Analytical Quality Evaluation of the Tox21 Compound Library.

Area of Science:

• Analytical Chemistry
• Chemical Biology
• Toxicology

Background:

• High-throughput screening (HTS) relies on the analytical quality of chemical compounds.
• The Tox21 library, comprising over 8900 diverse chemicals, presents quality control (QC) challenges for HTS.
• Accurate compound QC is essential to prevent false positives/negatives in HTS assays.

Purpose of the Study:

• To detail the analytical quality control (QC) methods applied to the Tox21 library.
• To report on the purity, identity, and concentration of Tox21 compounds over time.
• To establish a compound-level QC score to support structure-based analyses and HTS interpretation.

Main Methods:

• Compounds from the Tox21 library were analyzed using liquid chromatography-mass spectrometry (LC-MS), gas chromatography-mass spectrometry (GC-MS), and nuclear magnetic resonance (NMR).
• Samples were stored in DMSO at ambient conditions for 0 (T0) and 4 months (T4).
• Expert review of analytical results led to the assignment of QC grades, condensed into quality scores for global analysis.

Main Results:

• Of successfully graded T0 samples, 92% were analyzed, with 76% exceeding 90% purity.
• For samples tested at T4, 89% showed no degradation or loss after 4 months.
• Chemotype analysis identified structural features associated with compound instability and varying quality.

Conclusions:

• The study provides a robust QC framework for the Tox21 library, improving data reliability for HTS.
• A significant majority of compounds maintained high purity and stability over a 4-month period.
• The developed QC metrics and future public browser will enhance HTS interpretation and predictive modeling.