ABSTRACT
Cancer chemoprevention or chemotherapy for overt cancer has received increasing attention in recent years. A number of agents, including naturally occurring and synthetic compounds, have been demonstrated to exhibit anti-cancer activity. Of particular signifi cance is the realization that many dietary components have anticancer activity. Carcinogenesis is inhibited by dietetic factors such as retinoids, vitamins C, D3, E, polyphenol fi ber, calcium, soya, polyunsaturated fat acids, and selenium. Among them, selenium (Se) is an essential dietary nutrient for all mammalian species, the defi ciency of which has been implicated in a number of disorders, including infertility, increased cancer incidence, susceptibility to viral infection, mental development retardation, and accelerated aging (Rayman 2000). Se is primarily taken up from the soil by Se-accumulating plants, such as garlic and broccoli, as selenate (SeO4
proteins in the form of selenocysteine (SeCys), and non-specifi cally incorporated as selenomethionine (SeMet) in place of methionine, which are used for the synthesis of selenoproteins, including glutathione peroxidase, thioredoxin reductase, and other enzymes (Ganther 1999). Epidemiological studies have suggested an inverse association of serum levels of Se with the incidence of squamous esophageal and adenomatous gastric cardia cancers (Mark et al. 2000). Se is also said to exert cytotoxicity against various cancers, including prostate, colorectal, lung, and various gastrointestinal cancers. Th e eff ects of Se compounds on cancer cells are strictly composition-dependent and concentration-dependent. Se compounds can be either cytotoxic or possibly carcinogenic at higher concentrations. Accordingly, sodium selenite was reported to induce DNA damage, particularly DNA strand breaks and base damage. When incorporated into selenoproteins, Se protects tissues and membranes from oxidative stress, and controls the cell redox status (Rayman 2000). Th is chapter addresses the progressive evidence for Se as a cancer cytotoxic agent and focuses mainly on endoplasmic reticulum (ER) stress as the possible mechanism of apoptotic action of Se compounds in anti-cancer activity.
