REACH alternative testing strategy for skin sensitization in practice: Fact or fiction?

From October 2016 the REACH Regulation requires an alternative testing strategy for skin sensitization. The current paper describes our experience when putting into practice the REACH alternative testing strategy with a modification for 50 industrial chemicals in total, including mono-constituents, multi-constituents and UVCBs. For mono- and multi-constituents, a tiered approach was followed starting with an in silico (Derek Nexus) assessment, DPRA and KeratinoSens™ assay, followed by a weight of evidence conclusion based on the generated data, or further testing using the U-SENS™ assay. For UVCBs testing started with the KeratinoSens™ assay followed by the U-SENS™ assay if additional relevant information could be gained for an overall conclusion. From the 50 substances tested, for 46% a conclusion on skin sensitization potential and potency could be drawn based on the non-animal testing strategy; however, 54% of the substances still needed to be studied in vivo due to discordant results from non-animal testing or the need for reliable potency data. Important issues with the currently available, validated non-animal methods are the lack or comparability of skin metabolism and lack of potency indication, which is present in the in vivo assays. Skin sensitization testing for UVCBs and multi-constituents is still in a grey area, as neither the in chemico, in vitro assays, and in vivo LLNA have been validated for UVCBs and multi-constituents.

Implementing the extended one-generation reproductive toxicity study (EOGRTS): important points to consider.

The hallmark of the extended one-generation reproductive toxicity study (EOGRTS) is that, based on certain criteria or triggers, selected offspring are assigned at weaning to different cohorts for further investigation of sexual maturation, reproductive organ integrity and function, neuropathological and behavioral endpoints, and/or immune function. The triggers allow for a more customizable design based directly on the data, while minimizing animal usage. Compared to the two-generation reproductive toxicity study, the EOGRTS design increases the number, extent, and duration of F1-offspring assessments resulting in more thorough and efficient utilization of the first generation while excluding the second generation of offspring unless triggered. Therefore, the EOGRTS has the potential to reduce the number of rats required by nearly 1200 animals per study. When performing the EOGRTS, the complexity of this study should not be underestimated and experienced flexible testing laboratories with sufficient resources and historical control data for all parameters are essential. The aim of this review is to discuss the important aspects of this challenging study design and to share our knowledge on the implementation of this study in our laboratories. In addition, we elaborate on the type of criteria for expansion of the study and logistical considerations. Altogether, this review can be used as guidance by other labs, study monitors, and registration officers.