Benefits, limitations, and validated utility of engineered primary human liver platforms for drug metabolism studies
| Model | Benefits | Potential Limitations | Drug Metabolism Applications (Primary Human Liver Cells) |
|---|---|---|---|
| Cellular microarrays | Can be used to evaluate the metabolism of many drugs simultaneously in a small footprint | Primarily dependent on imaging-based readouts when using cells | These arrays have so far been adapted to cancerous hepatic cell lines and application to primary liver cells is pending (Lee et al., 2005, 2008; Yu et al., 2018) |
| Low novel drug/chemical usage | Current array configurations are limited in their ability to interrogate responses of adhered cells to molecular gradients | ||
| Dual advantage with the ability to evaluate the effects of combinatorial biochemical and biophysical signals on enhancement of liver cell functions. | |||
| Conventional cocultures (random distribution) | No specialized systems/equipment is needed to create randomly distributed cocultures in standard multiwell culture plates | Function of hepatocytes is highly dependent on the choice of the nonparenchymal support cell type | Measured activities of NAT2, UGT1A1, SULT, AKR, AO, FMO, CYP1A2, CYP2B6, CYP2C9, CYP2D6, and CYP3A4 after 8 days of culture (Kratochwil et al., 2017) |
| Part of the randomly distributed cocultures can display morphologic and functional instability due to suboptimal (random) cell-cell contact/interactions | Measured activities of CYP2D6 and CYP3A4 for 14 days (Novik et al., 2017) | ||
| Typically, have lower activities of some drug metabolism enzymes than micropatterned cocultures | |||
| Micropatterned cocultures (MPCCs) | Controlled homotypic hepatocyte interactions on micropatterned protein domains allow for proper cell polarity and higher/stable liver functions in coculture with fibroblasts for 4–6 weeks | Specialized masks created using lithographic techniques are needed to pattern ECM proteins (e.g., collagen) to enable subsequent clustering of the hepatocytes | Measured activities of NAT2, UGT1A1, SULT, AKR, AO, FMO, CYP1A2, CYP2B6, CYP2C9, CYP2D6, and CYP3A4 after 8 days of culture (Kratochwil et al., 2017) |
| Available in industry standard multiwell formats (up to 384-well plates) | A single configuration containing all major liver cell types is currently lacking | Measured activities of CYP1A2, CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2E1, CYP3A4, UGT, and SULT for 30 days (Khetani and Bhatia, 2008; Lin et al., 2016) | |
| Diverse types of liver NPCs can be cultured in MPCCs without significantly affecting the homotypic interactions and polarity of hepatocytes on the micropatterned colonies | Use nonliver fibroblasts for inducing optimal functions in hepatocytes | Drug metabolite detection (Wang et al., 2010; Ballard et al., 2016) | |
| Drug clearance prediction (Chan et al., 2013; Lin et al., 2016) | |||
| DDIs including P450 induction and inhibition (Khetani and Bhatia, 2008; Lin et al., 2016; Kratochwil et al., 2018) | |||
| Transporter, metabolism, and/or P450 induction interplay on drug disposition (Ramsden et al., 2014a; Moore et al., 2016) | |||
| Self-assembled Spheroids | Many off-the-shelf plate formats are available for the creation of spheroids | Cellular necrosis can occur in the center of spheroids if their diameter exceeds 250–300 µm | Measured activities of CYP1A2, CYP2C8, CYP2C9, CYP2D6, and CYP3A4 for 35 days (Bell et al., 2016, 2018) |
| Some plate formats can cause large variations in the sizes of the spheroids, which leads to nonuniform viability and function | |||
| Single spheroids may not provide enough material for sensitive drug metabolite identification | |||
| Heterogeneous cell distribution without any defined architecture | |||
| Bioprinted spheroids/organoids | Printing head allows control over the placement of cells in different locations/compartments (e.g., hepatic, vascular, and other nonparenchymal cell compartments) | Microscale printing resolution for control of single cell placement is currently lacking | Measured activity of CYP3A4 for 28 days (Norona et al., 2016) |
| Software programming allows on-demand 3D architectures to the created with same instrumentation configuration (i.e., expensive masks are not needed as for lithographic techniques) | Low-throughput creation of the cultures | ||
| The method requires complex and often expensive instrumentation with the need for well-trained technologists | |||
| The method requires a larger number of cells than microscale patterning methods using lithography | |||
| Printed tissues on the millimeter to centimeter scale can potentially display necrosis in the core of the tissues in the absence of a connected/perfused vasculature | |||
| Perfused liver culture/coculture platforms (some are also known as liver-on-a-chip) | Enable fluid flow to allow automated nutrient and waste exchange as well as the generation of in vivo-like molecular gradients (e.g., oxygen), which can lead to zonated hepatic phenotypes | Perfusion requires specialized fluid pumps and control systems | Measured activities of CYP2D6 and CYP3A4 for 6 days of culture (Novik et al., 2010) |
| Many microfluidic perfusion devices are now commercially available for the creation of perfused liver cultures | Drugs can potentially bind and be sequestered by the tubing and materials used in the perfusion devices | Measured activities of CYP2C9, CYP3A4, and UGT for 14 days (Vernetti et al., 2016) | |
| Due to the need for tubing, perfusion devices have a large dead volume, which can necessitate higher quantities of the novel (and often very limited) compounds for treating cell cultures | Drug clearance prediction (Dash et al., 2009; Novik et al., 2010) | ||
| Most devices are currently low-throughput, allowing up to 12 devices to be perfused at a single time | Drug metabolite identification (Sarkar et al., 2017) |
AKR, aldo-keto reductase; FMO, flavin monooxygenase; NAT2, N-acetyltransferase 2; SULT, sulfotransferase; UGT1A1, UDP glucuronosyltransferase 1A1.