In recent years, the landscape of drug safety testing has undergone a profound transformation, marked by the rapid acceleration of New Approach Methodologies (NAMs). While this shift might appear sudden, driven by landmark regulatory changes like the FDA Modernization Act 2.0 in 2022, its true origins trace back over a decade of scientific innovation, collaborative efforts, and strategic regulatory groundwork. This evolution has culminated in a new era where human-relevant, mechanism-based assays, particularly in cardiac safety, are not merely alternatives but indispensable tools for predicting human outcomes and de-risking drug development.
The Genesis of a Paradigm Shift: Addressing the Limitations of Traditional Models
For decades, drug development relied heavily on traditional animal models for preclinical safety assessment. While these methods provided foundational insights, they often struggled to accurately predict human responses, leading to high rates of late-stage drug attrition due to unforeseen safety liabilities. Cardiac toxicity, in particular, represented a formidable challenge, with drugs occasionally reaching advanced clinical trials or even market, only to be withdrawn due to life-threatening cardiotoxic effects like drug-induced arrhythmias, most notably torsades de pointes (TdP). The inherent physiological differences between animal species and humans frequently obscured critical safety signals or produced misleading ones, costing pharmaceutical companies billions of dollars and delaying the availability of potentially life-saving therapies.
This growing recognition of predictive limitations, coupled with increasing ethical concerns regarding animal testing, spurred a concerted global effort to develop more reliable, human-relevant alternatives. Initiatives launched in the early to mid-2010s, such as the U.S. Environmental Protection Agency’s (EPA) ToxCast program and the multi-agency Tox21 collaboration (involving EPA, NIH, FDA, and NCATS), were pivotal. These programs aimed to revolutionize toxicology testing by employing high-throughput screening technologies to evaluate thousands of chemicals and compounds for potential hazards using in vitro assays. Their foundational principle was clear: human-relevant, mechanism-based assays, when appropriately applied, could equal or even surpass the predictive power of traditional animal models.
Cardiac Safety: A Model for NAM Maturity
Among the various areas of drug safety, cardiac assessment emerged as a critical proving ground for NAMs. The challenge of predicting drug-induced proarrhythmia, specifically QT interval prolongation and the risk of TdP, was particularly acute. The traditional gold standard, the hERG (human Ether-à-go-go-Related Gene) assay, while effective at identifying potential cardiac liabilities, often suffered from a high false-positive rate, unnecessarily halting the development of promising compounds. Moreover, in vivo animal QT studies, designed to complement hERG data, faced the species-difference hurdle, making direct extrapolation to human risk problematic.
This pressing need for improved cardiac safety assessment led to the formation of the Comprehensive in vitro Proarrhythmia Assay (CiPA) initiative in 2013. CiPA was a groundbreaking collaboration involving international regulatory agencies (e.g., FDA, EMA, Health Canada, PMDA), industry consortia (e.g., HESI, SPS), and academic experts. Its ambitious goal was to develop a new paradigm for evaluating proarrhythmic risk, integrating multiple in vitro assays, in silico modeling, and, crucially, assays utilizing human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs).
The Scientific Leap: hiPSC-CMs and Microelectrode Array (MEA) Technology
The advent of induced pluripotent stem cell (iPSC) technology, which allows for the reprogramming of adult somatic cells into stem cells that can then differentiate into various cell types, including cardiomyocytes, was a game-changer. These hiPSC-CMs provided a virtually unlimited supply of human heart cells that exhibit key electrophysiological properties relevant to cardiac function and drug response. This offered an unprecedented opportunity to study drug effects directly on human cardiac tissue in vitro, circumventing the limitations of animal models and primary human cells, which are scarce and difficult to culture long-term.
To effectively harness the potential of hiPSC-CMs, advanced detection technologies were required. Microelectrode Array (MEA) technology, such as the Maestro MEA system from Axion BioSystems, proved to be instrumental. MEA platforms enable continuous, noninvasive monitoring of the spontaneous electrical activity of cultured hiPSC-CMs. By measuring field potentials (analogous to action potentials), MEAs can detect changes in heart rate, beat duration, and the presence of arrhythmias, providing functional data that are both physiologically relevant and operationally practical for high-throughput screening in pharmaceutical and contract research organizations (CROs).
The CiPA initiative undertook extensive multicenter validation studies using hiPSC-CM MEA assays. These rigorous studies demonstrated that these assays could reliably detect delayed repolarization and arrhythmia-like events associated with TdP risk, across a wide range of compounds with known clinical outcomes. These findings were instrumental in establishing the credibility and predictive power of functional hiPSC-CM assays, showing that mechanistic, human-relevant data could significantly improve proarrhythmia risk prediction compared to isolated hERG assays or animal studies alone.
Regulatory Milestones and Growing Confidence
Despite the scientific advancements, the adoption of NAMs remained cautious for several years. Pharmaceutical companies often utilized these methods internally for lead optimization and candidate selection but hesitated to rely on them for formal regulatory submissions. This hesitancy stemmed from the lack of clear regulatory pathways and explicit guidance on what constituted "fit-for-purpose" evidence.
This began to change with the development of formal regulatory engagement mechanisms. The FDA’s Innovative Science and Technology Approaches for New Drugs (ISTAND) Pilot Program, launched in 2019, created a crucial framework for dialogue. ISTAND allows technology developers and drug sponsors to engage with the FDA early in the development process to qualify novel methodologies, providing a clear path for their acceptance in regulatory submissions.
