The antitumorigenic effects of carotenoids, in addition to their immuno-enhancing effects, may occur by their direct action on growing tumor cells. To test this hypothesis the direct inhibitory effect of various concentrations of canthaxanthin (CX; 4,4′-diketo-β-carotene), a non-provitamin A carotenoid, was tested on the in vitro growth of, B16F10 melanomas and PYB6 fibrosarcoma and murine non-transformed NIH-3T3 (ATCC CRL 1658) cells. At concentrations of 1 × 10-8 M up to 1 × 10-4 M, CX significantly reduced the overall number of tumor cells. The greatest inhibition was observed at a CX concentration of 1 × 10-4 M after 72 h and 96 h of incubation. However, CX had no inhibitory effect on the growth of the non-transformed NIH-3T3 cell line; rather it significantly enhanced growth of this cell line (P < 0.05) after 96 h of incubation. Thus, the inhibitory action of CX on growing tumor cells appears to be due to its direct actions on tumor cells and not via its conversion to vitamin A or its immuno-enhancing effects.
- transformed and non-transformed cells
- tumor growth
ASJC Scopus subject areas
- Cancer Research
- Molecular Biology