The last decade has seen a year on year increase in the production and testing of new biologically active compounds against a rapidly growing portfolio of potential therapeutic targets. This elevated research and development activity has arisen as a direct result of the completion of the human genome-sequencing project accompanied with advances in chemical synthesis and drug design.

(Read also the second part of this story: Micro Array Study)

To reduce costs the pharmaceutical industry is attempting to improve efficiency by investing in automated technologies that utilise more physiologically relevant cell based models. An example of such a technological approach is the newly emerging High content imaging technologies. High Content Imaging technologies are becoming increasingly used within drug discovery as they permit a rapid and robust means of identification and validation of therapeutic as well as providing a means of assessing the efficacy and/or toxicity of drug candidates. Despite the obvious advantages this technology offers, the reagent costs associated with cell based screening can be prohibitive.

With the advent of micron resolution robotics and nano litre capable liquid handlers, large scale and automated assay miniaturization is now possible. The advantages of miniaturization are clear, when one considers the savings in reagents and experimental materials. However miniaturization of cell based assays can be technically difficult and costly to deploy.

Miniaturization in Cell Based Screening
The growing trend toward biological assay miniaturization has been driven by the need to reduced costs and has been facilitated by scientific and technological progress in automation and detection instrumentation. The best contemporary example of biological assay miniaturization is the DNA microarray [1] and protein microarrays [2]. These analytical tools provide a fast and inexpensive means of gathering highly detailed information on gene expression or protein interaction at the cell or tissue level.

Cell-based assays are commonly performed in micro-titre plates which are now available in a multitude of well densities ranging from 96- 1536 wells/plate (with working reagent volumes from 5 to 100 μl per well depending on the plate format).

Although micro-titre plates are ubiquitously used in cell biology labs, the experimental costs of performing large scale experiments using these technologies even in the high density formats can be prohibitive. As such, many are now turning to cellular micro array technologies as an alternative to the more costly conventional micro plate technologies.

The use of cellular microarrays were first described by Ziauddin and Sabatini [3], who preprinted defined spots of plasmid and transfection reagent onto a glass slide before seeding with cells. It was demonstrated that seeded cells subsequently attached to the array substrate and absorbed the DNA and expressed the genes contained within the plasmid. The position of the spots and the in-situ transfected cells were identified by spatial correlation. Since then, the same principle has been shown to successfully work for RNA interference assays and drug discovery
screens [4; 5].

High Content and Analysis Technologies
Since its inception in the mid 1990's, High Content Screening and analysis (HCS/A) technologies have become ever increasingly adopted within the fields of drug discovery and cell biology. One of the most attractive features of this technology is that it provides contextual information at the level of the intact cell or tissue and permits the quick, straight forward and reproducible measurement of the morphological and structural properties cells and organelles [6; 7]

High Content and Screening and Analysis (HCSA) technologies represent the convergence of several mature laboratory analysis technologies, namely fluorescent light microscopy coupled with the automation and ease of use of a plate reader and the ability to analyze cellular subpopulations functionality associated with flow cytometry. The key feature of this technology is the ability to perform highly detailed analysis on cellular images acquired by these platforms.

This combined functionality hence enables for the first time the study of the functional characteristics of genes and proteins in the context of the whole cell (A definition of the discipline cellomics).

The High Content Screening Process

The High Content Screening process can be divided into 5 discrete steps, 1. Assay preparation; 2. Image acquisition; 3. Image analysis; 4. Data storage and retrieval; 5. Data analysis and visualization. In this review we will focus on steps 1 to 3.

1. Assay Preparation
Involves setting up the cell based assay for the screen, this step is often preceded by an assay development step where the assay is optimized and assessed for use within the High Content Screen.