Triaging compounds by entropy is often a much more time effective and unbiased way than manual evaluation of four parallel columns of data.
To test the hypothesis deacetylase inhibitor that clinically approved inhibitors are more selective, we binned the compounds in the public kinase profile according to their clinical history, and calculated their average entropies. Compared to the average discontinued compound, the average marketed kinase inhibitor is not more selective, and the average Phase III compound is even significantly more aselective. To exclude therapy area effects, we also performed the analysis for compounds in the oncology area, which is the only therapeutic area with a statistically significant amount of projects. This leads to a similar conclusion. To exclude effects of time from this analysis, we repeated the analysis for compounds that entered clinical phase I before 2005.
In order to quantify compound selectivity as a single value, based on data from profiling in parallel assays, we have presented a selectivity entropy method, and compared this to other existing methods. The best method should avoid artifacts that obscure compound ranking, and show consistent PARP values across profiling methods. Based on these criteria, the selectivity entropy is the best method. A few cautionary notes are in order. First, the method is labelled an entropy in the sense of information theory, which is different to entropy in the sense of vibrational modes in enzyme active sites. Whereas these vibrations can form a physical basis for selectivity, our method is a computational metric to condense large datasets. Secondly, any selectivity metric that produces a general value does not take into account the specific importance of individual targets.
If the inhibitor has a specificity for a target with a KM,ATP above the panel average, then that inhibitor will act even more specifically in a cell and vice versa. Selectivity inside the cell is also determined by factors such as cellular penetration, compartimentalization deacetylase inhibitor and metabolic activity. Therefore, selectivity from biochemical panel profiling is only a first step in developing selective inhibitors. Another point is that any selectivity metric is always associated with the assay panel used, and the entropy value will change if an inhibited protein is added to the panel. Adding a protein that does not bind inhibitor will not affect the entropy value. In this way the discovery of new inhibitor targets by e. g. pulldown experiments, can change the idea of inhibitor selectivity, and also the entropy value.
A good example is PI 103, the most selective inhibitor in Table 1, which in the literature is known as a dual PI3 kinase/mTOR inhibitor, and which appears specific in Table 1 because PI3 kinase is not incorporated in the profiling panel.
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