Genomics
Live cell imaging will help cell biologists over- come one of the main challenges they have faced: fluorescence microscopy has largely been per- formed in fixed tissue samples and scientists have had to draw conclusions about what drives cell behaviour based on these findings. Other advances in imaging technology, such as electron microscopy, have given researchers a more detailed view of the cell, and each of these offers its own advantages and limitations. Electron microscopy, for example, provides a snapshot of the cell at one point in time and not a dynamic view. No single tool can provide all the answers a cell biologist needs, but together the range of imaging technolo- gies and techniques available offers a window into the cellular world.
Because advanced cellular imaging technologies such as super-resolution microscopy can give researchers the ability to follow a sequence of events over time under changing conditions, they make it possible to take advantage of innovative label-free technologies to observe cell activity without disruptive interventions, and to experi- ment with nanoparticle-based approaches to probe the intracellular space without disturbing normal cellular function. Advances enabling nanoscale cellular imaging are making it possible to leverage emerging innovations in the field of nanotechnology and apply them to explore high- speed, molecular-scale events. For example, researchers can mimic or inhibit interactions that may impact the integrity or activity of subcellular complexes or organelles. Latest super-resolution imaging systems can fol- low labelled proteins within a living cell over time in three-dimensional (3D) space at near molecular resolution. This allows researchers to observe and measure biological activity in live cells growing in a monolayer on a glass slide or cultured in multi- cellular 3D constructs that more closely imitate human tissues. The images obtained may reveal the translocation of a tagged protein (eg, indica- tive of G-protein coupled receptor signalling across a cell membrane) or the opening and clos- ing of an ion channel. They may capture the time- lapse sequence of protein-protein, receptor-ligand or pathogen-host interactions, for example; depict the precise morphologic and structural changes that take place in a cell in preparation for cell divi- sion, apoptosis, or metastasis; reveal the changes underlying stem cell differentiation or pathogenic transformation such as tumorigenesis; or expose the dynamics of engineered nanoparticles in intra- and intercellular environments.
The potential for high resolution live cell imag- 20
ing to accelerate the discovery and characterisation of new drug targets, drug classes and therapeutic compounds is enormous. Consider, for example, if it were possible to study the dynamic movement of individual protein components of microtubules, which are part of the skeleton-like network that maintains cell structure and play an essential role in chromosome alignment during cell division. A drug discovery campaign aimed at identifying com- pounds capable of disrupting a cancer cell’s ability to replicate by targeting its microtubule assembly could benefit greatly from this information. Looking ahead, the ability to screen and compare compounds in a high throughput assay format by evaluating their ability to inhibit the function of these proteins, thereby disrupting microtubule for- mation, would yield direct information on the mechanism of action of the compounds. It would no longer be necessary to rely solely on binding assays, on surrogate markers of drug activity, or merely on assumptions.
Not only would there be visual evidence of a compound’s mode of action and interaction with the designated target, but the effects of subsequent lead optimisation efforts could also be chronicled through a visual record. Furthermore, all measure- ments, data and analyses derived from cellular imaging and mined from data stores could be linked to the images from which they were derived, creating a reliable and easily accessible audit trail and resource for comparative or historical studies. Data of interest would link directly to the relevant stored image. Similarly, the development of new classes of antibacterial or antiviral drugs would benefit from high-resolution imaging data in live cells that could reveal in greater detail than was pre- viously possible how a pathogen infects a host cell, replicates, or causes cell death. The ability to pinpoint a specific area of vulnerability in a microbe or a key step in the process of infectivi- ty or replication could lead to more effective antimicrobial strategies. Furthermore, identify- ing drug targets that are highly conserved across microbial species offers the potential for broader therapeutic efficacy.
The power of super-resolution imaging – real-world examples To illustrate the potential benefits of high-speed, super resolution and high resolution microscopy, below are summarised two published examples of how the technique has been used to gain a clearer understanding of cellular mechanisms. The first study shows how an immune cell can distinguish
Drug Discovery World Spring 2013
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