Secalonic acid D as a selective cytotoxic substance on the cancer cells adapted to nutrient starvation

Cancer cells adapted to the microenvironment in tumor such as hypoxic and nutrient-starved conditions are now paid much attention as the therapeutic target of cancer. In the course of search for selective cytotoxic substances against cancer cells adapted to nutrient starvation, xanthone derivative of secalonic acid D (1) was isolated from culture extract of marine-derived Penicillium oxalicum. Compound 1 showed cytotoxic activity on the human pancreatic carcinoma PANC-1 cells adapted to glucose-starved conditions with IC50 value of 0.6 µM, whereas IC50 value of compound 1 against PANC-1 cells under general culture conditions was calculated to be more than 1000 µM. Further study indicated that compound 1 inhibited the Akt signaling pathway under glucose-starved conditions, and slightly affected the induction of glucose-regulated protein 78 (GRP78), and these effects would be mediated by the uncoupling action of compound 1 on the mitochondria.