This presentation provides examples of the use publicly available tools to for rapid estimation of Margin of Exposure for chemical prioritization. Presented at NURA: Integrated Approaches to Testing and Assessment, Houston, TX, December 2020

1. Rebecca Clewell
21st Century Tox Consulting
NURA: Integrated Approaches to Testing and Assessment
11-12 Dec 2019
Houston, TX
Rapid Risk Estimation
- Using current tools for quick estimates
of MoE

2. Bioactivity
Components of a risk assessment
Dosimetry
Margin of
Exposure
(MoE)
Safe Dose
Estimated
Exposure
Blood
Fat
Liver
Tissues

3. Wetmore et al. 2015. Toxicol Sci. 148(1):121-36..
Margin of Exposure (MoE)
MoE

4. Ultra-high throughput in silico
- Rapid exposure estimation – ExpoCast, etc
- In silico ADME models
- QSAR bioactivity models – TTC, read-across
High throughput in vitro
- HT-IVIVE
- In vitro parent chemical clearance
- In vitro screening (ToxCast/Tox21)
Organotypic in vitro
- Q-IVIVE
- Bioactivation, metabolite ID
- AOPs, organotypic in vitro models
Traditional, in vivo
- AEPs
- PBPK models
- Mode of action, targeted endpoint evaluation
Throughput
Confidenceinaccuracy
Prioritization/compound selection
- Relative potency
- Margin of Exposure (MoE)
Hazard ID
- Putative Mode of Action (MOA)

5. ToxTree: http://toxtree.sourceforge.net

6. For Mac users

9. Cramer
Class
TTC
(ug/kg/day)
I 30
II 9
III 1.5

10. If your compound of interest is a
metabolite, you will have to
specify that.
Note that when you change
compounds, the classification
from the previous compound
remains highlighted.

11. Updates to TCC in Kroes et al 2004.
Neurotoxins – acetylcholinesterase inhibitors (organophosphates and
carbamates – reduced to 0.3 mg/kg-day
DNA reactive carcinogens – based on Cheeseman et al. Carcinogenic
Potency Database and 1 in 1e6 lifetime cancer risk – reduced to 0.0025
https://efsa.onlinelibrary.wiley
.com/doi/epdf/10.2903/j.efsa.
2019.5708

13. Exceptions to TTC
https://efsa.onlinelibrary.wiley
.com/doi/epdf/10.2903/j.efsa.
2019.5708

14. https://efsa.onlinelibrary.wiley
.com/doi/epdf/10.2903/j.efsa.
2019.5708

25. The link between these exposure and
bioactivity is the dosimetry (IVIVE)
The caveat is that all models are only as
good as the data they are built on.