A tiered approach to threshold of regulation

Threshold of toxicological concern (TTC) for developmental and reproductive toxicity of anticancer compounds

Pharmaceutical companies develop specialized therapies to treat late stage cancer. In order to accelerate life-saving treatments and reduce animal testing, compounds to treat life-threatening malignancies are allowed modified requirements for preclinical toxicology testing. Limited data packages in early drug development can present product quality challenges at multi-product manufacturing facilities. The present analysis established an endpoint-specific threshold of toxicological concern (TTC) for developmental and reproductive toxicity (DART) for anticancer compounds. A comprehensive database was created consisting of over 300 no-observed adverse effect levels (NOAELs) for DART of 108 anticancer compounds. The 5th percentile NOAEL for developmental and reproductive toxicity was 0.005 mg/kg/day (300 μg/day), resulting in a human exposure threshold of 3 μg/day assuming standard uncertainty factors and a 60 kg human bodyweight. The analysis shows this threshold is protective for developmental and reproductive toxicity of highly potent groups of anticancer compounds. There were similar TTC values calculated for direct-acting and indirect-acting anticancer compounds.

A novel safety assessment strategy for non-intentionally added substances (NIAS) in carton food contact materials

One of the main challenges in food contact materials research is to prove that the presence of non-intentionally added substances (NIAS) is not a safety issue. Migration extracts may contain many unknown substances present at low concentrations. It is difficult and time-consuming to identify all these potential NIAS and concurrently to assess their health risk upon exposure, whereas the health relevance at low exposure levels might not even be an issue. This paper describes a scientifically based, but pragmatic safety assessment approach for unknown substances present at low exposure levels in food contact matrices. This complex mixture safety assessment strategy (CoMSAS) enables one to distinguish toxicologically relevant from toxicologically less relevant substances, when related to their respective levels of exposure, and allows one to focus on the substances of potential health concern. In particular, substances for which exposure will be below certain thresholds may be considered not of health relevance in case specific classes of substances are excluded. This can reduce the amount of work needed for identification, characterisation and evaluation of unknown substances at low concentration. The CoMSAS approach is presented in this paper using a safety assessment of unknown NIAS that may migrate from three carton samples.

Mutagenic impurities in pharmaceuticals: a critique of the derivation of the cancer TTC (Threshold of Toxicological Concern) and recommendations for structural-class-based limits

The cancer TTC (Threshold of Toxicological Concern) concept is currently employed as an aid to risk assessment of potentially mutagenic impurities (PMIs) in food, cosmetics and other sectors. Within the pharmaceutical industry the use of one default cancer TTC limit of 1.5 μg/day for PMIs is being increasingly questioned. Its derivation, originally in the context of foodstuffs, can be broken down into five key elements: dataset composition; determination of carcinogenicity/mutagenicity status and carcinogenic potency (based on TD₅₀s) of compounds in the dataset; linear extrapolation of carcinogenic potencies; evaluation of the more potent compounds in each structural category, and presence of representative structural alerts amongst the more potent compounds. A detailed evaluation reveals that the derivation process is distorted by the use of the lowest statistically significant TD₅₀s (which can produce a false-carcinogen phenomenon) and by employing linear extrapolation for non-mutagenic carcinogens. By correcting for these two factors, it is concluded that only around 50% of conventional structural-alert categories were adequately addressed and that limits higher than the default value appear to be justified in many cases. Using similar criteria for PMIs in pharmaceuticals, four distinct potency categories of conventional structural alerts can be distinguished, ranging from alerts with questionable validity to those with high potency, which are considered to provide a range of flexible and pragmatic limits for such impurities.

