Chemopreventive potential of dietary bioflavonoids against 20-methylcholanthrene-induced tumorigenesis.

The effect of dietary supplementation of flavonoidal compounds such as quercetin, rutin, luteolin and (+)-catechin on the incidence of fibrosarcoma induced by 20-methylcholanthrene (20-MC) in male Swiss albino mice was observed. Subcutaneous injection of 20-MC produced 100% tumor incidence and the onset of tumor appeared within 7 weeks, while flavonoid-treated mice (1% quercetin- and luteolin-mixed diets) produced tumors in the 9th week, and the tumor incidences in mice treated with quercetin- and luteolin-mixed diets were 52% and 60%, respectively. Subcutaneous administration of 20-MC along with the flavonoidal compounds (quercetin, luteolin) was found to have significant effect on tumor expression. The compounds rutin and (+)-catechin did not influence tumor expression in both experiments. Elevated levels of lipid peroxides, cytochrome P450 and decreased activity of glutathione-S-transferase (GST) were observed in the tumor bearing animals. Test-diet-treated animals showed reduction in the lipid peroxides and cytochrome P450, and increased activity of GST (P < 0.001). In vitro [3H]thymidine incorporation showed the inhibition of DNA synthesis in fibrosarcoma cells by the flavonoids. The possible mode of action of the flavonoidal compounds may be through their influence on the initiation and promotion phases of the carcinogenic process coupled with enhancement of the detoxification process.