Open (Quantitative) Structure-activity/property Relationship App
Quantitative structure–activity/property relationship (QSAR/QSPR) models provide predictions of chemical activity that can augment non-animal approaches for predicting toxicity. However, the performance of QSAR models highly depends on the quality of the data and modeling methodologies used.
To provide robust QSAR/QSPR models for chemical properties of environmental interest that can be used for regulatory purposes, EPA NCCT created the Open (Quantitative) Structure-activity/property Relationship App (OPERA) (Mansouri et al. 2018). OPERA is a free and open-source/open-data suite of QSAR models providing predictions for physicochemical properties, environmental fate parameters, and toxicity endpoints. All OPERA models were built on curated data and QSAR-ready chemical structures standardized using an open-source workflow (Mansouri et al. 2016).
OPERA is an ongoing collaboration between NICEATM and EPA. Additions to OPERA include predictions for:
- Estrogenic activity from the Collaborative Estrogen Receptor Activity Prediction Project (CERAPP) (Mansouri et al. 2016).
- Androgenic activity from the Collaborative Modeling Project for Androgen Receptor Activity (CoMPARA) (Mansouri et al. 2020).
- Acute oral systemic toxicity from the Collaborative Acute Toxicity Modeling Suite (CATMoS) (Mansouri et al. 2021)
- Physicochemical properties such as acid dissociation constant (pKa) and octanol-water dissociation coefficient (logD) (Mansouri et al. 2019).
Other endpoints predicted by OPERA models include:
- Physicochemical parameters such as octanol-water partition coefficient (logP), water solubility, and melting point.
- Parameters for inputs into pharmacokinetic models, such as hepatic clearance and plasma fraction unbound.
- Ecotoxicity parameters such as fish bioconcentration factor, soil adsorption coefficient, and biodegradability.