Discovery “screen” assays level

Table 13.1 Rules for discovery (nonCLP) "screen assays (level I). Adapted from [6], with permission from Taylor and Francis Group.

While clear rules apply to the acceptance criteria for GLP assays,12,14 15 114 little agreement surrounds what should be included in the acceptance criteria for discovery PK (non-GLP) assays. Korfmacher16 published a set of rules for discovery PK assays based on the simple concept that the rules should become more rigorous as one moves from early PK screening (Level I) of many compounds to rapid PK studies for lead compounds (Lead Optimization—Level II), and finally special PK studies for compounds that are likely to be recommended for development (Lead Qualification—Level III). 

The rules for level I (screening) assays are shown in Table 13.1. An example of the type of samples where a level I assay could be used is the CARRS samples [85] that can be used for screening NCEs using a rat PK model [vide supra). The concept behind this assay is that it should use a small number of standards and a simple linear extrapolation. For level II assays (see Table 13.2) that might be used for discovery PK studies in preclinical species, a complete standard curve is required. In this case a complete standard curve is defined as 10-15 standards in duplicate assayed with at least five standards used in the final calibration curve. Neither level I nor level II assays require the use of quality control (QC) standards. When a compound is in the lead qualification stage, then a level III assay would be required. As shown in Table 13.3, the main distinction for level III assays is that they are required to include at least six QC standards. As described in Tables 13.1-13.3, these rules show the requirements for how an assay should be set up before the samples are assayed and then these rules describe the acceptance criteria for the assays after they have been performed. 

The concept of combinatorial screening can be further divided into two subsystems, focus level screening and discovery screening [2]. While the focus system provides more detailed information such as kinetics and selectivity on many catalyst samples per test, a discovery system can screen thousands of catalytic materials with sufficient resolution to identify promising hits. An example of a discovery assay for reactivity testing that has been successfully implemented at UOP LLC is the laser activated membrane introduction mass spectrometry (LAMIMS) system [2, 3]. 

Directed evolution relies on the analysis of large numbers of clones to enable the discovery of rare variants with unproved function. In order to analyze these large libraries, methods of screening or selection have been developed, many of which use specialized equipment or automation. These range from the use of multichannel pipettes, all the way up to robotics, depending on the level of investment [59]. Specialized robotic systems are available to perform tasks such as colony picking, cell culture, protein purification, and cell-based assays. 

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