Determining the applicability of threshold of toxicological concern approaches to substances found in foods

Threshold of Toxicological Concern (TTC) decision-support methods present a pragmatic approach to using data from well-characterized chemicals and protective estimates of exposure in a stepwise fashion to inform decisions regarding low-level exposures to chemicals for which few data exist. It is based on structural and functional categorizations of chemicals derived from decades of animal testing with a wide variety of chemicals. Expertise is required to use the TTC methods, and there are situations in which its use is clearly inappropriate or not currently supported. To facilitate proper use of the TTC, this paper describes issues to be considered by risk managers when faced with the situation of an unexpected substance in food. Case studies are provided to illustrate the implementation of these considerations, demonstrating the steps taken in deciding whether it would be appropriate to apply the TTC approach in each case. By appropriately applying the methods, employing the appropriate scientific expertise, and combining use with the conservative assumptions embedded within the derivation of the thresholds, the TTC can realize its potential to protect public health and to contribute to efficient use of resources in food safety risk management.

The central role of chemistry in ‘quality by design’ approaches to drug development

The quality of medicines reaching the consumer is strictly controlled and maintained by the regulatory agencies of the world. Pharmaceutical companies have to meet and maintain these regulatory quality standards. For this purpose, an increasing number of processes are incorporating quality by design (QbD) principles. Implementation of QbD involves chemistry in several ways, such as in the development of new synthetic and analytical methods, avoiding formation of genotoxic impurities and designing drug-like compounds to improve the quality of biological profile of medicines. A combined effort from regulatory authorities, pharmaceutical industries and academic research groups could also facilitate QbD implementation.

Application of the threshold of toxicological concern concept when applied to pharmaceutical manufacturing operations intended for short-term clinical trials

In the manufacture of pharmaceuticals, if a multiproduct facility shares equipment amongst drug substances/products it is incumbent upon the manufacturer to demonstrate removal of the pharmaceutical through a robust cleaning validation/verification program. Removal must be to below limits considered acceptable from a quality and toxicological perspective. In order to address the toxicological concerns, an acceptable daily exposure (ADE) was developed which is the "dose that is unlikely to cause an adverse effect if...exposed, by any route...at or below this dose every day for a lifetime" (ISPE, 2010). For compounds in development, defaulted ADEs were proposed by Dolan et al. (2005) and adopted by the International Society of Pharmaceutical Engineers (ISPE) as conservative cutoffs for compounds with limited data. In Phase 1 clinical trials, exposure is typically short-term (single dose or repeated doses for ≤30 days) compared to the chronic doses used to derive ADE and defaulted ADEs. An analysis of publicly available databases for toxicological and pharmacological effects supports the use of 10-fold higher defaulted values when the residual drug substance is in a developmental pharmaceutical intended for Phase 1 clinical trials (exposure ≤30 days).

Guiding principles for the implementation of non-animal safety assessment approaches for cosmetics: skin sensitisation

Characterisation of skin sensitisation potential is a key endpoint for the safety assessment of cosmetic ingredients especially when significant dermal exposure to an ingredient is expected. At present the mouse local lymph node assay (LLNA) remains the 'gold standard' test method for this purpose however non-animal test methods are under development that aim to replace the need for new animal test data. COLIPA (the European Cosmetics Association) funds an extensive programme of skin sensitisation research, method development and method evaluation and helped coordinate the early evaluation of the three test methods currently undergoing pre-validation. In May 2010, a COLIPA scientific meeting was held to analyse to what extent skin sensitisation safety assessments for cosmetic ingredients can be made in the absence of animal data. In order to propose guiding principles for the application and further development of non-animal safety assessment strategies it was evaluated how and when non-animal test methods, predictions based on physico-chemical properties (including in silico tools), threshold concepts and weight-of-evidence based hazard characterisation could be used to enable safety decisions. Generation and assessment of potency information from alternative tools which at present is predominantly derived from the LLNA is considered the future key research area.

