The interdependence between screening methods and screening libraries

The most common methods for discovery of chemical compounds capable of manipulating biological function involves some form of screening. The success of such screens is highly dependent on the chemical materials - commonly referred to as libraries - that are assayed. Classic methods for the design of screening libraries have depended on knowledge of target structure and relevant pharmacophores for target focus, and on simple count-based measures to assess other properties. The recent proliferation of two novel screening paradigms, structure-based screening and high-content screening, prompts a profound rethink about the ideal composition of small-molecule screening libraries. We suggest that currently utilized libraries are not optimal for addressing new targets by high-throughput screening, or complex phenotypes by high-content screening.     

Cervical cancer screening, screening errors and reporting

Screening for cervical carcinoma by cervicovaginal cytology has led to a marked reduction in the incidence of and mortality from this tumor over the last 50 years in essentially all countries with a functioning screening program. It is the most successful cancer prevention program of all times. Consequently, approximately 80% of the current incidence of and mortality from this disease occurs in geographic areas of underserved and underscreened women. Essential components of a successful program are a high coverage rate of the female population, screening at regular intervals, well-trained clinical and laboratory staff, and an efficient follow-up and treatment system. Deficiencies in any of these areas may lead to a failing screening system. Thus, the most important reason for the remaining mortality from cervical carcinoma in developed countries is lack of complete coverage. It is questionable if new and more expensive technologies will be able to renmedy the remaining failures of the system if no improvement in the coverage rate is achieved. Screening errors do occur but represent only a small fraction of screening failures. Currently, there are a number of terminology systems around the world; thus, a unified terminology is currently not a realistic goal.     

Dual screening

We discuss the problem of screening a general population for characteristics such as HIV or drug use. Our main approach is Bayesian, which allows for the incorporation of prior information about parameters. In the particular problem we consider, there is currently no information in the data for estimating the sensitivity of the screening test, and consequently, the prevalence of the characteristic among screened negatives cannot be estimated from the collected data alone. Our inferences are straightforward to obtain using Gibbs sampling techniques, and they are valid for large or small samples and for arbitrary prevalence or accuracy of screening tests. We also develop the maximum-likelihood approach using the EM algorithm.     

Practical approaches to efficient screening: information-rich screening protocol

The past approach of high-throughput screening of everything in the corporate collection has been shown to be very expensive in terms of reagents cost, disposal cost, and compound collection depletion. It is well known that screening campaigns produce several hits, of which only 50% confirm on average. More efficient ways of screening can provide an informative structure-activity relationship (SAR), which in turn can be used to build mathematical models for further probing the activity space and directing chemical synthesis. The authors report new methods and insights to extract the maximum possible information from a screening experiment and find most of the possible hits in the corporate collection while screening as few compounds as possible.     

Cardiac screening procedures

Seven per cent of a sample group of civil service employees were found to have diagnosable heart disease. The diagnosis was made on the basis of a complete physical examination and history taken by a specialist in internal medicine and/or heart disease. In addition a questionnaire form related to symptoms of heart disease was filled out by the patient, and various laboratory tests were made. As a technique in cardiac case-finding, the electrocardiogram was the best single device. Of all the cases of heart disease in this survey 65 per cent were detected from tracings obtained by using all 12 leads, and 57 per cent if only the three standard limb leads were taken; but of the presumably normal persons, 13 per cent would be erroneously suspected of possible heart disease by this technique. Heart disease was detected in 50 per cent of the diagnosed cases on the basis of answers to three of the questions in the questionnaire. Eighteen per cent of normal persons would also have been suspected of having heart disease by this case-finding device. Although the survey reported did not develop a simple cardiac case-finding technique, the data presented indicated that a questionnaire history-form, if judiciously used and evaluated, may be of value to physicians who examine large numbers of patients who are unwilling to submit to a complete cardiac evaluation.     

Anal screening cytology

This issue of CytoJournal contains an article on screening for anal intraepithelial neoplasia in high-risk male patients. This accompanying Editorial focuses on current understanding of this relatively new disease entity, with insights as to the potential role of screening cytopathology in the epidemiology, pathophysiology and clinical management of this HIV and HPV related anal lesion, which predominates in male patients living long-term with AIDS. Mention is made of techniques of obtaining samples, methods of preparation, and morphologic classification. Issues of anoscopic confirmation, as well as topical and surgical management are emphasized. The similarity of initial experiences in anal screening to problems encountered early in cervical cancer screening programs several decades ago, are highlighted.     

High-content siRNA screening

Very recent developments in instrumentation and image analysis have made microscopy applicable to high-throughput screening (HTS). For 'High-Content Screening' modern automated microscopy systems provide a throughput of up to 100,000 (confocal) images, with amazingly high resolution, of cells fluorescently stained using multiple colours that are imaged simultaneously during the screen. Image analysis tools provide multi-parametric pattern extraction and quantification on-the-fly. Big pharmaceutical companies have presented image-based screens of more than 100,000 compounds, while academia has published data on large RNA interference screens for functional genomics. Numerous whole-genome sequencing projects have been completed and published. Gene annotation is still in flux. Nevertheless, about 23,000 human genes have been reliably annotated. Additionally, gene expression array technologies and proteomics have added further data on molecules present in cells and tissues. The major challenge of the present and future is to unravel the detailed function of all these gene products and their interaction. One way to gain insight, is to design oligonucleotides that induce lack-of-function phenotypes by specifically inhibiting protein production.     

Image-based chemical screening

Technological advances have made it feasible to conduct high-throughput small-molecule screens based on visual phenotypes of individual cells, using automated imaging and analysis. These screens are rapidly moving from being small, proof-of-principle tests to robust and widespread screens of hundreds of thousands of compounds. Automated imaging screens maximize the information obtained in an initial screen and improve the ability to select high-quality leads. In this Perspective, I highlight the key steps necessary for conducting a high-throughput image-based chemical compound screen.