Tapinarof

Tapinarof binds and activates AhR in multiple cell types, including cells of the target tissue –human skin. In addition, tapinarof moderates proinflammatory cytokine expression in stimulated peripheral blood CD4+ T cells and ex vivo human skin, and impacts barrier gene expression in primary human keratinocytes; both of these processes are likely to be downstream of AhR activation based on current evidence.^[1]

HaCaT cells (10,000 cells/well) are cultured in 96-well plates in 100 μL DMEM with HEPES, Glutamax and 10% FBS to confluence. Media is replaced with 100 μl media containing 0.2% heat-inactivated, charcoal-stripped FBS and incubated overnight. Titrating concentrations of tapinarof are added for 30 minutes followed by washing and fixing in ice-cold methanol:acetone (50:50). Samples are blocked with 3% BSA for 1 hour, then washed again in PBS with 0.1% Tween-20. Next, cells are stained with 50μL of 1:50 dilution anti-AhR antibody in 3% BSA, followed by 50 μl secondary antibody in 3% BSA/PBS.

The anti-inflammatory properties of tapinarof derive from AhR agonism is conclusively demonstrated using the mouse model of imiquimod-induced psoriasiform skin lesions. Topical treatment of AhR-sufficient mice with tapinarof leads to compound-driven reductions in erythema, epidermal thickening and tissue cytokine levels. In contrast, tapinarof has no impact on imiquimod-induced skin inflammation in AhR-deficient mice.^[1]