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Antiproliferative effect of carotenoids on human colon cancer cells without conversion to retinoic acid

Onogi, N., Okuno, M., Matsushima-Nishiwaki, R., Fukutomi, Y., Moriwaki, H., Muto, Y., Kojima, S.
Nutrition and cancer 1998 v.32 no.1 pp. 20-24
alpha-carotene, beta-carotene, canthaxanthin, colon, neoplasms, retinoic acid, viability, DNA, biosynthesis, cell division, receptors, genes, messenger RNA, gene expression, cell lines, humans
The present study employed two human colon cancer cell lines, DLD-1 and Colo 320DM, to investigate whether the provitamin A activity of carotenoids is necessary for their antitumor effect on colon cancer. Carotenoids, including alpha- and beta-carotene and canthaxanthin, significantly suppressed cell viability [measured by tetrazolium (MTT) assay], DNA synthesis (measured by (3H]thymidine uptake), and cell proliferation (measured by cell counting) and thus showed growth-inhibitory effects on both cancer cell lines. Because canthaxanthin does not have provitamin A activity, these results suggest that the carotenoid directly inhibited the cell growth. Moreover; the effective dose of retinoic acid, an active metabolite of vitamin A, was much higher than that of alpha- or beta-carotene. A retinoic acid-inducible gene, retinoic acid receptor-beta, was not enhanced in either type of cancer cell by treatment with alpha- or beta-carotene. Therefore, like canthaxan thin, alpha- and beta-carotene might also exert their tumor-suppressing effects without being converted to retinoids. These results suggest that a certain antitumor activity of carotenoids may not necessarily require their provitamin A activity.