Existing developmental toxicity testing guidelines for chemicals and drugs

1. Introduction

1.2. Developmental Toxicity

1.2.3. Existing developmental toxicity testing guidelines for chemicals and drugs

Pharmaceuticals for human use and industrial chemicals each have their own legislatory framework. The new European Union (EU) regulatory framework for Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) entered into force by June 2007. The legislation requires reproductive/developmental toxicity screening tests for chemicals produced in more than 10 tonnes/year and detailed reproductive/developmental toxicity testing for chemicals produced in more than 100 tonnes/year (EC, 2006). In addition to reproductive/developmental toxicity testing of new chemicals, data must be provided for more than 5000 existing chemicals, which are currently on the market, but are probably missing these data (EC, 2006; Pedersen et al., 2003). The standard data requirements for reproductive/developmental toxicity testing requested by REACH may be obtained by following test guidelines published by the Organisation for Economic Co-operation and Development (OECD) (EC, 2007). The relevant guidelines are OECD 421 or 422 (reproduction/developmental toxicity screening tests), OECD 414 (prenatal developmental toxicity studies) and OECD 416 (two-generation reproductive toxicity studies) (Table 1.2) (OECD, 1995b; OECD, 1996; OECD, 2001a; OECD, 2001b). The OECD guidelines for reproductive/developmental toxicity request only in vivo experiments. OECD 414, 416 and 421 use up to 150, 3200 and 560 animals/test, respectively (Hofer et al., 2004). Two-generation reproductive toxicity and prenatal developmental toxicity studies are therefore estimated to contribute the most to the overall use of animals in the implementation phase of REACH (Fig. 1.4) (van der Jagt K et al., 2004). The offspring of the two-generation reproductive toxicity and prenatal developmental toxicity studies have not been taken into account in these estimations, so including the offspring would reveal an even higher contribution of these studies to the numbers of animals needed (van der Jagt K et al., 2004). Overall, REACH will most likely increase the number of animals needed for developmental toxicity testing of chemicals.

The current European Community legislation relating to medicinal products for human use is given in Directive 2001/83/EC, which is amended regularly to align it with new requirements (EC, 2001). The legislation requirements include examination of toxicity to reproductive function as well as embryo/foetal and perinatal toxicity. The European Medicines Agency (EMEA) is authorising human pharmaceuticals for the European market, although the national medical regulatory authorities can give national authorisations. EMEA also releases guidelines on how to meet the regulatory requirements for safety evaluations of new drugs. In contrast to industrial chemicals, pharmaceuticals must be safety assessed in non-clinical in vivo studies as well as in human clinical trials before they can receive approval. No current guideline

1. Introduction

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for reproductive hazard identification of drugs considers the use of in vitro tests for primary developmental toxicity testing. Non-clinical developmental toxicity is addressed in the International Conference on Harmonisation (ICH) S5(R2) guideline on “Detection of Toxicity to Reproduction of Medical Products & Toxicity to Male Fertility” (EMEA, 1994). The guideline considers the 3-study design as adequate for most medical products. The design aims to reveal effects on different phases of the reproductive cycle (Table 1.4): 1) fertility and development of the pre-implantation stages of the embryo, 2) pre- and postnatal development, including maternal function and 3) embryo-foetal development. The ICH S5(R2) guideline suggests to test in two species, to use 16-20 litters of each species per dose tested and to include one control and two dose levels. Hence, 96-120 litters of each species are required per assay per 3-study design.

Developmental toxicity of drugs is of high concern due to the thalidomide disaster and because medical treatments may be applied in the very early phase of pregnancy when the conception is still unknown. Despite this, a drug is almost never tested clinically in pregnant women before marketing, but is instead labelled as not recommended for use duringpregnancy (Koren et al., 1998). The reason is the high level of ethical concern related to exposure of the human embryo/foetus (EMEA, 2000a). In fact, Directive 2001/83/EC does allow to omit clinical data on embryo/foetal and perinatal toxicity in cases where the medicinal product will not normally be used by women capable of childbearing or for other adequately justified reasons.

Ideally, an in vivo model for human developmental toxicity hazard evaluations should metabolise, distribute and transfer the toxicant across the placenta in ways similar to humans.

The mechanisms of embryo developmental should also reflect those of humans. No single species has been found to fulfil these criteria, but it is universally recognised that developmental toxicity studies should be conducted in mammals (EMEA, 1994; Schardein, 2000). Moreover, the OECD guideline 414 and the ICH S5(R2) guideline suggest to perform developmental toxicity testing in two species in order to ensure that false negatives are avoided. In both cases, the rat is the preferred rodent species and the rabbit is the preferred non-rodent species (EMEA, 1994; OECD, 2001a). In spite of the use of a second species, developmental toxicity testing in vivo is strongly hampered by the high interspecies differences (Bremer et al., 2007).

1. Introduction

Test guideline

Study type Exposure

OECD 421 Reproduction/developmental toxicity screening test

From 2 weeks prior to mating until day 4 postnatally

OECD 422 Combined repeated dose (chronic)

From 2 weeks prior to mating of parental generation until 3 weeks postnatally of first generations offspring Table 1.3 Overview of the OECD test guidelines which may provide the standard data for

reproductive/developmental toxicity testing requested by REACH.

Females are exposed from implantation to the end of lactation

Embryo-foetal development Females are exposed from implantation to the closure of the hard palate in the roof of the mouth

Table 1.4 Overview of the 3-study design of the ICH S5(R2) test guidelines which may provide data for reproductive/developmental toxicity testing requested by EMEA.

Fig. 1.4 Estimations of percentage of test animals needed for the different toxicological endpoint studies in the implementation phase of REACH, i.e. the studies needed to fill the gaps in the toxicological dossiers for existing chemicals. Prenatal developmental toxicity studies are assumed to be carried out in two species. Offspring are not taken into account in the estimations for the two-generation reproductive toxicity and developmental toxicity studies. Source: van der Jagt et al. (2004).

% of total test animals needed

1. Introduction

Im Dokument In vitro Assessment of Developmental Toxicity and Cardiac Pharmacology using Embryonic Stem Cells (Seite 25-28)