Cell Culture
High-throughput spheroid culture
The cost of drug development is becoming unsustainable, partly due to the high attrition rate of drugs in clinical trials. The predominant reasons for drug failure are lack of efficacy, poor pharmacokinetics and adverse toxic side-effects not identified during preclinical studies. These challenges of optimising drug discovery mandate a need for improved preclinical models – specifically those that better recapitulate the pathophysiology of the underlying disease, as well as more accurately predict in vivo responses to therapeutic compounds.
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wo-dimensional (2D) cell culture models are frequently used in drug discovery due to their ease of use and established com- patibility with high-throughput screening automa- tion and detection instrumentation. While 2D cell cultures are widely used in drug research, it is clear that they exhibit different structural and functional properties than observed in the body. Therefore, three-dimensional (3D) spheroid cell culture mod- els that closely mimic in vivo conditions are gain- ing acceptance, thus bridging the gap between in vitro studies and predictive activity in the clinic. Cellular spheroids are 3D models generated from many cell types; spheroids form because of the ten- dency of adherent cells to aggregate. Common examples of spheroids include embryoid bodies, mammospheres, tumour spheroids, hepatospheres and neurospheres. Furthermore, adherent cells nat- urally aggregate and form spheroids, particularly under circumstances that impede adhesion to cell culture substrates. Common matrix-free methods employed for generating spheroids include the use of attachment-resistant cell culture surfaces or by maintaining the cells as suspension cultures in media (eg hanging drop technology, rotary cultures
Drug Discovery World Winter 2017/18
and bioreactors). Several cell types also form spheroids when grown in hydrogels and, to a lesser extent, in solid scaffolds, depending on the struc- tural and physical properties of the material. Taken together by recapitulating cell-cell interac- tions, metabolic gradients and cell polarity observed in vivo, 3D multicellular spheroids pro- vide more physiologically-relevant models com- pared to two dimensional (2D) cell culture. For this reason, the use of 3D technologies, already established in basic research, is now gaining accep- tance in drug discovery.
Spheroids mimic various aspects of solid tissues and possess inherent gradients for optimal diffu- sion of oxygen and glucose, for example, as well as the removal of metabolic wastes. These cellular aggregates can emulate avascular, solid tumour behaviour more effectively than standard 2D envi- ronments because spheroids, much like tumours, contain a heterogeneous population. These can comprise surface-exposed and deeply-buried cells, proliferating and non-proliferating cells, as well as highly-oxygenated and hypoxic cells. Spheroids thus represent good physiological 3D models for studying solid tumorigenesis. In terms
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By Hilary Sherman, Dr Richard M. Eglen and Audrey Bergeron
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