Assessment of the carcinogenic potential of chemicals is considered an important element of human health risk assessment. However, the approaches currently used for different regulatory sectors have some shortcomings. To overcome these, an alternative testing strategy, like an IATA (Integrated Approach to Testing and Assessment), for the detection of non-genotoxic carcinogens (NGTXCs) is in demand. Such an IATA should be mechanism-based and, wherever possible, consist of New Approach Methodologies (NAMs) to avoid testing in experimental animals. To explore which type of NAMs (in silico and in vitro) should be included in the first tier of an IATA for NGTXCs we performed a case study, in line with various international initiatives focusing on this need. The case study comprised a diverse set of 29 chemicals that together cover different modes of action relevant for non-genotoxic carcinogenesis. Different NAMs, including in silico tools (e.g., QSARS, ADME predictions) and high-throughput in vitro assays such as ToxCast and CALUX, were explored. The findings from the case study reveal the complementarity of the NAMs studied as well as the need for additional NAMs to be included, to ensure a broader coverage of MOAs relevant for carcinogenicity. As such, the case study nicely contributes to a more defined composition of a first tier for an IATA for NGTXC.

Opinion to be cited as: SCCS (Scientific Committee on Consumer Safety), Opinion on HAA299 (nano), preliminary opinion July 22, 2021, final opinion 26–27 October 2021, SCCS/1634/2021.HAA299 is a UV filter active intended to be used in sunscreen products as skin protectant against UVA-1 rays. Its chemical name is ‘2-(4-(2-(4-Diethylamino-2 hydroxy-benzoyl)-benzoyl)-piperazine-1-carbonyl)-phenyl)-(4-diethylamino-2-hydroxyphenyl)-methanone’ and INCI name ‘Bis-(Diethylaminohydroxybenzoyl Benzoyl) Piperazine’ (CAS 919803-06-8). This product was designed and developed to deliver to the consumer stronger UV protection on skin and is most effective as a UV filter when it is milled to a smaller particle size, a process we refer to as micronization.Currently HAA299 normal form and nano form is not regulated under the Cosmetic Regulation (EC) No. 1223/2009. In 2009, Commission' services received a dossier from industry to support the safe use of HAA299 (micronised and non-micronised) in cosmetic products, which was further substantiated with additional information in 2012. In its corresponding opinion (SCCS/1533/14), the SCCS concluded that “the use of non-nano HAA299 (micronised or non-micronised, with median particle size distribution around 134 nm or larger, as measured by FOQELS) at a concentration up to 10% as an UV-filter in cosmetic products, does not pose a risk of systemic toxicity in humans”. In addition, SCCS stated that “[the Opinion] … covers the safety evaluation of HAA299 in non-nano form. The opinion does not cover the safety evaluation of HAA299 which is composed of nano particles' and highlighted that ‘[the Opinion] … does not apply to inhalation exposure of HAA299 since no information on chronic or sub-chronic toxicity after inhalation is provided”. With the current submission, received in September 2020, and in view of the previous SCCS opinion (SCCS/1533/14) on the normal form of HAA299, the applicant requests to assess the safety of HAA299 (nano) intended to be used as UV-filter up to a maximum concentration of 10%.

