Modelling atopic dermatitis in healthy human skin for the characterization of topical compounds.

Suitable human models for the development and characterization of topical compounds for inflammatory skin diseases such as atopic dermatitis are not readily available to date. We describe here the development of a translational model involving healthy human skin mimicking major aspects of AD and its application for the characterization of topical Janus kinase inhibitors. Full thickness human abdominal skin obtained from plastic surgery stimulated in vitro with IL4 and IL13 shows molecular features of AD. This is evidenced by STAT6 phosphorylation assessed by immunohistochemistry and analysis of skin lysates. Broad transcriptome changes assessed by AmpliSeq followed by gene set variation analysis showed a consistent upregulation of gene signatures characterizing AD in this model. Topical application of experimental formulations of compounds targeting the JAK pathway to full thickness skin normalizes the molecular features of AD induced by IL4 and IL13 stimulation. The inhibitory effects of topical JAK inhibitors on molecular features of AD are supported by pharmacokinetic analysis. The model described here is suited for the characterization of topical compounds for AD and has the potential to be extended to other inflammatory skin diseases and pathophysiological pathways.

Discovery and Characterization of the Topical Soft JAK Inhibitor CEE321 for Atopic Dermatitis.

The JAK kinases JAK1, JAK2, JAK3, and TYK2 play key roles in cytokine signaling. Activation of the JAK/STAT pathways is linked to many diseases involving the immune system, including atopic dermatitis. As systemic JAK inhibitor pharmacology is associated with side effects, topical administration to the skin has been considered to locally restrict the site of action. Several orally bioavailable JAK inhibitors repurposed for topical use have been recently approved or are in clinical development. Here, we disclose our clinical candidate CEE321, which is a potent pan JAK inhibitor in enzyme and cellular assays. In contrast to repurposed oral drugs, CEE321 does not display high potency in blood and has a high clearance in vivo. Therefore, we consider CEE321 to be a "soft drug". When applied topically to human skin that was stimulated with the cytokines IL4 and IL13 ex vivo, CEE321 potently inhibited biomarkers relevant to atopic dermatitis.

Design of a Supersoft Topical JAK Inhibitor, Which Is Effective in Human Skin but Rapidly Deactivated in Blood.

We describe the discovery and characterization of the supersoft topical JAK inhibitor 3(R), which is potent in biochemical and cellular assays as well as in human skin models. In blood, the neutral ester 3(R) is rapidly hydrolyzed (t1/2 ∼ 6 min) to the corresponding charged carboxylic acid 4 exhibiting >30-fold reduced permeability. Consequently, acid 4 does not reach the intracellular JAK kinases and is inactive in cellular assays and in blood. Thus, hydrolysis by blood esterases leads to the rapid deactivation of topically active ester 3(R) at a rate beyond the maximal hepatic clearance.

Adriforant is a functional antagonist of histamine receptor 4 and attenuates itch and skin inflammation in mice.

BACKGROUND: Histamine has been postulated to play a role in atopic dermatitis via histamine receptor 4, mediating pruritic and inflammatory effects. The H4R antagonist adriforant (PF-3893787 or ZPL389) indicated clinical efficacy in a Ph2a study in atopic dermatitis. Preclinical investigations of adriforant had been scarce as experiments in transfectants with H4R from several species suggested partial agonism, not seen in human cells. OBJECTIVE: During the Ph2b trial in AD, we performed experiments to understand the pharmacology of adriforant in primary murine cells and in vivo models. We assessed its effects on ERK phosphorylation and transcriptional changes in bone marrow-derived mast cells, histamine-dependent Ca2+ flux in neurons and histamine-induced itch response. In addition, its impact on MC903-induced skin inflammation was evaluated. RESULTS: We show that, contrary to transfectants, adriforant is a competitive antagonist of the murine histamine receptor 4, antagonizes histamine-induced ERK phosphorylation, normalizes histamine-induced transcriptional changes in mast cells and reduces histamine-dependent Ca2+ flux in neurons. Administration to mice reduces acute histamine-induced itch response. In addition, adriforant ameliorates inflammation in the mouse MC903 model. CONCLUSIONS: Our results suggest that functional inhibition of histamine receptor 4 by adriforant reduces itch and inflammation in vivo. The effects observed in mice, however, did not translate to clinical efficacy in patients as the Ph2b clinical trial with adriforant did not meet pre-specified efficacy endpoints. Given the complex pathogenesis of AD, antagonism of histamine receptor 4 alone appears insufficient to reduce disease severity in AD patients, despite the effects seen in mouse models.