OPERA

Open 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 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) (Kleinstreuer et al. 2018).
• 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.