HIGH THROUGHPUT SCREENING FOR NEW DRUGS

In terms of medical discovery the cost represented to a drug developing pharmaceutical company is immense; hundreds of millions of dollars can be spent in developing a new medical treatment for molecular identification to final registration after clinical trials. The “magic number” introduced in 2003 by a group of economists was $802 000 000 per new drug reaching final approval [1;2]. This number has been challenged [3] but still it represents the huge financial commitment pharmaceutical companies have to make. If the drug makes it through to phase III clinical trials or even registration it can still fail due to a variety of reasons (mostly safety) and have to be withdrawn, the biggest examples of this are Vioxx (2007, Merck&co) and Thalidamide (1957, Chemie Grunenthal). The total costs to these two companies for these drugs have never been documented but it has been estimated as to be in billions.

What is High Throughput Screening

This being the case the development of a new medicine has certain fixed costs associated with it. In an effort to reduce the costs and maximize the number of new molecules in development, procedures have been established in all areas in bringing a drug to market. One of these areas is the first screening of molecules for pharmaceutical activity. For the process a methodology referred to as “High Throughput Screening (HTS screening)” utilizes advanced technology to screen, assess and weed out new molecules for pharmaceutical activity [4]. To put it into perspective HTS investigations should be able to average 20 000 compounds per week. To achieve this output various techniques used; combinatorial chemistry, peptide & protein libraries and genomics. A reference search on a reference database for high throughput screening will give approximately 10 000 responses, indicating the significance of these techniques. The are many high throughput screening reviews available for the discerning research to assist in developing individual codes of practice but technology never sleeps and now methodologies are being introduced continuously.

Techniques of High Throughput Screening:

High throughput screening system of analysis begins with the first pass HTS assays which compared to traditional biological assays are far less quantitative but qualitative in their nature. The first pass assay is usually performed only once or at most twice and at one single concentration (ranging between 1-10 µM). For positives found a second screening using the positive plus any structurally related molecules is performed more accurately and several more times to generate IC50 and quantitative information. Assays used for this process are binding assays, reporter assays, SRB / MTT and ELISA assays. New techniques that can be added to this are the chip based screening assays (such kinase screening) and genomic screening [5]. To aid in this process robotic systems are available with either 96, 384 or 1056 well plate technology. Since the volumes involved are in the µl range the cost savings on drug use and cell culture is significant despite the initial out lay for the equipment being used. A high throughput screen can be divided into two subcategories, the heterogeneous and homogeneous assays. A heterogeneous is one in which the test sample is processed using assays steps beyond dilution and incubation into areas including filtration, centrifugation and washing steps. Ideal homogeneous assays simply involve the pipetting, incubating and reading of a sample, however most industrial assays are heterogeneous assays. In addition to the typical adapted biological assays new technology is beginning to introduce the researcher to “chip” base assays and to combinatorial chemical strategies. Combinatorial assays involve the use of large libraries of compound building blocks (>10 000) via this approached huge numbers of molecules can be screened rapidly. Another type of assay being developed are the chip base assays. Typically these are focused on the enzymes and proteins in cellular materials such as kinases which when treated with a molecule will demonstrate up regulation or down regulation of a particular enzyme or protein activity [6-10]. Chip technology has also been applied to high throughput genomics [11;12] and high throughput sequencing [13] assessing the genetic impact of new molecules. The commercial throughput screening market is a growing industry and now even includes virtual high throughput screening [14;15] where computational knowledge of the protein structure can be used to design a molecule which will inhibit.

Data management in High Throughput screening:

High throughput screens have major flaw, they geranate so much data it can be impossible for the individual researcher to comprehend the full concept of what is being represented. To assist the researcher in this arena are software designed to assess, calculate, summarize and report results for the high throughput screening assays

References

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14.   Gong LL, Fang LH et al. Integration of virtual screening with high-throughput screening for the identification of novel Rho-kinase I inhibitors. J Biotechnol 2010; 145(3):295-303.

15.   Lee HS, Choi J et al. Optimization of high throughput virtual screening by combining shape-matching and docking methods. J Chem Inf Model 2008; 48(3):489-497.