The concept of the Maximum Tolerated Dose (MTD) was introduced in the seventies for carcinogenicity testing and was defined as the highest dose inducing clear toxicity, but not mortality by causes other than cancer. As estimation of the MTD in a carcinogenicity study, the highest dose that causes a 10% decrease in body weight compared to control animals over the course of a 90-day study, was formulated as a suitable criterion. This criterion was not seen as indicator of excessive toxicity but as a means to avoid false negative outcomes in a carcinogenicity study, as tumor formation may be reduced when body weight is significantly decreased. The body weight-based MTD criterion, however, turned up in carcinogenicity test guidelines and guidance (e.g., from OECD) as the highest dose that causes a 10% decrease in body weight gain relative to controls. Moreover, the 10% decrease in body weight gain criterion for MTD also ended up in test guidelines and guidances for toxicity endpoints other than carcinogenicity, so outside the context it was intended for. A 10% decrease in body weight gain relative to controls is however not a biologically relevant effect as it corresponds to less than 3% body weight reduction relative to controls in a 90-day study, which is within the normal variation in body weight. It therefore should certainly not be considered as a condition of excessive toxicity. Using the 10% lower weight gain criterion and incorrectly associating it with excessive toxicity has major implications for top dose selection in regulatory safety studies, resulting in tests performed at doses too low to elicit toxicity. This negatively impacts the reliability of studies and their regulatory usability; moreover, it results in a waste of experimental animals, which is ethically highly undesirable. Hence, our plea is to remove this MTD criterion for top dose selection in test guidelines and guidances for toxicity endpoints other than carcinogenicity and to reinstall the original 10% decrease in body weight criterion in test guidelines and guidances for carcinogenicity.

In the EU, one of the key determinants in the regulation and management of substances to ensure adequate protection of human health is the outcome of toxicity studies. These studies should therefore be performed in a way that the data generated are adequate to fulfil all regulatory requirements. However, in recent years, an increasing number of toxicity studies use dose levels that induce only slight, or even no toxicity, while the top dose lies well below the limit dose of 1000 mg/kg bw/d. The results of these studies have limited value for the hazard and subsequent risk assessment and risk management of substances. This paper shows why conducing toxicity studies with too low doses has severe consequences for among others classification and labelling, identification of endocrine disruptors, health impact assessment, and incident management. With this paper we aim to raise awareness on this issue and want to stress the importance of the use of sufficiently high dosing in toxicity studies. Given their central role in toxicity testing, it is therefore key to adapt where necessary the descriptions in OECD test guidelines and guidance documents on requirements for dose level setting, to make sure they are as explicit and unambiguous as possible.

The KMD (kinetically-derived maximum dose) is an increasingly advocated concept that uses toxicokinetic data in the top dose selection for toxicity testing. Application of this concept may have serious regulatory implications though, especially in the European Union. The basic assumption is that the relationship between internal and external dose (IED) shows an inflection point where linearity transits into non-linearity due to saturation of underlying processes; top doses in toxicity tests should not be above the inflection point, provided human exposures are well below this point. A critical analysis of the KMD concept and its underlying assumptions shows, however, that the IED relationship is non-linear over the whole dose range, without any point of inflection. The KMD concept thus aims to estimate a non-existing point, rendering it invalid for use in toxicity testing. Moreover, the concept ignores the key question in toxicology: What kind of toxic effects occur at which doses? These and several other reservations against the KMD concept are discussed and illustrated with three existing applications of the KMD approach. Hence, we recommend to abolish the KMD concept for selecting top doses in toxicity testing. This requires the updating of regulations, guidance documents and OECD test guidelines.

The REACH (Registration, Evaluation, Authorisation and Restriction of Chemicals) data requirements for mutagenicity and carcinogenicity have been compared to the criteria for classification under Classification, Labelling and Packaging (CLP) and the studies used as key evidence by Committee for Risk Assessment (RAC) in drafting its opinions on the appropriate classification. This comparison revealed that the REACH information requirements will not provide sufficient information to conclude a substance is a Cat 1B mutagen and/or carcinogen. In addition, requiring such information via a substance evaluation under REACH requires a large investment from the Member States and takes years. Classification and labeling is essential in the communication of the hazardous properties of substances and mixtures and is amongst others an important first step in the identification of a substance as a Substance of Very High Concern (SVHC). REACH will hardly generate sufficient information for classification of substances as category 1B for mutagenicity and carcinogenicity. Therefore, indications of very severe hazards of substances are missed and health risks could occur. There are various ways to deal with this problem, however as most of these require adaptation of regulations this will cost considerable time and political will. This study is a first step to raise awareness for the problem and to start a discussion to search for a sustainable solution.

