A novel RORγt inhibitor is a potential therapeutic agent for the topical treatment of psoriasis with low risk of thymic aberrations.

BACKGROUND: Retinoic acid receptor-related orphan receptor gamma t (RORγt) has critical roles in the development, maintenance and function of interleukin (IL)-17-producing cells and is a highly attractive target for the treatment of IL-17-mediated autoimmune disease, particularly psoriasis. On the other hand, RORγt is also critical for controlling apoptosis during thymopoiesis, and genetic RORγt ablation or systematic RORγt inhibition cause progressive thymic aberrations leading to T cell lymphomas. OBJECTIVE: We investigated whether topical administration of our novel RORγt inhibitor, S18-000003 has therapeutic potential for psoriasis with low risk of thymic aberrations. METHODS: We evaluated the effect of topical S18-000003 on psoriasis-like skin inflammation and influence on the thymus in a 12-O-tetradecanoylphorbol-13-acetate-induced K14.Stat3C mouse psoriasis model. RESULTS: S18-000003 markedly inhibited the development of psoriatic skin inflammation via suppression of the IL-17 pathway. In the skin, S18-000003 suppressed all subsets of IL-17-producing cells that we previously identified in this psoriasis model: Th17 cells, Tc17 cells, dermal γδ T cells, TCR- cells that probably included innate lymphoid cells, and CD4-CD8- double-negative αß T cells. Notably, neither reduction of CD4+CD8+ double-positive thymocytes nor dysregulation of cell cycling was observed in S18-000003-treated mice, even at a high dose. CONCLUSION: Our topically administered RORγt inhibitor is a potential therapeutic agent for psoriasis with low risk of thymic lymphoma.

Potential role of IL-17-producing CD4/CD8 double negative αß T cells in psoriatic skin inflammation in a TPA-induced STAT3C transgenic mouse model.

BACKGROUND: Psoriasis is one of the most common immune-mediated chronic inflammatory skin disorders and is accompanied by erythematous scaly plaques. There is growing evidence that the IL-23/Th17 axis plays a critical role in development of the disease. It was recently shown that in addition to CD4+ Th17 cells, various IL-17-producing cell subsets such as CD8+ Tc17 cells, dermal γδ T cells, and innate lymphoid cells are also involved in the development of psoriatic inflammation in humans. OBJECTIVE: To investigate which subsets of IL-17-producing cells are involved in psoriasis-like skin inflammation in a TPA (tumor promoter 12-O-tetradecanoylphorbol-13-acetate)-induced K14.Stat3C mouse model. METHOD: Skin-infiltrating cells were isolated from inflamed lesions of TPA-treated K14.Stat3C transgenic mice, and analyzed for IL-17 producing cell subsets by flow cytometry. RESULTS: We observed significantly increased numbers of IL-17-producing CD4+ T cells, CD8+ T cells and dermal γδ T cells in TPA-induced skin lesions of K14.Stat3C mice. Additionally, we found that another IL-17-producing T cell subset, αß-TCR+ CD4CD8 double negative T cells (DN αß T cells), was also increased in lesional skin. These IL-17-producing DN αß T cells are NK1.1 negative, suggesting they are not natural killer T cells or mucosal associated invariant T cells. As well as other IL-17-producing cells, DN αß T cells in the inflamed skin can also respond to IL-23 stimulation to produce IL-17. It is also suggested that DN αß T cells may express retinoic acid-related orphan receptor gamma t and CC chemokine receptor 6. CONCLUSION: In TPA-induced lesional skin of K14.Stat3C mice, IL-17-producing CD4+ Th17 cells, CD8+ Tc17 cells, dermal γδ T cells and TCR- cells probably containing ILCs all participated in skin inflammation, which is similar to human clinical psoriatic features. Furthermore, we showed for the first time the possibility that an IL-17-producing DN αß T cell subset is also involved in psoriatic inflammation.

S-777469, a novel cannabinoid type 2 receptor agonist, suppresses itch-associated scratching behavior in rodents through inhibition of itch signal transmission.

We have previously reported that S-777469 [1-([6-ethyl-1-(4-fluorobenzyl)-5-methyl-2-oxo-1,2-dihydropyridine-3-carbonyl]amino)-cyclohexanecarboxylic acid], a novel cannabinoid type 2 receptor (CB2) agonist, significantly suppressed compound 48/80-induced scratching behavior in mice in a dose-dependent manner when it was administered orally. Here, we demonstrated that the inhibitory effects of S-777469 on compound 48/80-induced scratching behavior are reversed by pretreatment with SR144528, a CB2-selective antagonist. In addition, we investigated the effects of S-777469 on itch-associated scratching behavior induced by several pruritogenic agents in mice and rats. S-777469 significantly suppressed scratching behavior induced by histamine or substance P in mice or by serotonin in rats. In contrast, the H1-antihistamine fexofenadine clearly inhibited histamine-induced scratching behavior but did not affect scratching behavior induced by substance P or serotonin. Moreover, S-777469 significantly inhibited histamine-induced peripheral nerve firing in mice. In conclusion, these results suggest that S-777469 produces its antipruritic effects by inhibiting itch signal transmission through CB2 agonism.

Mechanism of pathogenesis of imiquimod-induced skin inflammation in the mouse: a role for interferon-alpha in dendritic cell activation by imiquimod.

Topical application of imiquimod (IMQ), a Toll-like receptor (TLR)7 ligand, can induce and exacerbate psoriasis, a chronic inflammatory skin disorder. In a mouse model of IMQ-induced psoriasis-like skin inflammation, T-helper (Th)17 cells and interleukin (IL)-17/IL-22-producing γδ-T cells have been shown to play a pivotal role. However, the mechanisms of induction of the Th17 pathway and development of psoriasis-like skin inflammation by IMQ treatment remain unclear. In this study, we investigated pathogenic mechanisms of IMQ-induced psoriasis-like skin inflammation in mice. We first confirmed that, together with an increase in IL-17 and IL-22 production, application of IMQ to mouse skin induced the expression of cytokines required for activation of the Th17 pathway, and pro-inflammatory mediators involved in the pathology of psoriasis. Analysis of Tlr7(-/-) mice demonstrated that most of the in vivo effects of IMQ were mediated via TLR7. In an in vitro study using plasmacytoid dendritic cells (DCs), IMQ induced production of interferon (IFN)-α, IL-23, IL-6 and tumor necrosis factor (TNF)-α. Furthermore, when we analyzed in vitro-generated bone marrow-derived DCs with features similar to TNF-α and inducible nitric oxide synthase (iNOS)-producing DCs, IL-23, IL-6, IL-1ß, TNF-α and iNOS/NO production was weakly induced by IMQ alone and further enhanced after co-stimulation with IMQ and IFN-α. These in vitro effects of IMQ were also mediated via TLR7 and the synergistic effect of IMQ, and IFN-α was suggested to be caused by upregulation of TLR7 expression by IFN-α. These results demonstrate part of the mechanism by which the Th17 pathway and psoriasis-like skin inflammation are induced by IMQ and IFN-α in a mouse model.