Isolation of Caldorazole, a Thiazole-Containing Polyketide with Selective Cytotoxicity under Glucose-Restricted Conditions
Osamu Ohno, Arihiro Iwasaki, Kyouhei Same, Chihiro Kudo, Erika Aida, Kazuya Sugiura, Shimpei Sumimoto, Toshiaki Teruya, Etsu Tashiro, Siro Simizu, Kenji Matsuno, Masaya Imoto, Kiyotake Suenaga
Abstract
Caldorazole (1) was isolated from the marine cyanobacterium Caldora sp. collected on Ishigaki Island, Okinawa, Japan. Its structure was determined to be a new polyketide that contained two thiazole rings and an O-methylenolpyruvamide moiety. Caldorazole (1) showed strong cytotoxicity toward tumor cells that had been seeded at a high density. Cell death induced by 1 in HeLa and A431 cells was also observed only in the presence of the glycolysis blocker 2-deoxy-d-glucose (2DG). Co-treatment with 1 and 2DG remarkably decreased ATP levels in these cells. Furthermore, 1 selectively inhibited complex I in the mitochondrial respiratory chain. Thus, 1 was demonstrated to exert cytotoxicity toward human tumor cells by blocking mitochondrial respiration.