A significant regulatory milestone reflecting this progress occurred recently with the acceptance of a letter of intent from Axion BioSystems for its human iPSC-derived cardiomyocyte MEA assay into the FDA’s ISTAND program. This acceptance is not an isolated event but the culmination of years of sustained investment across industry, academia, and regulatory bodies in functional electrophysiology and regulatory science. It signifies growing confidence in the ability of functional assays to directly measure human cardiac electrophysiology in vitro for drug safety decision-making.
Further solidifying this shift, the insights gleaned from the CiPA validation studies directly informed the International Council for Harmonisation (ICH) E14/S7B Questions & Answers (Q&A) document, finalized in 2022. This updated guidance officially recognized hiPSC-CM data as supportive evidence for proarrhythmic risk assessment, a pivotal moment that cemented the role of these NAMs in global regulatory frameworks. This wasn’t just a recommendation; it was an acknowledgment that the scientific, technical, and regulatory groundwork had been thoroughly established.
The FDA Modernization Act 2.0: A Legal Endorsement, Not a Sudden Mandate
The signing of the FDA Modernization Act 2.0 into law in December 2022 was widely celebrated as a turning point for NAMs. By removing the statutory requirement for animal testing in drug development and explicitly allowing non-animal methods, the legislation appeared to signal a sudden regulatory embrace of alternative approaches. However, as industry experts like Mike Clements, SVP Scientific Partnerships & Strategy at Axion BioSystems, emphasize, this legislative change was more of a legal formalization of an existing scientific and regulatory trajectory rather than an overnight shift. It provided the legal clarity and encouragement necessary for broader adoption, building on the decade of research, validation, and regulatory engagement that preceded it.
The impact of these developments is already visible. A 2025 study authored by FDA scientists found a significant increase in Investigational New Drug (IND) applications submitted with iPSC-CM data over the past decade. Notably, between 2020 and 2023, the number of submissions including hiPSC-CM MEA assays doubled compared to the total number submitted prior to 2020, reflecting the accelerating adoption of these approaches in drug development programs. This voluntary inclusion of data, despite it not being a mandatory requirement for IND submissions, underscores the perceived value and utility of these assays by drug sponsors. More than 16 contract research organizations now offer CiPA-style hiPSC-CM assays as a standard service, often utilizing platforms like the Maestro Pro MEA system, indicating robust industry infrastructure and expertise.
Further reinforcing the predictive power of these assays, a new paper, currently under review, has demonstrated strong concordance between hiPSC-CM data and clinical QT outcomes. Crucially, this study showed higher predictive performance than commonly used methods such as hERG assays, multi-ion channel approaches, and traditional animal QT studies. The findings suggest that using hiPSC-CM data in combination with other in vitro assays significantly reduces nonclinical QT false negatives and provides predictive value comparable to multiple animal studies, opening the potential to replace additional animal studies entirely. This represents a monumental step forward, promising to reduce reliance on animal testing, accelerate drug development timelines, and ultimately bring safer drugs to patients faster.
Ensuring Consistency and Future-Proofing NAMs
As functional NAMs transition from validation into broader regulatory use, the next critical challenge is ensuring consistency across different laboratories and studies. Variability in model performance, assay protocols, and data interpretation could quickly erode the confidence built over years of validation. To address this, initiatives like the Axion iPSC Model Standards (AIMS) have emerged. This collaborative effort, involving leaders in the safety field, aims to define meaningful functional standards for hiPSC-CM assays. The goal is to establish benchmarks for baseline electrophysiological performance, acceptable variability, and expected responses to reference compounds. Such standardization is crucial for enabling NAMs to scale responsibly and to underpin future regulatory frameworks, ensuring reliability and reproducibility.
This managed transition for safety organizations presents both a significant opportunity and a responsibility. The opportunity lies in adopting tools that provide earlier, more human-relevant insights into cardiac risk, thereby de-risking drug candidates much earlier in the development pipeline. The responsibility involves implementing these advanced methodologies without introducing added uncertainty into already complex decision processes. The real risk today, as many experts argue, is relying on outdated approaches that haven’t kept pace with our evolving understanding of human cardiac biology and the predictive power of human-relevant in vitro models.
The journey of functional NAMs in cardiac safety, from the early recognition of animal model limitations to the sophisticated hiPSC-CM MEA assays now accepted by regulators, is a testament to the power of scientific collaboration and regulatory foresight. Efforts spanning CiPA validation studies, IND data inclusion, the ISTAND program, and the AIMS initiative collectively illustrate how cardiac safety has become a blueprint for NAM maturity. This model, built on strong science, proactive regulatory engagement, and a shared commitment to human-relevant physiology and robust standardization, promises to reshape drug safety assessment for decades to come, extending beyond cardiac safety to other organ systems and ultimately fostering the development of safer, more effective medicines for patients worldwide.
Mike Clements, PhD is the SVP Scientific Partnerships & Strategy at Axion BioSystems. There, he focuses on initiatives advancing the use of human stem cell-derived models in drug discovery and toxicology. He earned his PhD in neuropharmacology from the University of Oxford, with postdoctoral training in the UK and the US. In 2014, Clements published the first study using the Maestro multielectrode array (MEA) system with stem cell-derived cardiomyocytes. This research demonstrated their potential as predictive tools for preclinical cardiac safety screening, which would later help inform the Comprehensive in vitro Proarrhythmia Assay (CiPA) initiative. He was also the editor of Stem Cell-Derived Models in Toxicology, a resource that reviewed next-generation in vitro toxicology platforms. Clements previously served as president of the stem cells specialty section of the Society of Toxicology.
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