for many cytokines and growth fac- tors; JAK 1 and JAK 3 are necessary for signalling for IL-4, IL-13 and IL-31, and are potential targets for the treatment of AD in humans and dogs. 2,3 Topical tofac- itinib citrate, a JAK1/JAK3 inhibitor, has been shown to remarkably reduce the severity of refractory AD in humans, with early onset of effect and good local tol- erability. 4 The primary goals of this study were to determine the immunomodulatory potential of the topical tofaci- tinib on cutaneous allergic reactions in dogs and to Abbreviations: GWS, global wheal score; JAK, Janus kinase; LPR, late-phase reaction; PLO, pluronic lecithin organogels; STAT, signal transducer and activator of transcription. Accepted 8 January 2018 Sources of funding: This study was self-funded. Conflict of interest: No conflicts of interest have been declared. © 2018 ESVD and ACVD, Veterinary Dermatology 1 Vet Dermatol 2018 DOI: 10.1111/vde.12532