High-throughput screening or HTS technologies include robotic liquid handling and assay detection in 96-well and 384-well plates and implementation of screens of over 100,000 small molecule, drug-like chemicals or 18,000 human siRNAs. Experienced staff is available to assist in assay development, assay validation, assay implementation, data analysis and chemical informatics.
The first step in initiating a high-throughput screen at SMSSF is to contact Dr. Gene Ananiev, the co-director for HTS, or Dr. Michael Hoffmann, the Faculty Leader of the facility, to make an appointment to discuss your goals. There is no charge for these initial discussions. In addition to a primary HTS assay, it will be important to identify secondary orthogonal assays to confirm hits and counterscreens to eliminate the inevitable false positives. We strongly encourage, but do not require, a student, postdoc or technician from the client lab to assist “hands-on” with the HTS at SMSSF.
A frequently asked question is “How much will it cost?” This depends on the specifics of the assay, availability of reagents from the client lab and the number of compounds or RNAi pools screened. Generally HTS assays cost from $0.10 to $1.00 per well, including reagents and the time of the SMSSF scientists. Every effort will be made to provide the client with a realistic estimate of costs prior to beginning a project. This is an estimate and not a contract price.
The greatest uncertainty in staff time required and therefore costs is during the initial phases of development of a client assay that is not already in a multi-well plate format and the assay validation of the statistical properties of the assay using control compounds in a multi-well plate format. Charges for time and supplies will be billed on a frequent, usually monthly, basis thereby allowing the client to decide on whether a project should be continued.
The in-house compound collection includes over 100,000 small molecules but most clients only screen a subset of the compound libraries. The number of compounds screened is a key variable in determining the overall costs of a project. Radioactive assays are currently not supported by SMSSF and substances requiring a higher containment level than BSL2 are not permitted.
A terrific resource on HTS assays is the NIH-supported Assay Guidance Manual. Signal/background ratio (S/B) and well-to-well variability (CV) are key variables in HTS. See the HTS Assay Validation Chapter in the Assay Guidance Manual for a discussion of how the statistical robustness of an HTS assay will be determined by SMSSF scientists.
Once HTS is demonstrated to be statistically robust, a small pilot screen of 100-400 compounds will be run in duplicate plates to confirm assay reproducibility and assess the hit rate. The client may then make a decision as to how many compounds to screen from the in-house collection.
At the completion of an HTS project, a detailed protocol of the assay as finally implemented will be provided to the client along with the raw screening data. SMSSF scientists are available to assist in analysis of the data and the hits. After completing a primary HTS, clients will have many screening "positives" or hits to follow-up in secondary screens. There are several different criteria for assigning hits. Subject to compound availability, SMSSF will provide clients with 1 µl of each selected screening hit (~5 µg). These are called “cherry picks”. If you require more than 1 µl of compound, SMSSF scientists will assist you in ordering it directly from a commercial source. Generally, 1-5 mg of a compound can be purchased for less than $50 from the manufacturers of commercial libraries.
In addition to secondary assays, the SMSSF and the NIH strongly support the use of chemical informatics methods to evaluate the compounds, scaffold and pharmacophores of the hits. Dr. John Feltenberger, co-director for chemistry at SMSSF, is available to assist client with the chemical informatics analysis.