@misc{oai:repo.qst.go.jp:00071222,
 author = {Yoshii, Hiroshi and Yoshii, Yukie and Hobo, Kazuki and Fujii, Ayumi and Asai, Tatsuya and Furukawa, Takako and Fujibayashi, Yasuhisa and 古川 高子 and 藤林 康久},
 month = {Sep},
 note = {A possibility of carotenoids as a photosensitizer in photodynamic therapy (PDT) was explored using fluorescence imaging.
Singlet oxygen (1O2), one of the reactive oxygen species (ROS), is known to have toxicity to cells. Green plants use several carotenoids, which have n>10 length of the conjugated double bond, to relax 1O2 involuntarily generated by photosynthetic process. Some carotenoids have the T1 level (first triplet excited level) just below the energy level of 1O2 and can plunder energy from 1O2 by energy transfer and change the energy to heat by intersystem crossing. Conversely, some carotenoids with n<10 length of conjugated double bond, of which the T1 level is just above the energy level of 1O2, should generate 1O2. Additionally, carotenoids would have high affinity to cell membrane. We, therefore, anticipated carotenoids are useful as the photosensitizer in PDT.
We performed in vitro experiments using neoxanthin (Neo) which has n=8 length of conjugated double bond. First, tumor cells were incubated in the medium containing 2 mu M Neo under the blue light (BL). After 24-hour incubation, cells changed to round morphology and the viability was remarkably decreased in contrast with controls. Second, ROS production of Neo excited by BL was investigated using HeLa cells expressing fluorescent protein activated by ROS (HeLa-R). HeLa-R were incubated in the medium containing 2 mu M Neo for 3h and additionally irradiated BL for 3h. We detected strong fluorescent signals from cytoplasm of HeLa-R. Moreover, the cells, in which carotenoids were removed before BL irradiation, showed the same results.
We concluded from these results that carotenoids have high affinity to tumor membrane and they can produce 1O2 within tumor cells. ROS generated by photo-excited carotenoids and their toxicity to tumor cells were observed for the first time. We expect photosensitizing ability of carotenoids can be utilized in PDT., Joint Molecular Imaging Conference},
 title = {ROS generated by photo-excited carotenoids attacks tumor cells},
 year = {2007}
}