Advanced In Vitro Models for Replacement of Animal Experiments

Abstract

In the last decade there has been an exponential increase in the scientific focus given towards enhancing the physiological relevance of in vitro systems and expanding their applications to support the movement towards replacing, reducing, and refining (3Rs) the use of in vivo experimentation. Beyond socio-economic considerations towards public stakeholders, this has also had a substantial impact upon ongoing changes in regulation surrounding the application of animal testing strategies. Despite the continuing advancements within the field there remains a constant need to develop, enhance and implement in vitro model systems in order to: (i) deduce their potential to reduce and potentially replace animal experimentation, as well as (ii) progress their implementation and acceptance by regulatory and legislative stakeholders. The intention of this special issue was to bring together a wealth of expertise and knowledge regarding the plethora of ongoing research activities regarding in vitro model systems, specifically providing current insight into the advances made and to discuss the issues being encountered. Introducing the topic area there are two essays that discuss the problems and challenges of animal experiments (10.1002/smll.202004182), and then how these problems can be counteracted by new in vitro methodologies (10.1002/smll.202006298). The paper of Burden and colleagues is further supported and expanded upon by reviews authored by both Bas et al. (10.1002/smll.202006027) that highlights the specific requirements for the development of standardised in vitro approaches for validation purposes; as well as Halappanavar and colleagues (10.1002/smll.202007628) that highlights non-animal strategies for toxicology testing, particularly engineered nanomaterials, focussing upon adverse outcome pathways. The specific use of in vitro models of the liver for nanomaterial genotoxicology testing (10.1002/smll.202006055), and the cardiovascular system to assess myocardial infarction (10.1002/smll.202003765) are then introduced. While Fritsche and colleagues highlight the potential application of models based on embryonic stem cells and induced pluripotent stem cells of human origin within next level in vitro toxicology assessments (10.1002/smll.202006252). Building upon these expansive reviews of different in vitro tools available and how they can be used to support efficacy and safety testing, 11 original articles then highlight the multitude of ongoing activities with in vitro systems. With the comparisons continually made towards in vivo data sets, and its relevance towards regulatory acceptance of in vitro approaches, Ma-Hock and colleagues (10.1002/smll.202005725) focus upon the necessary dose setting for in vitro studies based upon previous in vivo studies relevant to engineered nanomaterial lung burden. Further to this, studies demonstrating the advantages offered by advanced in vitro and in silico models for nanosafety assessment are highlighted by Kampfer and colleagues (10.1002/smll.202004223), Burgum et al. (10.1002/smll.202002551), Chiou and colleagues (10.1002/smll.202001432), as well as Jagiello et al. (10.1002/smll.202003465), utilising a range of approaches from (geno)toxicity testing to microscopic evaluation and predictive modelling based on quantitative structure-activity relationship models for nanomaterials (Nano-QSAR). In terms of advancing systems towards re-creating the physiological and anatomical human structures in vitro, the work of Poventud-Fuentes and colleagues (10.1002/smll.202004889), Kohl and colleagues (10.1002/smll.202006012), as well as Lee and colleagues (10.1002/smll.202004258) expand upon organ-on-a-chip technologies and microfluidic devices. Tang et al. (10.1002/smll.202006050) discusses the possibility of 3D bioprinting in vitro glioblastoma models, and Suhito et al. (10.1002/smll.202002436) applies the use of spheroid cultures to create a nanostructured platform that facilitates the electrochemical detection of cellular changes in cancer cells. These papers further highlight the expansive possibilities associated with in vitro technologies. The final original article published in this special issue takes another direction with Hsu and colleagues (10.1002/smll.202006091) reporting the effects of the oxygen microenvironment and matrix composition on the 3D endothelial cell network formation, providing a further example of how to alter variables within in vitro systems to more closely mimic human physiology. Recreating the physiological nature of the human body is further discussed in the concept article by Llewellyn and colleagues (10.1002/smll.202004630) whereby they simulate acellular lung and gut micro-environments to assess the impact of nanomaterial transformation in such biological compartments, upon toxicological outcomes in advanced in vitro models of the gastro-intestinal tract and liver. This special issue therefore highlights the qualities that in vitro systems can provide in terms of understanding mechanisms of toxicology, or interactions of xenobiotics with specific cellular structures of a tissue/organ. It further progresses towards introducing the current state of the art in terms of advanced in vitro technologies (e.g. microfluidics, organ-on-a-chip, bioprinting and re-creation of physiological components). With the expansive introductions at the beginning of the special issue, setting the scene for ‘alternative models’ and advanced in vitro systems, this collection of papers provides a fantastic basis for both people being introduced to the field, but also the experienced in vitro scientist.

Topics & Concepts