Alternative (non-animal) methods for cosmetics testing: current status and future prospects-2010

The 7th amendment to the EU Cosmetics Directive prohibits to put animal-tested cosmetics on the market in Europe after 2013. In that context, the European Commission invited stakeholder bodies (industry, non-governmental organisations, EU Member States, and the Commission's Scientific Committee on Consumer Safety) to identify scientific experts in five toxicological areas, i.e. toxicokinetics, repeated dose toxicity, carcinogenicity, skin sensitisation, and reproductive toxicity for which the Directive foresees that the 2013 deadline could be further extended in case alternative and validated methods would not be available in time. The selected experts were asked to analyse the status and prospects of alternative methods and to provide a scientifically sound estimate of the time necessary to achieve full replacement of animal testing. In summary, the experts confirmed that it will take at least another 7-9 years for the replacement of the current in vivo animal tests used for the safety assessment of cosmetic ingredients for skin sensitisation. However, the experts were also of the opinion that alternative methods may be able to give hazard information, i.e. to differentiate between sensitisers and non-sensitisers, ahead of 2017. This would, however, not provide the complete picture of what is a safe exposure because the relative potency of a sensitiser would not be known. For toxicokinetics, the timeframe was 5-7 years to develop the models still lacking to predict lung absorption and renal/biliary excretion, and even longer to integrate the methods to fully replace the animal toxicokinetic models. For the systemic toxicological endpoints of repeated dose toxicity, carcinogenicity and reproductive toxicity, the time horizon for full replacement could not be estimated.

Overall impact of the regulatory requirements for genotoxic impurities on the drug development process

In the last decade a considerable effort has been made both by the regulators and the pharmaceutical industry to assess genotoxic impurities (GTI) in pharmaceutical products. Though the control of impurities in drug substances and products is a well established and consolidated procedure, its extension to GTI has given rise to a number of problems, both in terms of setting the limits and detecting these impurities in pharmaceutical products. Several papers have dealt with this issue, discussing available regulations, providing strategies to evaluate the genotoxic potential of chemical substances, and trying to address the analytical challenge of detecting GTI at trace levels. In this review we would like to discuss the available regulations, the toxicological background for establishing limits, as well as the analytical approaches used for GTI assessment. The final aim is that of providing a complete overview of the topic with updated available information, to address the overall GTI issue during the development of new drug substances.

Safety of botanical ingredients in personal care products/cosmetics

The key issue of the safety assessment of botanical ingredients in personal care products (PCP) is the phytochemical characterisation of the plant source, data on contamination, adulteration and hazardous residues. The comparative approach used in the safety assessment of GM-plants may be applied to novel botanical PCP ingredients. Comparator(s) are the parent plant or varieties of the same species. Chemical grouping includes definition of chemical groups suitable for a read-across approach; it allows the estimation of toxicological endpoints on the basis of data from related substances (congeneric groups) with physical/chemical properties producing similar toxicities. The Threshold of Toxicological Concern (TTC) and Dermal Sensitisation Threshold (DST) are tools for the assessment of trace substances or minor ingredients. The evaluation of skin penetration of substances present in human food is unnecessary, whereas mixtures may be assessed on the basis of physical/chemical properties of individual substances. Adverse dermal effects of botanicals include irritation, sensitisation, phototoxicity and immediate-type allergy. The experience from dietary supplements or herbal medicines showed that being natural is not equivalent to being safe. Pragmatic approaches for quality and safety standards of botanical ingredients are needed; consumer safety should be the first objective of conventional and botanical PCP ingredients.

Overview of Genotoxic Impurities in Pharmaceutical Development

This symposium focuses on the management of genotoxic impurities in the synthesis of pharmaceuticals. Recent developments in both Europe and United States require sponsors of new drug applications to develop processes to control the risks of potential genotoxic impurities. Genotoxic impurities represent a special case relative to the International Conference on Harmonisation Q3A/Q3B guidances, because genotoxicity tests used to qualify the drug substance may not be sufficient to demonstrate safety of a potentially genotoxic impurity. The default risk management approach for a genotoxic impurity is the threshold of toxicological concern unless a more specific risk characterization is appropriate. The symposium includes descriptions of industry examples where impurities are introduced and managed in the synthesis of a pharmaceutical. It includes recent regulatory developments such as the “staged threshold of toxicological concern” when administration is of short duration (eg, during clinical trials).