General information: High Throughput Screening
Pharmaceutical Companies have decided that high
throughput screening is to be the modus operandi for drug discovery.
The plan is fairly simple: screen a large number of small molecule
compounds for interaction with the target system. The hope is
to find at least one (called a “hit”) that has the
desired effect on the target system: protein, gene, pathway, process,
organism, etc. The pharmaceutical industry’s intent is to
find a chemical that can be developed into a drug. The drug development
process, however, requires a heavy investment of resources: capital
The benefit to academic researchers:
Academic researchers are not in the business of developing drugs, nor do they possess the resources to do so. Nonetheless, academic researchers are in the business of finding useful probes for their systems of interest. Regardless of whether these probes can be developed into marketable drugs, the researcher finds them valuable because they disclose information about the system of interest. In the search for useful probes an academic researcher can benefit from some of the technology and resources that are available to colleagues in industry. There are at least 3 aspects of the early stages of the drug discovery process (the part called “high throughput screening”) which could be beneficial to an academic researcher:
1. High throughput screening
The MSSR has automated equipment and data collection that make it possible to test about 30,000 compounds (or more) on a system of interest in about a day. Material and media usage are minimized by conducting the experiments in microplates and by using instruments that can read from about 30 uL of material per well. Scanning time is typically about 2 minutes per plate.
Of course, it’s not quite that simple. Assays normally need to be converted to high throughput mode. This involves not only scaling down amounts but also testing with appropriate controls to ensure that the assay is robust enough for high throughput screening. MSSR personnel are available for consultation in this process. The MSSR also possesses liquid handling devices which can automate tedious steps of pipetting.
Unfortunately, not all types of assay are amenable to high throughput mode. In general, fluorescence and luminescence based assays are easily adapted. In addition, ELISA’s and colorimetric assays typically present no problem for adaptation. It is important to keep in mind, however, that this adapted assay is just a screen. There are any number of artifacts and interferences that could arise. Therefore (again following the lead of the pharmaceutical industry), it is imperative to follow up on any “hit” before claiming any interaction between it and your system of interest. Follow up normally takes the form of a secondary, non high throughput assay, of a different type than the high throughput screen. For example, if fluorescence were used in high throughput mode, a secondary assay should not employ this mode of detection. Otherwise, any artifacts that existed in the primary screen are likely to carry over into the secondary assay. Appropriate controls are necessary.
2. Chemical Libraries:
The larger the compound collection, the greater one’s chances of finding a hit. Currently, the MSSR has over 75,000 chemicals and plans to expand even further! Generally, one wants not only a lot of chemicals, but also many different types of chemicals. Besides the more familiar classes of chemicals, for example, steroids, peptidomimetics and carbohydrates, a chemical librarian is concerned with chemical space.
Axes for chemical space are defined by parameters of interest, for example hydrophobicity, partition coefficients, aromaticity, or hydrogen bonding capability might be used. Chemicals are then located in “space” according to these parameters. One’s chances of finding a hit improve with libraries that cover a lot of space. The libraries available at the MSSR are diverse; they cover quite a bit of chemical space.
The wealth of information contained in a database pretty much speaks for itself. The Molecular Screening Shared Resource will maintain a database of all assays run and the results of these assays. In this way chemicals will become fairly well characterized, and assay artifacts should become apparent. One should be able to discern non-specific ligands with a fair degree of certainty. Information in the database might also help a researcher to discern mode of interaction or possible target (if unknown). By cross referencing and collaborating with researchers who employed related assays, additional information may be gained. In short, for any one application or user, there is usually quite a bit of useful information contained in such a database.