Phenotypic Profiling in BioMAP® Human Primary Cell Systems Identifies a Tox Alert Signature for Skin Irritation
Rationale. We have elucidated toxicity mechanisms of known adverse effects (AEs) associated with clinical drugs using a chemical approach in our BioMAP human primary cell-based systems modeling human tissue and disease. In previous work with the Environmental Protection Agency’s (EPA) ToxCast™ program and in downstream studies, we tested compounds across a diverse panel of BioMAP systems and defined consensus mechanism profiles of particular target classes, one of which was the class of retinoid receptor agonists. Since retinoids are known to cause adverse effects to the skin, we wanted to determine if any of these consensus biomarker activities are associated with the skin irritation side effect of retinoids.
Method. The prominent consensus biomarker activities of retinoid receptor agonists were compared to 28 previously developed consensus mechanism class profiles. These prominent activities include increased prostaglandin E2 (PGE2) and decreased TNFα in a primary human endothelial cell co-culture model with human peripheral blood monocytes stimulated with lipopolysaccharide (LPS). Using a statistical approach, we identified four mechanism classes that share these activities and are also known to cause skin irritation: Aryl Hydrocarbon Receptor (AhR) agonists, Retinoic Acid Receptor (RAR) and Retinoid X Receptor (RXR) agonists, Prostaglandin EP Receptor agonists and Vitamin D Receptor (VDR) agonists. We then extended this analysis to a large reference database of more than 3,400 agents (biologics, approved drugs, chemicals and experimental agents) to identify additional agents and mechanisms that share this irritation biomarker signature which was defined as increased levels of PGE2 in the BioMAP LPS system and deceased levels of TNFα (>20%) at two or more concentrations, without causing overt cytotoxicity.
Results. This irritation signature was highly specific, with only 29 of the 3,400 agents (0.9%) sharing this biomarker activity pattern. In addition to compounds from the four mechanism classes identified previously, we identified 2-Chloroethyl Ethyl Sulfide, a chemical vesicant, and inhibitors of Thromboxane A2 synthetase.
Conclusions. We have identified an in vitro biomarker signature (increased PGE2 and decreased TNFα in a monocyte driven model of vascular inflammation) that is shared by specific compound classes that cause skin irritation using a chemical biology approach in our BioMAP phenotypic screening platform. PGE2 is known to regulate immune responses by supporting Th2-type inflammation, suggesting that the mechanism of irritation by these agents may involve promotion of Th2-type immune responses. These data suggest that one mechanism by which retinoids, VDR agonists, RAR/RXR agonists, Thromboxane A2 synthetase inhibitors, and chemical vesicants induce skin irritation is by promoting Th2 immune responses through PGE2.