Lycopene has been known as a potential food component for
cancer prevention, since tomato consumption was shown to be associated with reduced risk of certain
cancers. We used HL-60 cells as a model of
cancer cells to investigate whether acyclic
carotenoids, such as
phytoene,
phytofluene, and
zeta-carotene present in tomatoes, other than
lycopene, as well as oxidation mixtures of these
carotenoids, are potentially involved in the
cancer-preventive action of tomatoes. When HL-60 cells were grown in the
carotenoid-supplemented medium for 120 hours,
zeta-carotene and
phytofluene at 10 microM inhibited cell growth to 3.7% and 22.6% of the growth in control culture, respectively, although they were extremely unstable in the culture medium. The oxidation mixture of each
carotenoid, which was prepared by incubation in
toluene at 37 degrees C for 24 hours, more strongly inhibited cell growth than each intact
carotenoid. The growth inhibition by
lycopene was remarkably enhanced by its oxidation before supplementation to the medium.
Phytofluene,
zeta-carotene, and the oxidation mixture of
lycopene induced apoptosis in HL-60 cells during incubation for 24 hours. The addition of
alpha-tocopherol to the medium did not eliminate growth inhibition by the oxidation mixture of
lycopene. These results suggest that the acyclic
carotenoids inhibit cell growth through apoptosis induction and that oxidation products of the
carotenoids participate in the growth inhibition.