Structure–Activity Relationship between the in Vivo Skin Sensitizing Potency of Analogues of Phenyl Glycidyl Ether and the Induction of Nrf2-Dependent Luciferase Activity in the KeratinoSens in Vitro Assay

Abstract

Because of regulatory constraints and ethical considerations, research on alternatives to animal testing to predict the skin sensitization potential of novel chemicals has become a high priority. Ideally, these alternatives should not only predict the hazard of novel chemicals but also rate the potency of skin sensitizers. Currently, no alternative method gives reliable potency estimations for a wide range of chemicals in differing structural classes. Performing potency estimations within specific structural classes has thus been proposed. Detailed structure-activity studies for the in vivo sensitization capacity of a series of analogues of phenyl glycidyl ether (PGE) were recently published. These studies are part of an investigation regarding the allergenic activity of epoxy-resin monomers. Here we report data on the same chemicals in the KeratinoSens in vitro assay, which is based on a stable transgenic keratinocyte cell line with a luciferase gene under the control of an antioxidant response element. A strong correlation between the EC3 values in the local lymph node assay (LLNA) and both the luciferase-inducing concentrations and the cytotoxicity in the cell-based assay was established for six analogues of PGE. This correlation allowed the potency in the LLNA of two novel structurally closely related derivatives to be predicted by read-across with errors of 1.4- and 2.6-fold. However, the LLNA EC3 values of two structurally different bifunctional monomers were overpredicted on the basis of this data set, indicating that accurate potency estimation by read-across based on in vitro data might be restricted to a relatively narrow applicability domain.

Analogues of the Epoxy Resin Monomer Diglycidyl Ether of Bisphenol F: Effects on Contact Allergenic Potency and Cytotoxicity

“…Previously reported LLNA EC3 values for DGEBA, DGEBF and PGE indicate that they are equipotent at 36 mM, 36 mM and 31 mM (1.2, 1.1 and 0.46% w/v), respectively. 21,23 According to suggested regulatory classifications, all three are sensitizers of strong potency. 26 The monoepoxide 1 has reduced sensitization potency in the LLNA compared to DGEBF and is classified as a moderate sensitizer according to its EC3 value of 2.3% w/v.…”

“…Previously published values predict DGEBA, DGEBF and PGE to be sensitizers, giving a 1.5-fold induction at low micromolar concentrations. 21 The KeratinoSens™ assay predicts 1 as a sensitizer (Table 1). Partial cytotoxicity of a chemical may lead to a luciferase induction in dying cells and therefore chemicals are rated as sensitizers only when luciferase induction starts at non-cytotoxic concentrations.…”

“…On the basis of the results above, 3 would be expected to be a 20 strong sensitizer in the LLNA due to the presence of the epoxide groups, analogous to PGE. 21 Conversely, 4 is structurally related to 2 and would not be expected to act as a sensitizer due to the lack of epoxide groups.…”

“…The three compounds were chosen to investigate the relative reactivity of a biaromatic diepoxide, a biaromatic monoepoxide and a monoaromatic monoepoxide. The hexapeptide chosen, 21 AcPHCKRM, contains both cysteine and lysine amino acid residues. All compounds were stable in the conditions of the assay.…”

Epoxy Resin Monomers with Reduced Skin Sensitizing Potency

“…24,25 Epoxy chemicals are also implicated in non-occupational contact allergy. 17,26 Skin sensitization potential has been investigated experimentally in vivo in mice and guinea pigs for DGEBA, 27,28 DGEBF 28,29 and others. 30,31 DGEBA and DGEBF are classified as strong sensitizers in both species according to regulatory guidelines.…”