Inhibition of Interleukin-23-Mediated Inflammation with a Novel Small Molecule Inverse Agonist of RORγt.

Blockade of interleukin (IL)-23 or IL-17 with biologics is clinically validated as a treatment of psoriasis. However, the clinical impact of targeting other nodes within the IL-23/IL-17 pathway, especially with small molecules, is less defined. We report on a novel small molecule inverse agonist of retinoid acid-related orphan receptor (ROR) γt and its efficacy in preclinical models of psoriasis and arthritis. 1-(2,4-Dichloro-3-((1,4-dimethyl-6-(trifluoromethyl)-1H-indol-2-yl)methyl)benzoyl)piperidine-4-carboxylic acid (A-9758) was optimized from material identified from a high-throughput screening campaign. A-9758 is selective for RORγt and exhibits robust potency against IL-17A release both in vitro and in vivo. In vivo, we also show that IL-23 is sufficient to drive the accumulation of RORγt+ cells, and inhibition of RORγt significantly attenuates IL-23-driven psoriasiform dermatitis. Therapeutic treatment with A-9758 (i.e., delivered during active disease) was also effective in blocking skin and joint inflammation. Finally, A-9758 exhibited efficacy in an ex vivo human whole blood assay, suggesting small molecule inverse agonists of RORγt could be efficacious in human IL-17-related diseases. SIGNIFICANCE STATEMENT: Using a novel small molecule inverse agonist, and preclinical assays, we show that RORγt is a viable target for the inhibition of RORγt/Th17-driven diseases such as psoriasis. Preclinical models of psoriasis show that inhibition of RORγt blocks both the accumulation and effector function of IL-17-producing T cells.

ACT1 Is Required for Murine IL-23-Induced Psoriasiform Inflammation Potentially Independent of E3 Ligase Activity.

Psoriasis is a debilitating skin disease characterized by epidermal thickening, abnormal keratinocyte differentiation, and proinflammatory immune cell infiltrate into the affected skin. IL-17A plays a critical role in the etiology of psoriasis. ACT1, an intracellular adaptor protein and a putative ubiquitin E3 ligase, is essential for signal transduction downstream of the IL-17A receptor. Thus, IL-17A signaling in general, and ACT1 specifically, represent attractive targets for the treatment of psoriasis. We generated Act1 knockout and Act1 L286G knockin (ligase domain) mice to investigate the potential therapeutic effects of targeting ACT1 and its U-box domain, respectively. Act1 knockout, but not Act1 L286G knockin, mice were resistant to increases in CXCL1 plasma levels induced by subcutaneous injection of recombinant IL-17A. Moreover, in a mouse model of psoriasiform dermatitis induced by intradermal IL-23 injection, Act1 knockout, but not Act1 L286G knockin, was protective against increases in ear thickness, keratinocyte hyperproliferation, expression of genes for antimicrobial peptides and chemokines, and infiltration of monocytes and macrophages. Our studies highlight the critical contribution of ACT1 to proinflammatory skin changes mediated by the IL-23/IL-17 signaling axis and illustrate the need for further insight into ACT1 E3 ligase activity.

Mechanistic and pharmacological assessment of murine IL-23 mediated psoriasiform dermatitis; implications for drug discovery.

BACKGROUND: Animal models of Psoriasis (PsO) are important for our understanding of the pathophysiology of human disease but rarely manifest all features of the disease. In order to facilitate greater understanding of the underlying biology of PsO it is key that we understand the strengths and limitations of models used. OBJECTIVE: While humanized mouse models are available for PsO they remain technically challenging, expensive, require prolonged timelines and require a continued source of human tissue. Another approach is to focus on developing mechanistic models which recapitulate key features of human PsO. The role of the IL-23/IL-17 pathway as a key driver of human PsO is both well characterized and clinically validated. The goal of this manuscript is to provide a comprehensive disease and pharmacological assessment of IL-23 driven skin inflammation and its similarity to human psoriatic skin. METHODS: Intradermal injection of IL-23 has been used to study the IL-23 pathway in rodents, and this current study further characterizes pathology, cellular infiltrate, and gene signature kinetics, as well as the modulation of disease features by clinically relevant agents. RESULTS: Our results indicate that IL-23 triggers an early and robust activation of the immune system resulting in accumulation of T cell and monocyte/macrophage populations. It also supports changes in gene expression that parallel those observed in human PsO samples and is responsive to biologics commonly used to treat PsO in the clinic. CONCLUSIONS: Collectively, our studies indicate that a 5 day model of IL-23 psoriasiform dermatitis can be used to assess the pharmacology of novel small molecules/biologics in the treatment of PsO.