Hepatic Spheroids for Long-Term Toxicity Studies

Characterization of a long-term mouse primary liver 3D tissue model recapitulating innate-immune responses and drug-induced liver toxicity

Three-dimensional liver in vitro systems have recently attracted a lot of attention in drug development. These systems help to gain unprecedented insights into drug-induced liver injury (DILI), as they more closely reproduce liver biology, and as drug effects can be studied in isolated and controllable microenvironments. Many groups established human-based in vitro models but so far neglected the animal equivalent, although the availability of both models would be desirable. Animal in vitro models enable back- and forward translation of in vitro and in vivo findings, bridge the gap between rodent in vivo and human in vitro scenarios, and ultimately support the interpretation of data generated with preclinical species and humans. Since mice are often used in drug development and physiologically relevant in vitro systems are lacking, we established, for the first time, a mouse liver model that encompasses primary parenchymal and non-parenchymal cells with preserved viability and functionality over three weeks. Using our three-dimensional liver spheroids, we were able to predict the toxicity of known DILI compounds, demonstrated the interaction cascades between the different cell types and showed evidence of drug-induced steatosis and cholestasis. In summary, our mouse liver spheroids represent a valuable in vitro model that can be applied to study DILI findings, reported from mouse studies, and offers the potential to detect immune-mediated drug-induced liver toxicity.

Engineering HepG2 spheroids with injectable fiber fragments as predictable models for drug metabolism and tumor infiltration

In vitro cell and tissue models are playing essential roles in the identification of active pharmaceutical ingredients. Though HepG2 cells have attractive profiles over primary hepatocytes in the availability and viability retention, the expression of metabolizing enzymes is quite low. In the current study, three-dimensional (3D) HepG2 spheroids with smaller sizes of 150 μm (3Ds) and bigger sizes of 300 μm (3Db) are engineered using injectable fiber fragments as the substrate. In contrast to two-dimensional (2D) culture, the enzyme activities for drug metabolisms are restored in 3Ds and the pathophysiological profiles of tumor tissues are rebuilt in 3Db spheroids. Compared with spheroid culture without fiber fragments, 3Ds spheroids show higher activities of metabolizing enzymes (CYP3A4, CYP2A9, and phase II) and higher sensitivities to enzyme inducers (rifampicin and glutathione) and inhibitors (ketoconazole and probenecid). The drug clearance and toxicity to 3Ds spheroids predict better the clinical observations and drug-drug interactions. In addition, compared to scaffold-free spheroid culture, stronger expressions of E-cadherin and hypoxia-inducible factor-1α (HIF-1α) and higher fibronectin secretions are determined in 3Db spheroids, displaying apparent hypoxic and apoptotic regions similar to those found in solid tumors. In contrast to the overestimated drug toxicity in other systems, the infiltrations of free drug and drug-loaded micelles are apparently restricted in 3Db spheroids, exhibiting drug resistance just like in tumor tissues. Thus, this study demonstrates HepG2 spheroids with different sizes as predictable and physiologically relevant models for high-throughput screening of drug metabolism and tumor infiltration.

Amino acid levels determine metabolism and CYP450 function of hepatocytes and hepatoma cell lines

Predicting drug-induced liver injury in a preclinical setting remains challenging, as cultured primary human hepatocytes (PHHs), pluripotent stem cell-derived hepatocyte-like cells (HLCs), and hepatoma cells exhibit poor drug biotransformation capacity. We here demonstrate that hepatic functionality depends more on cellular metabolism and extracellular nutrients than on developmental regulators. Specifically, we demonstrate that increasing extracellular amino acids beyond the nutritional need of HLCs and HepG2 cells induces glucose independence, mitochondrial function, and the acquisition of a transcriptional profile that is closer to PHHs. Moreover, we show that these high levels of amino acids are sufficient to drive HLC and HepG2 drug biotransformation and liver-toxin sensitivity to levels similar to those in PHHs. In conclusion, we provide data indicating that extracellular nutrient levels represent a major determinant of cellular maturity and can be utilized to guide stem cell differentiation to the hepatic lineage.

An Automated Multiplexed Hepatotoxicity and CYP Induction Assay Using HepaRG Cells in 2D and 3D

Drug-induced liver injury (DILI) and drug-drug interactions (DDIs) are concerns when developing safe and efficacious compounds. We have developed an automated multiplex assay to detect hepatotoxicity (i.e., ATP depletion) and metabolism (i.e., cytochrome P450 1A [CYP1A] and cytochrome P450 3A4 [CYP3A4] enzyme activity) in two-dimensional (2D) and three-dimensional (3D) cell cultures. HepaRG cells were cultured in our proprietary micromold plates and produced spheroids. HepaRG cells, in 2D or 3D, expressed liver-specific proteins throughout the culture period, although 3D cultures consistently exhibited higher albumin secretion and CYP1A/CYP3A4 enzyme activity than 2D cultures. Once the spheroid hepatic quality was assessed, 2D and 3D HepaRGs were challenged to a panel of DILI- and CYP-inducing compounds for 7 days. The 3D HepaRG model had a 70% sensitivity to liver toxins at 7 days, while the 2D model had a 60% sensitivity. In both the 2D and 3D HepaRG models, 83% of compounds were predicted to be CYP inducers after 7 days of compound exposure. Combined, our results demonstrate that an automated multiplexed liver spheroid system is a promising cell-based method to evaluate DILI and DDI for early-stage drug discovery.