Drug Discovery


Scientists need to pay significant attention to cell Figure 2


enhanced cellular models mirroring in vivo systems. For instance, in vitro cell-based assays help in repro- ducing the complexity of biological environment and are generally predictive of how a compound behaves in vivo. Immortalised cell lines, primary cell cultures and, more recently, human pluripotent stem cells (hPSCs) have shown to be invaluable phenotyp- ic models for basic research and drug discovery efforts. Immortalised cell lines, such as CHO-K1 and


HEK-293, are still very popular in several labora- tories. The fact that they proliferate indefinitely and are easy to maintain in culture at low cost makes them very convenient, namely for executing HTS campaigns. However, immortalised cell lines have a very limited biological relevance, especially when they are used to overexpress exogeneous pro- teins. That is why a growing number of cell biolo- gists rely on primary cells since they closely resem- ble the function of the organ or tissue they com- pose. Primary cells require limited handling or manipulation to preserve their original characteris- tics and functions which somehow limits their use at large scale. Stem cells, namely inducible pluripo- tent stem cells (iPSCs), have found their way in fundamental and applied research. They can be used at all stages of the drug discovery workflow: from target identification to ADMET studies. Since stem cells are capable of unlimited self-renewal, they represent reliable sources of physiologically relevant cells upon controlled differentiation. These two properties make stem cells very suitable alternatives to recombinant/immortalised cell lines and primary cells. However, a more general use of stem cells is hampered by challenges related to directed differentiation and associated cost of maintenance13.


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culture conditions since they can drastically alter cel- lular phenotype and biological functions. Whereas cells are traditionally grown and used either in sus- pension or as adherent monolayer monocultures, cells sometimes need to be co-cultured with other cell types found in their natural environment to bet- ter adapt and react with biological relevance. This is namely the case of neurons co-cultured with either astrocytes or microglial cells14. Furthermore, numerous reports show that cells differ in structure and function when used in suspension or as adher- ent forms. Similar observations were reported with cells grown on 2D surface-coated support compared to 3D scaffolds. It is worth noting the strong interest in growing cells in 3D since such cultures, namely co-cultures, spheroids and organoids, are closer to in vivo natural systems providing more biologically relevant information than single cell populations15. Organoids are specialised 3D cell cultures, derived from pluripotent stem cells such as hPSCs or other progenitors, generated to replicate functions of a specific organ. The possibility to obtain any cell type composing the human body through hPSCs together with the potential of generating patient-specific tis- sues using human-induced pluripotent stem cells (hiPSCs), allows for significant breakthroughs in personalised medicine16. Recently-reported 3D matrix and cell printing capabilities should facilitate the latter efforts in a foreseeable future17.


Label-free technologies for unbiased assay development and biomarker quantitation Most assay technologies commonly used to charac- terise molecular mechanism of action (MOA) of drugs rely on labelled biosensors derived from endogenous molecules known to interact with bio- logical target(s) of interest. Labels used to modify


those biosensors include either radiometric (eg 125I, 35S) or non-radiometric markers such as fluors. Labelling biomolecules is always at risk of modifying their biochemical properties and phar- macological profiles that could lead to biased anal- yses. Label-free platforms were developed to allevi- ate the molecular biases inherent to using labelled reporter molecules so one could produce more rel- evant information. Two of the most popular label-free technologies


used to date rely on either optical biosensors based on the detection of dynamic mass redistribution (DMR) or impedance biosensors relying on cellular dielectric spectroscopy (CDS). Both techniques can measure changes of live cell morphology in real time18. Since the modulation of signal transduction pathways affects cell morphology, DMR and CDS


Drug Discovery World Fall 2018


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