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Epidemiological studies, preclinical investigations and clinical intervention trials support the role of selenium compounds as potent cancer chemopreventive agents; the dose and the form of selenium are critical factors in cancer prevention. Induction of apoptosis and inhibition of cell proliferation are considered important cellular events that can account for the cancer preventive effects of selenium. Toxicity should always be considered a determining factor in the selection of potential chemopreventive agents. Prior to induction of apoptosis, selenium compounds alter the expression and/or activities of a number of cell cycle regulatory proteins, signaling molecules, proteases, mitochondrial associated factors, transcriptional factors, tumor suppressor genes, polyamine and glutathione levels. Depending on the form, selenium compounds can target separate pathways but more efforts are needed to learn about disrupting different pathways converging to apoptosis. Numerous selenium compounds are known to inhibit carcinogenesis in several animal models but not all of these have been examined for their efficacy to induce apoptosis or vice versa in the corresponding target organ. Studies aimed at investigating the effects of selenium compounds on apoptosis in the target organ in vivo and in vitro are limited. On the basis of information provided in this review, we recommend that additional molecular markers should be added to those proposed in the Selenium and Vitamin E Cancer Prevention Trial (SELECT) on prostate cancer. Apart from the selenium compounds reviewed here, several novel synthetic organoselenium compounds need to be examined both in vitro and in vivo for their potential to induce apoptosis; such an investigation may provide better and mechanism-based cancer chemoprevention as well as chemotherapeutic agents.
Sinha et al. (Sun,) studied this question.