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Threshold dose response for tumor induction by genotoxic carcinogens modeled via cell-cycle delay
1Department of Toxicology, University of Wuerzburg, Germany. lutz@toxi.uni-wuerzburg.de
Summary
This study proposes a J-shaped dose-response model for carcinogenicity, suggesting thresholds exist even for genotoxic carcinogens. The model reconciles opposing views by incorporating cell cycle dynamics and DNA damage.
Area of Science:
- Toxicology and Carcinogenesis
- Quantitative Risk Assessment
- Mechanistic Toxicology
Background:
- Carcinogenicity dose-response relationships are often debated regarding thresholds.
- Nongenotoxic chemicals may show thresholds due to cell proliferation effects.
- Genotoxic carcinogens are typically assumed to lack thresholds.
Purpose of the Study:
- To postulate and model thresholds for genotoxic carcinogens.
- To explore the mechanistic basis for J-shaped (or U-shaped) dose-response curves.
- To provide a quantitative estimation method for threshold doses.
Main Methods:
- Utilized the 2-stage clonal expansion model of carcinogenesis.
- Modeled cell turnover rates with J-shaped curves using shifted quadratic functions.
- Integrated linearly increasing mutation rates with cell turnover dynamics.
Main Results:
- Decreased cell turnover rates led to reduced spontaneous tumor incidence.
- The model generated J-shaped dose-response curves for tumor incidence under specific conditions.
- A threshold dose was identified at 0.8 dose units in an example scenario.
Conclusions:
- A biologically plausible mechanistic basis for thresholds in genotoxic carcinogens is proposed.
- The J-shaped dose-response model can reconcile differing views on carcinogen thresholds.
- The presented approach offers a method for quantitative threshold dose estimation.