Proposal to Eliminate Urethane-Treated Positive Control Dose Groups in 26-Week Tg.rasH2 Carcinogenicity Studies

Area of Science:

• Toxicology
• Carcinogenicity Studies
• Genetically Modified Models

Background:

• Short-term Tg.rasH2 mouse carcinogenicity studies serve as an alternative to traditional 2-year studies.
• Urethane is a validated positive control, inducing lung and spleen tumors at 1,000 mg/kg.

Purpose of the Study:

• To evaluate the efficacy of a reduced urethane dose (500 mg/kg) in Tg.rasH2 mouse carcinogenicity studies.
• To determine if a lower dose with fewer animals can validate the assay.
• To propose modifications for future Tg.rasH2 study designs.

Main Methods:

• Conducted three pilot studies across different sites using Tg.rasH2 mice.
• Administered urethane at 500 mg/kg on days 1, 3, and 5, followed by a 12-week observation.
• Compared results to established protocols using higher urethane doses.

Main Results:

• A reduced urethane dose of 500 mg/kg successfully validated the Tg.rasH2 assay.
• Fewer animals per sex were required to demonstrate assay validity.
• The lower dose effectively induced characteristic tumors, confirming assay sensitivity.

Conclusions:

• A lower urethane dose is effective for validating short-term Tg.rasH2 carcinogenicity studies.
• Optimized protocols can reduce animal usage while maintaining assay integrity.
• Eliminating positive control groups is proposed for future Tg.rasH2 studies based on cumulative experience.