Thiostrepton suppresses colorectal cancer progression through reactive oxygen species related endoplasmic reticulum stress.

Colorectal cancer (CRC) is the second leading cause of cancer-related deaths worldwide. Due to the poor therapeutic efficacy of CRC treatments and poor prognosis of the disease, effective treatment strategies are urgently needed. As long-term proteotoxic stress is a major cause of cell death, agents that induce proteotoxic stress offer a promising strategy for cancer intervention. Thiostrepton is a natural antibiotic derived from the Streptomyces genus. In the present study, we found that thiostrepton triggered apoptosis, reduced the migration of CRC cells, and inhibited xenograft tumour growth in vivo. Mechanistically, thiostrepton reduced proteasome activity; induced the aggregation of ubiquitinated proteins; caused endoplasmic reticulum (ER) stress, which was characterized by increased protein levels of GRP78, ATF4, P-eIF2α, and CHOP and cytosolic calcium release; and ultimately resulted in cell death. Thiostrepton-related changes in cell survival and cell migration, as well as mechanistical processes, were almost completely reversed by treatment with the antioxidant N-acetylcysteine (NAC), suggesting that the mechanism is dependent on reactive oxygen species (ROS). These results demonstrated that thiostrepton induced apoptosis and inhibited migration through ROS-induced ER stress and proteotoxic stress in colorectal cancer.