Whereas the terms 'validation' and 'acceptance' are used in the context of the implementation of NAMs for the safety assessment of chemicals, the terms 'qualification' and 'adoption' are preferred for NAMs for the efficacy and safety assessment of pharmaceutical products. Although the implementation of NAMs for these two areas is different, many steps are similar. Hence, the NAM Navigator uses the terms ‘validation’, and ‘acceptance’ for the benefit of readability. If information is meant specifically for either chemical or pharmaceutical domain, this is specified. Although the process of validation, as described in the NAM Navigator, is divided into distinct phases, in practice the process is continuous. Each stage of the process uses and builds on the results of other stages of the work.

Validation is essential to facilitate the international acceptance of NAMs and to ensure that decisions are based on sound science (Ref6).  It is also an important process for maintaining the scientific integrity, credibility and utility of NAMs (Ref53).

Validation sits at the interface between test method development and optimisation, regulatory acceptance and international acceptance. It ensures a scientifically sound and rigorous evaluation of test methods to determine their overall performance, suitability for a given purpose and scientific validity.

In principle, test methods and approaches could be validated by actors other than validation bodies, such as test method developers in academia and industry, and then reviewed in other neutral (with respect to the test method) processes, such as the OECD review process under the OECD Test Guidelines Programme (Ref67). The process can be accelerated if essential information is provided by test developers in advance (Ref18).

To validate a test method, a test method sponsor often plays a crucial role in adopting the method into a testing guideline. This sponsor is  an entity, which commissions, supports, and/or submits a non-clinical health or environmental safety study and also normally finances the study.  In practice, the sponsor drives and assigns a validation manager/management team to design and carry the validation out. There are several potential candidates to be a sponsor of a validation study such as international bodies, government entities, or validation organizations for alternative methods (ECVAM, ICCVAM), national organizations, other independent organizations, or commercial sponsors (Ref13). 

The sponsor of a study will normally appoint a validation manager with well-defined roles and responsibilities, to coordinate the study.  In the case of validation studies performed under the auspices of the OECD the sponsor may be an OECD Expert Group, Task Force, Working Group, or Working Party whose members are nominated by the governments of the respective Member countries. Member countries or stakeholders, such as national and international organisations, industry associations, or non-governmental organisations may also represent the sponsor.

A project plan should be produced so that all involved parties will have a clear understanding of the validation work to be performed. The project plan will form the basis of an agreement among the sponsors, the validation management group, and the lead and participating laboratories (Ref54).

Sponsors should ensure that all information and data generated during validation of the test method are archived and are available for independent review. Sponsors or other appropriate parties could contact organisations that specialize in test method evaluations, for example ECVAM or ICCVAM, to arrange for an independent peer review. These organisations provide a resource for assessing the validation status of test methods and a source of guidance for other organisations and can conduct and assess validation status (Ref54).

Validating test methods and models requires substantial time and financial resources. Estimates for the costs of a validation study range from €200,000 to €500,000; however, this is likely an underestimation since it does not fully account for labor costs, report preparation, and expert analysis. Some estimates suggest that the costs for validating in vitro test methods can exceed €1 million, although this is presumably covering the whole process of development, optimisation and validation. Overall, the entire process—from development to regulatory approval, including validation of a test method—is a long-term effort and commitment. Some processes averages around 10 years (Ref13, Ref16, Ref17). But this can also be done much faster! Take a look at the In Practice page for examples and inspiration.

It is logical that new methods and tests must demonstrate effectiveness comparable to the methods and tests they aim to replace. However, this presents a challenge: the value of existing animal testing methods is often unclear, as they typically have not undergone proper validation. Testing is also a slow, expensive, and demanding process, which creates a barrier to evaluating these existing methods.

Additionally, there is contention surrounding the "gold standard" to which new data are compared; this standard often relies on data derived from animal testing, which frequently lacks established value (Ref19).

Many new projects are working on the new paradigm of comparing data with human biology, such as Adverse Outcome Pathways (AOPs). The framework on AOPs allows the identification of the cascade of biological events following exposure to a chemical to yield an adverse outcome in humans and in environmental species. AOPs provide the mechanistic underpinning for several in vitro methods that have been developed as OECD Test Guidelines (Ref63). Good examples are projects in the ASPIS cluster, such as ONTOX and RISKHUNT3R, as well as the VHP4safety project.

To make the validation process of NAMs more efficient, ECVAM has developed a modular approach  to define what data is required for independent validation and peer review. The various aspects of validation are broken down into seven independent modules, and the information necessary to complete each module is defined (Ref13). Briefly, the seven modules are as follows:

1. Test definition
2. Within-laboratory variability
3. Transferability
4. Between-laboratory variability
5. Predictive capacity
6. Applicability domain
7. Performance standards

See figure 1. of Hartung et al. (Ref69) for “The modular approach for applying the ECVAM principles on test validity”.

• ​The process of validating test methods, as well as determining when a test method is ready for validation, can be unclear—particularly for test developers coming from an academic background. Academic researchers often have a different perspective on what readiness means; for instance, they may focus on the scientific functionality of the test method. In contrast, toxicologists are primarily concerned with whether a method yields a positive or negative result for toxicity, while regulators look for methods that can accurately identify hazards and assess risks related to exposure (Ref12).
• ​It is essential to have clear test method protocols available. The Guidance on the Validation of Information Management Processes (GIVIMP) can assist in establishing a protocol along with a site-specific standard operating procedure (SOP). Additionally, various online platforms, such as Protocols.io, offer the opportunity to share detailed protocols freely.
• ​Staff training is vital for those working on test methods and their validation, particularly when transferring responsibilities to another laboratory (Ref15).

Involvement of regulators/stakeholders (see also step 1)

Involving stakeholders, such as regulators, early in the process can greatly assist in validating your test by providing valuable feedback. Moreover, maintaining regular communication with stakeholders throughout the process is highly recommended (Ref14).