Cell experiment:

HaCaT cells (10,000 cells/well) are cultured in 96-well Greiner μCLEAR plates in 100 μL DMEM with HEPES, Glutamax and 10% fetal bovine serum to confluence. Media is replaced with 100 μL media containing 0.2% heat-inactivated, charcoal-stripped fetal bovine serum and incubated overnight. Titrating concentrations of Tapinarof (10-8 μM ,10-6 μM, 10-4 μM, 0.01 μM, and 1 μM) 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, and then washed again in phosphate buffered saline with 0.1% Tween-20. Next, cells are stained with 50 μL of 1:50 dilution anti-AhR antibody in 3% BSA, followed by 50 μL secondary antibody (1:500 dilution chicken anti-rabbit AlexaFluor488 and 1:2,000 dilution Hoechst 33342) in 3% BSA/phosphate buffered saline. Images are acquired on InCell 2000 and/or Opera. Image analysis is performed using InCell Analyzer Workstation and/or Columbus[1].

Animal experiment:

Mice[1]Female BALB/c mice (BALB/cByJRj) are used. Studies are performed using 100 μL of Tapinarof (1%) or FICZ (0.01%, at the limit of solubility) in 60% ethanol: 40% water[1].

Tapinarof is a natural aryl hydrocarbon receptor (AhR) agonist with an EC50 of 13 nM.

Tapinarof activates the AhR pathway through direct binding. Tapinarof dose-dependently induces nuclear translocation of AhR in immortalized keratinocytes (HaCaT) (EC50=0.16 nM)[1].

Tapinarof acts through AhR to reduce inflammation in IMQ-treated mice. AhR-sufficient mice on a C57Bl/6 background exhibit a reduced clinical score after treatment with Tapinarof or 6-formylindolo(3,2-b)carbazole (FICZ). In contrast, AhR KO mice do not respond to the anti-inflammatory effects of Tapinarof. FICZ is used as a comparator in these studies and yields similar results, with dramatically reduced inflammatory responses in wild-type, but not AhR KO mice[1].

[1]. Smith SH, et al. Tapinarof Is a Natural AhR Agonist that Resolves Skin Inflammation in Mice and Humans. J Invest Dermatol. 2017 Oct;137(10):2110-2119.