GADD45α induction in the GreenScreen HC indicator assay does not occur independently of cytotoxicity.

Mammalian chromosomal integrity assays are influenced by cytotoxicity, a phenomenon which impacts data interpretation, assay specificity, and regulatory testing guidelines. Concordance of the GADD45α GreenScreen HC indicator assay to established in vitro and in vivo genetic toxicological assays has previously been described, yet a detailed description in the manner by which cytotoxicity influences its performance has not. Here we present a post-hoc analysis of a previously tested set of 91 proprietary and nonproprietary compounds investigating the influence of cytotoxicity on GADD45α induction and how varying assay cutoff criteria impacts assay performance. Significant cytotoxicity was identified to accompany the majority (72%) of compounds classified as genotoxic by GADD45α induction. Decreasing the GADD45α genotoxic induction criteria (from a 50 to a 30% increase over solvent controls) resulted in an increased assay sensitivity (from 30 to 68%) and concordance (from 55 to 68%), though a concomitant decrease in specificity was also observed (from 97 to 68%). We conclude that GADD45α induction in the GreenScreen HC indicator assay is influenced by cytotoxicity and that assay performance can be improved if different cutoff criteria are implemented.