title: Non-stoichiometric inhibition in integrated lead finding - a literature review.
abstract: BACKGROUND
  Non-stoichiometric inhibition summarizes different mechanisms by which low-molecular weight compounds can reproducibly inhibit high-throughput screening (HTS) and other lead finding assays without binding to a structurally defined site on their molecular target. This disqualifies such molecules from optimization by medicinal chemistry, and therefore their rapid elimination from screening hit lists is essential for productive and effective drug discovery.
  
  
  METHODS
  This review covers recent literature that either investigates the various mechanisms behind non-stoichiometric inhibition or suggests assays and readouts to identify them. In addition, combination of the various methods to distill promising molecules out of raw primary hit lists step-by-step is considered. Emerging technologies to demonstrate target engagement in cells are also discussed.
  
  
  CONCLUSIONS
  Over the last few years, awareness of non-stoichiometric inhibitors within screening libraries and HTS hit lists has considerably increased, not only in the pharmaceutical industry but also in the academic drug discovery community. This has resulted in a variety of methods to detect and handle such compounds. These range from in silico approaches to flag suspicious compounds, and counterassays to measure non-stoichiometric inhibition, to biophysical methods that positively demonstrate stoichiometric binding. In addition, novel technologies to verify target engagement within cells are becoming available. While still a time- and resource-consuming nuisance, non-stoichiometric inhibitors therefore do not fundamentally jeopardize the discovery of low molecular weight lead and drug candidates. Rather, they should be viewed as a manageable issue that with appropriate expertise can be overcome through integration of the above-mentioned approaches.
authors.affiliation: a Novartis Institute of Biomedical Research Basel, Novartis Pharma AG , Basel , Switzerland.
authors.forename: Martin
authors.initials: M
authors.lastname: Klumpp
mesh_terms: D002626:Chemistry, Pharmaceutical / Q000379:methods; D003198:Computer Simulation; D017076:Computer-Aided Design; D015195:Drug Design; D055808:Drug Discovery / Q000379:methods*; D057166:High-Throughput Screening Assays / Q000379:methods*; D006801:Humans; D058990:Molecular Targeted Therapy; D004364:Pharmaceutical Preparations / Q000737:chemistry; D015203:Reproducibility of Results; D013329:Structure-Activity Relationship
chemical_list: D004364:Pharmaceutical Preparations
keywords: HTS (high-throughput screening); Non-stoichiometric inhibition; PAINS (pan-assay interfering compounds); binding assay; compound aggregation; counterscreen; false-positive; frequent hitter; integrated lead finding; orthogonal assay; redox cycling; target engagement