Genotoxic mixtures and dissimilar action: concepts for prediction and assessment

Abstract

Combinations of genotoxic agents have frequently been assessed without clear assumptions regarding their expected (additive) mixture effects, often leading to claims of synergisms that might in fact be compatible with additivity. We have shown earlier that the combined effects of chemicals, which induce micronuclei (MN) in the cytokinesis-block micronucleus assay in Chinese hamster ovary-K1 cells by a similar mechanism, were additive according to the concept of concentration addition (CA). Here, we extended these studies and investigated for the first time whether valid additivity expectations can be formulated for MN-inducing chemicals that operate through a variety of mechanisms, including aneugens and clastogens (DNA cross-linkers, topoisomerase II inhibitors, minor groove binders). We expected that their effects should follow the additivity principles of independent action (IA). With two mixtures, one composed of various aneugens (colchicine, flubendazole, vinblastine sulphate, griseofulvin, paclitaxel), and another composed of aneugens and clastogens (flubendazole, doxorubicin, etoposide, melphalan and mitomycin C), we observed mixture effects that fell between the additivity predictions derived from CA and IA. We achieved better agreement between observation and prediction by grouping the chemicals into common assessment groups and using hybrid CA/IA prediction models. The combined effects of four dissimilarly acting compounds (flubendazole, paclitaxel, doxorubicin and melphalan) also fell within CA and IA. Two binary mixtures (flubendazole/paclitaxel and flubendazole/doxorubicin) showed effects in reasonable agreement with IA additivity. Our studies provide a systematic basis for the investigation of mixtures that affect endpoints of relevance to genotoxicity and show that their effects are largely additive.

Prediction and assessment of ecogenotoxicity of antineoplastic drugs in binary mixtures

“…For this reason, Kocaman and Topaktas (2010) discourage application of CA and IA models for the prediction of genotoxicity of mixtures. In contrast, other studies showed the applicability of CA and IA for investigating the genotoxic potential of anticancer mixtures (Ermler et al 2014;Mater et al 2014). …”

“…Indeed, different from ecotoxicity tests where there was a clear concentration-response relationship with a sigmoidal-shaped curve (0-100 % effect), in genotoxicity tests, such as the comet and micronucleous assays, this relationship is more variable. It has to be taken into account that spontaneous DNA damage occurs detected in these assays as a baseline response above zero, while at high exposure levels, cytotoxicity could occur interfering with the genotoxic response (Ermler et al 2014). For this reason, Kocaman and Topaktas (2010) discourage application of CA and IA models for the prediction of genotoxicity of mixtures.…”

“…Compounds with the same mode and biological site of action could act in mixture according to the CA model (Loewe additivity or isoadditivity); compounds with different mechanisms and/or different biological sites of action cannot be considered as dilutions of each other and may rather act in mixture according to the IA model (Bliss independence or heteroadditivity) (Katsnelson et al 2011). Some recent studies concerning the effects of anticancer drugs in mixtures suggest that combinations might follow or deviate from expectations based on these reference models (Ermler et al 2014;Mater et al 2014). In the present study, genotoxicity of anticancer drugs in binary mixture was statistically compared to the genotoxic activity of single compounds at two distinct effect levels.…”

Challenges in risk assessment of multiple mycotoxins in food

“…Furthermore, the application of mathematical models to ascertain genotoxic interactive effects, similarly to what has been done for combined cytotoxicity assessment, is highly relevant to have firm and reliable conclusions about genotoxic interactive effects. In this sense, Ermler et al (2014) have already shown that the CA, IA and hybrid CA/IA models are applicable to data obtained for several model compounds with similar and dissimilar MoA, using the micronucleus assay.…”

Scientific Opinion on the relevance of dissimilar mode of action and its appropriate application for cumulative risk assessment of pesticides residues in food

“…If some chemicals produce the effect by similar mechanisms, the principles of independence of action are not met anymore, and it is likely that observed mixture effects deviate somewhat from those predicted by the independent action concept. A recent paper examining the joint effects of several substances producing micronuclei through different modes of action has given indications that the number of different mechanisms available for the induction of this effect is smaller than the number of chemicals capable of producing this kind of toxicity (Ermler et al, 2013b).…”