Advanced cell imaging: looking at the whole picture
Keeping up with the candidates!
Today’s culture is often: “We want things done quickly; we want things done efficiently; and we want everything done at once!” This is especially true in areas like drug discovery – but with the added pressure of devising treatments for a myriad of diseases… so no pressure there then! In light of this, drug discovery has made heavy use of high throughput screening (HTS) to screen drugs against individual targets of disease. However this is shifting to phenotypic screening methods during preclinical stages to identify physiologically relevant and non-toxic drugs in a whole cell environment at an earlier (and cheaper) stage.
Phenotypic screening can be a massive time and resource intensive procedure, so you need to grab every chance you get at optimising the process. Technologically, most high content screening systems simply cannot provide imaging data at the required throughputs for true HTS and, even if higher throughputs can be achieved, they result in a data mountain headache. To work around this, imaging departments focus on screening library subsets, which are much smaller than their entire company compound library. But screening subsets comes with an inherent compromise. The difficulty is that slight differences can substantially change a drug’s behaviour in a cell – thalidomide being one example – so you may miss the hit you are looking for. This compromise is widely accepted when screening biochemical libraries to see what binds to a target, as reliable historical compound data exists to narrow down the likely candidates. However the same is not true of a candidate’s behaviour against the cell phenotype.
From a screener’s perspective, the quality of hits is paramount, and the challenges – such as cost of cells and reagents, workflows and technological capability – have to be arranged to give the optimal process. As a company, TTP Labtech has collaborated with cell biologists since 1997 – something that enabled us to spot a market opportunity early on: a need for a screening system that was as fast as a bulk reader but gave the high content data expected from an imaging system. We had already been talking to pharma companies that were early adopters of HTS, and people like this were quickly realising that their kit wasn’t up to the job.
Taking a different perspective on screening
Always fond of a challenge, our passionate team of experts worked with researchers to understand their particular cell-based assays and the data they were trying to capture. From there we set out to engineer a device capable of facilitating faster and more informative data capture and analysis. Instead of a microscope-based imaging approach, we utilised the properties of cytometric systems using laser excitation and photomultiplier tube (PMT) detection. With a lot of technological and engineering effort, the laser scanning imaging cytometer, acumen® was born in 2001. It can scan whole wells very fast and has a wide depth of field to cope with 3D structures. Even recently, imagers have only just achieved whole well scanning and they have to carefully stitch images together to do it, while 3D structures require Z-stacking of images.
Crucially, the acumen is capable of combining the speed necessary to screen an entire compound deck with the robust high content data required when profiling cell phenotypes. acumen’s speed, whole well scanning plus simultaneous data capture and analysis enable it to scan 1536-well plates in the same fast time as 96-well plates. Along with lower cell counts and miniaturised reagent needs, this makes full compound deck screens possible. The intelligent design of acumen means that researchers are afforded the flexibility to perform rapid screens and generate hit lists for detailed follow up analysis, exporting open source, whole well TIFF files if needed. These distinct yet integrated workflows allow for a high degree of adaptability for various applications.
A better reflection of nature
acumen is already being used in many labs for high throughput phenotypic screening, and also aiding work into the identification of anti-cancer drugs through 3D culture models. The need for more accurate in vitro tumor models has led to the development of 3D cell culture models, including multicellular tumor spheroids, which retain many of the morphological and genetic traits of tumors. Traditional imaging systems come up short when tasked with analyzing 3D structures in a high throughput environment, because of the need to combine multiple images into a Z-stack to gain data. acumen is all over it! Its F-theta lens has the depth of field so that the whole object can be imaged in a single scan without any need for z-stacking.
In addition to being able to handle spheroids (or even whole animals like C. elegans!), acumen can help to overcome of the practical difficulties of bringing phenotypic screening into a truly high throughput screening environment.
Interested in phenotypic screening? Why not check out our new e-book ‘Phenotypic Screening: A new dimension’ – put together in collaboration with Genetic Engineering and Biotechnology News.