Cancer chemoprevention by natural carotenoids and their related compounds.

As one of the most promising cancer chemopreventive agents, beta-carotene has been studied extensively. However, other natural carotenoids have also suppressed tumorigenesis, and some are more potent than beta-carotene. For example, alpha-carotene shows higher potency than beta-carotene in suppressing tumorigenesis in mouse skin and lung models. In the two-stage mouse skin carcinogenesis model (initiator, 7,12-dimethylbenz[a]anthracene; promoter, 12-O-tetradecanoylphorbol-13-acetate), topical application of alpha-carotene at a 200 nmol dose per painting twice a week significantly decreased the mean number of skin tumors per mouse. The greater potency of alpha-carotene over beta-carotene in suppression of tumor promotion was confirmed in the two-stage mouse lung carcinogenesis model (initiator, 4-nitro-quinoline-1-oxide; promoter, glycerol). Oral administration of alpha-carotene (0.05% in drinking water) significantly decreased the mean number of lung tumors per mouse. In contrast, beta-carotene showed no suppression of lung tumor formation under the same experimental conditions. Fucoxanthin, a carotenoid as abundant in nature as beta-carotene, was also found to have antitumorigenic activity in mouse skin and duodenum models. Thus, further studies on various natural carotenoids, other than beta-carotene, should be carried out in the field of cancer chemoprevention.