Exposure timing could play an important role in the effects of estrogenic endocrine disrupting chemicals (EEDCs) on early pregnancy. This study examined the sensitivity of different exposure periods from weaning to gestation day 4.5 (D4.5) to 50 ppb diethylstilbestrol (DES, a test EEDC) diet on embryo implantation and potential recovery upon temporary cessation of DES exposure in CD-1 mice. Peripubertal (3–5 weeks old) DES exposure reduced the numbers of corpora lutea and implantation sites. Postpubertal (5–7 weeks old) DES exposure did not have significant effects on early pregnancy. Postmating (D0.5–D4.5) DES exposure affected postovulation events leading to impaired embryo implantation. A 5-day premating rest from 5-week DES exposure (3–8 weeks old) resulted in recovery of early pregnancy rate. These data demonstrate that peripubertal and postmating periods are sensitive windows to endocrine disruption of early pregnancy and temporary cessation of exposure could partially alleviate adverse effects of DES on early pregnancy.

The local lymph node assay (LLNA) is the preferred method for classification of sensitizers within REACH. To reduce the number of mice for the identification of sensitizers the reduced LLNA was proposed, which uses only the high dose group of the LLNA. To evaluate the performance of this method for classification, LLNA data from REACH registrations were used and classification based on all dose groups was compared to classification based on the high dose group. We confirmed previous examinations of the reduced LLNA showing that this method is less sensitive compared to the LLNA. The reduced LLNA misclassified 3.3% of the sensitizers identified in the LLNA and misclassification occurred in all potency classes and that there was no clear association with irritant properties. It is therefore not possible to predict beforehand which substances might be misclassified. Another limitation of the reduced LLNA is that skin sensitizing potency cannot be assessed. For these reasons, it is not recommended to use the reduced LLNA as a stand-alone assay for skin sensitization testing within REACH. In the future, the reduced LLNA might be of added value in a weight of evidence approach to confirm negative results obtained with non-animal approaches.

The possible impact on classification and labelling decisions of effects observed in second generation parental (P1) and offspring (F2) parameters in multi-generation studies was investigated. This was done for 50 substances classified as reproductive toxicants in Europe, for which a multi-generation study was available. The P1 and F2 effects were compared to parental (P0) and first generation offspring (F1) effects with regard to type of effect as well as incidence, magnitude and severity (IMS), at any dose level. For every study with unique P1/F2 effects, or differences in IMS, the influence of the P1/F2 findings on the classification decision was investigated. Unique P1/F2 generation findings did not play a crucial role in the classification decision of any of the 50 classified substances, except for fenarimol. This substance however provided abundant alerts on the basis of its endocrine activity and developmental neurotoxicity and would therefore also be expected to be identified as a developmental neurotoxicant in an Extended One Generation Reproductive Toxicity Study (EOGRTS). These findings, in addition to the increased number of parameters analysed, increased statistical power and reduced animal use, provide strong further support for replacement of the classical two-generation reproductive toxicity study by the EOGRTS in regulatory reproductive toxicity assessment.

Current suggestions towards amending the OECD two-generation protocol include omission of the second generation and inclusion of additional parameters. This study analysed the relative parameter sensitivity in 18 individually published multi-generation studies with substances toxic to fertility. Among parameters that most often determined the reproductive LOAEL were weight of testis, dam and pup as well as litter size. Several other parameters were found to be unaffected in all studies evaluated. Some substances affected a specific set of parameters, indicating that rarely affected parameters may prove crucial in individual situations. This argues for the inclusion of a wide spectrum of parameters to cover all possible effects. Less sensitive parameters, mechanistically related to more sensitive ones, may be omitted as they will unlikely contribute to the overall LOAEL. This study gives first insights and needs follow-up by more extensive analyses before firm conclusions on the design of the two-generation study protocol can be drawn.