Cancer prevention by carotenoids.

Epidemiological investigations have shown that cancer risk is inversely related to the consumption of green and yellow vegetables and fruits. Since beta-carotene is present in abundance in these vegetables and fruits, it has been investigated extensively as a possible cancer-preventive agent. However, various carotenoids have also anti-carcinogenic activity. And we found that some of them, such as alpha-carotene, showed higher potency than beta-carotene to suppress carcinogenesis in animal experiments. Thus, we have carried out more extended studies on the cancer-preventive activities of natural carotenoids. For example, lutein, zeaxanthin, lycopene, phytoene, fucoxanthin, peridinin and astaxanthin seem to be promising. In the present study, we confirmed the anti-carcinogenic activities of fucoxanthin and peridinin. Among natural carotenoids, phytoene has not been evaluated precisely since it becomes unstable when it is purified. Here, the cancer-preventive activity of phytoene was demonstrated using new a biotechnological method; i.e., establishment of mammalian cells producing phytoene was followed by the introduction of crtB gene which encodes phytoene synthase, and these cells were proven to acquire the resistance against transformation imposed by transfection of activated oncogenes. Further studies on various natural carotenoids, besides beta-carotene, should be continued to get proper information regarding natural carotenoids in the field of cancer prevention.