Image-based screening: a technology in transition.

Image-based screening (IBS) has proven itself with whole-well assays in which throughput and assay miniaturization are priorities. Recent interest, however, has centered upon the use of automated imaging technology to conduct assays at subcellular resolution. These in vitro assays have the potential to increase lead quality at early stages in drug discovery. Subcellular IBS is not yet mature and, although some assays provide reliable data at reasonable throughput, many others have yet to demonstrate robust application. Developments in image acquisition, analysis and informatics technologies are ongoing and are expected to broaden the usefulness of subcellular IBS.

Automated screening of neurite outgrowth.

Outgrowth of neurites in culture is used for assessing neurotrophic activity. Neurite measurements have been performed very slowly using manual methods or more efficiently with interactive image analysis systems. In contrast, medium-throughput and noninteractive image analysis of neurite screens has not been well described. The authors report the performance of an automated image acquisition and analysis system (IN Cell Analyzer 1000) in the neurite assay. Neuro-2a (N2a) cells were plated in 96-well plates and were exposed to 6 conditions of retinoic acid. Immunofluorescence labeling of the cytoskeleton was used to detect neurites and cell bodies. Acquisition of the images was automatic. The image set was then analyzed by both manual tracing and automated algorithms. On 5 relevant parameters (number of neurites, neurite length, total cell area, number of cells, neurite length per cell), the authors did not observe a difference between the automated analysis and the manual analysis done by tracing. These data suggest that the automated system addresses the same biology as human scorers and with the same measurement precision for treatment effects. However, throughput of the automated system is orders of magnitude higher than with manual methods.

Image-based screening of signal transduction assays.

Imaging techniques have played a vital role in signal transduction research over several decades. Recently, industrialized macro- and micro-imaging systems have found application in drug discovery laboratories, where they increase the throughput and efficiency of drug screening. Macro-imagers are used for primary screening, where they favor compound conservation (through assay miniaturization), and achieve unprecedented rates of throughput. Micro-imaging systems achieve relatively high throughput, at the same time providing sub-cellular resolution with fixed or living cells. These micro-imaging analyses were previously conducted at very low throughput and, typically, were the sole domain of the academic researcher. Although both macro and micro forms of image-based screening remain technologies in development, they have already made substantial contributions to screening programs and will continue to do so.