Preclinical perspectives on garlic and cancer

Evidence continues to point to the anticancer properties of fresh garlic extracts, aged garlic, garlic oil, and a number of specific organosulfur compounds generated by processing garlic. These anticarcinogenic and antitumorigenic characteristics appear to arise through both dose-and temporal-related changes in a number of cellular events involved with the cancer process, including those involving drug metabolism, immunocompetence, cell cycle regulation, apoptosis, and angiogenesis. The ability of garlic and related allyl sulfur compounds to block tumors in the colon, lung, breast, and liver suggests general mechanisms that are not tissue specific. Whereas relatively few studies have compared the relative efficacy of water- and lipid-soluble allyl sulfur compounds, those that have when using chemically induced carcinogen models suggest little difference in response, whereas tumor proliferation/apoptosis is highly dependent on the species provided. A shift in sulfhydryl groups, alterations in glutathione:oxidized glutathione ratios, and resultant changes in cellular redox status may be involved in some of the phenotypic changes caused by allyl sulfur compounds. Such changes in thiols by allyl sulfurs may also account for the observed hyperphosphorylation of specific cell cycle proteins and the histone hyperacetylation that has been correlated with suppressed tumor cell proliferation. Whereas the anticarcinogenic and antitumorigenic data to date are impressive, additional studies are needed with more modest exposure to allyl sulfur compounds over prolonged periods. Likewise, additional studies are needed that incorporate transgenic and knockout models to assist in the identification of molecular targets for garlic and its associated allyl sulfur components.