3,5-Dihydroxy-4-Isopropylstilbene (Tapinarof) Is a Partial Aryl Hydrocarbon Receptor Agonist in Fish

Author

Conner A. Dicks, Clemson UniversityFollow

Date of Award

8-2025

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Biological Sciences

Committee Chair/Advisor

Charles D. Rice, Ph.D

Committee Member

Yanzhang Wei, Ph.D.

Committee Member

Tzuen-Rong Jeremy Tzeng, Ph.D

Abstract

The aryl hydrocarbon receptor (AHR) is a ligand activated transcription factor that is essential in regulating development, immune homeostasis, and drug and xenobiotic metabolism. Activation of the AHR by specific ligands results in its translocation to the nucleus where it induces a myriad of gene products, including cytochrome P450 (CYP) drug metabolizing enzymes (e.g., CYP1A1) and other components of the chemical defensome, as well as inflammatory control. Interestingly, the AHR can bind a wide variety of endogenous and xenobiotic ligands which are able to induce unique downstream effects dependent on cell type, inflammatory context, and ligand stability. The AHR is often considered to be promiscuous in this regard. Along with AHR’s implicative role in immune regulation, this transcription factor is now a potential target for drug therapies against autoimmune disorders and carcinogenesis. 3,5-dihydroxy-4-isopropylstilbene (tapinarof) is a natural (and synthetically produced) stilbenoid approved in 2022 by the FDA as a topical treatment for plaque psoriasis, presumedly by acting as an AHR agonist. However, much remains unknown about the ability of tapinarof to activate AHR with respect to concentration and species. Here, I queried tapinarof’s ability to activate AHR in fish, modulate macrophage inflammatory responses, and characterize a novel antibody I generated against zebrafish AHR isotype 2 (zfAHR2) in terms of inducibility of the AHR compared to CYP1A. In PLHC-1 hepatoma cells, tapinarof was found to activate AHR at concentrations (10 µM) to a similar degree as that of a model co-planar halogenated hydrocarbon (HAH) commonly used as a potent AHR ligand. However, lower concentrations of tapinarof (1 µM) revealed antagonistic activity, completely blocking the induction of CYP1A1 by the positive HAH. Furthermore, tapinarof induced CYP1A1 expression in zebrafish embryos, and showed antagonistic activity when zebrafish embryos were co-exposed to both HAH and tapinarof. Despite being shown to alleviate psoriatic inflammation, tapinarof exhibited no anti-inflammatory effect on trout or murine macrophages stimulated with polyinosinic-polycytidylic acid (poly I:C, PIC) or lipopolysaccharide (LPS) respectively. Finally, my anti-zfAHR2 antibody (mAb CD-R2) was validated through tissue and whole mount immunohistochemistry (IHC) in zebrafish. Using this mAb, it appears that zfAHR2 is induced to a much lesser degree than CYP1A, though regional differences in tissue expression between treatments were observed. These results infer that tapinarof is a partial AHR agonist with antagonistic abilities at low concentrations.

Recommended Citation

Dicks, Conner A., "3,5-Dihydroxy-4-Isopropylstilbene (Tapinarof) Is a Partial Aryl Hydrocarbon Receptor Agonist in Fish" (2025). All Theses. 4607.
https://open.clemson.edu/all_theses/4607