Xiaoxia Li - Executive Technical Director, WuXi AppTec
Reliance on animal testing for drug development has long been a subject of ethical scrutiny and scientific debate. While the age-old practice contributes much to medical advancement, it raises legitimate concerns about animal welfare and the precision of toxicological assessments. But the toxicological landscape is evolving. The industry is witnessing a concerted push towards more humane and accurate methods in the form of in vitro testing.
Participants in 2023’s annual American College of Toxicology (ACT) meeting saw firsthand the industry’s growing interest in alternative toxicity evaluation methods. At the first in-person ACT meeting since the onset of COVID-19, much was made of the pandemic’s impact on drug development, particularly the challenges with using non-human primates (NHPs). The discussions at ACT revolved around the scientific tenets of the 3Rs—refinement, reduction, and replacement—and may mark a new chapter in the pursuit of ethical toxicology.
The excitement around in vitro assays signals a broader recognition of the need to transcend traditional methods for more ethical, reliable, and scientifically robust alternatives. However, these methods today are neither perfect nor fully operational.
The U.S. Food & Drug Administration (FDA) and the European Medical Device Regulation (MDR) have documented limitations with in vitro test methods, specifically in providing direct quantitative predictions of human disease risk. These agencies recognize that in vitro methods are valuable for generating qualitative and quantitative data, but they cannot be relied upon as the sole method to accurately predict human risk.
The following discussion explores the most exciting developments in new in vitro toxicological assays and the benefits and challenges of the approach. It also delves into the profound implications these assays hold for the future of drug development and responsible safety assessment.
Areas of Greatest Promise for In Vitro Toxicological Assays
If in vitro assays were to become a cornerstone of early-stage research, it would represent a major shift in toxicological methods and practices. These assays would likely demonstrate their greatest value in drug development’s exploratory and discovery stages.
During initial drug screening, where evaluating potential compounds is critical, these assays are starting to help minimize animal use and reduce development costs. In pharmaceutical research, combining in vitro assays and in silico predictions is becoming indispensable, efficiently screening numerous compounds and flagging potential safety concerns without immediately resorting to animal testing. This approach mirrors the principle of refinement in the 3Rs, ensuring that animals are used only when necessary.
The role of in vitro assays extends to regulatory toxicology as well. Animal studies are still mainstream in this area, but there is a growing acceptance and requirement for in vitro methods. These assays can be integrated with in vivo data to form a comprehensive assessment package for regulatory submissions. A prime example is the Ames test, a widely used in vitro assay crucial for genotoxicity assessments. This assay and others have become staples in the regulatory toolbox.
In more specific applications, in vitro assays that assess cardiovascular toxicity and genotoxicity have become very influential. For example, larger animals are typically used for cardiovascular risks due to their closer resemblance to human cardiovascular responses. However, in vitro assays that evaluate sodium channel effects are integral to preliminary assessments and are often mandated by regulatory bodies like the FDA and the European Medicines Agency (EMA). This approach allows for a more targeted and humane investigation of potential toxic effects before involving in vivo test models.
Moreover, in vitro assays are critical in investigative and post-market scenarios. When unexpected toxicity arises in clinical trials, these assays become the framework for mechanistic studies, helping to understand phenomena that weren’t apparent during preclinical in vivo testing. This adaptability underscores the versatility of in vitro assays in responding to unexpected challenges.
Put simply, the rise of in vitro toxicological assays heralds a new era in the field—one where ethical considerations and scientific rigor redefine the standards of harm. This move reflects changing norms and is a testament to the scientific community’s resilience and adaptability in the face of unprecedented challenges. The clearest advantages to using in vitro toxicological assays include:
- Reducing animal use. A primary goal of the 3Rs principle, “reduction” addresses ethical concerns and contributes to scientific advancement by evolving industry research.
- The potential for cost savings in conducting toxicological studies. In vitro methods do not require the significant resources needed to maintain and care for animals round-the-clock in research settings.
- Less time and personnel than what’s needed for in vivo studies. Reducing labor includes saving time and resources to train staff on evolving technologies and keep certifications current.
Such advancements promise more humane, efficient, and potentially more accurate toxicity testing methods, significantly altering the research landscape.
Addressing Nonclinical Toxicology’s Universal Challenge
Toxicology is a rapidly evolving field with immense potential for technological advancements to revolutionize current practices. The most universal challenge in nonclinical toxicology is the translational gap between laboratory findings and their application to human safety. This gap is particularly pronounced in in vitro assays, where differences in species’ responses to various compounds can create discrepancies in toxicity prediction.
Today, in vivo studies are more predictive than in vitro ones, but even these studies cannot guarantee accurate predictions for human responses due to the inherent variability among humans. Individual characteristics like age, genetics, family history, and lifestyle can lead to vastly different reactions to the same drug or compound.
