Counter-screen

Screen/Counter-Screen Early Assessment of Selectivity... 

Screen/Counter-Screen Early Assessment of Selectivity (a) -Antagonist (b)... 

Today, large-scale counter screening can be technically handled using parallel screening systems. However, these methods are quite expensive and so, especially for academic groups and small companies, parallel VS for novel drug candidates can be a cost-effective alternative to identify new lead structures with good selectivity profiles. 

Several additional projects evolved from the initial TNAP project. Thanks to the broad dynamic range of the luminescent assay, several TNAP activator scaffolds were observed during HTS, resulting in an independent project with a potential therapeutic indication for osteomalacia and osteoporosis. Other human APs, intestinal (lAP) and placental (PLAP) isozymes, were initially utilized to establish counter screen assays based on CDP-star. One of the TNAP scaffolds demonstrated inhibition of lAP, and was further optimized to produce a selective chemical probe for human lAP. Later, the assays for lAP and PLAP were utilized for full-scale screening of these isozymes, eventually leading to identification of selective inhibitors for both isozymes. Interestingly, human lAP... 

Single Point Confirmation, DRCs, Counter Screens, ... 

Logistics, automation and data handling systems will have to be adapted to support the new paradigm, which necessitates follow-up such as orthogonal screens, counter screens and other iterative interrogations of a primary hitlist. HTS systems have to be designed to support experimentation, such that one addresses... 

Target-specific counter-screens (identified through TSA) Acceptable profiles... 

Hypothesis-driven investigation FoUow up to TSA assessment of possible on-target risks and develop customized counter-screens Follow up to observed toxicities during in vivo studies to determine drivers (on-target versus off-target) and characterize translation risk and monitoring... 

Figure 17.1 A schematic depicts the flowchart of chemical genetics screening approach. A primary cell-based assay that captures pathways or phenotypic readouts is established and validated to screen a compound library. Owing to the frequent off-target effects of primary screen compounds, it is essential to implement counter screens and secondary screens to filter nonspecific hits to arrive at a group of high-confidence hit compounds. In silica methods for scaffold hopping and compound similarity searching can be utilized to select groups of similar molecules to generate SAR data to better understand the relevant war...

Figure 20.3 Schematic representation of (a) an AlphaScreen assay and (b) the counter screen for the identification of false positive hits. See text for details.

In the plot, there are regions in which only a few values or only values with > operator (not plotted) can be found (e.g., around assay ID 5850). We are not able to draw any conclusions in these areas. On the other hand, there are several assays in which we have a large overlap with the current hit set (e.g., assay IDs between 4550 and 4750). In these cases, we only found yellow and green symbols for an assay in which the compounds of the actual hit set were not active, so that we have no issue here. If we find many red or dark red compounds for an assay (e.g., assay ID 4890), we need to check the assay more closely as a possible selectivity counter-screen. Analyzing the plot in more detail, for example for assay 4890, one can determine whether compounds are already available that are selective against the target and therefore obtain some first hints about how to address the cross-reactivities. 

Our BioProfile approach makes it easily possible for research project teams to access information about cross-reactivities within a given hit set. This information can be used to prioritize compounds or compound classes. It is also used to check for potential selectivity targets or counter-screens and to identify screening artifacts. Identification of fi equent hitters in the screening collection is anoth example of use. 

I Counter screen and orthogonal screen I Concentration response curves (CRC) Profiling, clustering, NN analysis... 

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