Macs in Chemistry

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PAINS Vortex script


One of the great features of the latest version of Vortex (> build 29622) is the ability to script multiple sub-structure searches using SMARTS. There are many occasions when this sort of feature is useful, if you want to flag molecules that contain reactive functional groups, toxicophores, or PAINS functional groups that have been shown to interfere with high-throughput screens. Vortex tutorial 24 described how to do this multi-substructure searching.

There have now been a couple of new publications describing the identification of false positives in high-throughput screening campaigns in which the binding of glutathione S-transferase (GST) to glutathione (GSH) is used for detection of GST-tagged proteins.

  • Identification of Small-Molecule Frequent Hitters of Glutathione S-Transferase–Glutathione Interaction DOI
  • Identification of Small-Molecule Frequent Hitters from AlphaScreen High-Throughput Screens DOI

There have also been some suggestions as to how some of the motifs might be interfering with the assay, as shown below.


I've now added the additional structural motif definitions taking the total to 550 SMARTS definitions. It is perhaps worth mentioning that some of these motifs may not be an issue when using alternative screening technologies, but it may be very worthwhile to double check any molecules flagged by this script before committing significant resources to follow up.

This comment in Nature is perhaps worth noting

Academic researchers, drawn into drug discovery without appropriate guidance, are doing muddled science. When biologists identify a protein that contributes to disease, they hunt for chemical compounds that bind to the protein and affect its activity. A typical assay screens many thousands of chemicals. ‘Hits’ become tools for studying the disease, as well as starting points in the hunt for treatments. These molecules — pan-assay interference compounds, or PAINS — have defined structures, covering several classes of compound. But biologists and inexperienced chemists rarely recognize them. Instead, such compounds are reported as having promising activity against a wide variety of proteins. Time and research money are consequently wasted in attempts to optimize the activity of these compounds. Chemists make multiple analogues of apparent hits hoping to improve the ‘fit’ between protein and compound. Meanwhile, true hits with real potential are neglected.

I've updated the tutorial and the scripts for download.

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