In addition, the influence of human factors in the laboratory setting cannot be ignored. The conditions under which an in vitro assay is set up, the handling procedures, and the interpretation of results all involve human factors that can affect extrapolation. These factors underscore the importance of standardizing processes and creating accurate protocols to mitigate the risks of misinterpretation.
Despite advancements in toxicological testing, translating in vivo or in vitro test results to human trials remains complex and sometimes unpredictable. Surprises and unexpected outcomes during clinical trials can be stark reminders of the limitations of current testing methods and the need for continuous improvement and caution in the field.
Toxicologists across the industry remain cautiously optimistic for the future despite some of the challenges outlined above. Advanced technologies promise to enhance the accuracy of in vitro assays and potentially bridge some of these gaps.
Integrating In vitro Assays with Emerging Technology and Regulators’ Response
The evolving nature of technology in toxicology exemplifies the principle of refinement in scientific research. Integrating computerized methods, including 3D human tissues or cultured cells combined with computerized predictions, could improve data accuracy and drive better outcomes. While these advancements could someday replace current methods and better protect human safety, that day is still far into the future.
Another emerging technology, so-called “organ-on-a-chip” (or “OoC”), is also a promising option for early-stage exploratory research. These micro-engineered devices mimic the structure and functionality of human physiology in vitro, helping translate in vivo and in vitro data. However, OoCs cannot be used for regulatory toxicology due to stringent requirements for assay reliability. Although promising, this technology is also not yet ready to become a mainstream tool for toxicological assessment.
The future of toxicology is one in which advanced technologies refine current methods and potentially replace them. However, this future depends on these technologies’ ability to produce consistent and accurate results that can effectively predict human responses. This is the only way to responsibly integrate technology into drug development and introduce safer and more humane practices.
The regulatory response
Regulators’ responses to the burgeoning field of alternative toxicological methods, particularly in vitro and in silico approaches, have been topics of significant interest and importance. Regulators are actively discussing these trends at conferences like ACT and across the broader scientific community. One thing that’s clear, however, is that regulatory agencies are willing to discuss alternative approaches as long as they promise more efficient, accurate, and humane approaches to toxicological testing.
Drug developers and sponsors must recognize that integrating these new methods into regulatory frameworks will not happen overnight. It will likely take several years before these methods are fully embraced and integrated into regulatory standards. This timeline reflects the careful consideration and validation processes needed to ensure that new methods meet stringent requirements for safety and efficacy. However, the growing popularity of these methods and regulatory bodies’ increasing openness to them are promising signs of progress.
A Final Word On The State of In vitro Assays and New Technology
The dynamic and often-changing world of nonclinical toxicology is at a pivotal moment. Ethics, science, and technology are converging and reshaping drug development and safety assessment. The advent of in vitro toxicological assays represents a new era that is not just about alternative methods but also a fundamental rethinking of toxicological research.
A deepening commitment to the principles of the 3Rs is driving this evolution. These are not just ethical mandates; they represent a scientific embrace of humane, efficient, and potentially more accurate toxicity testing methods. The excitement around these advancements is real—but so are their challenges. Reduced animal use, cost savings, and decreased labor requirements are noble and measurable outcomes, but the translational gap between laboratory findings and human applications remains a significant hurdle.
Looking ahead, advanced technologies like computer-driven predictions and OoC devices could one day replace some traditional methods. But this future is contingent upon these technologies’ ability to deliver consistent and accurate results that reliably predict human responses. The regulatory response to these changes is equally crucial. The willingness of regulatory agencies to consider and discuss alternative approaches is a positive sign, and integrating these new methods into regulatory frameworks is a journey that will take time. This approach reflects a balance between innovation and safety, between what’s new and what’s tried and true.
The road toward more humane, efficient, and accurate toxicity testing methods may be long; there will inevitably be challenges along the way. But the possibilities this innovation brings are too great to ignore.
Author Biography
Joining WuXi AppTec with more than 15 years of preclinical drug development experience, Dr. Xiaoxia Li provides scientific support to WuXi AppTec's clients and will enhance the quick response rate for technical questions. She began her career at a preclinical contract research organization (CRO), BOZO (Biology and Zoology) in Tokyo, and then spent more than 13 years working as a Study Director at ITR Laboratories in Montreal, Canada. Afterward, she worked as a Scientific Leader in nonclinical development for a pharmaceutical company in Toronto, Canada, before starting her own consulting firm, Sunrise IDD Inc. Dr. Xiaoxia Li is a Diplomate of the American Board of Toxicology (DABT). She completed her PhD in Pharmacology in Japan and received her MD and MSc in China.
Publication Detail
This article appeared in American Pharmaceutical Review:Vol. 27, No. 1Jan/FebPages: 26-28
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