New Human Liver Model Advances Drug Safety Testing with Enhanced Metabolic Capacity

A research team at Toho University in Japan has developed a novel human liver cell model with significantly enhanced activity of CYP2D6, a crucial enzyme in drug metabolism. This breakthrough promises to improve the accuracy of predicting drug-induced liver injury and reduce reliance on animal testing.

The Challenge of Drug-Induced Liver Injury

Drug-induced liver injury (DILI) remains a major obstacle in pharmaceutical development. Current methods for assessing liver toxicity, including animal models, often fail to accurately predict human responses due to species-specific differences in drug metabolism. Human-derived in vitro models offer a promising alternative, but existing models often lack the full spectrum of human liver metabolic capabilities.

HepaRG Cells and the CYP2D6 Limitation

HepaRG cells, a human hepatocyte-derived cell line, are widely used for liver toxicity assessment due to their ability to differentiate into functional hepatocyte-like cells and their high expression of Cytochrome P450 (CYP) 3A4, a key drug-metabolizing enzyme. Though, HepaRG cells naturally exhibit low CYP2D6 expression. CYP2D6 is a highly polymorphic enzyme – meaning it varies significantly between individuals – and plays a critical role in the metabolism of numerous drugs, influencing both efficacy and the risk of adverse drug reactions. ¹

Engineering CYP2D6 Enhancement

Researchers led by the late Professor Masako Tada and Associate Professor Shinpei Yamaguchi addressed this limitation by genetically engineering HepaRG cells to boost CYP2D6 expression. The team successfully created multiple transgenic cell lines with varying levels of CYP2D6 activity. ² They developed cells expressing FLAG-tagged CYP2D6 and CYP2D6 co-expressing green fluorescent protein (GFP), allowing for real-time monitoring of CYP2D6 levels.

Significant Increase in Metabolic Activity

The engineered cells demonstrated a remarkable 5- to 8,000-fold increase in CYP2D6-mediated metabolism of bufuralol, a drug used to treat hypertension. Notably, CYP2D6 expression in one cell line (CYP2D6-iGFP) reached levels comparable to those found in native human liver tissue. ¹

Improved Toxicity Prediction and Reduced Cytotoxicity

Experiments using perhexiline, a drug primarily metabolized by CYP2D6, showed a tendency towards reduced cytotoxicity in the CYP2D6-enhanced HepaRG cells. This suggests the model can more accurately predict toxicity related to individual variations in CYP2D6 activity, a challenge for traditional animal models. ¹

Maintaining Differentiation Potential

Importantly, two of the developed cell lines retained their ability to differentiate into hepatocyte-like cells expressing CYP3A4, preserving the key characteristics of the original HepaRG cells. The researchers also confirmed that the enhanced CYP2D6 expression remained stable even after differentiation. ¹

Implications for Drug Development

This CYP2D6-enhanced HepaRG cell model represents a significant advancement in in vitro drug metabolism and toxicity studies. It offers a more human-relevant platform for early-stage drug safety assessments and holds the potential to reduce the require for animal testing. The study was published in PLOS ONE on December 29, 2025. ⁴

Key Takeaways

• A new HepaRG cell line with enhanced CYP2D6 activity has been developed.
• The engineered cells exhibit CYP2D6 expression levels comparable to human liver tissue.
• The model demonstrates improved prediction of drug toxicity and reduced cytotoxicity.
• This advancement offers a promising alternative to animal testing in drug development.