OPERA updates
The Open (Quantitative) Structure–activity/property Relationship App (OPERA) is a free and open-source/open-data suite of QSAR models developed to support a range of research and regulatory purposes. In addition to physicochemical and environmental fate properties, OPERA offers a number of models to predict ADME endpoints that are important to PBPK modeling and IVIVE studies. All OPERA models were built using curated datasets split into training and test sets and molecular descriptors calculated based on standardized QSAR-ready chemical structures. Modeling adhered to the five principles for QSAR model development adopted by OECD. These principles support the development of scientifically valid, highly accurate models with minimal complexity that support mechanistic interpretation, when possible. For consistency and transparency, OPERA provides a tool for standardizing chemical structures, an estimate of prediction accuracy, an assessment of applicability domain, and incorporation of experimental values when available. Technical and performance details are described in OECD-compliant QSAR Model Reporting Format reports.
Existing OPERA models are updated regularly when new experimental data become available. In 2024 and 2025, OPERA models were expanded with newly curated datasets covering a number of physicochemical properties and ADME parameters, as well as new input/output features and bug fixes. OPERA predictions are available through the EPA CompTox Chemicals Dashboard and NICE. The OPERA application can also be downloaded from the NIEHS GitHub repository as a command-line or graphical user interface for Windows and Linux operating systems. It is also available as an extension to OECD’s QSAR Toolbox, a resource provided by OECD and the European Chemicals Agency to support animal-free chemical hazard assessment and on the FDA’s Precision platform.