Imaging
A more complete picture of cellular processes As well as offering a better understanding of cell behaviour and function, live-cell imaging offers drug discovery several other advantages over the traditional endpoint approach. This includes the ability to study dynamic cellular processes, behaviour and function from both spatial and tem- poral perspectives to get an enhanced picture of the pharmacological or molecular effect on the cell. Additionally, as live-cell imaging allows cellular structures to be studied in their native environ- ment, it is less prone to experimental artefacts. This means the technique typically provides more reliable and statistically-relevant information than fixed-cell microscopy. Live-cell imaging can also reduce workload and
streamline laboratory operations: “Live-cell imag- ing allows both controls and treated samples to be placed in the same plate, with the same sample fol- lowed over an extended period. This can dramati- cally reduce the experimental set-up time and com- plexity, as well as the number of samples required compared to endpoint experiments,” comments Joffry Maltha, CEO, CytoSMART Technologies BV. “On top of that, live-cell imaging typically doesn’t require the calibration or normalisation that endpoint assays need, which can save a lot of pre-experiment preparation time.” Live-cell imaging is already facilitating a wide
range of drug discovery applications, including early target discovery and validation, information- al screens, secondary cell-based assays and ADME- Tox (Absorption, Distribution, Metabolism, Excretion and Toxicity) studies for prioritising pri- mary hits. Prominent examples where live-cell assays have been particularly valuable include the assessment of fast signalling responses, and exper- iments where multiple cell types interact to affect the disease model, such as in complex cellular models such as organoids and immune cell killing assays, which require both spatial and temporal insight.
Overcoming the challenges of live-cell imaging To harness the power of live-cell imaging and the many benefits it offers drug discovery research, it is vital to overcome the challenges that commonly arise throughout the workflow, from image acqui- sition to analysis. One major issue is to sufficiently mimic the in vivo environment and avoid disrupt- ing the cells throughout the entire duration of the experiment, which can last days, weeks or even months.
Drug Discovery World Fall 2019
“Controlling environmental parameters, such as
temperature, humidity and CO2 is critical for reducing the variability between observations and
guaranteeing the relevance of the results in live-cell imaging assays,” notes Karin Boettcher, Associate Product Manager for High-Content Screening and Applications, PerkinElmer. “The use of an onstage incubator can help manage the environmental con- ditions to keep the cells alive and functioning nor- mally for extended periods.” As cells often move during a time-lapse exper-
iment, it is beneficial for live-cell imaging sys- tems to be capable of keeping the cells of interest within the image. Furthermore, because there tends to be inhomogeneous growth and response of biological wells in culture plates, modern live- cell imaging systems must be able to take a full scan of the entire plate to produce statistically- relevant data. There are further issues associated with data
storage and processing power. Time-lapse imaging at high resolution and high magnification gener- ates large numbers of images, particularly when data is collected over extended time periods, such as for long-term cultures like 3D spheroids. This means that modern live-cell imaging systems need enough data storage for potentially hundreds of thousands of large images, as well as a high levels of processing power for image stitching and run- ning image analysis software. “It’s also crucial to minimise photobleaching
and phototoxicity caused by the fluorescent illumi- nation in live-cell imaging, especially in the UV range, says Chris Shumate, CEO, Etaluma. “Repetitive exposure to illumination and excita- tion sources can bleach the fluorescent labels and create reactive oxygen species that cause cell dam- age. Often, this effect isn’t recognised until an extended time lapse has been performed.”
Commercially-available live-cell imaging products Many commercially-available products overcome the challenges associated with live-cell imaging. Here we provide a summary of some of the key products available on the market:
CytoSMART™ – imaging with cloud-based storage and analysis The CytoSMART™ Lux2 is a cell-culture monitor that operates at low-voltage and can be safely used
in any regular CO2 incubator. The system can run for extended periods (days or weeks) and will image cells in a wide range of cell-culture vessels, including slides, petri dishes, T-flasks and
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