Topical application of activator protein-1 inhibitor T-5224 suppresses inflammation and improves skin barrier function in a murine atopic dermatitis-like dermatitis

Background: Selective activator protein (AP)-1 inhibitors are potentially promising therapeutic agents for atopic dermatitis (AD) because AP-1 is an important regulator of skin inflammation. However, few studies have investigated the effect of topical application of AP-1 inhibitors in treating inflammatory skin disorders.
Methods: Immunohistochemistry was conducted to detect phosphorylated AP-1/c-Jun expression of skin lesions in AD patients. In the in vivo study, 1 % T-5224 ointment was topically applied for 8 days to the ears of 2,4 dinitrofluorobenzene challenged AD-like dermatitis model mice. Baricitinib, a conventional therapeutic agent Janus kinase (JAK) inhibitor, was also topically applied. In the in vitro study, human epidermal keratinocytes were treated with T-5224 and stimulated with AD-related cytokines.
Results: AP-1/c-Jun was phosphorylated at skin lesions in AD patients. In vivo, topical T-5224 application inhibited ear swelling (P < 0.001), restored filaggrin (Flg) expression (P < 0.01), and generally suppressed immune-related pathways. T-5224 significantly suppressed Il17a and l17f expression, whereas baricitinib did not.Baricitinib suppressed Il4, Il19, Il33 and Ifnb expression, whereas T-5224 did not. Il1a, Il1b, Il23a, Ifna, S100a8, and S100a9 expression was cooperatively downregulated following the combined use of T5224 and baricitinib. In vitro, T-5224 restored the expression of FLG and loricrin (LOR) (P < 0.05) and suppressed IL33 expression (P < 0.05) without affecting cell viability and cytotoxicity.
Conclusions: Topical T-5224 ameliorates clinical manifestations of AD-like dermatitis in mice. The effect of this inhibitor is amplified via combined use with JAK inhibitors.