Inhibition of rat mammary carcinogenesis by monoterpenoids.

We have previously demonstrated the cancer chemopreventive activities of the monocyclic unsaturated monoterpene d-limonene. In the present work we report data evaluating the chemopreventive effects of limonene and five other monoterpenes with various chemical structures using a 7,12-dimethylbenz[a]anthracene (DMBA)-induced rat mammary carcinogenesis model. The terpenes tested include: oxygenated [(-)-menthol] and non-oxygenated (d-limonene) monocyclic forms, oxygenated (1,8-cineole) and non-oxygenated [(+/-)-alpha-pinene] bicyclic forms and oxygenated [(+/-)-linalool] and non-oxygenated (beta-myrcene) acyclic forms. Dietary additions of each of the monocyclic terpenes, d-limonene or (-)-menthol resulted in a significant inhibition of mammary carcinogenesis. Furthermore, menthol was found to be a more potent chemopreventive agent than limonene during the DMBA initiation of rat mammary tumors. The acyclic and bicyclic terpenes had no significant chemopreventive activities at the dose levels used in these studies.