Reduction in tamoxifen-induced CYP3A2 expression and DNA adducts using antisense technology
Brinda Mahadevan1, Vikram Arora, Laura J Schild
1Department of Environmental and Molecular Toxicology, Oregon State University, Corvallis, Oregon 97331, USA.
Abstract:
Tamoxifen (TAM) is widely used in the treatment and prevention of breast cancer. There is clear evidence that cytochrome P450 (CYP) 3A enzymes play an important role in TAM metabolism, resulting in metabolites that lead to formation of TAM-DNA adducts. We have investigated the effect of CYP3A2 antisense (AVI-4472) exposure on CYP3A2 transcription, enzyme activity, translation, and TAM-DNA adducts, in livers of rats administered TAM (50 mg/kg body weight [bw]/day) for 7 days. The study design included administration of 0, 0.5, 2.5, or 12.5 mg AVI-4472/kg bw/day for 8 days, beginning 1 day before TAM exposure. The specific activity of CYP3A2 was increased after TAM administration, and decreased significantly (approximately 70%) in the presence of 12.5 mg AVI-4472. CYP3A2 protein levels, determined by immunoblot analysis, showed a similar pattern. Hepatic TAM-DNA adduct levels were measurable in all TAM-exposed groups. However, when rats were co-treated with 2.5 and 12.5 mg AVI-4472/kg bw/day, statistically significant (approximately 50%) reductions in TAM-DNA adduct levels (2.0-2.8 adducts/10(8) nucleotides) were observed compared to rats treated with TAM alone (5.1 adducts/10(8) nucleotides). Rat toxicology U34 arrays (Affymetrix) were used to investigate the modulation of gene expression patterns on co-administration of TAM with AVI-4472. Results indicated that several CYP genes were down regulated although no significant induction of CYP3A2 was observed in the TAM-exposed rats co-treated with AVI-4472. Overall the data suggest the utility of antisense technology in the redirection of TAM metabolism thereby lowering TAM genotoxicity in rat liver.
Insights
This study shows that antisense technology can reduce tamoxifen-induced DNA damage in rats. AVI-4472, an antisense agent, lowered tamoxifen metabolism and genotoxicity in rat livers.
Area of Science:
- Pharmacology
- Toxicology
- Molecular Biology
Background:
- Tamoxifen (TAM) is a crucial breast cancer therapeutic.
- Cytochrome P450 (CYP) 3A enzymes are key in TAM metabolism, producing DNA-damaging metabolites.
- Understanding TAM metabolism is vital for reducing its genotoxicity.
Purpose of the Study:
- To evaluate the impact of CYP3A2 antisense (AVI-4472) on TAM metabolism and DNA adduct formation in rats.
- To assess the efficacy of antisense technology in mitigating TAM-induced genotoxicity.
Main Methods:
- Rats were administered TAM and varying doses of AVI-4472.
- CYP3A2 transcription, enzyme activity, and protein levels were measured.
- Hepatic TAM-DNA adducts were quantified using established methods.
- Gene expression patterns were analyzed using Affymetrix U34 arrays.
Main Results:
- TAM increased CYP3A2 activity, which was significantly reduced by AVI-4472 (approx. 70%).
- AVI-4472 co-treatment (2.5 and 12.5 mg/kg) significantly reduced TAM-DNA adducts by approximately 50%.
- Gene expression analysis revealed downregulation of several CYP genes.
Conclusions:
- Antisense technology, specifically AVI-4472, effectively modulates TAM metabolism in rat livers.
- This modulation leads to a significant reduction in TAM-induced genotoxicity.
- Antisense technology shows promise for lowering TAM-related DNA damage in cancer treatment.
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