Screening
When High Content Screening meets High Throughput
The terms ‘High Content Imaging’ (HCI) and ‘High Throughput Screening’ (HTS) were introduced more than a decade ago1 and are defining the use of automated microscopy and automated image analysis in the context of drug discovery. Considered historically as two very separate disciplines with very few crossovers, this paper discusses whether you can ever do high-content imaging assays in high throughput.
E
ver since the technology has evolved signif- icantly to enable not only medium through- put assays for target identification or sec- ondary screens, but also higher throughput assays compatible with primary hit identification using large compound libraries2,3. With the clear bene- fits of performing phenotypic cellular assays gener- ating biologically relevant and multi-parametric data sets, the technology has established itself as a powerful tool for drug discovery. This evolution was partly made possible by the hardware improvements of the automated microscopes (eg auto-focus, plate/sample positioning enabling the use of high density formats) as well as the enhance- ment of the image analysis software enabling fast data extraction saving both time and costs in the screening process. In addition, innovations in the automation of plate preparation enabling the per- formance of non-homogenous assays in 1536-well plates (eg high density plate washers) were of great benefit for the establishment of the HCS technolo- gy for large scale screening campaigns. This article describes how we perform HCS with high through- put at the Lead Finding Platform of the Novartis Institutes of Biomedical Research (NIBR) explain- ing the benefits and challenges we are facing in pri- mary hit finding. Until recently, HCI and HTS have been con- sidered as two separate worlds sharing only
Drug Discovery World Winter 2011/12
some borders. HCI is enabling multiplexed assays providing cellular or sub-cellular resolu- tion and generating multivariate data sets. These assays can deliver different insights of the com- pounds’ mode of action as well as their putative unspecific effects (eg toxicity). Due to their com- plexity, the HCI assays were often limited in throughput and were generally used to screen focused libraries or to perform secondary or counter screens. Homog-enous fully automated HTS assays are enabling fast data acquisition compatible with the screening of large com- pound collections. These assays generally deliver uni-variate data (eg cAMP accumulation, Ca++ release, protein production) and their resolution is limited to the well level4. High-throughput HCI assays are resulting from a combination of both worlds enabling fully automated primary screening of large compound collections with high resolution in multiplexed mode. To validate the use of imaging technology versus conven- tional assays, the variability and sensitivity of an imaging assay has been compared to a reporter gene assay (RGA) for the screening of inhibitors for PI3K – Akt – Foxo3A pathway5. Both assay formats were equally reproducible, with the HCS assay having a better statistical quality. In addition, the HCS assay was more sensitive than the RGA although no additional chemical scaf-
By Dr Vincent Unterreiner and Dr Daniela Gabriel
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