The evolving role of investigative toxicology in the pharmaceutical industry

Abstract

For decades, preclinical toxicology was essentially a descriptive discipline in which treatment-related effects were carefully reported and used as a basis to calculate safety margins for drug candidates. In recent years, however, technological advances have increasingly enabled researchers to gain insights into toxicity mechanisms, supporting greater understanding of species relevance and translatability to humans, prediction of safety events, mitigation of side effects and development of safety biomarkers. Consequently, investigative (or mechanistic) toxicology has been gaining momentum and is now a key capability in the pharmaceutical industry. Here, we provide an overview of the current status of the field using case studies and discuss the potential impact of ongoing technological developments, based on a survey of investigative toxicologists from 14 European-based medium-sized to large pharmaceutical companies.

Fig. 1. Key goals of investigative toxicology in drug discovery and development.

The figure shows a roadmap of investigational toxicology activities that can be applied at each stage of the pipeline. In the earlier stages, these activities typically involve computational assessments to support target selection and batteries of routine in vitro molecular and cellular assays to support lead identification and optimization. These assays evaluate broad characteristics such as cytotoxicity, mitochondrial and genetic toxicity, as well as effects on specific cell types such as hepatocytes and cardiomyocytes to evaluate the risk of toxicity to particular organs. At later stages of the process, regular in vivo toxicology studies that support progression into clinical development may be complemented by bespoke project/target-organ-specific assays — for example, with more advanced cellular models (microphysiological systems (MPS) and multicellular assays) — to address the human relevance of preclinical in vivo findings and gain mechanistic insights (for example, on off-target effects). It is important to stress that approaches may vary significantly between companies based on internal drivers, priorities, resources and history. The focus of the figure is on approaches for small molecules, with selected activities specific for other modalities shown below. It is currently unclear whether the roadmap of toxicology activities for small molecules adequately covers the safety evaluation needs for targeted protein degraders such as proteolysis-targeting chimeras (PROTACS). There are several PROTAC-specific attributes that must be considered, including off‐target degradation, intracellular accumulation of the natural substrates for the E3 ligases used in the ubiquitin–proteasome system and proteasome saturation by ubiquitylated proteins^–. PK, pharmacokinetic.

Fig. 2. Assessment of the ‘game-changing potential’ of novel assays and technologies in investigative toxicology.

We assessed the perceived immediate, mid-term (<2-year) and longer-term (<5-year) benefit from the routine application of various emerging technologies and assays through surveys of pharmaceutical company experts in 2015 and 2020 (Box 1 and Supplementary information). a, Summary of current technologies or methods that offer a step change in investigational toxicology; impact according to consensus and time frame identified by experts from Europe-headquartered pharmaceutical companies (n = 14) responding to the question “Which new technologies do you foresee may become game-changers for investigational toxicology?” in 2020. Variations in perceptions across the respondents potentially reflect current practices and usage within their organizations. b, Evolution among the respondents of the impact perception for each technology or method from 2015 to 2020. The positive perception of some technologies such as organs-on-chips, genomic profiling and high-content imaging increased, while the perception of others barely changed or the time frame for impact was adjusted (systems toxicology and induced pluripotent stem cells (iPSCs)). Other technologies have clearly lost ground, with the ‘no potential game-changer’ category becoming more prominent (metabolomics, microRNAs (miRNAs) and mass spectrometry imaging). qPCR, quantitative PCR; RNA-seq, RNA sequencing.

Fig. 3. In vitro models of target-organ toxicity.

The figure summarizes the status of in vitro test systems that are amenable across key target organs. Key characteristics of each organ and its model options are summarized. Boxes are coloured according to the currently perceived confidence in safety translation among the survey participants. This empirical assessment is based on published data, considering the ability of the model to emulate key organ phenotypes (and stability for extended periods of culture) and toxicology validation data. More details on in vitro cell culture assays for each organ system with associated references are available in Supplementary Table 1. CNS, central nervous system; CYP, cytochrome P450; GI, gastrointestinal; iPSC, induced pluripotent stem cell; iPSC-CM, iPSC-derived cardiomyocytes; MEA, microelectrode array; MPS, microphysiological systems.