Optimization of metabolic activation for four mutagens in a bacterial, fungal and two mammalian cell mutagenesis assays

Abstract

The optimum concentrations of Aroclor-induced rat liver S9 microsomal fraction for the mutagenic activity of the four standard mutagens 2-aminofluorene (2-AF), acriflavine (ACR), benzo[a]pyrene (BP) and cyclophosphamide (CP) were determined in four mutation assays. The four assays were the Ames test using Salmonella typhimurium strain TA100, cycloheximide resistance in the yeast Saccharomyces cerevisiae, the mouse lymphoma TK assay and the human peripheral lymphocyte cytogenetic assay. BP was the only mutagen to be most active at comparable S9 concentrations, of approximately 1%, for all four assays. The optimum S9 concentrations for each of the remaining three mutagens varied substantially between the four assays. ACR was a potent direct-acting mutagen in both mammalian cell assays. The mouse lymphoma TK assay results showed similar optimal values of 1.5% S9 or below for each of the four test agents. The assay with the largest variation of optimal S9 values for the four mutagens was the Ames test in strain TA100, although it also had the widest peaks of activity over the range of S9 concentrations tested. It is likely that the diversity of findings is due to a variety of metabolites affecting the different genetic endpoints that are measured in these assays. Thus from these results it is not possible for bacterial optimization data to be related to other routine in vitro systems. The use of more than one concentration of S9 would contribute useful information.

Acriflavine, a clinically approved drug, inhibits SARS-CoV-2 and other betacoronaviruses

“…On the other hand, a substantial amount of long-term clinical data is available for systematic applications of ACF ( Gama et al., 2020 ; Mathé et al., 1996 , 1998 ), thus alleviating concerns related to the potential mutagenic effects, especially for short-term antiviral therapy. Importantly, the antiviral effects are observed at concentrations of 2–3 orders of magnitude lower than those used in experiments assessing in vitro mutagenicity of ACF ( Obstoy et al., 2015 ; Rees et al., 1989 ).…”

Application of the TGx‐28.65 transcriptomic biomarker to classify genotoxic and non‐genotoxic chemicals in human TK6 cells in the presence of rat liver S9

“…The dendogram revealed that the signature was most similar to non‐genotoxic agents for all three replicates of dexamethasone, but the PCA placed the outlier sample on the borderline between genotoxic and non‐genotoxic agents. Given that one of the three replicates of dexamethasone was classified as genotoxic, and based on the observed cytotoxic effects of S9 and recommendations in the literature for TK6 cells [Rees et al, ; Xiao and Fontanie, ; OECD, ], we advise the use of lower concentrations of S9 when possible to avoid false positives. We thus performed our subsequent experiments using 2% Aroclor‐induced S9.…”

Acriflavine, a clinically aproved drug, inhibits SARS-CoV-2 and other betacoronaviruses

“…On the other hand, a substantial amount of long-term clinical data is available for systematic applications (Gama CRB, 2020;Mathé et al, 1996;Mathé et al, 1998), thus alleviating concerns related to the potential mutagenic effects of short-term antiviral therapy. Importantly, the antiviral effects are observed at concentrations of two to three orders of magnitude lower than those used in experiments assessing in vitro mutagenicity of ACF (Obstoy et al, 2015;Rees et al, 1989).…”

“…Importantly, the antiviral effects are observed at concentrations of two to three orders of magnitude lower than those used in experiments assessing in vitro mutagenicity of ACF (Obstoy et al, 2015;Rees et al, 1989).…”