Discussion

A significant proportion of actives identified in protein based HTS campaigns are inappropriate for further study as part of lead discovery programs. A proportion of them inhibit targets via undesirable mechanisms of inhibition (uMOI). One such undesirable mechanism is caused by redox cycling compounds (RCCs). These catalyse a radical mediated redox cycle between reducing agent and molecular oxygen. This cycle produces reactive oxygen species which can inhibit proteins by oxidising residues. To avoid wasting time and resource pursuing these artefactual HTS actives we have implemented 2 literature reported methods to detect them. Interestingly we found little overall agreement between these assays although compounds highly active in both did hit multiple cysteine proteases (known to be susceptible to RCCs). These compounds have been used to enhance the uMOI set of compounds at AstraZeneca, a capability to evaluate HTS assay susceptibility to different uMOI.